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

[Zedyone_kenobi]

They have no numbers on them, I looked. But the invoice from Z therapy said N27 I am 99% sure. I will check for you and get back.

I agree about the low float bowl having little to do with part throttle popping, but I have to check everything at this point...

I will figure this out if I have to replace every single part on this car one at a time. If that means building up an entirely new L24 so be it, but as GOD as my witness I will track this down!

Edited January 7, 2012 by Zedyone_kenobi

[Captain Obvious]

Yeah, I understand completely. I don't fault you one bit for trying the seemingly unrelated. I'd be trying anything by now as well.

Something else I forgot to ask a while ago... I wanted to confirm the circumstances of the mid-RPM misfire. Does it occur only under light load (like when you are cruising along at a steady speed at 4500 RPM-ish) or does it occur under no load just sitting still with your foot a little bit on the gas pedal? (Or both?)

Thanks for the needle info. I've been messing around with my flat-tops and have measured a few different needles recently including the N-27. I should probably post my findings sometime.

[Zedyone_kenobi]

Only occurs when I am actually driving, sitting still and revving it is perfect

[240260280z]

I don't think it is carbs.

I think it is related to any of these

-slop in the drive spindle to distributor

- slop at crank gear to distributor drive spindle

- mechanical timing not correct by PO (crank timing chain and cam)

I re-read your early posts and this stuck with me:

"Seems I have had this issue since I owned the car in some form of severity or another. When I first bought the car, it would simply NOT rev past 4500 rpm at all. Now I can get it to rev to 6500 rpm thanks to the Z therapy carbs, but now it is popping pretty bad on the top end. "

Looks like the ZT carbs may have masked a deeper issue.

[steve91tt]

I'm starting to think along the same lines as Blue. I think it's time to open the valve cover and check timing marks to confirm valve timing.

To check for slop in the distributor drive system you can use a timing light to see if the timing jumps around or stays nice and constant at various RPM's In other words, check for nice solid timing at 1000, 2000, 3000, 4000 and 5000. If you see the timing mark jumping around then there is slop in the system. It should be very steady and consistent.

[madkaw]

So did I miss something or did you test after float adjustments?

[240260280z]

Ah ha, I dug deeper and found that you had the same problem in 2008 and fixed it with a distributor cap and rotor, and now you say a ZT carb fixed it:

http://www.classiczcars.com/forums/showthread.php?31577-Revving-problem-is-solved!!&highlight=

A lot of folks are trying to help you out but you gotta give us ALL THE DATA ....well just don't cry Wolf.

Think you got slop in the spindle linking the oil pump to the distributor or in the gear drive off the snout of the crank.

Get your buddy's Z over, pull the distributors like you did and compare how the tang at the end of the spindle move when wiggled,lifted,turned. Use a dial gauge rigged up to an extension out of the mounting for emperical measurements.

Quick and dirty test that just came to mind:

For ease and consistent measurments, use the same distributor on both cars locked down with a dial gauge on the rotor. Any slope in the distributor will be nulled out by using the same distributor. Also repeat this many times throughout a whole revolution of the crank as the problem could be a broken or worn tooth in the drive helical gear.

Also try cranking with a socket at the crank back and forth while holding the rotor in your fingers to see how the tang behaves/feels between the two cars.

Edited January 7, 2012 by Blue

[Zedyone_kenobi]

Well I took her out for a spin and to no surprise the float adjustment did not fix anything, BUT I can definitely rule out the floats not being adjusted...

So while the engine was warm, I took the plugs out and looked at them and then decided to do a compression test.

I taped up the pistons in the domes, but like a dummy I forgot to push the accelerator to the floor while I cranked the engine so the butterflies would be open. Still, these are my results

1 2 3 4 5 6

175 175 172 178 175 178

FAr better than I thought. Those numbers were with 5 compression cycles.

I also did some runs pulling the choke when it was making a popping....This is what happened.

I was in second gear and slowly gave it gas until I was into the severe popping regime. Then I pulled the choke back a bit where I knew the jet tube was being moved down. The car surged forward and started to accelerate again, but started popping again at almost 6000. The car seemed to like the enrichment.

This led me to think the car was running lean despite the popping noises it is making... so I pulled the plugs after driving home normally..

Here are the results.

[5thhorsemann]

Have you tried capping off the brake booster and going for a spin to see if that effects the condition?

[madkaw]

I thought it sounded like it was running lean by your description-thus why I was pushing for an enrichment of the floats. The plugs look at little white from what I can tell-maybe leaner on the front 3.

So she felt like she had more power with increased fuel??

This could also be a vacuum issue, but your vacuum showed strong signal at idle.

After setting the rear float-did it pass the test of being able to see fuel sitting at the top of the jet with the piston removed??

[30 Ounce]

After seeing those plugs and your results from the compression test with the throttle closed I would be looking for a vacuum leak in the intake system!!

[Diseazd]

Certainly smells like a vacuum leak.....