Hey folks,

Well after a lot of other issue eliminating. I must have a vac leak?? The truck has a 390, the PO had the carb off and on another vehicle, now it has a miss.

At Idle the vac will vibrate between 14-16 fast @ 850rpm and timing set at 10degbtdc and run at 20"Hg steady if I give it gas.

Now, if I put my hand over the primaries or choke it some the Idle increases from lumpy 850 to 1100 and smooth. SO again I'm thinking Vac leak.

I replaced the carb gasket, even though the old one looked new. I plugged and/or removed the vac lines (tranny/brake/vac adv) Still not better.

I have the engine lumping at about 700-750 and give a squirt of carb cleaner in the carb and the idle picks up. So I wait for it to drop and spray around the back of the carb and spacer, all the vac connection. still no leak.

I will try to replace the lower carb spacer gasket next.

Am I missing something???

Could it be the carb itself e-brock 1405. Is it warped or and internal leak?? The cab adj screws were not seated at first which caused me some issues. But I think I got them down, then out 1 1/2 turns. I'd buy a new carb in minute. but I hate to drop $200 and get no results. I have no friends to borrow one.


I must say I'm a bit frustrated. I got this rig 'cause it was supposed to be a nicer ride. Everything I touch turn to poop.

bob

 

did you spray carb cleaner/brake cleaner/ether around the throttle shaft? Do you have an aluminum manifold? pcv valve grommet cracked? try tightening the carb body screws. look for cracks around the mounting holes.

 

Did the shafts and the adj screws.

Popped the top on the carb and retightened the screws but will try again and spray there.

Steel manifold -- only one vac port it is brass tee-ed for tranny and brakes. sprayed

I have a lower port on the block to the air cleaner and the valve covers have chrome breathers.

thanks good ideas

bob

 

Does that carburetor draw warm air from an exchanger on the exhaust manifold for heating the choke? That can take a lot of air and the idle mix adjustment screws may need to be opened more to compensate.

I know it's a different carb, but the idle screws in my Motorcraft 2150 have to be out about 3-1/2 turns.

 

Nope no warm air exchanger.

Special note I can kill the engine if I cover the carb with my hands. First it picks up then, if I seal it better with my hands it will choke out.

I keep going back to the carb for 2 reasons.

1. Owner said he parked it running., When I bought it idle good with only a slight miss.

2. I pulled out 9 gallons of what looked like kerosene out of the tank. Bad gas.

So can a bad carb give you the impression of a vac leak???

bob

 

Sure it can. Do you have a carb spacer? If you do, that could be warped also.
But if you got a miss, gotta check the ignition system while you're at it.