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I have a 75 F800 with a 391. It had a Holley 4 barrel list 6339. It would start, run, and idle very well and pulled good, but it was a terrible fuel hog even by grain truck standards. It was averaging something near 2 gallon per mile... Then the crossover tubes started leaking. I took some advice and put and Edelbrock 1405 on it. Put the jets and needles in for right in the middle of the curve, and it runs and pulls well. During warm weather it was hard to start, now that winter is here its nearly impossible. I never was able to get the Edelbrock to start or idle how I wanted it, no matter how I fiddled with it, but it ran well and put the fuel mileage in a more acceptable range (close to 3 gpm, which is still bad but for a short haul with several stops and a big load I consider it acceptable). So the question is, without starting a war, is there a way to make an edelbrock start and idle in cold weather, or should I rebuild the Holley? I can turn wrenches but I dont consider myself an artist. Is a Holley rebuild something I should do on my own? Thanks for the advice.
I did not get instructions with the Edelbrock, so I have mostly just been using the adjustment screws. Both carbs have manual chokes.
The edelbrock has 2 small vacuum lines and 1 large one. I plugged the large pcv port, am using one as the vacuum advance and the other one is running to the vacuum governor. Should I bypass the governor?
I did not get instructions with the Edelbrock, so I have mostly just been using the adjustment screws. Both carbs have manual chokes.
The edelbrock has 2 small vacuum lines and 1 large one. I plugged the large pcv port, am using one as the vacuum advance and the other one is running to the vacuum governor. Should I bypass the governor?
Don't defeat the GOV (IMO) and is the DIST SIGNAL ported or manifold vacuum?
The EDEL manual choke does not work correctly? Maybe cable adj is not correct.
Thank you for the replys. The choke functions as it should (opens and closes fully) according to a diagram i found online one of the ports is labeled as dist. Advance for non emission controlled motors and the other one is for emission controlled motors. The other thing that has me wondering now: the truck had a direct line from the manifold to the brake booster and a riser plate between the carb and the manifold that had a port to the pcv. The Edelbrock diagram has ports labeled for pcv and power brake. I have both of them plugged. Could that be affecting the air flow within the carb enough to be causing issues?
Sorry to be confusing and thank you for bearing with me. Yes. The truck is hard to start, especially when the motor and weather is cold. It takes lots of attention to keep messing with the choke and the accelerator to keep it running at all until it warms up. After it is finally warmed up, it seems like the idle cant be trusted. The idle rpm is not constant. It will either be idling too fast, or will die when you stop for a stop sign etc. Without changing anything, like sitting in the truck while it dumps at the grain elevator, the rpm is likely to run between 1300 and 800. It slowly climbs or slowly falls as it pleases, and sometimes will just die. I'm at a loss. Thank you for your patience and assistance
Sorry to be confusing and thank you for bearing with me.
You're not confusing.
Yes. The truck is hard to start, especially when the motor and weather is cold. It takes lots of attention to keep messing with the choke and the accelerator to keep it running at all until it warms up. After it is finally warmed up, it seems like the idle cant be trusted. The idle rpm is not constant. It will either be idling too fast, or will die when you stop for a stop sign etc. Without changing anything, like sitting in the truck while it dumps at the grain elevator, the rpm is likely to run between 1300 and 800. It slowly climbs or slowly falls as it pleases, and sometimes will just die. I'm at a loss. Thank you for your patience and assistance
Did he truck do this before the carb swap?
Is your choke cable attached by retainer to the RR side of the carb body? Does the choke butterfly operate fully and smoothly? There should be two adj screws @ the throttle linkage attachment, one curb the other fast idle. Try and adjust the fast idle (with cable pulled) and see if the cold start will function. The choke butterfly should have just a very small opening when the cable is pulled out.
As for RPM wandering, do you have a vacuum gauge ($20)? It sounds like you have a vacuum leak and the RPM is wandering. It may also be the emission control(s) but verify good vacuum first.
Are you able to take photos of the engine and post them here?
Thank you again
I dont know how to attach pictures, but the truck is old enough the only emission control is the PCV valve. Other than that the vacuum lines are pretty short and seem to be good, but I can spray some carb cleaner and check. The truck has a vacuum gauge on it and it stays constant while the rpm hunting occurs. The choke control is attached firmly and doesnt seem to wander.
I have only ever adjusted the main idle stop screw, so maybe that is my problem. I will look for the other screw and see what I can accomplish. It was a warm day yesterday, but I still couldnt get the truck to start. I didnt have much time to fool with it though and just used a different truck.
Thank you again for the help! I'm really frustrated with the issue. Having a finicky truck you cant trust is almost worse than not having one...
If the emission controls have been defeated, make sure all source manifold vacuum sources are blocked off. Any vacuum leak(s) will give a lean mixture. Does the engine have an EGR System and was it defeated also? The test gauge will tell you if there is a vacuum leak somewhere (also tell you fuel pressure/volume).
The vacuum gauge, is it monitoring direct manifold vacuum or booster vacuum? I am guessing it has a form of vacuum over hydraulic brakes.
Next time before you attempt to start, remove the ACL and work the throttle by hand to see if there is a good accelerator pump shot. You may have a fuel/delivery/bowl evaporation problem. Your being where you are, I guess no ethanol gasoline is available?
When was the last time it had a tune?
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KEY WORDS
Forget the EMISSION CONTROL questions. Does it have DURASPARK or points?
Finally had time to dig back into this. I hooked a vacuum gauge into the left port on the carb instead of having that go to the governor. I left everything else as was. The linkages all worked as they should. After a lot of effort, and starting fluid, I got it started, but I had to continue using some either to keep it running for at least 30 seconds. After that, it ran fine and would restart fine. I wonder if the mechanical fuel pump is failing and that is part of the trouble also?
I found the second idle adjust screw you mentioned and that made a big difference in getting it warmed up.
The vacuum was a steady 12 at 1500 rpm. After it warmed up, i was able to drop the idle down to 1100 or so and the vacuum came down to 7, but was steady. If i slowed it down anymore, the slight vacuum drop when i would hit the accelerator would bog and stall the engine. If revved up to 2k i could get the vacuum gauge to 17 or so, but that seemed to be about top.
The truck is currently buried in the back of the shed, so i wasnt able to road test it, but it acted better after it was warmed up than it has in a long time. Thank you very much for your assistance!
7 inches of vacuum at near-idle rpm is pretty low.
If the distributor advance diaphragm is attached to the timed-vacuum port (the one on the carb's left-front, as viewed from the front), move it to the manifold-vacuum port on the right side of the PCV connection.
That could help.
Make sure the diaphragm isn't leaking, and that the distributor's spark advance mechanism is working, and that the initial timing (with the diaphragm vacuum line disconnected and plugged) is correct.
Does sound like your engine has a seriously lean idle and off-idle situation, suggesting a substantial vacuum leak.
Also, make sure the carb mates up with the manifold correctly.
If not, a large vacuum leak can be happening there.
I had a carb-to-manifold mismatch once, it about drove me nuts finding the problem.
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