drivability

[spanky55amg]

Ok, its been a long time that I have bitched about my truck. Ha. Anyways, so let me run something by y'all. Ive had all these drivability issues.

So, I started running 91 octane and it improved a bit. I think at the same time I fatted up my idle mixture. My gas mileage got a little better to 10 mpg, up from 8 mpg. But while turning the truck off, it would diesel. Ok, I thought that the idle at 900 ish in gear and 1200 out of gear was too high. So I started messing with the carb again and phucked it up.

After fiddle phucking with it, I ended up fatting it up to 3.5 turns each screw and disconnected the vacuum advance. Holy ****, except being a little boggy on the bottom end, this thing is now running better than it ever has..... but the mileage has gone to shiiiiiiiiiiiit.

So Im thinking, maybe I have an intake leak. I mean, no more misfiring while cruising. No more bogging. I can actually hit the gas and the secondaries open up. It shifts correctly.

 

[yevgenievich]

Have you verified initial timing and checked how much advance vacuum advance gives?

 

[spanky55amg]

Initial yes. I put a new dist in about... 4 months ago. I had it set to 10 and it backfired always at cruise and high load. Wouldn't run if secondaores are open. At the advise of someone, I dropped the timing down to 4. Less backfiring but still did. And could use the secondaries.

 

[spanky55amg]

Though to answer your question, I didn't check the total advance. Or if we did, I forgot because it was where it should have been at 10.

 

[RustyPile]

What cam do you have that requires 1200 rpm idle speed.. Or for that matter -- why do you have the idle speed set at 1200?? although they will effect the idle speed, Idle mixture screws are not used to set the idle speed.. Have you checked to be sure the mechanical advance mechanism is working properly??

 

[Dougnsalem]

Holy ****, except being a little boggy on the bottom end, this thing is now running better than it ever has..... but the mileage has gone to shiiiiiiiiiiiit

If you wanna play, then you gotta pay.....

Lol

 

[yevgenievich]

Set idle and then idle fuel mixture for best vacuum. Stock motor should be able to idle 500-600rpm in gear.

 

[75gmck25]

If you have an extra $200 to spend, I would buy an Innovate AFR gauge and install the O2 sensor in one of your header pipes. Watching the AFR in real-time will give you a much better idea of what is going on with the carburetor.

Your timing settings also seem to be off. On a relatively stock 350 you should be able to run up to about 10-12 degrees BTDC without any pinging. If you have aluminum heads it may tolerate even more. Then make sure that your centrifugal advance adds about 20 degrees more by about 2500 RPM. This gives you about 32 degrees of base+centrifugal.

With a higher base timing you may have to dial your vacuum advance back from the stock 18-20 degrees so that you don't get pinging at part throttle cruise. Use an adjustable canister and get it right on the edge of pinging during part throttle tip in.

Bruce

 

[Craig 85]

I had a problem on my '79 K15 right before I sold it. The factory manifold had warped at the #8 cylinder causing a vacuum leak and irratic idle. It also cause me to fail smog. I installed a new intake an solved the problem.

 

[spanky55amg]

On a relatively stock 350 you should be able to run up to about 10-12 degrees BTDC without any pinging.
Bruce

Stock 305. about 95% of the late 70s and 80's squarebodies have/had 305s. I have had this discussion with many people that the 305s do not like a crap load of timing in them.