popping through the exhaust at 4500 rpm or so.. HELP!

[Zedyone_kenobi]

I have 2 extra fuel filters lying around. I will put one on when I get home today before I check out my car for vacuum leaks. Cant hurt.

[motorman7]

I have 2 extra fuel filters lying around. I will put one on when I get home today before I check out my car for vacuum leaks. Cant hurt.

Yes, I was surprised because my fuel filter (made in Israel) was pretty new. May have been some remnants of debris from the earlier fuel tank mess. I also got a new fuel pump several months ago, but that made no difference when swapped out with my old one. May put the old one back in as it is the original Nippondenso (?) pump. The new one is that cheapo stamped sheet metal type. (Looks like the old one would pump more fuel as the diaphragm diameter is larger. Of course the lever arm fulcrum would need to be compared to verify). I thought this may have been part of my earlier popping problem, but I never did switch back to the old one. May do this when I get some time. You may also want to try the timing advance and a run or two without the air cleaner to see if that makes a difference. For me, with the ZX dizzy ‘over-advanced’, I get a bit of ping at the lower RPM, but the car is VERY happy at 3K. Car pulls very nicely from 3K-6K now. And, no popping at all.

Best regards,

Rich

[madkaw]

WOW, a 20 degree timing advance- that would make a difference on any set up. That's like being a tooth off!!

After experiencing what sounds like the exact same popping issue, as I noted earlier, I can say that I did very little adjusting to my SU’s to fix the issue, other than minor mixture adjustment. I even had the popping at idle at one point and then again at 3K. My SU mixture nuts are now at about 1.5 turns. I could adjust these either way ¼ turn and not make much difference in the way it is now running, which is just about perfect. I think the fuel delivery/fuel filter was the issue. I thought what I had installed originally was pretty new and clean, but apparently it was not. I installed the new filter (made in China) and did the 20 degree advance on the timing and that seemed to do the job.

As I mentioned before I also punched some holes in the air cleaner housing. Not sure if this was a contributor; the car just seemed to pop at higher RPM’s when I tested with the air cleaner off (when I was having the popping issue). Another problem I had with the air cleaner housing (a couple months earlier) was I had somehow accidentally flipped the cold/hot baffle on the front of the housing to “cold” (I live in SoCal so never need this setting). Anyway, the Z was really dogging and popping at about 3.5-4K in this condition. Flipped this back over to hot and made a big difference. Anyway, Just thought I’d pass this on. Definitely a very frustrating issue.

[Zedyone_kenobi]

I currently run 17 degrees BTDC per the european spec dizzy I had mine recurved to match.

I do not run a Vacuum Advance. I have made the runs with the BARE SU;s with no air cleaner (just plain easier to adjust quickly), with the air cleaner base on but no filter or housing (to get the benefit of the air horns), and with the air cleaner.

NO noticeable difference either way. Get popping from the exhaust in all part throttle situations near 4000 rpm.

I just do not see it being a fuel delivery problem when I will run at WOT, but not part throttle

[motorman7]

WOW, a 20 degree timing advance- that would make a difference on any set up. That's like being a tooth off!!

No Vacuum advance. Very similar to Zedyone, with just 3 degrees difference. Manual says 17 for non-smog equipped cars, so not too far off.

[Zedyone_kenobi]

I'm still stuck on float adjustment.

The jet needles are being set flush against the piston with the jet collar flush??

With the float hung upside down, I picked up the float and the instant it touched the needle with the tang, I took the measurement. It was about .55" as per the factory manual. This differs from the SU video as he showed the float top parallel with the float bowl cover when held upside down. Maybe I should ask Bruce for an explanation of this.

[doradox]

Ah, I never really looked that hard into that. Yup, That goes to my crank case ventilation, check, PCV valve is new when I got the carbs.

I removed it and it rattles when I shake it...

I will check to see if there are some diagnostic checks I can do on it.

Did you ever check this? The PCV valve could be causing you to go lean at tip in if the spring is defective. Simply pull off the hose, cap the valve, and go for a drive.

Also, have you tried running at 3, 3.5, 4 turns out on the mixture? If you are lean this should make an improvement. If it does then you can continue on your quest to find out why you are lean.

Steve

[Zedyone_kenobi]

I cannot go more than 3 turns out as the car will not run anymore. It stumbles so badly it barely runs...

I took off the PCV and blew into it from both sides... only could blow through it in one direction

I will cap it though and go for a drive..

[Captain Obvious]

I cannot go more than 3 turns out as the car will not run anymore. It stumbles so badly it barely runs...

I took off the PCV and blew into it from both sides... only could blow through it in one direction

I will cap it though and go for a drive..

Yeah, the PCV "rattle" and blow through tests only goes so far. Capping it and going for a drive would be a better test.

What happens when you go more than 3 turns out on the nozzle? It goes so rich that the car won't run at all?

I'm with you on the exhaust leak and fuel delivery stuff. If you are OK at full throttle, then it's not fuel delivery, and anything downstream of the exhaust valve (like a headpipe leak) isn't going to give you any significant performance impact. Popping noise maybe, but no performance changes.

So. Let me jump ahead a little just for cuiosity... So you put the wideband on and it shows you are very lean at midrange. What are you going to do then?

And conversely, if the wideband shows you are very rich at midrange. What then?

What's "the plan" in either event? :bulb:

[steve91tt]

I would be happy to swap my SU's with yours for trouble shooting purposes. Just as we did with the distributors. A couple of gaskets and an afternoon and we'll know if the carbs are to blame.

[steve91tt]

I'd bet the wideband will show a lean condition when the engine is popping. A missfire will almost always show as lean as unburnt fuel and extra air gets to the sensor. The interesting data will come just before 4500rpm and just after.

[Zedyone_kenobi]

I have spent some time thinking of this actually Captain.

The answer varies so wildly with the results. I do not forsee the wideband being so cut and dry. I hope it does, but in reality we both know that it will be XXX at idle, and YYYY at 2500 rpm, then ZZZZ when it is popping. I am hoping to see a trend.

If I know I am leaning out, then I can try to find out where in the fuel delivery I am leaning out. Is my fuel pump providing enough fuel, is the float level adjustment right. Is unmetered air entering into the system.

If I know I am rich, then the list gets easier. Try to find out where the extra fuel is coming from.

the thing is, all it does is put me into the right ballpark, and gives another data point to help diverge ideas from one another. It also is a quantifiable piece of data which directly relates to the engines running.

My thought is that I should not be running rich here and lean there too much. My car is stock except for the header and the custom curved dizzy. Head, cam, block, etc is all stock. Stock SU's should be able to compensate for any small variances between my setup and a totally stock setup. Perhaps my engine is not totally healthy, although that would surprise me. Maybe my cam is not totally up to snuff, but that would surprise me as well.

Your question is one of great importance...and one I shall have to deal with eventually.