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mr mikey

Weird dysfunctional SU carb issue, rebuilt and floats reset going on 8 times now.....

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Do you have access to any spare carbs that you could bolt on?

I borrowed a pair from my buddy off his 240z, and they did similar, but what they would do is let you idle it down to 700 and stay running fine for a while. Then after about 5min or so, it would just act like you turned the key off(with the exception that it would still reverse rotate and spew smoke from the relief vents of carbs).

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Can you elaborate more about what's blocked off and do you have anymore pictures showing the induction system ?

Yes, I can take more pics. All vacuum hoses that lead directly to a vacuum source have been blocked off, so any/all accessories you see with vacuum hoses are just dead hoses. I'll eventually mill down the blockoff plates I made for all the components and install them, just been super busy with work. Also, the heater crossover channel(preheats manifold)has been blocked off internally. I need to figure out how to get the screw-in hose barbs out to replace with brass plugs.....they look like they're in there pretty good, didn't want to break one.

I'll get more detailed pics when I get back, gotta go outta town, cousin is getting married in Indiana. I don't like that drive.

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I couldn't help notice that you were measuring 23mm below the top edge of the bowl.

According to the factory manual, the 23mm starts from the bottom of the float bowl

lid. Turns out the distance from the bottom of the float bowl lid to the bottom of the

lid is exactly 3mm, if you don't count the thickness of the gasket, the proper level

for the fuel would then be 20mm below the top edge of the bowl. Nobody has ever

said how accurate this has to be, but we know if the level is too high, we get a

rich mixture.

I re-read your comment, I measured 3.0mm, you measured 3.4mm, close enough.

It's so much easier to just measure 20mm down from the edge, why is everybody

stuck on 23mm?

Jim

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Well I stopped trying to figure it out for now, got alot of body work to do. But if someone could confirm their advance at these 3 rpms, it would give me an idea of which way to adjust. With the vac advance hooked up, in neutral, no engine load. 18 degrees @2200rpm, 15 degrees @2000rpm, 12 degrees @1800rpm. If I adjust idle to 1700, you can hear it go from a perfectly smooth idle to an every so often hiccup, like it's either loading up or ignition is being cut for a split second.....then adjusting down to about 1650rpm will make it die and do it's reverse rotate thing.

Floats are set per Blue's post, and that's with the jets set to 2 turns down.

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Well, I found something interesting. When I began to idle it down, the moment it starts acting up is when the spark becomes erratic, then I lose spark and it stalls, then regains spark the second it begins to reverse rotate. Talk about weird.

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Ok, I reversed the polarity on the ignition control module, where it reads the spark trigger, and it fires right up and idles fine(with a slight hiccup every so often). So used that time to make sure carbs were set, advance was correct, etc etc etc. Only prob with running reverse polarity is you cannot rev it any, it'll only idle(set idle to 700rpm). Reversed the polarity back to correct, and it still does the same thing. Base timing is at 9 degrees advanced, advance tube plugged. Everything is doing right, but now have an issue. My old service manual is well used, especially in the ignition areas. I need to know what to set the hall effect trigger to, as far as gap is concerned. I cannot see the numbers, too much smudge. Local guy told me that I can't just set it to almost touching, without touching, because it would cause the ignition module to see too many breaks in the magnetic field, and the spark control would be all over the place. So I guess I can't set it like I do the gap on an old magneto engine.

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Ok, set to .010", and it idles down to about 1300 then loses spark. Set to .008", and it's down to about 1000rpm, any lower and it loses spark. I tried adjusting to .006", but the very bottom of the "fins" on the dizzy shaft are touching the pickup. The fins look like they're straight until the very bottom, and they stick out a little. I figured I'd been ripped and gotten sent a worn out dizzy, so I ordered a new one and the fins are the exact same way. Anyone notice their electronic dizzy's "6-point star piece" on the shaft being shaped like this? The gap throughout top to bottom is the same, except the very bottom, each "fin" of the star piece has a lip that sticks out a little farther?

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Ok, I kept going down in size of feelers until it would idle at 400rpm, so I'm guessing the size it requires is .004". I had to mill the bottom lip off each fin so it wouldn't scrub the pickup, but everything seems to work fine now. Thanks a bunch, this thread can be closed now.

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Just goes to show to keep an open mind when troubleshooting.

Not sure why you want to idle at 400rpm?

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Just goes to show to keep an open mind when troubleshooting.

Not sure why you want to idle at 400rpm?

You're so right, can't believe it wasn't carb related after all LOL. I don't idle at 400rpm, but I also didn't want it stalling right below idle speed. I've got it set to idle when fully warm at 700rpm, but if I'd set the gap to 700rpm(.006"), then it would stall the second it started to go below that. I guess I could've set it to .005"(mathematically stable down to 550rpm), but my gauges go from .006-.004", no .005" feeler gauge. I guess what I did, was give myself a 300rpm buffer zone below idle speed, as a precautionary measure.

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