I built up a 65 Chevy 292 with a 3/4 RV cam, 3 carbs on a Offenhouser intake, full length headers, and a HEI ignition. The problem is tuning it in. I have adjusted the down draft on the carbs with a vaccuume meter. Jetted and synced the carbs together but I cannot get it workin right. I know the timming is really close, by turning the distributer a little it kinda gets better. HALP!!! Sputtering in Seattle.
what are the cam specks? Was it degreed in?( straight up?+ or - any degrees?) was the dist. installed 100% on the money or could it be a tooth off?
Dont know the cam specs, just was told it was a 3/4 RV cam. The dist is keyed and its horrible the other way. It runs kinda, i get it to idle then it sputters and bangs with the throttle. When driving, it hates hills and looses all power.
It could be that you have no provision for intake manifold heat,,yes heat.Look at a stock 292 intake and exhaust manifold combination and you'll see that a flap in the exhaust which is controlled by exhaust heat allows the "floor"of the intake to be heated. Even when the flap is closed some exhaust heat is influencing the intake manifold. Without heat in the intake the fuel charge bounces off the interior of the intake and becomes liquid.you want the fuel to enter the cylinder as a vapor not a liquid.Hence ,, stumbles and bogs galore when you give it gas. Manifold heating in inline sixes is discussed at great length on http://www.inliners.org/. Another possible cause might be in your carbs themself. Basically if all three carbs are running with thier idle circuits intact, your engine is getting too much fuel. As with tri power carbs on 8 cylinder setups , you may need to eliminate the idle circuits from two of your three carbs to make it run clean when you hit it.
HEI's need a cheap and easy reflog to get you a decent set of curves, vac and centrifugal. Vac is set up for EGR engines in most cases. Total vac advance generally stamped on bracket...I think you will see a number in the 20's, WAY too much. Get a big truck can (V8 applications fit), an aftermarket can, or a parts store can for a BIG truck with HEI...don't remember my setup exactly, I think about 12 degrees on it. I went to a Moroso centrifugal kit, V8 type fits 6, and my 6 liked the weakest springs. The weights with this kit shorten the curve a bit, the springs quicken it, and you can set static advance up some from stock. I ended up happiest with vac on manifold...in your case, try that later because it requires resetting idle down, and you don't have carbs adjusted yet. Stock HEI curves are just too long and slow, and the vac will cause all sorts of part throttle pinging if you do not have EGR.
www.inliners.org I'm not familiar with that particular intake manifold, but you should have communication between the three carbs, not an isolated runner (IR) setup. Also, the term "3/4 cam" is nebulous and archaic. It was popular about fifty years ago and used to describe just about any cam grind that wasn"t "full race", another archaic term. The "term RV" cam generally refers to a cam with timing specs close to O.E.M. specs with usually a little more lift and more agressive ramps. A cam like that works well in street driven cars. I don't think the cam is part of the problem, assuming it is correctly installed. Yes, manifold heat will aid driveability, but I have none on my inline powered Willys coupe with two dueces, and it runs great when it gets warm, so I think your problem goes deeper than not enough carb heat. Good luck
a lack of carb heat usually results in a hesitation at take off on a cold engine. You are describing something alot worse than that. The carbs are setup as progressive, correct? Have you tried running with just one carb? Check the mechanical advance to see if it is working correctly. While recurving the advance may make it better overall, you shouldn't be having a problem like this just because you didn't do it. The problem is more basic than that. With the vac advance disconnected, what is the timing setting and what is the rpm? Also, since the carbs still have the idle and power circuits, you need to make sure you didn't block off the hole on the base of the carbs. This is what gives the power valve its signal. Also, keep in mind that a larger cam and multiple carbs will show a weaker vac signal to the carbs. Ideally, you would want to run weaker springs on the power valves, but none exist for this type of carb. This is one of the reasons for running progressive instead of direct. Also, you will find that you won't want to engage the end carbs below a certain rpm, probably around 2500...
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