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Valve lash 'hot' adjustment results: 'ticking' sounds!?!?


CamoKing

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Novice owner/mechanic with this '82 720 4x4 king back again with questions regarding valve lash on this Z22. 

Some Background :

This  DIY project started many months ago as a head gasket replacement.  I was subsequently drawn into a great deal more including a carb rebuild and a refurbishment of the head replacing seals, lapping, and getting new intake valves after discovering that they weren't seating fully; slightly bent.   It has been reassembled and thoroughly cleaned over this Summer; I replaced all fluids, gassed up 5 gals. and turned the ignition key last week preparing for the 'fine tuning' .          

  VXz3MTc.jpg

 

Initially, the idle was very high (though I was glad it started up!) and resisted any adjustments until I found that the fast idle cam seemed to be sticking. 

I did get the idle tamed but I couldn't sustain anything near 850 rpm;  more like 1,000 rpm.  OK.  It was running roughly, but running.  Not too bad, I thought.  After all, the valves were set cold during

head reassembly and everything has been sitting for many months.

 

Note: I do not recall any unusual noises during this phase of start up.

 

 As prescribed,  I proceeded to do a hot valve adjustment.  Did it in about a half hour.  Back to idle to hear ticking/clicking noise from the head!!  Thought I messed up on the clearances.  Came back at it later in the day to try again.  Did it in much less than a half hour.  Same results ):  Tick, tick, tick and still idling roughly (and burning oil - that's another issue).

 I think I know when the gauge 'feels' right; a moderate drag when pulling.  I was expecting the idle to smooth out a bit and proceed to check timing....I think I need to address this noise first. 

What is going on here?jPnlf2e.jpg

 

Could it be a problem with lubrication?   It doesn't look like the head is being starved of lubricant though I am seeing blackened oil in the galley whereas the dipstick looks fresh.(?)-- Residue old oil and gunk from months ago?  The oil pressure gauge reads as before around 35 psi.  Maybe there isn't enough new oil getting to the valves rocker arms?  Can I run the engine with the rocker arm cover off to view oil distribution?

 

I'm thinking of resetting the clearances back to 'cold' and listening for any noise.  But, then what?

ANY feedback would be appreciated.  Thanks

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Engine must be HOT. Take for drive or idle at least 20 min. Gauge should read 1/2 or just above. Lash is 0.012" for all.

 

Set TDC and do both on #1, intake on #2, exhaust on #3...... turn engine ONE full turn to TDC and adjust exhaust on #2 intake on #3 and both on #4. This is the fastest way to set the lash without the engine cooling down. If you can't do it in 10 min button up and warm it up before doing the last half.

 

Assume the picture above is before starting? When you set the lash the rocker shafts and arms should have oil on them. 

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4 hours ago, datzenmike said:

Engine must be HOT. Take for drive or idle at least 20 min. Gauge should read 1/2 or just above. Lash is 0.012" for all.

 

Set TDC and do both on #1, intake on #2, exhaust on #3...... turn engine ONE full turn to TDC and adjust exhaust on #2 intake on #3 and both on #4. This is the fastest way to set the lash without the engine cooling down. If you can't do it in 10 min button up and warm it up before doing the last half.

 

Assume the picture above is before starting? When you set the lash the rocker shafts and arms should have oil on them. 

The engine had been idling for at least 20 minutes.  I did not see the coolant temp rise any more. .   I actually put a digital thermometer in the oil trough to get a read of temperature decline.  It was 182º when I 'got in' and dropped about 12º during my time adjusting.  Does that seem HOT enough?   I will try again but I don't see how one can gain access and perform the adjustments so quickly.  I guess practice makes perfect.  What bugs me is that it seems that there was no ticking on initial idle where lash was at a cold setting.

Edited by CamoKing
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A lot of people mess up the first couple of times doing a valve adjustment. I’ll tell you how my instructor told me. Run the car on the street and nail the throttle (do some pulls) you want to get as much heat in the engine as possible...not to the point of blowing up. Once you turn the engine off you have about 20 mins to finish adjusting before the engine cools enough to change the clearance. But it sounds like you did most of this. Double check your cam positions and try to be consistent when you check the base circle...meaning if the lobe is at 6 o’clock check all of them at the same position. 

 

Take me your time and if you need more heat pop the cover back on with the old gasket and get it hot again. It has never failed me. 

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1 hour ago, john510 said:

I've always had better results doing valve adjustments cold.Some will disagree with this but it works for me.I've tried doing it when hot and always have valve ticking when finished.

I agree. Too many variables with "hot". How hot is hot?

 

Setting them cold is my preferred method.

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Hot is what it runs at normally... about 185F. Cold setting is anywhere from below freezing to 100+ F. It's variable unless you only do in the summer. Cold assumes that it will expand to the correct clearance.

 

 

I just checked and the hot lash setting is 0.014" not 0.012" which was my poor memory. So if still ticking probably not the lash setting.

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14 hours ago, datzenmike said:

Hot is what it runs at normally... about 185F. Cold setting is anywhere from below freezing to 100+ F. It's variable unless you only do in the summer. Cold assumes that it will expand to the correct clearance.

Setting valve lash is not as simple as it sounds. There is a certain amount of "feel" one needs to do the job. Pulling the feeler gauge is an example. It needs to stick, but not be tough to pull.

 

A cold engine will have the least amount of variables, and over years of wrenching, one develops their own or uses lash settings that are known to work. Having the cam in the right location is also another area where experience matters. I set valves one cylinder at a time, with both cam lobes up in a V.

 

Nobody really sets their valves while it's below freezing.

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Thanks for the responses to this special subject.  Given my situation, I think I will go back and set 'cold'  (.008" - intake, .009" -exhaust), idle it up to hot temp, than pull the cover of an check to see where the valve lash has landed.  Curious to see the results.

But, things must wait as I am leaving town for a while, AND I have discovered that the alternator is toast!  

Going to the parts store when I get back to see what I can get in the re-manufactured area.

I'll get back to the work next week.

 

thanks again for all the informative comments..

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Lets just say that the cold setting can be 50 to 60 degrees different depending on outside weather. Setting when it's 45 degrees out is going to give a different result than on a hot summer day. That's all. Setting hot is..... well it's set at running temperatures.

 

0.008" and 0.010" is for an L series engine that in theory will expand to 0.010" and 0.012" when hot. The FSM for the '84 Z24 says 0.014" for both and there is no suggested cold setting. My '78 FSM for the 620 also has no cold setting.

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It is worth noting that the Z engine has a pair of separate rocker shafts mounted in aluminum pedestals. These can grow much more freely than a cam tower setup on an L motor.

 

Adjusting hot is not foolproof though.

 

In automatic transmission tuning, the vehicle needs to be above a set temp or you can actually do damage. Ironically, some of the ECMs GM uses don't offer a trans temp reading. Go figure.

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  • 1 year later...
On 9/23/2019 at 1:13 PM, CamoKing said:

As prescribed,  I proceeded to do a hot valve adjustment.  Did it in about a half hour.  Back to idle to hear ticking/clicking noise from the head!!  Thought I messed up on the clearances.  Came back at it later in the day to try again.  Did it in much less than a half hour.  Same results ):  Tick, tick, tick and still idling roughly (and burning oil - that's another issue).

 I think I know when the gauge 'feels' right; a moderate drag when pulling.  I was expecting the idle to smooth out a bit and proceed to check timing....I think I need to address this noise first. 

 

 Hi, its a year later -- BACK under the hood.   I had abandoned this outdoor project due to seasonal constraints and disappointing results;  fired up this '82- 720- Z22 a few times in 2020 to see if the oil burning and clicking-ticking sounds had 'magically' vanish.  -  Of course, nothing changed.  So, with favorable weather and renewed 'enthusiasm', I have given it another go-round.  Signs are pointing to a worn engine that will require a mastery of skills that this novice grease monkey does not possess.  But, before I conclude that this engine is 'toast, let me relate what I have accomplished so far. You generous mentors may have some insights.

 

       Some background:  The odometer is @ 88.8K; seems like it should be higher.   I know that it has had a hard life in the trout fishing environs of Gunnison, Colorado where at some point, the original 5 speed tranny failed and was replaced with a 4 speed.  Pretty sure the engine is original.  I drove in from Gunnison to Santa Fe without problems and subsequently put about 300 miles driving around town.  Then, I started fussing with the mucked up mess in the engine compartment and made the ill-fated decision to do a 'tune-up' before a roadie to the Texas panhandle. 

     That was my 1st mistake.  The head gasket failed and thus my mechanic's adventure began.  And so did my strict adherence to wearing nitrile gloves.  (Would you believe that this little beast had an faulty connection at the exhaust manifold flange AND No tail pipe.  Exhaust had been spewing into the engine bay for years!!  And someone removed the catalytic converter (assumed dead) and put a second muffler there.

 

Issue #1)     Clicking and ticking/Valve lash:  Set clearances following Datzenmike's recommended sequence which is slightly different from the Haynes manual.  Wonder of   wonders...the ticking noise is GONE and the idle is much smoother and I can adjust it steady to @900 rpm! 

                        Note - As I manually turned the crank for the adjustments, I could hear squishing, gurgling, hissing noises accompanying the movement of pistons.  Is this expected??

 

Issue #2)      Oil burning:  Symptoms seem to be indicative of blow-by and/or stem seals (?) I replaced all the seals when refurbishing the head.

        -all these relatively new plugs look oily (some more than others); much to my dismay, these are oilier than the plugs that came with the truck.

        -smoke from the tail kinda grey-blue and smelly.  More smoking at initial start up than when operating temperature is reached.  I don't find any coolant loss.

 

         Bought a INNOVA 3612 compression tester to perform a Dry/Wet test.  FYI- I did this test before completing the valve lash adjustment mentioned above.  I pulled all the exhaust  plugs after warming up.  Smoke puffed out of #1!   

Here are the results:

                           Dry                       Wet

Cyl. #1              145                        140

Cyl. #2              142                        140

Cyl. #3*            135                        143     *(I discovered later that #3 was most in need of lash adj.  Could this account for the lower reading?)

Cyl. #4              145                        142

 

        I don't know what to expect as 'normal' psi for this Z22.  These number seem low but except for #3 seem consistent if that means anything.  The truck does drive with power                  enough though I haven't left the neighborhood. 

 

Issue #3)    Rod and/or bearing noise:   With the valve/head noise quieted, I can hear some knock-a-knocking from down low, like in the oil pan...main bearings, rod knock??  ):

 

.Now, I am at a decision point.  IF, in fact, the rings and bearings are too worn, I will consider my work concluded, i.e., sell this vehicle to some ambitious younger person looking for experience with vintage internal combustion technology.   I don't have a garage or covered area to pull the entire engine;  accessing rings from underneath also seems difficult if not completely wrong.

 

OR, if I can do something to improve the oil burning besides a ring job, I might keep the run this truck for my light construction and recreational desires.

How do you feel about the use of oil additives to combat smoking??   How about a crankcase flush and 'heavier' oil.  I had a Ford F-150 back in the last century that developed significant knock which cleared after I flushed and refilled several times. 

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I would set the idle at or below 800. If too high mechanical advance can creep in.

 

Totally normal to hear gurgling noises when hand cranking the engine. This is just air compressed into the combustion chamber squeezing past the rings trying to equalize.

 

1/You're sure the new valve seals are on and pushed down tight?

 

2/ If you drive and warm it up and then stop for half an hour and restart when warmed up do you get a big poof of blue smoke that goes away??? This would indicate worn valve guides and or bad valve guide seals.

3/ What are you basing oil burning on? How often or how many miles can you drive before adding a quart?

 

Those compression numbers are... ok, could be higher but it's more important that they are even. Valve lash would have no effect on compression numbers unless there was no clearance at all. 

Wet numbers should be higher than dry as the added oil seals tighter. Can you explain how you did this test?

Generally, wet numbers that go up significantly over a dry test indicate worn rings including the oil control.

 

 

You can't remove or replace rings from the bottom.

 

4/ As for bottom end noise, what is your oil pressure reading at hot idle?

 

 

4 questions.

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 Thanks for the questions/reply, Mike.  Here are my answers.

 

 

On 11/1/2020 at 3:44 PM, datzenmike said:

3/ What are you basing oil burning on? How often or how many miles can you drive before adding a quart?

 

Mike, I don't drive this truck except for test drives around the 'hood.  Can't make any judgments on actual oil consumption rate.  It burns and smokes enough to draw looks of disgust from my spouse.  

I can tell you that the truck sat outdoors for months, all fluids drained, as I worked on the head.  I packed the exposed cylinders with clean shop rags and a little WD40 and covered the headless block with plastic sheets. 

I base the burning oil conclusion on:   a)  Plugs are blackened and oily.     b). Grey blue smoke at idle and higher RPM from tail that stinks of oil.

 

 

 

On 11/1/2020 at 3:44 PM, datzenmike said:

4/ As for bottom end noise, what is your oil pressure reading at hot idle?

 

The on board gauge reads about 2/3 between 0 and 45 psi.  I am guesstimating 30 psi.  I can watch the gauge drop from almost 45 at cold start to that level when hot (hot= temp gauge almost straight up).  This apparent rod knock noise is new to me.  It became apparent after the clicking-ticking valve noise was 'tamed'.  I am not sure whether it has just developed or has been there all along. 

 

 

On 11/1/2020 at 3:44 PM, datzenmike said:

1/You're sure the new valve seals are on and pushed down tight?

2/ If you drive and warm it up and then stop for half an hour and restart when warmed up do you get a big poof of blue smoke that goes away??? This would indicate worn valve guides and or bad valve guide seals.

 

I know I pushed them on tight upon reassembling head.  Haven't done the warm up/stop/ restart yet.  All I see is substantial smoking at cold start which diminishes as engine warms and idle drops.  Puffs increase as I throttle up.

 

On 11/1/2020 at 3:44 PM, datzenmike said:

I would set the idle at or below 800. If too high mechanical advance can creep in.

 

 

The  idle stutters and stalls below 900 .  I've tried adjusting the idle/mixture screws without success at achieving a lower RPM.  Idle holds @ 900 but is not what I would call, "smooth and steady".

 

 

On 11/1/2020 at 3:44 PM, datzenmike said:

Those compression numbers are... ok, could be higher but it's more important that they are even. Valve lash would have no effect on compression numbers unless there was no clearance at all.   Wet numbers should be higher than dry as the added oil seals tighter. Can you explain how you did this test?

 

Warmed up engine.  Removed exhaust plugs.  Started at cyl.#1 with screw in gauge.  Got readings for all four cyls. then squirted about a Tbls. worth of oil in plug hole to get 'wet' readings.  Will repeat test to verify (or create more confusion)

 

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32 minutes ago, CamoKing said:

 Thanks for the questions/reply, Mike.  Here are my answers.

 

 

Mike, I don't drive this truck except for test drives around the 'hood.  Can't make any judgments on actual oil consumption rate.  It burns and smokes enough to draw looks of disgust from my spouse.  

I can tell you that the truck sat outdoors for months, all fluids drained, as I worked on the head.  I packed the exposed cylinders with clean shop rags and a little WD40 and covered the headless block with plastic sheets. 

I base the burning oil conclusion on:   a)  Plugs are blackened and oily.     b). Grey blue smoke at idle and higher RPM from tail that stinks of oil.

 

Did it smoke before the head was removed and worked on? If after then it's something from that. Lets assume that there is no problem... so what else can cause smoking? Is the choke stuck on? Have a look next time it is thoroughly warmed up 15-20 min of running. Driving around short trips the choke is on more than if you went for a long drive. Choke on forces a rich mixture that will carbon up the plugs. A nice long drive might help to clean everything out. 

 

Every time an engine is worked on oil and coolant can spill and or get into the exhaust or there is assembly oil on valves and on start up there may be smoke till it all burns off.

 

 

32 minutes ago, CamoKing said:

The on board gauge reads about 2/3 between 0 and 45 psi.  I am guesstimating 30 psi.  I can watch the gauge drop from almost 45 at cold start to that level when hot (hot= temp gauge almost straight up).  This apparent rod knock noise is new to me.  It became apparent after the clicking-ticking valve noise was 'tamed'.  I am not sure whether it has just developed or has been there all along. 

 

2/3 of 45 is 27 so that's not too bad, however the idle is a bit high. See if you can get the idle down to 700-750.

 

 

32 minutes ago, CamoKing said:

 

 

I know I pushed them on tight upon reassembling head.  Haven't done the warm up/stop/ restart yet.  All I see is substantial smoking at cold start which diminishes as engine warms and idle drops.  Puffs increase as I throttle up.

 

 

 

32 minutes ago, CamoKing said:

 

The  idle stutters and stalls below 900 .  I've tried adjusting the idle/mixture screws without success at achieving a lower RPM.  Idle holds @ 900 but is not what I would call, "smooth and steady".

 

Have someone turn the ignition on off on off (don't start JUST ON OFF) while you listen near the carburetor. You should hear a soft clicking sound THIS IS IMPORTANT. If you idle cut solenoid is connected you should hear this. Without the idle cut there will be no fuel down to the idle mixture adjustment and you won't be able to idle lower.

 

 

32 minutes ago, CamoKing said:

 

 

 

Warmed up engine.  Removed exhaust plugs.  Started at cyl.#1 with screw in gauge.  Got readings for all four cyls. then squirted about a Tbls. worth of oil in plug hole to get 'wet' readings.  Will repeat test to verify (or create more confusion)

 

 

Try 2 tablespoons just to be sure the rings get wet. The piston tops have a 15cc dish and one spoonful may not be enough. Again oil should seal better and give a slightly higher reading. It will definitely smoke for a while after till it all burns off.

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On 11/9/2020 at 1:50 PM, datzenmike said:

Have someone turn the ignition on off on off (don't start JUST ON OFF) while you listen near the carburetor. You should hear a soft clicking sound THIS IS IMPORTANT. If you idle cut solenoid is connected you should hear this. Without the idle cut there will be no fuel down to the idle mixture adjustment and you won't be able to idle lower.

 

Did this test but a loud beeping sound in the 'On' position is too loud for me to hear clicking.  I will check again and test the electricals involved and Ohms on the solenoid.  But, do I understand this:  If the anti-diesel solenoid is faulty, setting an idle  will be possible but the RPM level will exceed normal specs.  Yes? No? 

This may describe my situation.  (I hope not because I don't think I can get a replacement solenoid??) 

The idle is responsive to the screwing in/out at the two points on the carb., but I'm not been able to bring idle RPM down to less than 900 without stalling.  There is no dieseling at ignition off. 

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 The solenoid is closed with key off and this blocks gas flow down to the mixture screw. Without fuel to the idle circuit the idle can't really be set below 1,000-1,200 RPMs and is actually running and getting it's fuel and air on the primary barrel. It may just not be getting voltage. Check the second fuse over from the left side of the fuse box. It may also be plugged with dirt.

 

There shouldn't be any beeping under the hood or near the carburetor. Have someone else work the ignition while you stick your head hear the carb. Failing this put your finger on it and you'll feel the click.

 

Yes there is a screw for idle speed and one to adjust the amount of fuel or mixture.

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✌️

 

On 11/12/2020 at 12:48 PM, datzenmike said:

Have someone else work the ignition while you stick your head hear the carb. Failing this put your finger on it and you'll feel the click.

 

Went another route, Mike.  I jumped the battery to the solenoid - nothing.  Also checked voltage on the connector with ignition 'on' -- 12.3V.  So, I assumed wiring to the solenoid to be faulty.   I have taken the thing out to inspect.  And What the heck: 

KcUUGie.jpg

The darn spring is outside, riding on the pin!!!!  No wonder there was no 'click'.   So I've reassembled the right way, I think.

 

FjDGAw8.jpg

 

Now, on the bench, the pin does move in and out about 5 mm when applying 12 volts.  WOnder of WonDers.  The solenoid has been functioning, at least, partially.  I guess I am glad that I don't need an 'unobtainable' part.

I haven't reinstalled to see if there are changes in the idle adjustment.  I'm not too optimistic.  I was almost hoping to find the solenoid defective and stuck in the 'shut- off' position since this would account for abnormal idle speed.

Maybe the cock-eyed spring was interfering with fuel flow?  Will be testing soon..(if I see sunshine and 50ºF).   More later. 

Thanks, datzenmike.

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On 11/1/2020 at 3:44 PM, datzenmike said:

1/You're sure the new valve seals are on and pushed down tight?

 

2/ If you drive and warm it up and then stop for half an hour and restart when warmed up do you get a big poof of blue smoke that goes away??? This would indicate worn valve guides and or bad valve guide seals.

3/ What are you basing oil burning on? How often or how many miles can you drive before adding a quart?

 

.....I cannot rule out the possibility of valve seal failure or worn guides.  There is definitely more smoking at cold start/restart and the plugs are black and oily.  Maybe I overlooked something when reassembling the head.   Maybe I was too aggressive while lapping the valves?  I was very careful with the compound and kept the stems lubed with clean oil. 

Why NEW seals would leak is beyond me but the symptoms suggest such is the case.   Maybe they got stretched out and deformed at initial start-up?  WTF

 

I tried to gain some insight by visually inspecting the seals with the rocker cover off -- No dice.    No way to draw any conclusions this way.  ---  time for a tear down!?!?

 

 I must consider undertaking the process of inspecting and/or replacing these valve seals WITHOUT removing the head. 

I think I can do this using the 'nylon rope' trick to keep the valves from falling down the cylinders. 

However, I need some pointers as to how one insures that the position of the cam and pistons is retained since the rocker arm assembly must be removed and the engine will be hand cranked cylinder to cylinder during this process.

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Preferably use a 27mm socket on the crankshaft nut and a long breaker bar or pipe on a ratchet handle.

 

Take exhaust side plugs out because they are the easiest to get at and this relieves the compression when turning.

 

Loosen off the rocker arm assembly bolts a little at a time till all the valve springs relax and lift the assemblies away carefully and set them down level and keep track of intake and exhaust sides so they go back the same way without confusion. At this point all the valves are closed so you can turn the engine all you like the pistons can't hit them.

 

Insert at least 2 feet of rope in through a spark plug hole. If you have a short length of rope tie a large knot in the other end so there's no chance it will fall in.

 

Turn engine ahead by hand till it meets firm resistance. Don't worry the valves are closed and the piston is extremely strong.

 

Change the valve seals on that cylinder with confidence.

 

Back the engine up slightly to relieve the rope and remove it. On to the next.

 

When finished, install rocker arm assemblies in their places. Take care that all the rockers are properly fitted on their lash pads and the other ends on the cam lobes. Then put the retaining bolts on and go round and round slowly tightening them down.  

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On 11/18/2020 at 9:38 PM, datzenmike said:

Loosen off the rocker arm assembly bolts a little at a time till all the valve springs relax and lift the assemblies away carefully and set them down level and keep track of intake and exhaust sides so they go back the same way without confusion. At this point all the valves are closed so you can turn the engine all you like the pistons can't hit them.

 

Insert at least 2 feet of rope in through a spark plug hole. If you have a short length of rope tie a large knot in the other end so there's no chance it will fall in.

Thanks for the guidance, Mike.  Do you have a preferred brand/source for replacement seals?  I may attempt this if only to confirm or refute the presumption of faulty seals ...

 

.....BUT, now,  I am preoccupied with this high idle problem.  As I stated previously , I can't adjust to an idle below 1000 without stalling out; steady but still rough.   I'm thinking the problem is with the carburetor.   Maybe the smoking tail pipe and rough idle is, in part,  due to a very rich fuel mixture.  Right?  White smoke could be coolant or fuel?  I find NO loss of coolant; just smelly white exhaust fumes.   The plugs are definitely carbonized.   The anti-dieseling solenoid is working.  Seems like I need to trouble - shoot carburetion.  (History note:  The idle was too high when I obtained this vehicle.  And must have been driven this way for years.)

 

What are the typical causes of too rich a fuel mixture that defies adjustments?  Where might this novice start looking for answers?  (I mean before this Hitachi gets junked)

      

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Anti dieseling solenoid AKA 'Idle Cut Solenoid'. Remove the solenoid. Locate and remove the idle mixture screw counting the turns so it can be replaced in same position. Get a can of carburetor spray that comes with a straw. Push straw into the idle mix screw hole and spray. Solvent should shoot out the idle cut hole. If not spray into the idle cut solenoid hole till it clears. If it does, put finger over the hole and continue to spray. This should force cleaner back into the carburetor.

 

White 'smoke' is normal exhaust condensation when it's cool out. Less noticeable when in warmer weather. Excessive white when engine is warm could be coolant steam and smell faintly of antifreeze from a bad head gasket but rad level will constantly need topping up.

Black smoke is excessively rich fuel mixture. This is gas left over that can't be burned. Plugs will be dry and sooty.

 

 

Too rich condition.

1/ Choke is is on and not shutting off fully when engine warms. May need adjusting. May not have power to the choke heater. May be dirty linkage and stuck.

 

2/ Extraordinarily dirty air filter. This will act like a choke.

 

3/ Fuel level too high or flooding. Float level set too high. Inlet needle worn and not closing or dirt in way preventing it closing.

 

4/ Wrong jet. Only happens if carb is rebuilt. Primary and secondary jets can accidentally be swapped. Primaries are usually around 105 and secondaries are about 160.

 

 

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