Hot Rod Forum banner

1 - 9 of 9 Posts

·
Glad the Jeep is on the road
Joined
·
809 Posts
Discussion Starter #1
Well, son B is home from college for a few weeks so it is time to tune up the Jeep. It starts ok, but just does not want to idle slower than about 1400-1500 rpm -- any slower and it dies. Pulled the plugs, the color looked good, I had adjusted the mixture last summer. Put a vacuum gage on it, it's pulling about 17. The carb is a new Holley 2 barrel I put on last spring to replace the pos Carter BBD.

That much is knowledge. Speculation:
Maybe rejetting it smaller will help? Its a 350 CFM carb on a 258 cid six that rarely sees 3500 rpm....

I am stumped and looking for clues.....
 

·
Grumpy Old Goat Herder
Joined
·
1,397 Posts
Without a hands on, I would guess that it has a bad vacuum leak. Check for leaking gaskets that may have dried out and shrunk.
 

·
Hates: Liver. Loves: Diesel
Joined
·
5,659 Posts
Don't change the jets. The problem isn't that the jets changed while sitting, something else has happened.

I would first check to make sure the choke is coming off. Is the choke plate opening after a few minutes? Turn it off and look down the throats. Are the throttle blades closed? Is the throttle stop tang against the idle adjustment screw? Is the fast idle cam coming off? Any linkages stuck? Is the choke getting a full 12v? Is it grounded properly?

A carb is a very complicated, but logical piece. Start with the choke and follow the linkages. You'll find the fast idle cam that holds the throttle open, the linkage to the choke plate, etc. Just follow the linkages and use logic to make sure everything is operating like it should.

Vaccuum leak is also a good thought. You can test for vacuum leaks by spraying something like carb cleaner at all the gasket mating surfaces; under the carb, where the intake meets the head, and threaded plugs or hoses. If the idle changes (rises) after you spray stuff, that's you leak.
 

·
Glad the Jeep is on the road
Joined
·
809 Posts
Discussion Starter #4
Thanks for the suggestions. I haven't been able to get to it for a couple days, but I will be out there later looking for vacuum leaks.

It is a manual choke carb, so automatic chokes aren't an issue. The throttle blades and the choke blade appear to work properly, and I have been warming it up at around 1500 rpm (it runs ok there once it is a little warm) and backing down the idle screw til it eventually quits, now about 1200-1300 rpm.

I should mention that this is a new Holley 2 barrel and when I installed it in the hot summer, it ran better but it really didn't like to idle below about 900 rpm. So perhaps there was a small vaccuum leak that got worse sitting?
 

·
Glad the Jeep is on the road
Joined
·
809 Posts
Discussion Starter #6
Don't have a timing light -- set the timing with the vacuum gage and tach......
 

·
Grumpy Old Goat Herder
Joined
·
1,397 Posts
pmeisel said:
Don't have a timing light -- set the timing with the vacuum gage and tach......
Did you do that with the vacuum unplugged from the vacuum advance? If not, try it, but be sure to plug the line.
 

·
Ford Man to the bone!!!
Joined
·
112 Posts
OK guys...Back to basics.

The carb puts out fuel two ways.

1. Jets: From the throttle plates being open and the air flow pulling fuel thru the jets and mixing it with the right amount of air. Wider open = more air = gets more fuel. (These plates are called butterflies also, BTW)

2. IDLE Fuel passages: Most carbs have needle screws to adjust how much or how little fuel gets fed into the small amount of air slipping by the almost closed throttle plates. (Look for two small counter sunk adjustment screws on the body of the carb, not the one used to adjust the throttle plate positions. They may or may not be counter sunk on your carb. If not you might see a spring on the screw shaft, since they are never tightened down and need some way to keep from vibrating out of adjustment.)

Having said that, I would check the Idle Fuel adjustment screws. If they are tightened down then loosen them 1 turn and try lowering the throttle screws. If when they are wide open (screwed out more to three turns) and it still won't idle, then you may have a clogged passage.

The possible reason problem has gotten worse could be gasket pieces in the passage or bowl have swollen and are restricting the idle fuel more. Maybe the factory installed the gasket a little off and it was partially blocking the Idle Fuel passages and has swollen. They may have left a hanging chad where the hole was punched in the gasket. A rebuild kit with new gaskets is cheap and easy to do.
 

·
Save a horse, Ride a Cowboy.
Joined
·
5,122 Posts
You didn't say why you changed the carb. But you still have continual carb problems.
Reading pllugs is pretty iffy with modern gasoline.
Last summer it didn't want to idle below 900, now 1300.
Last summer the air density was less so the mixture was richer then than now. 4-7 % leaner now.

In a border line situation that could be the difference.

You also need to check the static timing and the timing at 1300 rpm. Also see if the mechanical advance is stuck, and look for the proper operation of the vacuum advance can.

My guess is that you have a vacuum leak, or a mechanical advance stuck.
 
1 - 9 of 9 Posts
Top