620 with EI hard to start (when cold)

[Kirden]

Hey guys, I've installed an electronic ignition from Eagle Adam's old truck on my '74 and the truck runs amazing, however, the first start up of the day is a real pain. It takes pumping the gas and sometimes it sorta starts then dies back. We bypassed the ballast since Adam also sold me the coil, and that's about it for the install. Everything seems to be tuned correctly but I really need to track down why I'm having this cranking issues.

 

It will turn over, but not crank for about 2-3 10 second bursts, even pumping the gas, then it sorta stumbles like old gas or foul plugs (checked plugs they are fine). Rev it once or twice and it runs like a dream. Cut it off and it cranks right back up. Could this just be old gas? The truck has sat idle since August, but what else should I check?

[datzenmike]

Check the timing. No two dizzys are going to be set the same.

 

Also it may have a had a prior condition and the dizzy change isn't the problem. Put the old dizzy back in and see if it's the same.

[metalmonkey47]

Timing for sure? I'm with Mike though... takes 2 seconds to toss the points dizzy back on and give it a shot. Especially as long as it's sitting.... ethanol doesn't keep well, and we have a good bit in our gas down here... Might take a gas can with fresh gas and drop a hose down in it from the fuel pump. (Might get everything out of the carb first) 

[ggzilla]

Those are symptoms of a choke problem.

[Kirden]

I can't toss the old dizzy back on. The reason for the change was that the old dizzy broke the timing bolt and was free spinning. The gass is pretty suspect so I am going to get a can, some fresh filters, and let it run for a bit.

 

Now one thing I had orgotten until gg mentioned it was that my uncle rewired my choke. He said that the wire I had it going to was not correct, so I'm wondering if the wire he hooked it to is one that is always live and therefore keeping the choke open. The damn PO painted everything blue so I can't even see what color the wires are supposed to be to check a wiring diagram.

 

When it first starts it's like it tries to crank, then sputters and you have to keep the key turned and pump the gas, almost like it's running out of gas (which it's not).

[DanielC]

This is confusing to me.  What do you mean by "crank", and "tries to start"?

Cranking is just the starter motor turning the engine.  When you are doing a compression test, the engine is cranking just fine, but will never start.

Do you have a cranks, no start or a no crank condition?

 

I think you have a "Cranks, no start condition.  If that is the case, begin with this.

Check compression.  if good go to next step.

Check for spark, at the spark plug.  I use a spark tester, with a variable gap.  You should get a nice fat blue spark, over about a 3/8 inch gap.  If you do, confirm the timing is OK.  With a matchbox distributor, turn the engine clockwise, until you are at 10 to 12 degrees before top dead center.  If you go too far, do not go backwards, go forward two turns, and stop at 10 to 12 degrees BTDC.   if you then aligh the points on the stator, and the rotor in the distributor, the timing will be close enough to run.  Confirm you have spark again.

 

If the engine still cranks, but does not start, pour about two teaspoons of gas down the carburetor.

 

It sounds to me like you might have a problem with the choke on the carb, and also possibly the accelerator pump.

 

Remember, compression, ignition, and fuel.  Give an engine these three things, in the proper amount, at the right time, and the engine will run.  Millions of engines prove that every day.

[datzenmike]

Wired or un-wired the choke will be on when cold starting.  Even if choke is not on (stuck open) a few pumps of the throttle should fire up. Georgia should be warm this time of year.

[Kirden]

I have a cranks but slow start issue. By "tries to start" I mean that the engine catches as if it is starting, you hear the exhaust and a slight roar, then you just hear the starter. If you pump the gas at this time, it will start, if you pump the gas before it tries to start, it will not start. I will check the timing again and double check the plugs. Does anyone have a diagram of the firing order? I just want to make sure the wires didn't get mixed up as well.

[LenRobertson]

Firing order here: http://www.davidcmurphy.com/olddat/620tech2.htm#TM

 

On a cold engine, the choke butterfly should be nearly closed or go closed when the throttle linkage is moved slightly. If the butterfly seems sticky, spray a little carb cleaner where the shaft goes into the carb top body. After the engine warms up, the choke butterfly should be wide open.

 

The supply wire to the electric choke shouldn't show power with a test light when the key is in the On position. It should show power when the engine is running ( the choke supply wire is hooked into the alternator circuit so is only powered if the alt is turning).

 

Len

[dr.feltersnatch]

i would check your compression

[Kirden]

I doubt it is compression, but I will check. The engine ran fine with the old distributor and runs great with this distributor once it starts, it's just getting it to start that is the problem.

 

Len, thank you for the diagram. I will double check everything once I get home.

[datzenmike]

So the title should read 620 hard to start (when cold)

[Kirden]

And done

[banzai510(hainz)]

sometimes splicing the HOT start wire to the ON wire will fix this,

Daniel pretty much explain the rest.

 

 

ck intake/carb for tightness

 

timming light

 

valve lash

[Kirden]

Just an update, I took off the carb hat and filter to check the choke since that seemed easiest. My choke is completely unresponsive. I checked my other weber that needs a rebuild and that choke seems to be sprung, it always returns to a certain point, but on my 620 there is no resistance on the choke. Even moving the throttle does not close the choke, but it does slightly open it. So I closed the choke, tried to start it at 7AM... and forgot to take it out of gear. Had a nice little run to pull the key (I was standing outside of the truck starting it...)

 

I did go ahead and check the plugs again, all have spark. Also, compression is low, but all cylinders are very close. Highest just under 145, lowest was just over 135. I'm just glad it started first try, didn't even stumble. I do need to adjust my valves badly, haven't done it since I bought the truck in Feb of last year.

 

Any tips on fixing the choke? It seems like the linkage is all hooked up correctly. I'm still new to carbs so if anyone has had this issue or has any advice please let me know .

[metalmonkey47]

Wired or un-wired the choke will be on when cold starting.  Even if choke is not on (stuck open) a few pumps of the throttle should fire up. Georgia should be warm this time of year.

 Unless someone wired it directly to 12V, which would hold it wide open 24/7 when the battery connected, which I think he might have been getting at.

 

Also, georgia is HOT right now, so choke is pretty much useless. 

[datzenmike]

The battery would be dead over night. Just my 710's choke relay killed the battery in 3 days. 

[DanielC]

First thing, you need to do a tune up, including valve adjustment.  Modern cars you can ignore, the computer adjusts everything as you drive.   Only when something gets way too out of range, does the "check engine light" come on.

 

Our Datsuns do not do that.  Things wear, and change, and we have to adjust them back to normal.  A 521 Datsun should have a minor tune up every 3000 miles.  It needs a few more things checked every 6000 miles, and a major tuneup every 12,000 miles.

 

The compression is a little low. 

An engine with low compression can run, but here is the deal.  The lower the compression, the closer the other two factors, (ignition and fuel) have to be, to perfect.   A nice strong ignition at the right time can fire a fuel air mixture that is not at the perfect ratio.  A perfect fuel air ratio, can be easier for a weak spark to fire. 

 

Liquid gasoline does not burn.  Gasoline has to be a vapor to burn.  The ratio of air to gasoline vapor IN THE CYLINDER has to be somewhere between about 12 to 1, to 15 to 1.   Below 12 to 1, too much gas, not enough air.  Above 15 to 1, the spark sparks, but not enough fuel to start a fire.  Even on a hot Georgia day, the liquid gas coming from the carb, into the manifold does not all turn to vapor, and you probably need some choke to get the correct mixture in the cylinder, so the engine will fire, and run.

 

If the accelerator pump works, you can get around a non functioning choke by pumping the gas pedal, this causes the accelerator pump to squirt some raw gas into the manifold, and compensates for no choke. 

 

Every engine with a carb is a little different.  Especially 40 year old engines.  You need to what your engine wants. 

I have an old tractor.  To start it, you need to crank it, with the choke pulled fully out, about two complete turns of the engine, then push the choke almost back in, and as it fires, add a little more choke.  Even then, if it is cold, the engine will start to die, and I have to pull the choke out, and back in, and the engine will catch again, and run.  Too much choke, and the engine floods, and does not start.  To little, and again, it does not start.

My 521 has a manual choke.  Like the tractor, I need more choke to start it, and as soon as it started, I need to push the choke back in, but not all the way.   To start this 521, in warm temperatures, I pump the gas about twice, with the choke fully in. then holding the gas pedal down, pull the choke knob out, but not fully.  Then crank it, and it starts, and I then push the choke in some, and also use the gas pedal to keep the engine running.  If it is colder, I have to pump it more, and use more choke.  Why am I telling you all this about a choke adjustment on my 521, with a manual choke?  Because you need to adjust all that happening in to an automatic choke carb.

 

Datsun's, in my experience are cold blooded.  My Datsuns all have ran much better in the Summer, than in the Winter.  Even in Summer, on short trips I leave the air cleaner pickup for hot air off the exhaust manifold in the hot position.  For longer trips, especially on the freeway, I will move it to the cold position.

 

Most of the time, with Weber carbs, the hot air feed to the carb is deleted.  Sometimes, the hot water feed to the intake manifold is also eliminated.  Both these will help your engine run better when cold.

[Kirden]

My choke has no tension at all. It just flops around. Once I pushed it totally closed the engine started with no problem even with the morning chill. I really would like to get that fixed but I can't figure out why it has no tension. I could have sworn that the choke worked just fine previously, but that was months ago. It was bought brand new from weber carbs direct, but the more I look at my other weber and the one on my 620, the more differences I see. I'm starting to think the one on my truck is a cheap reproduction.

[wayno]

My choke has no tension at all. It just flops around. Once I pushed it totally closed the engine started with no problem even with the morning chill. I really would like to get that fixed but I can't figure out why it has no tension. I could have sworn that the choke worked just fine previously, but that was months ago. It was bought brand new from weber carbs direct, but the more I look at my other weber and the one on my 620, the more differences I see. I'm starting to think the one on my truck is a cheap reproduction.

Can you use a choke cable to control the choke manually?

[LenRobertson]

I've never had the plastic choke cover off a Weber, but I suspect it isn't much different inside than a stock Hitachi. Inside the plastic cover (the one the choke wire plugs into) is a coil spring. This spring is what pulls the choke closed when cold. It sounds like your spring has broken or come unhooked from the arm on the choke butterfly shaft. On top of the carb body it an index line cast into the metal. Make a Sharpie mark on the plastic cover so you can get it back in the same position. If the three screws holding the plastic cover on are loosened, the cover can be rotated to adjust tension on the spring which determines how quickly the choke goes off as it warms up. I suppose it is possible your screws came loose and the cover backed off enough so you have no spring pressure, but that doesn't seem likely. If you have a broken spring, you may be able to swap the cover and spring from your old Weber over onto the new carb. It is a pretty simple fix to take the cover off and see what is going on in there. That may not be all of your problem, but having a working choke can't hurt anything.

 

Len

[Kirden]

Thanks Len, I'll take a look and see what I can do.

 

Wayno, I'm not sure I can rig up a manual pull for the choke, but my truck does have a manual cable installed from the old GM card. I'll see if there is a way to hook it up if I can't get the spring to work correctly.

 

I know that I need to adjust the valves badly, just waiting for a valve cover gasket to come in. Should be able to take care of that tomorrow. On a good note, the truck has fired right up every single time today. It turns over maybe one time then fires up, with no sputtering or bogging. 

 

I did find something interesting from checking the distributor. two of the wires seem to have week spark. I'm going to clean the cap and make sure the contacts are in good condition, but I may need a new cap. I checked the spark at the plugs and it was a bit weak, then checked at the distributor and it barely jumps a short gap. If you pull the wire and hold it close, it will only jump about 1mm. The others will jump 3mm and have a much stronger spark. I'm going to splice over the ignition and alt wires to the distributor if cleaning doesn't do any good.

 

Just a question, this is a matchbox module. Would I have any issues if the matchbox wires were connected to the wrong terminal or would it not start at all? Just testing the options.

[wayno]

It will not start if the 2 wires are backwards.

[Kirden]

Ok, well that's a relief. I checked out the plastic housing and the screws were all way too loose. I guess my uncle unscrewed them to open the choke when we were tuning it cause I remember he kept putting a screw driver in the port to hold the choke open the first time around, but not the second while he was tuning it. I wired it back to the wire he was using, it tests hot only when the ignition is switched on. Then I put some slight tension by turning the spring housing so that it would return to a mostly shut position on its own, but not tight enough to completely shut it. I started it and let it run for about five minutes and the choke was opening up on it's own. SUCCESS!!  :thumbup:

 

Thank you all for your help, I still need to figure out the weak spark from the cap for those two wires, but at least it will start and run now without burning out my starter or killing my battery. 

[LenRobertson]

It sounds like you have the choke problem solved. If the choke stays on for too long and kind of bogs the engine down when it gets warmed up, you may need to rotate the choke housing back to get a bit less spring pressure, Probably won't have to turn it back very much and maybe it is fine where it is right now.

 

When I went to start my L20b with matchbox dizzy after it sat all winter, I wasn't getting spark. It turned out to be the spade terminals on the matchbox were tarnished. I cleaned them and the terminals on the wires to the coil and it solved the problem. Also the matchbox needs to ground through the body of the dist., so if there is oil or tarnish on the back it may not be grounding well. Some guys even run a separate ground wire  from the matchbox. I believe there is a spade terminal or screw on the matchbox for a ground.

 

But the fact you have spark, just not good spark, makes me suspect the cap of wires.

 

Len