Q Jet Flooding

[68_Step]

I am one step away from striking a match...

1967 Chevy C10 V8 with Q-Jet (17041250) Truck was running fine until the other morning. When I tried to crank it, it cranked but would not go much above an idle. When I give it more gas, the sound of the motor changes but no more RPMs. Give it a bit more gas and it backfires through the carb and spits gas on the hood. I figure it is time for a rebuild anyway, so I pick up a rebuild kit and rebuild it tonight. No change at all. Any ideas? What am I missing? Is there something else I should be looking at?

[jeffspower]

It's not flooding. It backfires thru the carb because it is too lean, or the mechanical advance in the distributor is stuck. Or the dist. worked loose & retarded itself. Speed it up to the point it is bogging without backfiring and stroke the accelerator pump quickly without changing the throttle position. If it snaps to life (providing that the accel. pump is working) it is way lean. If it makes little difference or slows down, suspect dist. advance.

Stock fuel pump-

Fuel pressure should be around 4-6 psi

Free flow at cranking speed should pump 1/2 quart in about 10 seconds or less.

[57sailplane]

it could be a sliped timing chain. some of the old enjines had a nylon like plastic cam gear that wear out. just a thought..

[cooters]

good call guys, timing problem all the way.

[68_Step]

Just got back in from trying jeffspower's suggestion. When I stroked the accelerator pump almost nothing happens, motor stumbled just a bit.

So that means I am looking at a distributer/ timing problem, right? How can I narrow it down from either the distributer advance or the timing chain? 57sailplane mentioned it could be a timing chain problem.

If it is the chain and I put a timing light on it, will it read normal, or will it show the timing to be off? Of course my timing light chose this moment to die...

Can I take the distributer and tell if the mechanical advance is working?

I tried to get it above a rough idle, did not work. Backfired, coughed and died. I must admit that the flames were pretty...

Thanks for the help!

Originally Posted by jeffspower

...Speed it up to the point it is bogging without backfiring and stroke the accelerator pump quickly without changing the throttle position. If it snaps to life (providing that the accel. pump is working) it is way lean. If it makes little difference or slows down, suspect dist. advance.

[cooters]

if you have flames then you must have fuel, try rotating the distributer while it is running and see what happens, if you have flames then a valve is open when the plug fires.

[jeffspower]

Originally Posted by 68_Step

If it is the chain and I put a timing light on it, will it read normal, or will it show the timing to be off? Of course my timing light chose this moment to die...

Can I take the distributer and tell if the mechanical advance is working?

A timing light will show the timing way slow if the chain jumped a tooth (usually the balancer mark won't even show up anywhere on the timing tab) or if the distributor has worked loose, or if the roll pin in the dist. gear is starting to shear off (seen it before, but not often). If the dist. isn't loose, before you try moving it, bring the balancer around to align the mark with zero on the tab. Then pull the dist. cap & see if the rotor is pointing at # 1 or 7 tower. The rotor rotates CW and should be aligned with the 1 or 7 tower, or slightly CW from it (advanced). If it is CCW from the tower (retarded), your chain has probably jumped.

If you take the rotor & twist it CCW with your hand it should rotate back on its own if the mech. advance isn't stuck or springs broke. If it doesn't "spring" back or twists hard, or not at all, you will need to repair or replace the dizzy.

[68_Step]

Originally Posted by jeffspower

If you take the rotor & twist it CCW with your hand it should rotate back on its own if the mech. advance isn't stuck or springs broke. If it doesn't "spring" back or twists hard, or not at all, you will need to repair or replace the dizzy.

Finally had time to work on it today. It did not pass this test, very hard to turn and did not spring back. I pulled the distributer and replaced it with an Accel out of my 68 C-10, and she fired right up. The 67 runs better than it ever has, freshly rebuilt carb and a new distributer (maybe 5 hours on it...)

Thanks everybody, excellent advice as always!!

Had a problem checking the timing, but I will start a new thread for that.

[68_Step]

I knew I should have checked here first... I will try the accel pump test tonight.