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

[steve91tt]

Blue, We swapped my distributor into his car earlier this year...no change.

My offer stands Zedyone_kenobi, you can borrow my SU's or any other part of my car you want. Just pick a time when you want to get together.

[Zedyone_kenobi]

The reason I am hesitant Steve is two reasons

1 when I pulled the carbs off my intake the first time the gaskets on the insulators came off in pieces, if that happened to your car you would be in a tight place since yours is a daily driver

2 I really do not think its the carbs any more. I realize I need to try another pair for completeness. But I think the results will be the same

Blue we swapped dizzies and coils

Steve's dizzy had another pertronics as well

Carbs will be here next week hopefully the troubleshooting can continue

I am going to focus in great detail for vacuum leaks in strange places

[Zedyone_kenobi]

Steve we can try if you have a spare set of carbs, I will get an extra set of insulators

[steve91tt]

Why don't we try swapping the entire intake. All we'll need is a couple of intake gaskets and a spare afternoon for wrenching. Your place or mine?

[Captain Obvious]

If all of that does nothing. And a set of seemingly good carbs do not fix it I am going to go crazy

Mark my words, I will fix this

Your plan of attack seems sound. Especially the step where you go crazy.

I remember from earlier posts that you had swapped the distributor for another and there was no change, but I didn't realize you had swapped Pertronix for Pertronix. I suggest that you try an old school OEM non-Pertronix distributor. Whatever configuration is original for your year.

I don't see how the distributor could make you run leaner at midrange... Richer maybe (if you're getting a lean-misfire), but not leaner... But changing the distributor might reduce the popping effect of running lean in the midrange. Did I say that right? Does that make sense?

What I'm saying is that maybe between ZT's recommended additional turn of richness over the entire range and a different distributor, you might get better results. With the port vacuum advance source that we (normally) use, midrange light cruise is where you would have the most amount of distributor advance. Higher than at idle, and higher than WOT. Light to midrange cruise would be the most advance.

I know that you're not running any vacuum advance at all, and I'm saying that maybe you should?

Also, I've got a set of round top insulators and gaskets that you're welcome to borrow if you don't find a set to purchase outright. Shipping couldn't be more than a buck or two. Just LMK.

[Zedyone_kenobi]

Thanks very much sir. I certainly appreciate it

Steve, I will be in touch. The next time you hear from me though may be to help me take off my hood! HAHA

When I get the carbs back, I will report back in. I will look into another completely stock dizzy as well. I have time on my hands just sitting around waiting for carbs!

[AWAUDIO]

Just a thought, something I don't seem to have seen anyone reference here. Ran across a Datsun TS73-10 which indicated on the

!972 240Z with manual transmission, float bowl HJG46-R8B, that the front and rear carbs have different float bowl heights. Front carb 15.5 to 16.5 mm, Rear carb at 11.5 to 12.5 mm. Just throwing it out there FWIW. You seem to have tried everything else. Good luck on your odyssey.

Andy W.

[Zedyone_kenobi]

Thanks Andy, but I have a 71 240Z. I cannot imagine why it would be any different though

[Travel'n Man]

Not wanting to go back through 14 pages of info to review, but my '72 does have two differnet SU's setting for fuel height........FYI

[240260280z]

You saw the thread where a problem ~4500 rpm was due to a "weak spark".

Could be the coil...

Below are a few more threads and excerpts.

Philip

http://www.classiczcars.com/forums/showthread.php?42073-Rev-limiting-problem-at-4000-rpm&highlight=4500rpm

http://www.classiczcars.com/forums/showthread.php?14498-car-misses-at-high-rpms-(4500)&highlight=4500rpm

http://www.classiczcars.com/forums/showthread.php?41414-Mid-Range-RPM-Hesitation&p=391378#post391378

Arne

Administrator

Well, my best guess as of now is that the Pertronix will work fine in most cars, but only if everything else in the ignition is good also. The differences between what I have installed now and working fine (so far) and what was failing to rev past 4500 RPM when I last went back to points are two small things: 1.) I replaced the older BP6ES plugs with a fresh set; and 2.) I made up a new power supply wire to run to the Ignitor that was much larger gauge wire than the previous wire, hoping for less voltage drop to the Ignitor.

That's all I did differently, yet this time it's running fine. The jury is still out on this, as I don't yet trust it to stay this way.

[Zedyone_kenobi]

Thanks Blue.

I have acquired a very nice OEM distributor and will be swapping mine out with it. I have taken it on good faith that it was curved correctly and maybe it is. I am going to build up a whole new distributor with a new pertronix system and see where we go. I am currently STILL waiting on getting my carbs back. THey have been shipped apparently.

I did run a jumper from my battery straight to my coil before and the problem still persisted as I thought the stock tach was doing something crazy. I am getting 13.2 volts to the coil if I remember correctly.

for all intensive purposes this still looks like a smart vacuum leak, but I will be darned if I know where it may be. I still have to try to get a full suite of readings from my vacuum gage after I get the carbs back. Then hopefully somebody can do the same and we can compare.

I will take a look at the links you posted Blue.

[240Adam]

My car used to do that, I had a stock ZX dizzy and it had a bad vacuum diaphragm. I changed it out and no stumbling.