Fuel consumption and Hesitation

[Glliw]

I figured I need to post this one more time since my last time through was incomplete in the diagnosis so here's my problem one more time...please help me out on this:

The car is a 1974 260z with 3 screw round top SUs. The car starts up fine. Until it is COMPLETELY warmed up, it runs fine. Once fully warmed up, under acceleration, the engine will hesitate/buck. Pulling back on the choke lever alleviates this hesitation/bucking. Changing the Octane of the gas does not help. It seems to only be temperature effected.

If there is any other information I can get for you to be a help, please, let me know.

[Weasel73240Z]

If choking it makes the problem go away, I would think that you have the carbs running too lean. I would try backing the mixture screws out 1 turn, and see if there's any change.

[doradox]

I figured I need to post this one more time since my last time through was incomplete in the diagnosis so here's my problem one more time...please help me out on this:

The car is a 1974 260z with 3 screw round top SUs. The car starts up fine. Until it is COMPLETELY warmed up, it runs fine. Once fully warmed up, under acceleration, the engine will hesitate/buck. Pulling back on the choke lever alleviates this hesitation/bucking. Changing the Octane of the gas does not help. It seems to only be temperature effected.

If there is any other information I can get for you to be a help, please, let me know.

You have an ignition problem. Probably a bad plug/coil wire. Maybe coil. Could also be a bad points/condenser( does the 260 have points?). The hotter wires get the more likely they will arc to ground. The choke richens the fuel mixture which lowers the voltage required to fire the plug so the arcing stops. Anything in the the high voltage side of the ignition system could be suspect. The condenser, if you have one, will be sensitive to heat and cause problems. I am assuming you have released the choke prior to being fully warmed and the engine runs fine until fully warmed then needs the choke again. Otherwise it's probably what Paul said.

Steve

Edited October 25, 2008 by doradox

[Bruce Palmer]

Are you running during warmup with the choke at least partially on, then once warm taking the choke off and the problem starts?

[Glliw]

You have an ignition problem. Probably a bad plug/coil wire. Maybe coil. Could also be a bad points/condenser( does the 260 have points?). The hotter wires get the more likely they will arc to ground. The choke richens the fuel mixture which lowers the voltage required to fire the plug so the arcing stops. Anything in the the high voltage side of the ignition system could be suspect. The condenser, if you have one, will be sensitive to heat and cause problems. I am assuming you have released the choke prior to being fully warmed and the engine runs fine until fully warmed then needs the choke again. Otherwise it's probably what Paul said.

Steve

What's the proper procedure for testing the coil? I would rather not be throwing $100 parts at it in a guessing game. The 260z uses an Electrical Dizzy.

Are you running during warmup with the choke at least partially on, then once warm taking the choke off and the problem starts?

It depends, if its cold out, yes. But remember, this is Central Florida and has been lately no less then 80 degrees.

But, on those warmer days, and I start it without the choke, the problem is the same regardless.

[Bruce Palmer]

I line up on the lean side of the solution. If pulling the choke on solves it. It may only take half a turn to get to the sweet spot especially if it will at times start cold with no choke.

[Glliw]

I believe I missed to mention this in my first post considering the time of day(night) I posted. Adjusting the carbs makes no difference in the hesitation/bucking/whathaveyou.

[doradox]

What's the proper procedure for testing the coil? I would rather not be throwing $100 parts at it in a guessing game. The 260z uses an Electrical Dizzy.

It depends, if its cold out, yes. But remember, this is Central Florida and has been lately no less then 80 degrees.

But, on those warmer days, and I start it without the choke, the problem is the same regardless.

I'd start with the wires. Check the resistance of each wire with a DVOM. They should all be around 5K ohms or so. The actual reading isn't really important as you are looking for one that reads much higher than the others. So if they are 2K or 10K don't sweat it. Do the coil wire the same way. You can do a quick check of the coil by loosening the coil wire at the distributor cap and, while running, slowly move the coil wire away from the cap. Assuming you have a good coil wire it should give a nice strong spark up to about 1/2 to 3/4 inch or more. Beware, don't touch, or be within a couple inches of any other part of the car while doing this. You could get shocked. Actually, you probably will. You can do the same thing for each plug wire at the plug. You should again have the same strong spark at all six. If one is weak then it's the wire or the cap. A cracked rotor will effect all 6. And if this problem only occurs when the engine is fully warmed you'll need to do everything but the resistance check fully warmed.

Steve

[Glliw]

I just got off the phone with a well educated man about these cars and went through everything with him. Pretty much we are both stumped and the only possible outcome we can think of is the coil is getting heatsoaked, which is the only reason it shows at warmed up temps.

[doradox]

I just got off the phone with a well educated man about these cars and went through everything with him. Pretty much we are both stumped and the only possible outcome we can think of is the coil is getting heatsoaked, which is the only reason it shows at warmed up temps.

Did you resistance check the wires? I've seen wires cause this problem I'd guess 20:1 over coils. Wires are easy to check, and cheap to replace.

[Glliw]

No I have not, I won't have access to a Volt meter til Wednesday. I will do it then though.

I'm on the UCF campus here and the majority of my tools are about 6 hours away so I have to use what there is at the SAE shop if need be.

However, I highly doubt it to be the wires/plugs. They are less than 6 months old. I hope you prove me wrong though, because I certainly would like this problem to be over.

[Cutlass372]

I have this same exact problem... The car seems to run fine at idle, but then once you start to drive at higher rpms the motor will buck/hesitate like the clutch is slipping. It used to do this much worse, but has slowly gotten better over time. I think i'm going to check my coil and sand my points a little bit to see if that helps any. I'll know after that if i can check something else or if that is actually the cause. I hope you figure out the problem because it is bothering me too. Please let us know if you find out any other information

Edit: Also, the choke doesn't make the problem completely go away. It does seem to help though sometimes. If the car is acting up I will usually pull the choke a little bit.

Thanks, Elliot.

Edited October 26, 2008 by Cutlass372