backfires?

[clutch]

im wondering if a guy put a cam in a 350 got it a little off would the motor even start? i put a cam in recently.........any how.... my blazer runs pretty good at idle and when its revved up..but when i get it on the road and floor it it makes theses back fires its also got a new carb that im sure needs to adjusted by someone other than me.could the carb do that? ( backfires? ) not real loud ones but ones that u can hear for sure.im even woundering maybe its a burnt valve or not....

[ratlover]

Probably in the carb adjustment. MAybe a bit of timing too. A burnt valve will be very rythmic. always happening out the exhaust or is it the intake?

[ratlover]

and yes you can degree your cam different. without a special sprocket you would have to be off a tooth and it would run but run like crap.

[wyldman]

I agree with ratlover,it's most likely a carb or timing problem.

What kind of carb are you running ? What is the timing set at ?

[clutch]

hey guys thanks for the info..... hey i got a eddelbrock carb on the same eddl. intake. the carb is a 600 or 650.... i havent found any leaks at the base of the carb..... but ive heard everyone uses spacers on these set ups. the carb is brand new.... i do think someone other than me should mess with the carb though. the backfires happen right out the end of the exhaust i got timing at 12 degrees btdc

[wyldman]

12 degrees is enough timing,it shouldn't backfire at that setting.

If it's backfiring out the exhaust,then you probably are running rich,and the excess fuel in the exhaust lights off and backfires.Could also be something basic,like a cap\rotor,or plug wires causing a crossfire,or a bad valve spring letting the valve hang\bounce open.It may be worthwhile taking it to someone who can properly diagnose it,and correct the problem(s).

One other possibility is the valves may be set incorrectly,after the cam change.How did you adjust them ?

[clutch]

well... i went to the fireing order.....thru it and removed all lash... then additional3 quarter turn following hayes manuel........YESTERDAY i heard you only turn them 1 half turn after lash removed....you think maybe this could be it?i mean before i swapped the cam it never backfired

[ratlover]

I find it hard at times to figure out 0 lash on a hydralic cam, sometimes the with the motor running method works the best although it can get messy.

1-2 to 3/4 is generally what most people say. Might want to try to readjust it especially if it is a very constant rythmic thing. If it kinda sputters every now and then then its probably not that. Also doing lotsa adjust ment to the nuts can get thier interference fit a bit lose. Get some new nuts or whack the rounded top part of the nut with a hammer if they seem to keep losening themselves.

Does it seem to run rich? are the pipes all sooty or does it ever smoke black or does it stink? it may help to have somebody follow you.

[wyldman]

I usually set them at one turn past zero lash.The key is making sure you really find zero lash,which can be tough if the intake is on as you cannot see the lifter plunger.If your past zero lash to start with,then you may be too tight when you are finished.

[clutch]

yea the pipes are definitly sooty. i bought new headers ( coated black ) and boy they looked good. what a far cry they are now....yea man , it sure is hard to find zero lash especially when them push rods get a little oily. you mentioned the motor runing method? i wouldnt mind some oil all over if it meant my blazer would run good.geez you know ... i took the old cam out and i set it up ya know , on its end....well i was moving around and knocked it over. ( garbage anyway ) but when it fell to its side it busted in 2 peices! are they really that fragil?any how thanks for the advice...... hey just how much school does a guy gotta go through to be a master ase certified tech? or just certified?

[clutch]

hey also.... i pulled some plugs during my tuning....they were tan but only on half the tip... the other half was darker, like that on the few i pulled is that significate?

[sonjaab]

CLUTCH.......Are you sure the dist. wasn't installed off a
tooth ? To check.....Line up timing mark to 0 on the timing
scale and check to see if the rotor is on the #1 cylinder.

Also make sure the #1 cylinder is on the compression stroke.

Easy to do on a GM motor.............

Also find ya a old valve cover and cut in 1/2 lengthwise.
Install when adjusting valves to catch oil....handy trick!
..........geo

[wyldman]

Originally posted by clutch
hey also.... i pulled some plugs during my tuning....they were tan but only on half the tip... the other half was darker, like that on the few i pulled is that significate?

That is normal.Unless you do a clean hard run,and cut the engine clean,the plugs will look multi-colored.If they do have some tan coloring,and are not black and sooty,then your mixture is pretty close.