L20b Hitachi carb issue?

[Spootamunga]

Hey guys,

First post, but I've done a lot of reading on your forums, and have learned a lot. It's been a great resource! Thanks for your efforts here. Greatly appreciated. Sorry if this has been covered in another post somewhere, but I haven't been able to find it if it has.

 

I have a Canadian model 1980 510 2-door sedan (116,xxx kms) with the L20b, 4-speed manual,  and factory hitachi carburetor. I do have a header that goes back with 2.25" exhaust through a Thrush resonator and a supersonic muffler, but other than that the setup is stock. It has a new ignition coil, rotor, cap, plugs, as well as a new electric fuel pump and fuel filter.

 

I'm having a recurring problem with what I suspect is the Hitachi. I should mention off the top it has an automatic choke that isn't working, but I just warm up it up manually before running it. I tried installing a manual choke, but it doesn't work with how tight the aircleaner assembly fits on the hitachi; the air cleaner assembly binds with the choke's action. I have an alternate air cleaner assembly that (i think) is from a Z22 720 that fits, but I feel like it brings vacuum issues I don't have the knowledge to figure out, so I don't use it. Either way, car is warmed up, choke is open, and we're cruising when the problem occurs. 

 

Booting around town it almost never has a problem. However, longer drives at highway speeds, and especially steeper hills at highway speeds, (or even low speed steeper hills at times) it seems like it's flooding itself. it starts surging and bogging, especially at lower RPMs. If I floor it, it seems to pull itself out of the funk at about 3k RPM, but goes right back into the sputtering/surging/bogging until I can get up to that RPM range again. I'm wondering if the float valve assembly is maybe sticking, but I really don't have the knowledge to troubleshoot this, or the confidence without some instruction to start tearing it apart. I did empty a can of carb cleaner down the barrels last weekend, but other than that I really haven't done anything.....

 

When i bought the car, he had it idling really high, which caused dieseling on shutoff, but I don't recall having the surging issue at that time. I've brought the idle down to about 800 RPM (warmed up), but sometimes it also drops when I hit a stop sign pretty low, to the point that it has stalled itself once or twice.

Any advice? More information I can provide. Would really appreciate any feedback. I'll probably swap over to a 32/36 DGEV when I can afford it, but it's a pretty hefty bill importing one out of the US right now with the exchange on the Canadian dollar, shipping, and duties.

 

Thanks in advance.

 

[datzenmike]

Welcome to Ratsun where Canadians meet on an American forum. NICE looking 2dr!!!! Though I prefer the earlier 'round eye'.

 

 The US A10 got the newer Z20S engine in '80 but Canada continued with the L20B so this is normal if someone starts talking about their '80 Z20 engine.

 

First the choke.

Is it fully open when the car is warmed up? or do you have it wired open?

 

Poor running...

Does black smoke come out the exhaust? This could be from running rich from flooding or Is the choke partly on? This would help explain the poor driving.

[Spootamunga]

Thanks for the reply. 

 

Choke is fully open, I'm actually considering wiring it open though so I know for sure it's staying open. This Auto choke is a PoS and whoever wired this thing before made a real mess.... I'm waiting for a Haynes manual via Amazon to start making sense of what he's done. I tried to like I said in my OP to put in a manual and be done with it, but the air cleaner assembly binds with the action of the choke so it's a no go. It's kept in a heated garage, and only driven on sunny afternoons anyways..

 

I'm definitely getting black soot out of the exhaust, not black smoke though that I've seen. It's running rich im almost sure of that. I've done the "turn the air/fuel screw one way until it starts to struggle, turn it the other way until it starts to sputter, then figure out where the middle of those two is" I don't even know if that's right, but I feel, from sound, it's running where it should be.

[Spootamunga]

I'd like to lean the air/fuel mixture, like.. maybe half a turn or something, but I don't know which way to turn the screw to make that happen lol.

[datzenmike]

It's called the idle mixture screw and that's exactly what it does, it sets the mixture at idle. It has no effect above idle.

 

Your carburetor should have a small round glass window in the front of it. Have a look where the fuel level is when running. It should be at the dot in the center.  If over filling this could be the float is set wrong, dirt in the float needle valve won't let it close or the electric pump is too high a pressure. You want about 3 PSI.

 

 

Back to the choke. Check there is 12 volts power on the Blue wire going to the round black choke heater when the engine is running. If not it's simpler to jump that wire to the red idle cut solenoid wire beside it. Idle cut is always powered when the ignition is on so it will supply the choke now too.

[Spootamunga]

No dot that I can see but it’s sitting probably 2/3 full now.

[Spootamunga]

Thanks for the feedback. At least I have something to chase now. I think I saw a post somewhere where you explained how to take apart float assembly, I'll see if I can find it again. As for the choke, it's not a high priority to me right now, but I will check the power, and jumper over the other power if there isn't anything there. The ground for it seems to just be floating in the engine bay, not grounded to anything. Perhaps I'll ground it to something!

 

When putting the electric choke back on, how does it set up initially? Do i turn it until it just touches the choke lever and tighten it down, or do I have it turned so the choke is all the way on and then tighten it down from there?

 

Thanks again for answering my questions, this is huge for me.

[datzenmike]

When cold, turn till the choke 'flap' is fully closed. Naturally it will need resetting come winter as cold is relative. When the ignition is on, and presumably engine running, the heater takes 8-10 min to warm the bi metallic coil that unwinds and opens the choke.

 

The battery ground cable is bolted to the head near the #1 spark plug. The heater and idle cut solenoid ground through the carburetor bolts to the intake.

 

Take for a drive and the next time it acts like it's flooding, immediately get the clutch down and the ignition off and coast over to the side of the road safely. What you are trying to do is preserve the fuel level in the carburetor at exactly the time it acts up.  Now have a look at the level in the glass. Is it higher or about the same?

 

What pressure is this electric fuel pump? Where is your mechanical pump???

[Spootamunga]

The electric fuel pump was replaced before I bought the car. It's 4 PSI. Where is my mechanical pump? In one of the many boxes of spare parts i received! 

 

I checked the power to the choke heater and it's all good. Ground is flapping around so I'll ground that, and put the choke back on yet again and try it. The lower (of the 3) clasps to hold the auto choke on to the carb are gone so i've fashioned one.. sort of, so it's a bit of a thing to get it back on there, but at least now I know how to set it, and we can see if it works. It should I suppose if there's power. and it's set correctly.

[Spootamunga]

PS - Well theoretically... because I get no change in my idle when the choke is on or off. Having the choke on does not increase my idle speed.

[datzenmike]

Spray the carburetor linkages with WD-40. Hold the throttle half open and work all the linkages connected to the choke to loosen them. There should be a fast idle cam that is pulled on with the choke. Should be loose and free to move. Looks something like this...

 

[Spootamunga]

Awesome thanks, will check that for sure and see what I can find.

 

As for an update, put the auto choke back on, connected everything back up, grounded the ground, and set the auto-choke like you said, and..! It worked. It didn't change the idle, but it did actually actuate, turn on the choke, and then after a quick rev a few minutes later, opened up and stayed that way.

 

Took it for a rip out to what I've dubbed 'Failure Hill' and it ripped right up it, no sputtering. I'm not daft enough to call that case closed yet, but it was nice!  

 

Thanks for your help today.