Cutting out at 4000 RPM when warm

[StinkyCheese]

At the risk of getting booed offstage, I'm going to ask the same question I've been asking in "points vs pertronix". With a lot of help from Arne I got my pertronix ignition working. It starts and runs much better and no longer backfires. However, when the engine gets warmed up, the problems start.

Note that when I start out, it runs like a champ. I can rev all the way up to 6000 rpm without a hiccup, going uphill as fast as I can go, in all gears (keeping it under 80mph, mind you). But once that temperature guage gets near the half-way point, it starts having problems.

It will hiccup and run poorly around 4000-5000 RPM. Usually when its warm and I pull into my garage, it will die on its own. I have to keep my foot on the gas at stoplights because it will invariably drop to 500 RPM and then die within ~10 seconds.

This has been going on for while - for a long time I thought it was my ignition, but the behavior is the same with points. I had this looked at by an old Nissan mechanic that has been working on Z's since the 70's. I paid him $180 to adjust the carbs when it wouldn't pass emissions last year. He told me he adjusted my carbs "as lean as they would go". It still wouldn't pass smog until I got some vacuum hoses routed correctly. I put in new spark plugs (NGK BP6ES). The wires are new. EGR valve is working correctly.

What behavior in my engine cares whether it is hot or not? It seems like a switch is thrown when I get to certain spot on the temp guage. This isn't some fancy computer-controlled motor... What, if anything, is controlled by a temperature switch? If there isn't anything, what else could be affected by heat? I really don't think its an ignition problem..

I really appreciate your help. If I can't figure this out soon, I'm going to have to tuck my tail and take it to the dealer.:disappoin

[Zforce]

Just get rid of the flat tops, anything is better, get rid of the egr too.

[StinkyCheese]

Just get rid of the flat tops, anything is better, get rid of the egr too.

Yeah I looked at ZTherapy for some round-tops. Looks about $800 - I don't want to drop that much cash unless I know its the problem... Why would heat affect my carbs at 4000 RPM?

[5thhorsemann]

The flatties are garbage, I picked up a set of used R/T's off of a 72 and bolted them up on my 73 and it was as if God smiled down on the car and healed all its ills. I will bet you anything that it will fix alot of your troubles. If you cant swing the cash for fresh and beautiful ZT carbs, find a set of used for like $300 and clean em up, you will thank yourself in the end. Ditch the smog gear as well, its useless on a 73.

[30 Ounce]

Might want to replace the coil. Mine had a hicup similar to that and I never even considered the coil but replaced it with an MSD Blaster (not especting anything!) and it has never hicuped again. The flat top carbs were crap. You will always have drivability issues with those. As the engine warms up the air fuel ratio needs change and I suspect your carbs are running very rich. Take the domes off and clean the piston and dome with carb cleaner. Make sure everything slides smoothly before reassembling and fill the oil dashpot with ATF fluid. That might help.

[StinkyCheese]

Might want to replace the coil. Mine had a hicup similar to that and I never even considered the coil but replaced it with an MSD Blaster (not especting anything!) and it has never hicuped again.

Coil is new, too.

[StinkyCheese]

The flatties are garbage, I picked up a set of used R/T's off of a 72 and bolted them up on my 73 and it was as if God smiled down on the car and healed all its ills. I will bet you anything that it will fix alot of your troubles. If you cant swing the cash for fresh and beautiful ZT carbs, find a set of used for like $300 and clean em up, you will thank yourself in the end.

Any suggestions on where to get a set from a reputable source? I'm a littel squeamish buying sight-unseen.

[beermanpete]

Try Z Therapy. http://www.ztherapy.com/

[5thhorsemann]

I bought mine on ebay, I read the guys feedback and looked hard at the posted pics to be sure everything was there linkage wise. As I recall, I paid just under $300 without the air box. They are relitively simple to work on, and as long as they are complete you should have no problems.