Hello, I am new to the forum,I have just purchased a 1966 c10 stepside truck with 114,000 original miles on it. The truck has had 2 previous owners. The first owner from what I understand replaced the distributor on the 250 straight six with an HEI system. My question is it seems to miss when i'm coming out of first gear into second, is this a timing problem or carborator problem? I have replaced the HEI cap & rotor and have replaced the wires & plugs gapped 35 thousands. Also the vacuum advance seems to be working fine. If anyone has any ideas it would be helpful. Thank you, The Butcher
With the HEI ignition you should be able to run the plug gap at .045. The miss sounds like the timing could be too far advanced, I think you are supposed to set the timing with the vacuum advance disconnected. It sems like I seen some Info. on this on line a while back. You might try googeling HEI ignition and see if that helps.... Big Tim
The original gap of .035 should be opened up because the hotter spark of the HEI can easily bridge the larger gap, initiating a better flame pattern for the combustion mix. I generally use .040. I'm not sure if .045 is actually the preferred gap, either should work so long as the coil has enough zap to bridge the gap. And yes, the vacuum advance should always be disconnected from the distributor and the line plugged before the timing is set. If it remains connected, the distributor may be advanced by vacuum, and if the line is disconnected and not plugged, the resulting vacuum leak may increase rpm enough to advance the centrifugal distributor weights. As for additional diagnosis, there's a slight possibility the coil could have hairline cracks, but it's not likely. Usually they either work or they don't. You might also check any vacuum caps on the carb that could be brittle and cracked. But my focus would lean towards the mileage on the engine. It's been a long time since I worked on a Chevy six, but many of these engines came stock with a nylon timing gear to keep the noise down. It was very common on high mileage engines to get sloppy timing as the nylon teeth wore, eventually to the point where the teeth stripped off the gear and the engine would no longer function. If the gear is badly worn, it could account for the misfire when the engine is transitioning from a heavy load in 1st gear, to no load going to 2nd. Ignition timing becomes erratic because of excessive play in the gears. A worn timing chain on a small block Chevy creates a similar problem. An worn out timing chain can stretch so badly it can literally be lifted off the gears. When in operation, a chain in this condition develops a "wave" in the slack side, and when engine speed is quickly increased or decreased, the wave changes sides, causing the timing to become inconsistent.
If the ignition doesn't help you can check for vaccume leaks on the intake mainfold and around the carb base.
The Butcher Thank you all for the helpful hints, I have not found the problem yet but still going after it. I have checked for all vacuum leaks but none found, I am going to do a compression check on it next, to see if I may have a weak valve. Also could the float in the carb. be causing this problem? Thanks The Butcher PS> any more advice would be appreciated.
