Ignition Misfire

[devo]

make sure that the short rubber hose under the carb that goes from the float chamber to the adjusting nut, is not kinked. Happened to mine causing stumbling under load/acceleration.

[Linda]

Since you may be on to fuel, I would now check the banjo bolt screens and fuel valves. One of mine had a rubber tip and it was deteriorated so it was not sealing and working correctly. Do you have brass floats?
You are being very methodical...admirable

Linda

[nismou20]

Ok, maybe not fuel related. Then back to electrical. I also had a similar issue where it left me stumped and I just bought a new dist cap even though the old one looked visibly good. That worked. Then another time I found one ign cable arcing over to battery hold down post due to it rubbing and cracking. PIA I tell ya! On another instant a corroded connector at one cable/cap. With the MSD 6al they really burn up the 90* connectors at cap. Good luck you will persevere.

[Randalla]

Didn't have a lot of time today, but did eliminate the ignition wires as the culprit. I thought I'd discovered the problem in the course of swapping the wires. The distributor cap was too loose, even with the clamps on it. Tried moving it by hand with the car running and could actually feel the rotor contact the cap at times. Discovered one of the screws holding down the points plate was too short and wasn't fully threading in. After installing two slightly longer screws and bending the spring steel clamps, tightening everything up, I was sure I'd solved the problem. All I got for my work today was a couple more things to cross of the list. Arghhhh! this is arduous.

[notoptoy]

Still, you're attacking it the best possible way, one step at a time and eliminating the simple stuff. You'll find it, keep looking!

[Randalla]

Couple more things to cross off the list. Today I swapped in a new cap and rotor with no improvement. I did discover something that might be a clue however. The car seems less likely to act up when it's cold, when I first start it up and leave the driveway. As soon as there's temperature in the engine the problem surfaces. Still feels like it's missing under load. On to the next item...

[C.Costine]

Try checking compression. Quick and cheap. It was my problem once with the same symptoms.

[Datsunz]

Sounds like it's running slightly rich at operating temp. Cold air is more dense so at the same fuel delivery as warm will have more air to mix with,than when in warm temps. less air. it is a little too rich. That's my guess.

[sunbeam590]

Mine had same syptoms and after everything else it was the plugs, I had them gapped at 40 which was ok, but just fouled...was the problem...

[Lorna c]

oh and it stops . good mystery here. I was having stumbling issues and I've just found out they were giving me the wrong distributor cap ! and another time I was tooo rich . way to rich . how much room did you have after taking it down half a turn . the way mines set now I couldn't turn it half a turn without turning it off , or as far as it could go closed . ? idk but maybe your still way rich ? I don't think I heard an answer for plugs color after pulled ? black / gold / grey? .. plug wires touching each other . I personally never knew they shouldn't until recently .haha that helped . good luck . sounds frustrating for sure . but you'll find it . one of these guys will nail the answer .

[Randalla]

Well, after chasing what I thought was an electrical issue for two months (based on symptoms), exhausting every possibility I could think of (and some you suggested), I decided I'd shift my focus to fuel delivery. I'd just rebuilt the mechanical fuel pump with Dean's kit, so I crossed that off my list. I ran the car a few minutes to make sure I'd have the full measure of fuel in the bowls, then shut the car off and popped the float bowl lids to inspect levels. Both bowls had identical amounts of fuel in them, at the correct level. Last night I removed both carbs and stripped them on my bench to see if there were any obvious issues. Previously, I'd ordered new needles, nozzles and float valves from Z Therapy, intending to replace the components when I had time. I removed both the old needles and chucked them up in my drill motor to see how true they were. One was slightly bent but the other one was badly bent. Surprisingly, the pistons moved freely in each carb when doing the drop test (no binding at all). That led me to wonder if the nozzles were worn out (larger openings than spec). After comparing the new needles with the old, I also noticed the old ones were actually 1/8" shorter, which seemed strange. Now things were starting to make sense. With the shorter needles, the carbs would be running too rich and with the wallowed out nozzles and bent needles, fuel delivery to the engine was uneven at best. Long story short, after swapping in the new Z Therapy parts, the problem is finally gone. About 6 months ago I also swapped the same Z Therapy parts into my 240Z SUs, which were also running badly. Same result, the car was transformed. The moral of the story is, eliminate one potential issue at a time and stick with it. The other moral is, no matter how good the nozzles and needles may look, they do actually wear out. For about $100 you can replace them and also install new float valves. This has me wondering how many Roadsters are running around with sub optimal performance that could be made to run like new again.

[Linda]

At least all those other things you checked or fixed benefited from your doing so!
Glad you got it sorted out
Linda

[jamesw]

Glad you got it sorted out! Happy motoring.

James

[Lorna c]

fuel line plugging or slowing the fuel ? does it kinda flutter before and during ? check tank and lines in and out going . those start to clog and the pump can't feed the carbs with what it needs and it will do this same thing . good luck I'm battling headlights blowing my fuse today ,and all week . I only wanted led lights and now I'm tearing everything out trying to find my short .

[Oceancrosser]

Micro-crack distributor cap...