bogging engine

[evildky]

last fall I drained the tank, all gas came out looking good, I flushed about 2 galons of fresh gas through, plugged it and ran with it, I was gonna put tubing into a gas can tomorrow and see if that does anything, will be bypasing all metal lines and factory fuel tank, but the problem shows up only when it's warmed up so I don't expect that to solve the mystery

[beandip]

It sounds like fuel but this might be a red herring. If you have access to a coil , try a different coil. They can brake down when heated and cause the same thing you are describing. Any 12v coil will do. You did mention the fuel lines looked fine , did you look at the full length of them , just in case it was crimped or damaged from being struck by a rock or something. You stated that this problem has been going on for some time . Was it like this when you bought the car a year ago ? Or did it come on since you have owned the car ? Have you checked the pressure of the fuel since the new electric pump was installed,and between the regulator and the carbs? Have you tried to blow air pressure back toward the tank before the electric pump was installed . I dont think I would blow pressure through the pump so if you do this disconnect it first and blow air into the tank through the fuel line so if there is a blockage in the pick up you will clear it. There are filters in the inlets of the carbs also dont over look them if they are still installed.

[evildky]

yesterday I started by warming up and driving till the bogging started, I notice it is accompanied by backfiring through the exhause when I let off the gas, aslo in reving it while parked it did backfire through the intake once

I ran rubber hoses from the fuel rail into and out of a 3 gallon gas tank on my car, went for a run no change

I swapped the 78 dist and msd box in favor of a zx dist, went for a run still boggs once warmed, ( I did not replace the jacobs coil I am running as I did not have an extra coil but the problem was the same when I had the origional ballasted coil (and the jacobs coil was hardly even warm))

I swapped the SU's in favor of a set of tripple webbers and a cannon intake on loan from a friend ( loads of top end till they warmed up) once warmed up real nice it bogged the same as before ( I really want a set of those now)

I then replaced the motor, just finnished installing it tonight, F54 flattop with an N42 mild cam (on load from a frind who's car is in pieces), I put my SU's on it since the webbers behaved in the same maner, I havn't finnished dialing in the carbs and timing yet, I am gonna take it our tomorrow, I'll post my results

I am wondering if my head gasket might be blown between 2 cylinders and only leaks under load and at temperature ? sound like a reasonable theory ?

I have been looking at that car for so long I can't see streight any more, any more insights ? thoughts on my head gasket theory? I havn't cracked my motor open yet

[evildky]

well, I swapped in the Hi Po L28 and it still boggs, I swapped the webers on and it still boggs but it boggs differently I can accelerate past the point of bogginf and it still backfires, I think the problem was the cabs glad I swapped motors to find out any how looks to be a phantomg carb isse that doesn't make much sence, just wanted to let yoou know

[Gav240z]

I know this isn't what u wana hear but i think it's the Coil as Beandip said earlier they have a tendancy to heat up and go silly after that.

I dont think it's the carbs but it's very hard to diagnose over the internet as you can imagine.

Coils are dirt cheap and if it's looking old worth a change over anyway.

gav

[2ManyZs]

It's gotta be either in the ignition (distributor, if you used the same one on both motors), or in the fuel system since those are about the only things the two engines have in common that weren't changed.

[sblake01]

You've changed carbs and you've even changed engines! I would stop blaming either at this point. Get back to basics. Fuel, spark, etc. There are no 'phantom' issues. Everything has a cause. You have changed a lot of things around on that car and the more you change the harder it becomes to diagnose. It sounds to me like it's ignition related but like I said with so many changes, I would go back to basics and try to eliminate the possible causes one by one.

[evildky]

well....after all this fun and games I just bought a complete wrecked 280zxt 2+2 for $350, looks like it'll be turbo and injected no more fun with carbs

[sblake01]

Originally posted by evildky

well....after all this fun and games I just bought a complete wrecked 280zxt 2+2 for $350, looks like it'll be turbo and injected no more fun with carbs

Turbo and F.I. The real fun is about to begin!

[Jimbeaux]

Your bogging problem sounds just like the problem I had on my 72 240. I went through many of the same exercises you have including putting on a new coil. Same problem existed so I went through even more tests. Then one day due to information I read in these forums I decided to change the coil again...presto! the coil I had bought was bad out of the box! The 2nd fixed the problem right away.