Won't rev above 3K - running short of ideas

[WarrenZ]

Problem now completely solved.

Warren do you have regular SU's (early style) or the more complicated later style SU's which came on '73's??

JimmyZ - they are round top SU's (3 screws).

I fitted new plug leads and new lead from coil to distributor, new rotor and brand new spark plugs. Rev's strongly all the way to 6000 before the tacho drops to zero (needed to move the red wire from the pertronix ignitor to the other side of the ballast resistor as per IZCC how to post)

I am convinced it was mostly a points issue, but the rest of the ignition system was old and tired so probably was not helping.

Xray and Madkaw - how are yours going ?

Warren

[madkaw]

Warren,

I haven't had time to mess with it over the holidays. I will be considering both yours and Mat M's approach. I don't doubt there can still be a dirt issue with this car even though I thought I had fixed this. I also can't wait to update the ignition(pertronixs on order), to elimimate any possible ignition issues.

I plan on removing the sending unit and inspecting it closely and then blowing air thru the supply lines. I think I will also inspect the "new" filter to see how it looks.

The car still has points, wires with unknown history, autolite plugs-ordered NGKs, and original coil. So I still have things to eliminate in this process.

I appreciate you updating us Warren and congrats on your success.

[xray]

Problem now completely solved.

JimmyZ - they are round top SU's (3 screws).

I fitted new plug leads and new lead from coil to distributor, new rotor and brand new spark plugs. Rev's strongly all the way to 6000 before the tacho drops to zero (needed to move the red wire from the pertronix ignitor to the other side of the ballast resistor as per IZCC how to post)

I am convinced it was mostly a points issue, but the rest of the ignition system was old and tired so probably was not helping.

Xray and Madkaw - how are yours going ?

Warren

Hi Warren,

Glad to see things progressing for you...I thought mine was fixed, and was in a similar position to you. After new plugs the car runs quite well, revs to 6k, but they get carbon-fouled in about 5 miles of driving or 20 minutes at idle..:tapemouth. Since I've replaced all the ignition components and the Pertronix and its coil test out fine, I decided to pursue the fuel system some more. Car will idle with the mixture nuts fully screwed in, so there appears still too much fuel getting in the system. I adjusted the float level to 5/8" (instead of 9/16" recommended) and the problem seems to persist. I'm taking off my newly-rebuilt ZTherapy SUs today for a full inspection to be sure the needle is well seated and the choke isn't stuck.

If that all checks out, then it's back to the timing issue (again). Or, if I'm too tired of chasing my tail by then, I'll consider tossing in the towel and taking it to a local mechanic. I just hate the idea of giving up though....:mad:

[madkaw]

Well to continue my saga I installed my pertronix(coil and igniter) today and the car ran fantastic -all the way to 3000rpm-then just goes flat. I really didn't think ignition was the problem , but it was nice to eliminate that from the equation. I will have to say that the car idles better and smoother now and I still need to install the new wires.

The next thing for me will be the fuel pump. I have been suspect of a pump that has sat for 10 plus years without running. I don't have a pressure guage but I do have an extra pump to try. I would almost bet that diaphram has a coulpe of holes or cracks in it.

I also have changed the fuel filter which DID have dirt in it. I also blew compressed air thru the fuel lines and drained the tank again. Yes there was some junk in the tank but not significant enough to think it was clogging the pick-up.

Maybe next week I can throw the fuel pump on-I Do have AC so this won't be a fun job.

[chicago240z]

my cardid same thing it was vaccumm advance was frozen and bad vac leak off thriootle shaft on 1st carbb

[madkaw]

Okay, I changed the fuel pump which did help slightly. Unfortunately I think i have several things going on at once. I did get some more rpms out of it but then I started fouling the rear plugs.

so to recap;I changed fuel pump, plugs, plug wires, upgraded to pertronix, cleaned all fuel lines. Rechecked float levels, checked for dirt around needle and seat. I have checked timing-10 degrees static, approx 33 degrees full.

Checked compression levels-180 across the board

Engine revs up slowly with no real power. The rear three plugs foul after a short period of running. I guess I will mount my carbs which are almost new on this car and see if that makes a difference.

Any ideas?

What about you XRAY

[kenz240z]

Considering the front carb primarily delivers air/fuel to the front three cylinders and the rear carb primarily delivers air/fuel to the rear three cylinders and your observation that the rear three plugs are fouled makes me think there is an imbalance between the carbs. I'm using the word "imbalance" kind of loosely here, because it may not be entirely related to a difference in airflow between them. By the way, how do the front three plugs look?

You may try this approach: Start the car and warm up the engine. Pick a carb, any carb (ha, ha, couldn't resist...:stupid:) and turn the idle speed screw in a half turn. If the engine RPM increases it indicates the carb is delivering air/fuel to it's three cylinders. Repeat this procedure with the other carb. If the RPM increases then it, too, is delivering air/fuel. Or, use the hand test. With the air filter cover removed and the engine idling, place the palm of your hand over the mouth of the front carb. You should feel suction, the RPM's should drop and the engine may stall. Repeat with the rear carb. If both carbs are delivering air/fuel then proceed to balance the carbs.

If adjusting the idle speed screw on one of the carb does not result in an increase in engine RPM then check if the needle is sticking in the seat in the float bowl. Could be one of the carbs is not getting fuel/ If neither carb has a stuck needle then the problem lies in improper balance. In this case, the engine is running off one carb at idle, which can cause the symptoms you describe. Again, proceed to balance the carbs.

Hope this helps!

[Mat M]

I was going to also suggest checking your banjo filters, but if you have nearly new carbs you are going to install, it seems moot.

[madkaw]

Thanks for the suggestion and yes they were checked -the second time around. And one was pretty clogged but it made no real difference in the way it ran. The other carbs are off my car and it would be temporary in order to help troubleshoot. I still want to make these work.

[madkaw]

Well I found my problem-finally. One of my new fuel hoses that goes from the nozzle to the float bowl kinked. These were new hoses from Z therapy and I explained this on the SU carb central forum

The car revs up freely with lots of power. This had to be the problem all along even though the engine also needed all the other tune up items done. I found it interesting that i was focused on the rear carb because it was fouling when the whole problem was the front carb. The rear plugs showed up as fouling and the fronts looked okay, it really threw me off.

You just never stop learning when it comes to this stuff. Today though, I feel like an SU expert:laugh:

[ncolz]

Have you checked your points? Make sure they are good - be sure to check for proper dwell. I had this problem on my '71. The dwell was way off, now it wraps up great and runs like a dream.

Cheers,

Glen

[Mat M]

Congratulations, Madkaw!!

this was a burr in your side for a while!