Dialed In

[90crows]

I've got a 1954 261 rebuild on the engine test stand, single barrel Rochester B, stock manifold, Tom Langdons HEI with the wide gap spark plugs he recommends (.06 gap) , I've run it 4 times now for the 20 minute or so cycle, it ran hot the first few cycles but now it stays at 190 deg. Everything went better than expected except I've got this spitting or missing sound at the end of the exhaust pipe (cold or hot), forward of the tail pipe end everything sound good, but something's not quite dialed in, I've checked and adjusted everything I know to check - any ideas ?

Thanks

[Deve]

Sounds like you have made a lot of progress. It is really hard to say what that is. If it is fuel, the mixture screw will change it, if it is the HEI, try gapping to .045. If it is a Valve adjustment, follow the valve adjustment procedure in the How-To section. If it is timing, adjusting the Distributor will change it. Those are the four choices I would narrow it down to. Another possibility is the Carb. Is it a genuine 261 Carb or is it a 235 carb? 261 Carbs are very hard to find. Read http://www.devestechnet.com/Home/TheVenerable261 to see what the differences are. Wish I could tell you exactly what it is, but it's one of those things where you have to be there! Good luck!

[Pre68Dave]

It is possible there is nothing wrong.
People get use to how smooth computer controlled fuel injected engines are and forget that these older engines usually had a slight skip at idle.
One thing that may help though is to advance the timing slightly. With today's gas it helps to advance the timing about 5 degrees over stock timing.

[90crows]

I wondered the same thing- If I'm expecting modern results from 60 year old technology, but the skipping seems consistent at all RPM levels, its not bad but I really would like to find and fix the source of it.
Some more details, No its not the larger 261 carb just a "Plain Jane", I put a 5 deg advance offset key on the crank shaft gear, I've gaped the plugs to .045, the .060 was bothering me anyway, I made sure all the ignition and plug wires were firmly connected, I did a HOT valve adjustment (all the intakes needed to be backed off) I worked with the distributor adjustment while the engine was running to no effect, the only thing that "seemed" to remove the missing/skipping sound was adding choke, which I guess points back to the carb, which point me back to the How To pages. Does the choke thing add any clues for anybody ? Thanks -

[Deve]

Dave is the real expert here, but if adding choke (gas) to the issue fixes it, you might consider the Jet sizes on your 235 Carb, or tweak the mixture screw on the carb. The one with the spring surrounding it. The Jets are normally marked as to what they are, but do not put too much stock into that marking because alot of guys just drill them oversize and so you never know. I give Mike at Mike's Carbs the business when it comes to getting different Jets. He has all of them. The 235 Carb of course has less air intake because the throat is smaller. Needing more choke means needing more fuel so an increased Jet size could solve it, but I would want to hear from Dave before going out and spending your cash! Try turning the mixture screw first. Might solve it without going further.