The Stovebolt Site Forums The Shop Area Engine Shop 1954 235 engine "backfire"

i FINALLY got around to re-timing my 1954 235 stovebolt after the valve adjustment, and now it sorta sputters when at idle. (before i retimed it it was firing at top dead at idle. , ive since fixed this) the manual says to play with the idle speed and fuel mixture screw to equalize it.
now after about 40 minutes of fiddling with it, i got it to somewhat silence up (it would sputter once every 40 seconds or so) and i went back to adjust the mixture to try and get it better (which it wasnt doing at all) and i didnt notice but i screwed the idle mixture screw all the way in and the engine speed remained unchanged. is there a chance something got blocked? or was it because i had just noticed the gas can going empty. idk, it was a weird issue and ill see if fresh gas fixes it. feel free to discuss.. and one more thing, i do need a bit of advice for setting the idle mixture so it doesnt sputter and pop.

The engine shouldn't run at all at idle with the mixture screw bottomed out. You've either got the idle speed set high enough to draw fuel through the venturi (high speed system) or the float level is set so high that fuel is dribbling into the air stream without going through the idle system. What RPM is the engine running at "idle"? It should be around 500 +/- a little.
Jerry

it did that because it was out of gas from the can, it was pretty weird but everything works normally. anyway, i still cant seem to get it to stop popping and sputtering like a gocart when its slowing down, (it pops like 2 times in a minute, so its not BAD), im just wondering because ive set the idle and the timing is it supposed to just be that way because its almost 70 or is something still not right. (another valve adjustment.?)

I have had that problem also and it was running over rich and when it was set properly it stopped.

ive set it most positively, before mine was running rich too, but i set it to be just perfect and it still sputters. timings right, new carb, fuel has lead additive, could it be still a valve issue? they were set to .06 intake and .13 exhaust when hot..

I have had that situation happen with me a few times over the years. The problem that i found was a small blockage of debris somewhere in the carb. I cleared it by removing the air cleaner, starting engine, rev it up a couple times,then rev it up to around 2500 rpm and close off the carb air intake with a rag. Then open thottle wide open until the engine stalls.restart engine,you may have to hold throttle open initially to clear fuel out of the intake before it will start.reset carb air/fuel mixture and curb idle. The vacuum created by stalling eng out at high rpm generaly will pull out the blockage. Ive done this with other carbs with decent success. Change filter and also make sure fuel can is clean.Also if your timing is correct etc, and it been awhile since points and codensor have been changed, might want to give that a try..i gotta long story about that ...another day i know there can be more to look at, just a couple basic things to look at/ think about.

ill try a couple of em. everything brand new except for the manifold and the air cleaner, i mean my repro radiator had a rats nest in it and it caused me long hours of flushing, but it was good i did it because there was more than just cotton in there... anyway i don't think there's a blockage but ill definitely check, i hear the old manifolds are notorious for stuff like that.. i have yet to put a filter on the line so it could very well be a clog somewhere.. i will definitely try that a few times, it does wonders to small engines.

just as i thought. it was the timing. i checked it and sure enough the BB was half a inch ahead of the pointer. fixed that and it maybe pops once in a minute. ill take it to my local mechanic whos worked with inline 6s his whole life for a proper tune up with the right equipment, he should be able to make the final tweaks and small adjustments so its just right.

I didn't catch if it was already checked but my 235 was backfiring through the carb and after some research and troubleshooting it turned out to be the vacuum advance diaphragm on the distributor was shot and likely sucking air. I swapped it out and problem solved. Better throttle response as well. Just a thought.

Pour a can of Sea Foam into the gas tank, top the tank off with some non-ethanol gasoline if you can find some, and spend all day trying to keep up with traffic out on the highway. You'll be amazed at how much better the old rig runs after a few hours of heavy-footed highway driving. Most of us are far too conservative when it comes to making these trucks run like they were intended to.
Jerry

it isnt drivable yet but when it is itll be seeing some high rpms and heavy duty run. theyre dirt easy to rebuild so its no big deal if a main bearing wears out, it just costs some cash

Ive done everything Suggusted here and were back to step one.. i just cant get it to stop "popping". i made a video of this noise Here
I dont know what to do at this point, unless this is normal and i should just leave it alone.
Note: when i just barely accelerate it starts popping at a insanely high frequency (a good 10 pops in 4 seconds)... ALSO the engine was rebuilt so everything is new, timing is set, valves might need another adjustment, and everything else is pristine and brand new (except for the block, head, and manifolds..


EDIT: Link wasnt working

What type of muffler are you running? Sounds like a Cherry bomb/glasspack. It's not unusual for those types of mufflers to occasionally pop, especially if the carb is not adjusted or jetted properly.

Another easy test:
Hold a dollar bill close to the exhaust tip while it's isling, as close as possible. Notice if it sucks the bill towards the pipe when it pops or at any other time while idling. If it does you've got an exhaust valve either sticking or isn't closing all the way.
Good luck

Again...points and condenser, have you tried those? How about disturber cap? Is it cracked? Cracked cap causes spark to jump around. Bad condenser, consistent spark delievery. Was head rebuilt? Cracks ,bad valves,as in burnt valves...more to look at if you havent already..

i bought a stock repro from a off brand site, they custom make the systems in their shop, by hand, like they were originally built. ill try the bill trick, my no.2 exhaust was stuck after the rebuild (lifter wasnt lubricated right) but i fixed that. ill certainly check. as for the carb, the only thing it could be is jets.. which i still have new of from when i tried to rebuild my original one (bought new, old one leaked like mad).

ive checked all of the above, and the engine was just rebuilt, hasnt seen more than 4 hours of run time.. which also could be a factor. i bought another head (original was cracked) when i rebuilt it.. if the condenser was bad the timing light would have been acting up. perhaps i just need to put some more hours (eventually miles) on it?

also while im at it, does my engine sound dare i say "normal"? because many other 235s ive heard have a much more distinct rumble.. i know a guy with a truck with the same engine and it sounds way different too, granted his has clocked many miles.. in the end i think i just need to run it more..

also along with the occasional "pops" it seems to be sputtering with every rpm. what might cause this?

Back firing is also caused by fresh air leak in the exhaust system, so make sure there ar no leaks there.

Ed

one thing to check. thank you!