back fire under load

[79bonanza]

ok i was wheelin the other day and everytime i get my truck on good incline and kinda loading the engine down it starts to back fire and almost dies,( have to push the clutch in and let it idle befor reving up and tryin again).

i was wondering if this could just be a timing problem, any advice if not

[VegasBruce]

Sounds like its flooding through the floatbowl overflow vent.

[cr34t3d_by_d4rkd3n]

Originally Posted by VegasBruce

Sounds like its flooding through the floatbowl overflow vent.

[James McClure]

79, you don't give a year, but I an guessing it's 79. Back in the 80's GM had a problem with soft cams and replaced thousands under warantee. I replaced hundreds myself. Here the first check. Automatic trans, static load eng to about 1000 RPM and then to 2000 quickly. Manual trans, flat road surface, 2ND gear rolling at about 1500 RPM, accelerate to 2500 RPM rather quickly. If the cam is bad you will hear the eng backfire thru the carb in a steady pop, pop, pop that goes away when you back off the throttle. Second check is to pull both valve covers and watch the rocker arms at idle, you will see 1 or more rockers not moving as the others do. May also have a loose rocker noise, but not always. I am assuming you have checked for condition of tune up parts. A crossfire caused by a bad cap, rotor or wires can do the same thing. Suspect the cam if this just happened out of the blue, not after you did some work to the eng. Suspect the carb if you smell\see fuel leaking or have black exhaust smoke and\or a hard start issue hot or cold. jim

[79bonanza]

Originally Posted by VegasBruce

Sounds like its flooding through the floatbowl overflow vent.

how do i check and see if thats it

i dont think its the cam because it only did it after i rebuilt my carb

[VegasBruce]

What happens is, on a steep incline or rough roads with a lot of bouncing, gas comes up through the vent tube and loads up the engine. Basically flooding it out. The Qjet seems to work well in these conditions, Holley came out with the Truck Avenger to combat the problem. I've never used the Edelbrock off road so I don't know how it works. What I did to fix the problem with the Qjet was extend the vent higher.

Before



After

[79bonanza]

my bad man i forgot to say its on a I6 250 with a 1 barrel on it. it doesnt really matter on my angle its just after hard throttle

[cr34t3d_by_d4rkd3n]

wtf? get a feeler guage and check the float valve gap to c if its too hig or low... think of it as ur toilet, as the bowl emptys, the valve open and fills the chaimber until its full and then shuts it off....

on an incline it thinks its "low" and fills, thus creating a ritch condition, combine that with an already inefficient motor and it will cough and struggle. If the bowls outta spec it will give it even MORE fuel, and yeah, u get the picture

remember, when your dramatically forward or rearward u can starve the motor of oil, may wanna think of a high vol pump if serious 4x4 is goin down ahaha

giving u have a straight 6 on a 1b? (2b prob) its all gonna be different, go buy a rochester book, its worth it and impossible without one.

[VegasBruce]

Originally Posted by cr34t3d_by_d4rkd3n

wtf? get a feeler guage and check the float valve gap to c if its too hig or low... think of it as ur toilet, as the bowl emptys, the valve open and fills the chaimber until its full and then shuts it off....

on an incline it thinks its "low" and fills, thus creating a ritch condition, combine that with an already inefficient motor and it will cough and struggle. If the bowls outta spec it will give it even MORE fuel, and yeah, u get the picture

remember, when your dramatically forward or rearward u can starve the motor of oil, may wanna think of a high vol pump if serious 4x4 is goin down ahaha

giving u have a straight 6 on a 1b? (2b prob) its all gonna be different, go buy a rochester book, its worth it and impossible without one.

[79bonanza]

ahhhh ill have to give that check, for some reason i never even though of that

[VegasBruce]

Let us know what happens.