flames?

[blue beast]

backfire produces flame from tailpipes...is this just simply too much gas? i pulled my plugs after this summer and they weren't black or grudgy, but this year i want to address the problem and i was wondering what i could do to fix it, i'm using autolite spark plugs if that helps. It also stumbles a bit under the first hard acceleration, but then its fine afterwards. So to me it seems like its just too much gas, but i always thought that would leave evidence on the plugs as well?

[Ltngdrvr]

Hell, there are people that pay money to make their car belch flames out the tailpipe!!!

And you want to stop it from doing it?

[bob85gt]

as a general rule. if the engine backfires out the exhuast the fuel mixture is rich. if it backfires to the carb (if u have one) it is to lean.

[twister]

you don't have cats, right? Anyways, it could also be a timing issue, if the spark is not at the right time, un-burnt fuel can go out the pipes, if the car just stated doing this and the carb is fine, you might need a timing chain

[82mustang]

post a pic of your plugs all lined up if possible.. have you messed with the carb at all? jetting or float height?

[blue beast]

i'm thinking the timing issue, i installed the carb last winter, changes the float level but thats it, i'll bet alot that its the timing, i'll let you guys know when i do all the maintence stuff in the next couple weeks...and actually its both tailpipes : ) and i do have to admit, they are sweet to see, but, i'd rather have everything running as it should

[bob85gt]

you said it stumbles first and then runs fine. this is a sympton of to much fuel from the accel pump. (everything else being ok) did you install the 50cc pump? also what size carb and mech secondarys?

[twister]

did you take it to Nitro's Auto Service?

[blue beast]

its a 650 which, is a lil big...but, it was on another 302 with no problems...it does have mech secondaries

[ricko302]

Lean conditions cause backfiring out of the tailpipes too.

[blue beast]

ok? got it out on the road today, and it ran beautifuly with no problems? god, i hate when ppl randomly sneak up and fix my problems without me knowing!?! i didn't change anything besides the idle, so i don't know why it was doing it last summer...this is weird...

[bob85gt]

a 650 with mech. runs fine on another 302. welcome to the art of tuning a holley. this is of course my opinion from a dd point of view. depending on your rpm range 650 is big. the mech sec. makes it worse.(never answered about the 50cc). out of the holley book a good starting point for a carb is (engine cid divided by 2) times (max rpm divided by 172. this formula is 100% volume efficiency. example. 302ci 5500rpm .9 %efficient is 431 cfm. a vacum secondery will offer a more forgiving carb. also temp and track conditions (tire spin) will alter the carb stumble. initail timing is also important .

[blue beast]

k, stupid college kid here, hows that equation work out? i don't get those numbers...

[bob85gt]

it put a smiley in the formula. try again. this formula comes from my holley book.
(c.i./2) * (max rpm/1720) = cfm at 100% ex. (302/2) * (5500/1720)= 482
482*.9=434 incase it puts a smiley in the number is one thousand seven hundred twenty.