Carb Help?

BenL · 06-03-05, 11:08 PM

I'm having a problem with my engine (carb?). Can someone offer some diagnosis assistance? I'm good at taking things apart (and occasionally putting them back together), but I don't have the experience to identify this problem.

The engine is a 289 HiPo. It has a Holley dual bowl NASCAR carb (750CFM?). The points were replaced two years ago with an electronic unit that hides inside the distributor.

I haven't driven the car since December. Today was the first time I tried started to it and it wasn't happy. With the accelerator pedal to the floor it would start, but as soon as I lifted off the pedal, the engine would die (or sometimes as soon as I let go of the starter button). If kept my foot to the floor it would eventually catch, but at first it wouldn't rev high even though my foot was all the way down. Occasionally it would initially sound like it was running on only four cylinders before it came to life.

I decided to be brave and take the car out for a short drive on the highway, with the hope that it might clear out the problem. On the way to the highway, it stalled at a stop sign with a knocking sound (clatter?) as the engine came to a stop. After driving for a mile or two I got off the highway, and halfway up the off ramp it stalled again with the weird noise. With my foot to the floor, I got the engine to start again, but I had to be careful to keep the revs up. On the next bit of highway, the car stalled once more, but I was able to use the momentum to "push start" the car.

Before I set out, I replaced the spark plugs with a new set of Autolite 35s (0.028 gap). The old ceramic tips were brownish and dry (the threads were wet). When I got home (after about 8 miles of driving, half at highway speeds), I pulled one plug and it was still white on one side and a slight tan discoloration on the other side.

Fuel pressure is around 4 psi.

The air filter smells like gasoline. Staring down into the bowls while I moved the throttle I saw the two front jets squirt gas (the rear pair of butterflies appear to use engine suction to open up).

I don't think it's associated with the problem, but the battery light never went out while driving the car with the lights on. The voltmeter stayed slightly below 0.

Any suggestions will be welcomed. I was hoping to go to an event tomorrow. [img]/ubbthreads/images/graemlins/frown.gif[/img]

Thanks.

Eric · 06-03-05, 11:41 PM

I'm sure you will get a thousand different answers but anytime I leave a vehicle parked for a long time and it doesnt drive very welll next time I start it, it is a safe bet that fuel has hardened up inside the idle circuit. If it were me, start with turning the idle mixture screws all the way in while counting exactly how many turns you did, then pull them all the way out, fire some carb clean down there, hit it with a good shot of compressed air, stick the screws in where they were set to and try again, if that doesnt work, pull the carb, tear it down,try and take note of where the fuel level is in the bowl, poke out all the little orifices with a very fine wire (some say dont do that but whatever) hit it with more air and carb clean and try again, if that doesnt work, I dont think it is the carb.

BenL · 06-04-05, 12:05 AM

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If it were me, start with turning the idle mixture screws all the way in

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How do I find those screws?

Eric · 06-04-05, 01:57 AM

I'm no Holley expert, but in general, look for 2 screws somewhere closer to the base of the carb that look like they are not holding anything in. Usually they sit on the same end of the carb but are spread apart. They normally have a spring under them, usually a flat head screwdriver bit fits them but be very gentel when you screw then in, normally you can do it with your fingers, just screw them in till they feel like they might be touching something (probably only 1.5-2.5 turns). You will know you got the right ones when you pull them out, they have a needle point end on them.
good luck.
Juding by that question I am going to hazard a guess that you have never worked with a carb at all. They are very simple but i suggest if this doesnt work and you do need to take it apart, a manual is probably a good idea. I'm sure many will chime in and give you more specific advice but I hope this helps.

BenL · 06-04-05, 02:03 AM

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Juding by that question I am going to hazard a guess that you have never worked with a carb at all.

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I'm more familiar with Webers, but I haven't done much with them.

Howard Jones · 06-04-05, 03:50 AM

Try changing the coil with another one. A weak coil will act just like you are discribing. Also did you make a very human mistake with firing order when you changed plugs. The 0 volt issue, if it is real and not a bad meter, is telling you something. If you have the orginal points you might want to put them back in for a test. A very low battery voltage might cause you electronic points not to work right.

Now on to the carb. If it is the problem it is more than likely a stuck neddle and seat (stuck open, with little piece of crap stuck on the seat) This condition will flood the motor and cause it to run just like you discribe. Thsi will cause the motor to run Very, Very rich and will sort of clear with wide open gas peddle. Wide open delivers max air and partially offsets super rich condition.

Go to a hot rod shop and buy a Holley book. Look thru it and find float adjustment and needle and seat setup. This is easy to do with a book but hard for me to explain here. The investment in the book will be a good one.

Eric · 06-05-05, 03:51 PM

I'm more familiar with Webers

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Your a braver man than I, you should have no problems then.

emiel · 06-05-05, 04:46 PM

Its maybe too simple,but dont you have some sort of condensation in your distributor which causes an erratic ignition.

Russ Noble · 06-05-05, 06:58 PM

If you were in NZ and running unleaded fuel I'd say your fuel's gone stale. If the aircleaner element's wet with fuel it might indicate sticking inlet valves. Have you checked your compressions? Just go back to basics and work from there before blaming the carb. It could be the carb but you need to make sure everything else is OK first.

Regards

Mike Dozier · 06-07-05, 02:27 PM

Idle mixture screws on most Holleys are on opposing sides of the
fuel block...which is the piece sandwiched between the
float bowls and main body. I've seen cases where
turning them all the way has no affect because the screws
or the seat they sit on in the fuel block are worn.

That said...the most common problem with Holleys
is sticking or clogged needle/seat which Howard described.
Assuming (?) your igntion system is OK...that's what
I'd check first. Replace the fuel level screws in the side
of the float bowls with clear view screws...easier/safer
than opening them up and letting fuel dribble out...which
is the normal way.

MikeD

Howard Jones · 06-07-05, 04:48 PM

Unleaded crap Calif.gas will sieze up the threads of those plastic float sight plugs. They are a pain to get out then. I don't know about other gas buy I wouldn't leave them in all the time in any case. They do work well for adjusting the float level. Just take them out when you are done.

BenL · 06-23-05, 02:34 PM

Just before I went to France for Le Mans, I towed the car over to a mechanic. Yesterday, I spoke with him and he said the problem was that the Crane electronic ignition module failed. Everything else is okay.

So tomorrow I'll go pick it up. And hopefully, if the 90+dF weather doesn't kill me, I'll take it for a spin this weekend.

Phil · 06-24-05, 12:48 AM

Ben
You mentioned that your battery light was on, indicating no charge I would suspect. You may have a problem as simple as your alternator not charging. Most electronic units have a threshold of around 11 volts, and below that things get squirrely!. Put a meter on that system and see if you are charging...at least 13.5 V or higher, but not more than 14.5 or 15 Volts intermittently right after starting. Also if you can get the motor running take a jumper wire and attach it to a good ground (Engine Block) and the other end to a screwdriver or other metal with an insulated handle, run the end around the distributor cap and this will tell you if it is cracked. I would be willing to bet you have a low voltage problem, or are not charging.
Good Luck
Phil

BenL · 06-24-05, 06:17 PM

[ QUOTE ]
You mentioned that your battery light was on, indicating no charge I would suspect. You may have a problem as simple as your alternator not charging.

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It sounds like you might be right.

When I arrived to pickup the car, I was told that the problem wasn't the electronic ignition, but the ballast resistor (which he replaced) and the voltage regulator (which he is tracking down).

I was wondering if part of the problem might involve the ballast resistor, because I noticed that sometimes the engine would die as soon as I let go of the starter button.

Phil · 06-24-05, 10:24 PM

Ben
It might be the ballast resistor. Most systems have a bypass circuit that bypasses the resistor when cranking...This is to ensure enough voltage to fire the coil. Most systems show about 9 or 10 volts thru the resistor, and cranking drops the system down another 3 or 4 volts depending on starter load, If the system went totally thru the resistor you would only show about 6 or 7 volts on crank...definitely not enough!. The resistor is bypassed during cranking which already causes a voltage drop but is enough to fire the motor. If your resistor is faulty, you would get voltage during crank, but it would drop off as soon as you stopped cranking, or be poor enough to just get the motor fired. I think you are closer to the problem.
Good luck
Phil