Running rough

[YNOTBOB2007]

My 302/auto with 2150 carb is running rough. The carb was rebuilt a few hundred miles ago...was running good after. Let it sit for a couple months, took it out, now rough and stalls if I don't keep my foot into it. I opened up the carb and sprayed the jets...all looked good. Timing is good. Each plug wire has good spark. One thing I noticed is when I choke off the carb (by closing the plate while running) , it actually runs smoother (usually it will want to die if I do that). What do you think? Does that mean it's running too lean? I've adjusted the fuel/air screws to get the highest idle but no difference. Thanks.

 

[ared77]

Vacuum leak maybe?

 

[YNOTBOB2007]

Thanks....So far I haven't been able to find one....spraying around with carb cleaner and no change in idle.

 

[nvrstuk]

Gunk in the jets?

Either too much air or not enough fuel if you can cover the hat and it starts idling smoothly.

 

[73azbronco]

what is your idle vacuum reading? what is it with choke closed? BTW, if you close the choke, it should stall, not run better. Sign is of a real bad vacuum leak.

Like nvrstuk, bad gas/gummed up carb even though you just rebuilt it. When you rebuilt it, did you ensure clean fuel tank, lines and filter?

 

[YNOTBOB2007]

what is your idle vacuum reading? what is it with choke closed? BTW, if you close the choke, it should stall, not run better. Sign is of a real bad vacuum leak.

Like nvrstuk, bad gas/gummed up carb even though you just rebuilt it. When you rebuilt it, did you ensure clean fuel tank, lines and filter?

Agreed,,, usually it stalls when I close the choke. Vacuum at idle fluctuates between 14 and 15....(usually it is steady at 16). I didn't check when choke is closed. I sprayed everywhere....I did find something unusual. When I spray at the pcv valve (where it plugs into the rubber grommet on the valve cover) the idle increased. Is that my leak? The PCV Valve is good but doesn't seem to fit real tight into the rubber grommet.

 

[DirtDonk]

How do you know it’s good? Next time you have the engine idling, pull it out of the grommet and put your finger over the hole.
How does it run then?

Yes, being loose in the grommet is kind of like a vacuum leak. So get a new one, if you can, or at least add something to temporarily make it fit tighter.
But it’s either very loose to cause this problem, or is being held wide-open and sucking too much area to begin with.
It does suck air under normal circumstances, because even when it’s inserted into the engine and sucking through the crankcase, it’s still pulling in outside air through the air filter.
Maybe it’s got a clog at the other end?

 

[YNOTBOB2007]

OK...when I pull the pcv out of the grommet there is not much difference in idle. I think the pcv is good because it's new and the ball rattles inside. If the valve was bad, would the truck run like this? It's an easy part to replace but I don't think that's the problem. When I close the choke plate, the engine runs much better....adding almost 5" of vacuum up to 20". The other end of the hose is not clogged...all was disassembled and cleaned when I rebuilt the carb. Thanks for any ideas.

 

[DirtDonk]

Did you try putting your finger over the hole of the valve while it was running to see what it does?

 

[YNOTBOB2007]

Yes, no change in idle with my finger over the hole.

 

[DirtDonk]

Well, Hells Bells, General, this isn’t making this easy!

 

[YNOTBOB2007]

Yeah crazy. Obviously too much air because closing the choke plate corrects the low rough idle. As one poster said it could also be not enough fuel… the ratio is out of balance. Even though I popped the lid off & cleaned the 2 brass jets under the float, maybe there is another jet that is clogging. I’ve also been adjusting the high idle cam but don’t think that would cause this problem. Both fuel filters are just one year old….i really don’t want to remove the carb again. It’s becoming an annual chore

 

[stupidboy]

Ethanol gasoline it sucks. You can’t let it sit to long or it separates.

 

[YNOTBOB2007]

Ethanol gasoline it sucks. You can’t let it sit to long or it separates.

Yes....I probably let it sit too long...maybe a couple months. I always use Stabil but maybe it doesn't do much. I will limp it to the gas station and add fresh gas and see if it fixes it. Doubt it though because I added fresh gas a couple months ago. As fas as jets clogging....It's easy enough for me to clean the 2 brass jets below the float without removing the carb. Do you know if any other jets can be cleaned wit the carb in place?

 

[stupidboy]

I have found it’s the passages in the carb itself that get clogged up not the jets

 

[YNOTBOB2007]

I have found it’s the passages in the carb itself that get clogged up not the jets

Ah ok....so the passages can only be cleaned by removing and disassembling the carb?

 

[YNOTBOB2007]

Also, the only thing I have messed with since it was running good a few months ago is the fast idle cam screw below the choke housing. I’ve turned it different times to get my start up idle higher, then tap the gas to drop it lower like it should. Could this screw affect the fuel/air ratio causing the lean condition?

 

[stupidboy]

No, that screw has no involvement. When you have to use choke to make it run better it means not enough fuel, the choke is making it cut some air to make the fuel air mixture closer to correct. I have never seen it fix itself.
Pull it off and clean all passages.