C3 (69) Blues

[Rob M.]

Since the last months my C3 (69 L36) is running extremely bad. This behaviour started suddenly although the car never runned very smooth like a SB. When cold it runs reasonable but as soon as it starts to heat up it gets flooded really easily (e.g. by engaging the trottle) and it looses all its power. When it is really hot is drowns and shuts down and I can't get it started again...

Car has fresh spark plugs & spark cables.

So far we have tried:
1) replace carb, result same behaviour (choke is working correct on both carbs)
2) replace fuel pump, same behaviour
3) replace ignition coil, same behaviour
4) checked points, looks ok
5) checked compression (all cylinders vary between 9 and 11:1)
6) checked visually under the rocker covers, all looks normal

Plans:
We are planning replacing the points temp. for an electronic circuit to eliminate this item as well from the suspicion list

Any suggestions?

Your help is highly appreciated!!!
Rob Musquetier

[Joe L.]

Re: C3 (69) Blues

Rob-----

I realize that you've replaced the carburetor, but it sure sounds like a carburetion problem to me. If you replaced the carb with a REBUILT unit (likely, since new Q-Jets are not available), keep in mind that many times rebuilt carbs suffer from "core problems" that can't be re-manufactured out of them.

I recall once many years ago I was trying to fix my aunt's car. I knew it was a carburetion problem. My uncle (not my aunt's husband) said that he could get a good deal on a carburetor. I told him to get a NEW one only. He brought me a rebuilt one. I installed it on the car and the car had the same problems. So, I started to think maybe it was something else. Still, I knew that it just had to be a carburetion problem. So, I took the carb off and sent it back. My uncle came back with another rebuild. I put it on the car and had the same problem. So, now I'm really figuring it must be something else. However, I had to leave for home (this all happened while I was in the east on vacation).

So, my aunt took the car to a Dodge dealership after I left for home, but I told her to make sure she found out what the problem was because I was very interested. They installed ANOTHER rebuilt carb. Same problem. So, then they installed a NEW carburetor. The car then ran perfect.

[Robert Willis]

Re: C3 (69) Blues

Condenser for the point set. Runs good till the engine warms up and then missfires and hesitations.

[Joe T.]

Re: C3 (69) Blues

Hi Ron: It sounds like you have been down the fuel road and are frustrated. You didn't say if you smelled raw gas while or after the problem occurs. I would think that a fuel over-supply(flooding) or boiling problem would give you a very strong gas odor. Also check the exhaust for smoke or raw fuel smell. It still might be fuel, but be sure to check the ignition as well, especially the coil. A classic symptom of what you describe is a coil that heats up and the internal resistance (insulation) breaks down. I have a 69 L-36 and that car ran as smooth as any small block at idle and at speed. A bad condenser can also cause warm/hot problems. Is just another option not to be overlooked. Good luck...joe

[Thomas O.]

Re: C3 (69) Blues

Ron: I visited with a fellow with a big block in which he found that the gas was boiling in the carb. This only occurs when the car was hot. I guess that is what Joe is talking about. tom

[Rob M.]

Re: C3 (69) Blues

Hi all,

thank you very much for all your feedback. We have thought for a long time it was a fuel problem (that's why we even rebuild and eventualy replaced the carb and replaced the fuel pump. Still no show. Indeed we smell raw fuel...

We have replace the coil which didn't make a difference.

In one of the replies I read about boiling fuel. How can this happen and what can be done about it. The carb is mounted via a think, 1mm, gasket. Should this be a thick one?

Next step will be to replace the points and capacitors (in the distributor and on the coil) although it doesn't behave like one of the capacitors are faulty (no back-fires or heavely irregular fires but more like a flooding engine (when hot)...

greetings,
Rob.

[Joe T.]

Re: C3 (69) Blues

Clarification: Whether the fuel actually "boils" or not is secondary. What this actually refers to is the fuel (cool from the tank) standing in a static fuel bowl in the carb. As it heats up from the hot engine, it expands and overflows through the jets into the intake manifold causing the flooding condition. This is more of a standing problem, especially with the L-36 engine. Also: there is a stainless steel heat shield that goes between the carb and monfold gasket on this motor. It doesn't seem thick enough to have much effect, but Chevy put it there for a reason (I guess!). You might want to ensure that if your application calls for this heat shield, you have it in place. Good luck...Joe

[Terry F.]

Re: C3 (69) Blues

There are also a couple of plugs on the bottom of Quadrajet, they can loosen up and start leaking gas into the engine causing problems. The same issues will appear if the float is set way too high or is shot. But, I would expect a new carb to not have that problem. I recall having a quadrajet and looking down the throat and seeing gass dribling out the primaries at idle. You can check that easily. You can also take a can of starter fluid and spray around the car (carefully) and check for vacuum leaks. If you get a big surge around the base plate. That could be the problem. The carb gasket is faily thick and I am fairly certain you should have a stainless shield between the carb and the gasket. Also, make sure your return line to the gas tank is working. The gas boiling thing is talked about frequently enough around here. Gas heats up and the vapor pressure increases and the gas starts to spill over the primaries and secondaries. Not an expert on any of this stuff. Just guessing at where I would start looking. If you rebuild that carb, make sure you put a new float in it. Terry

[Terry F.]

Re: C3 (69) Blues

I meant "spray around the CARB" not spray around the car???????

Sorry! Don't blow yourself up. Terry

[Terry F.]

Re: C3 (69) Blues

Make sure your heat riser is opening all the way also. Terry

[Joe T.]

Re: C3 (69) Blues

Hi Rob: If you're still monitoring this post, there is one dead giveaway I have never seen fail on flooding in operating temp engines. When you have the problem, STOP THE ENGINE and take the air filter off. If you have a flooding problem you should see (I have ALWAYS seen) vapors rising out of the carburetor. BE CAREFUL of those vapors: That"s the gas that actually burns as opposed to the liquid. A handy fire extingusher is a good idea. But those vapors are the unmistakable clue to gas overflowing into the intake manifold. You can even generate them by using the accelerator to pump raw fuel into the carb with the engine at operating temp and not running. Good luck and and BE CAREFUL!!!

[Rob M.]

Re: C3 (69) Blues

Thanks all for these suggestions. I'll examine the carb a bit more to ensure it is not causing my problem. This week I'll also try an electronic equivalent of the points to rule that part out as well...

greetings,
Rob.