[mnm99]

I need some help here.... I have a 350 that I never had any problems with the idle. I went to start it last week and it kinda backfired and then took alot of turns to get started, kinda like it was flooded. Now it start up but runs rough. Above 2500rpm it sounds smooth. WHAT COULD IT BE? Does this sound like an intake leak?

Recap here is what I have done already..

1-Replace plugs and gap. All original plugs looked good.
2-Check and ohm wires
3-Replace cap
4-verify spark per MSD instructions
5-Compresson test GOOD
6-Check timing and verify 15* inital and 36* total. My old specs didn't change.
6-Remove all vac lines on manifold and plug. Same on carb.
8-Vac suction test. Tape up breather cap hole and put paper over pcv hole. The paper did not suck in. It was kind of blowing out.
9-Hand over the car. It killed the car and didn't notice any increase in RPM.
10-Replace power valve.
11-Adjust rockers
12-Adjusted air/fuel mixture screws
13-Disconnected tach lead from MSD
14-Verified all MSD wires were clear of any power wires or coil.
15-Carb cleaner spray test around intake and carb
16-No funny noises that I hear except a fluttering vac on manifold port
17-No dripping from carb booster venturiis

As you can see I'm trying all my options before I pull the intake. Is there ANYTHING else you can think of before I pull it?

 

[Tom Mobley]

sounds like either a vacuum leak or something stuck in the needle/seat assemplies. Is the carb dripping from the booster venturiis at idle? pinch off the vacuum line to the PB, any change? Does it have a vacuum line to the tranny? Lift the carb and visually inspect the gasket?

 

[mnm99]

-The carb isn't dripping at idle. I looked in there already.
-I removed the vac line to the booster and plugged it and no change ( note the trans has a tee on the same line so that was disconnected too)

I'll take the carb off when I get home and check.

Thanks ,anything else?

 

[dadeo-3]

Check the power valve. Sounds like the backfire may have ruptured it (assuming it is a Holley carb).

 

[BB_Mike]

Did you spray carb cleaner inside the carb?

If your at 1500RPM, and it's still running rough, how much vacuum do you have in the carb (both up high and near the base).

Could it be an partially siezed up accesory item, like a bad ALT or PS pump? Wouldn't hurt to loosen the belt and give each a spin by hand.

Was the compression check even across all cylinders?

 

[mnm99]

Check the power valve. Sounds like the backfire may have ruptured it (assuming it is a Holley carb).

Did that in my list.

 

[mnm99]

Did you spray carb cleaner inside the carb?

If your at 1500RPM, and it's still running rough, how much vacuum do you have in the carb (both up high and near the base).

Could it be an partially siezed up accesory item, like a bad ALT or PS pump? Wouldn't hurt to loosen the belt and give each a spin by hand.

Was the compression check even across all cylinders?

I'll check it at 1500. It smooths out more at 1500 and gone at around 2000 and up.

I'll try the acc, but I dont think it would be it.

The compression check was good. It's in the list.

Would a bad lobe on a cam smooth out after 2000 rpm? Just wondering.

 

[BB_Mike]

Would a bad lobe on a cam smooth out after 2000 rpm? Just wondering.

No.
Assuming it is an exhaust lobe, the backfiring through the carb through lack of exhaust getting out would increase as RPMS increase.
Assumingg it is an intake lobe, I doubt you would notice that, or call that a "rough idle" at 1500RPM. It'd be more like a mis or hesitation than a "rumpity-rump" kind of problem.

I"m more intersted in the "kinda backfired" statement. Did the motor just STOP when this happened? Or did it backfire while you had the key turned and gas peddle pumping?

 

[mnm99]

No.
Assuming it is an exhaust lobe, the backfiring through the carb through lack of exhaust getting out would increase as RPMS increase.
Assumingg it is an intake lobe, I doubt you would notice that, or call that a "rough idle" at 1500RPM. It'd be more like a mis or hesitation than a "rumpity-rump" kind of problem.

I"m more intersted in the "kinda backfired" statement. Did the motor just STOP when this happened? Or did it backfire while you had the key turned and gas peddle pumping?

I was wierd. Not really like a loud POP or It's hard to explain.The motor didn't stop or anything. Just started weird. Like I said hard to explain...

 

[BB_Mike]

I was fishing for a hydrolock kind of thing. My motor did that, and that bent the connecting rod. When I finally got it going (rod bent so much that the crank's counter wieght had to bust through the aluminum piston skirt) the idle was so sluggish and shaking that I shut the motor off 10 seconds later.

Just thought you might have had a lesser degree of my scenerio. It does sound you've covored a lot of the basis, almost too much consired the car ran fine some time ago and now you have an odd backfire and bad idle.

 

[ktrim]

check the idle air bleeds in teh top of the carb. if the get crud in them it will cause some of the thing you are seeing

 

[mnm99]

check the idle air bleeds in teh top of the carb. if the get crud in them it will cause some of the thing you are seeing

Thats what I was told from someone else too. I brought it up to 2000 rpm and sprayed carb cleaner at them with no change... Could it be somewhere in the carb? When I changed the power valve from a 9.5 to a 6.5 the response and seat of the pants went up, But the idle is still the same.

I went in AGAIN and readjusted the rockers and took a good look at the springs and lift of the rockers. They are all the same and all the springs appear fine..

Anyone around Miller Place NY with a carb I can borrow?