Hitachi Float Adjustment

[TrevDaddy]

I have consulted my Hanes manual, but the description is very weak. I have also searched with very minimal description of this process.

 

I have very poor fuel economy for such a small engine and lightweight truck. Just driving 30 miles took the needle from a mm past full to about 3mm below it. It also smells extremely rich when running... When my friend rebuilt the carburetor, I believe he simply installed a new float valve assembly and put the glass in upside-down (just a guess). I am new to carburetors so I was wondering if anyone else has dealt with this. I don't have a feeler gauge nearby, so how will I adjust the gap to the specified .039"? Also will I have to remove anything besides the glass and float valve assm. to do this? I appreciate the help, once I get the richness down, everything should be hunky dory with the engine.

 

Trev

[420n620]

just so happens, I'm rebuilting a friends 80 Hatachi carb today. here's a pic of how to adjust it, of course the carb is off the motor / engine. The measurement is 7.2mm or 5/16 where it shows to measure at #2. This is for the height of the float, let me know if you need the drop.

[datzenmike]

Pinch the rubber fuel line and run until empty, or place rags under front of carb to catch the gas and remove the three screws and sight glass, save the rubber gasket. (the level mark on the glass should be 2/3 or 3/4 up from the bottom) With glass off, lift the float gently with a pencil until the needle valve closes Don't force. Adjust the tab (#3 in the above picture) until the top of float is level with the top horizontal underside of the float chamber. (generally the #2 in the picture) This should be close enough, don't go overboard trying to get perfect, + - 1/8" is more than fine. There is a small brass spacer on the hinge pin between the glass and float... watch that you don't let it fall off the pin and get lost. Replace gasket, glass and screws and check level and look for leaks. Remember, as long as the fuel level is close to the mark on the glass it's fine.

[TrevDaddy]

Thanks guys, I'll try to get this done tomorrow before I have to go into work. As of now the level is far above the line. Is this the only possibility for crappy fuel consumption? I have no leaks in the fuel system, and the brakes are adjusted well enough, it seems like such a small thing couldn't cause so much fuel usage. I'm going to put some new iridium plugs and new wires in just for kicks as well, I don't know how old the current ones are.

[420n620]

I forgot to mention that when you install the sight glass piece, the float level line should be towards the top.

as for fuel consumption, make sure your valves are adjusted correctly and timing is dead on. If you don't know the age of the plugs and spark plug wire, I would change them also. gl

[TrevDaddy]

Have you adjusted the valves before? I should try to time it tomorrow as well and make sure that is correct. I'll look into the manual and see if there is a description on how to do so.

[Skib]

I'll look into the manual and see if there is a description on how to do so.

 

Its a basic maintenance procedure, youl need feeler gauges to do it.

[ppeters914]

Good Hitachi info:

 

Downdraft Tuning Guide

[ggzilla]

As of now the level is far above the line. Is this the only possibility for crappy fuel consumption?

Not the only possibility, but the one thing you know is wrong. Remember: don't fix it if it ain't broke. Fix the float level now, then see if the fuel economy is good.

[72wagun]

Have you adjusted the valves before? I should try to time it tomorrow as well and make sure that is correct. I'll look into the manual and see if there is a description on how to do so.

 

I did a valve adjustment on my wagon when I first got it. In my case it improved the power noticeably.

 

Check this link:

Mike Klotz valve adjust how to

[datzenmike]

You'll have to remove that float to bend the tang... don't forget that small piece of brass between the sight glass and the hinge pin, don't loose it!

 

 

Setting the lash hot is the most accurate method. Use a 0.010" feeler gauge for the intake valve clearance and a 0.012" for the hotter exhaust valve. A flat blade screwdriver and two open end wrenches, 17mm and 14mm? I forget.

 

Warm the motor up thoroughly, set TDC on compression, remove valve cover. Check the following:

 

Ex on cyl #1

Int on #1

Int on #2

Ex on #3

 

Rotate the crank ONE full turn and check:

 

Ex on #2

Int on #3

Int on #4

Ex on #4..... done!

 

To change the adjustment, hold the larger bottom bolt and loosen the top one. Use screwdriver to adjust clearance to just fit the feeler gauge. Hold bottom nut, tighten upper nut, and re-check clearance. This is important, as tightening the nut can throw the setting off.

[ggzilla]

Datsun recommends a valve adjust with every tune-up, every 12months/12Kmiles.

[TrevDaddy]

Alright, I'll adjust the valves sometime within the next two weeks. I'm going to mess with the float tomorrow at school, where I have my tools. Hopefully I'll be able to notice a difference afterward. Also needed to be purchased are a new set of plugs and wires, and a valve cover gasket. It may be that the PO never adjusted the valves at all. Mklotz's tutorial is great, I watched it previously. However, his method called for .008 for intake and .010 for exhaust. Was his done differently than Mike's suggestion?

 

I appreciate the help guys. Hopefully after those few things (and perhaps another seafoam) the truck get some power and economy back (maybe be less smelly too :lol: ).

[ggzilla]

Don't forget to set the idle-speed and idle-mixture after changing the float level.

Have fun, take your time.

[Skib]

Alright, I'll adjusHowever, his method called for .008 for intake and .010 for exhaust. Was his done differently than Mike's suggestion?

 

 

hot and cold adjustments

[mike]

Im not sure this will apply but do you still have the emissions crap on the side of the manifold and are your vacuum lines hooked up right? I plugged one of the vacuum ports on the side of the stock carb on the 74 because the factory ones were cracked and dry rotted. It caused the fuel level in the bowl to go up, it also made it race at the correct idle settings and it ran like shit when I adjusted the idle down. It took me a while to figure this out because I plugged them off after a carb rebuild and head gasket. After messing with everything else I figured I may as well replace the vacuum hoses, hooked them up correctly and readjusted the idle and I can barely hear it run and Im getting high 20s low 30s for mileage... I havent checked it since I finally broke down and replaced the original cap, rotor and points but Im sure its better.

[DanielC]

In your carburettor, there are holes that the gas is sucked out of when the engine is running. These holes are just a little bit higher than the level of the gas, set by the float level. If your float level, (the level of the gas in the float bowl) is too high, it is easier for the gas to run into the engine, with tha same amount of air going into the carb. High float level, your engine runs rich, and uses more gas.

If your float level is way too high, is is possible for gas to just "run over" even if the engine is not running, until the float bowl empties to a lower level.

[TrevDaddy]

Update: Took off the sight glass today and looked at the float level, it was almost perfectly parallel to the top of the chamber. Flipped the glass around (like I expected) and ran her up to refill the chamber. The fuel stopped right on the line. I did notice a small leak around the inlet of the ball valve, but there is a nut there so I will simply tighten that up. It doesn't seem like a great enough leak to cause poor economy, but a leak nonetheless. After all this, it seemed to smell better, but still rich. I did forget to mention, that sometimes the engine chugs a few times after I have turned it off. Probably what DanielC was describing.

 

I ordered a set of plugs and wires and a valve cover gasket all for $40. Later this week I'll find time to get them installed after valve adjustment. Maybe I'll have the stuff on Friday so I can get it done that night.

[ggzilla]

After all this, it seemed to smell better, but still rich.

Did you adjust the idle speed and idle mixture?

[TrevDaddy]

I have it runnin a little high for these colder months, but forgot to adjust the mixture screw. <_< I could do that today no sweat. From what I have heard, the best is achieved by turning it all the way in, then backin it our 2 1/2 turns correct? Or is there a more precise method?

[mike]

If youve got a vacuum guage you can hook it up to one of the vacuum ports and adjust the air fuel mixture until you get the highest vacuum reading. Or you can turn it till the motor races a little and back it off a tad till it slows down. Its usually pretty close to the highest reading of the vacuum guage this way. One nice thing about using the vacuum guage is that if it doesnt move much with major adjustments you know youve got a vacuum leak somewhere... which will also cause crappy economy.

[ggzilla]

From what I have heard, the best is achieved by turning it all the way in, then backin it our 2 1/2 turns correct?

That is NOT correct, that is just a 'baseline'. And maybe the whole answer to your fuel economy problem. To get an accurate adjust, you must set the idle speed to the specified (usally 750 RPM, depends on the year and model), then adjust the mixture for highest idle speed. Then adjust idle speed again. Repeat until stabilizes (won't go any higher by turning mixture). This is called "best idle", and yes, a vacuum gauge can be used too, but is unnecessary. Finally turn screw in until idle speed drops 50 RPM. This is called "best lean idle" and gives you beaucoupe economy.

 

Check your Datsun repair manual for the specific specifications and more details on the procedure.

[TrevDaddy]

Thanks for the detailed descriptions guys. This truck is my daily now, and I really need to get the carb tuned in such a way that I won't have to touch it every goddamn day.

 

Update:

I got the idle set to a decent level when I got home from school yesterday, and it ran just fine. It did have a little bit of white smoke, but that went away after I reset the mixture a little bit. However this morning on my way to school, I had no problems UNTIL I got on the highway. I revved it slightly high in 3rd on the on ramp, then as I was shifting into 4th I noticed that the idle had shot up. It sounded dangerous it was so high. I had to pull over and use a f'n fuse (forgot my screwdriver) to turn the screw down to an acceptable idle. I don't know why it's doing this, and I am really upset about this stupid warn out hitachi.

 

I was offered $140 for a new one from my buddy at the parts store, I might just do it. I know I want to keep the money for a really nice dual setup down the road, but this has to be driven daily and I want it to run right.

 

Good news though, I got hired yesterday to a company that pays 12/hour. That's 4 more than I am making now, and I start on Feb. 1st. That's really good, because now I'll have enough cashflow to really start fixing this engine up and start pricing an L20.

[Roadracer Al]

My thinking is that $140 for a reman carb that *should* resolve all the issues is probably well worth the money. Think about it this way -- how many hours have you spent dicking around with the worn out old one? If you value your time, that's money lost, and money you should apply to a new carb.

 

Once I figure out which carb is on my L20, I'm going to get a replacement - the thing runs horribly, gets crap fuel economy, needs starting fluid to start when cold, takes 10 minutes to warm enough to drive.... I'm throwing money away by *not* fixing the carb.

 

One thing that struck me when reading the Hitachi rebuild article referenced earlier is that the author stresses the importance of having all the emission control stuff working properly -- they apparently have a lot to do with drivability issues as well.

[ggzilla]

Yes, spark problem and vacuum problems can cause horrible driveability and fuel economy problem, even if you have perfectly working carburetor.

 

the importance of having all the emission control stuff working properly

Mainly this is about having no vacuum leaks in all those hoses and diaphragms. But also when connected incorrectly it can cause problems.

 

Ya gott start somewhere. Either with the carb or the other stuff. If that alone fixes all the problems, great. If not, don't give up. Tackle the next phase. I got ancient Datsuns running perfectly.