I have a 350 crate engine, approx 600 miles. when cold at idle I get a light pop sound out the exhaust intermitedly. and stumbles through the carb. Once warmed up it seems to go away, but I cannot drive this vehicle as it is still apart. But when up to 150 degrees plus it seems to rev smoothly and no miss or pop. If it were the cam/ lifter would it come out at temp or could this be the first sign of cam going flat? I have to pull the engine soon to finish my firewall, so a cam swap is no biggie, just hate to waste $'s if I am just missing something. Basically a stock 290 hp 350, 600 AFB, HEI etc, and timing is pretty close on it Thanks, Rusty
I think you have a plug (or a couple) starting to foul out,that once warmed up,starts firing. This happens to me when I'm building a car because it gets fired up quite often,but doesn't really get up to operating temperature.
Makes sense didn't check those plugs yet. If a cam is starting to go flat wouldn't the miss be constant? Especially when warm at higher rpms? Damn I don't want to change cams already,.
Sounds like it is running lean when cold. If you get a lean misfire, you are still getting some fuel in the exhaust which could account for the pop. A lean pop through the carb is common on cold engines with insufficient fuel.
ive only had one cam lose a lobe after about 40 yrs building them. when it started it was a miss and it wouldnt go away no matter what i did. i could adjust the rocker just a little and it would seem to clear up but after a little bit it run like shi- all the time.it would act like the timing was off so id play with that. didnt help so id co back check carb. everything good.got to watching the rockers and one kept getting loose. adjust. loose again. pulled out the cam and the lobe was a round as you can get.been about 4 yrs ago so i dont remember all the bs we went thru to find it but then i found out it was me that caused it. seems they took out the zinc in the oil and after i put in a new cam i used a zinc additive and never had that trouble again. oh well, live and learn.
In two posts you say good plugs, then you have not checked the plugs. you also say the timing is "pretty close". Time to do some checking for real.
Plugs were new when installed new 600 miles my assuption they are good, My bad for not pulling and checking. as for timing this is not my first rodeo, i got that close if not right on, just never had a pop like this before, and chatted with a previous owner and he had similar problems with it, kinda how I ended up with it I'm thinking. lost a cam once before, some of these problems seem the same, but the last one was a constant missfire and worse at higher rpms. just trying to see what all to check for before ordering a cam I may not need. also I guess there is a chance the fuel is going bad, but again a previous owner stated a popping/ missfire at times as well.
Heres what happened to my fast burn 385 crate motor.Started hearing a stumble in the left bank when started cold. Kinda got better when it warmed up.Then, some miles later, heard a clacking lifter noise, quite bad, Pulled the valve cover, both rocker arm studs on #7 cylinder had backed out. Asked a local short track engine builder who runs these motors in spec classes, never saw the problem before. Pulled all the studs, blue lock tight, torqued and the motor never ran better. My guess is they have been coming loose for quite a while. Also, if your 290 crate motor is fairly new, it should have roller lifters.The cam should not be bad. You can check by putting a dial indicator on each rocker and measuring lift to be sure.
Rusty I had that problem and it was the distributer gear going bad. The lower bushing had gone bad and let the gear wander once it was warmed up no problem untill it finally lunched the gear. Won't cost you much to find out.
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