Weber 38 idles high after driving a while

[Texas CJ7]

Hey guys, I usually figure most things out through some searching and what not but I have an issue that I can't find any help on...

I put on a Redline Weber conversion to dump the Chinese mc2150 that I had (tired of futzing with it every other week), everything went well got it pretty well dialed in and the motor is running better than it ever has (gained a few mpgs even with my issue).

The problem is that after driving around a bit the idle tends to stay up around 1000 rpm rather than dropping down to the curb set at 700 rpm. At first I figured it may be just be a little bind in the linkage, couldn't find anything, or possibly stiff joints fighting the return spring so I went through and added a little lithium grease to the joints and drove it to work a few days to see if it would loosen up with a little movement but it is still doing the same thing.

Any ideas as to what I should look for?

Thanks,
Tony

 

[Fastatv]

Tony, since you have checked your linkages and the are all apparently good, you might consider lowering the warm idle to 700 to 750. This will make for a much slower cold idle if you arent using any type of choke for cold starting. If the cold idle is too low, add a little bit of choke till the engine warms up for a few. Hope this helps.

 

[Texas CJ7]

Yup, 700 rpm once warmed up at idle is where it is set to. Made the last adjustments to it after driving for about 30 minutes so it was good and warm.

The carb has an electric choke that seems to be functioning as it should, the cooler the day the higher the initial rpm at startup. I setup the carb on a fairly cool day and set the fast idle to about 1200 as that is what I had read is appropriate, it has been staring at around 1000 rpm (I believe that this is due to the warmer weather 80°-90°).

I did just have a thought... would engine temp affect the rpm in this way? I swapped over to a contour fan a few months ago and have yet to put in a proper temp gauge (need to get one of those inline radiator hose adapters still), I just have the controller adjusted to kick on once the coolant starts flowing (195°-ish).

Thanks,
Tony

 

[Fastatv]

So is the problem now resolved? When you drive around for a while the rpm is now staying around 700....fully warmed up? I can't specifically answer your question but, the warmer an engine becomes, the idle will climb a bit as it warms, but there should be a point in which the idle climbing stops. I don't think the way you have the fan set to come on would be an issue.

 

[Kane]

If you have the idle air mixtures screws set to the best lean idle as they should then I would change the idle jets to smaller size. A high idle that you cannot lower anymore means you are getting too much fuel and the only way to reduce it is to install smaller idle jets.

 

[Texas CJ7]

Fastatv,
Nope, not resolved. I was trying to say that I reset the idle to 700 rpm after driving around for about 30 minutes (at which point it was sitting around 1100 or 1200 rpm), which would in theory be up to temp by that time, after initially setting the idle to 700 rpm in the garage once the the engine seemed to be at temp to begin with. After that it settles back down around 1000 rpm at stop lights and the like after driving any significant distance.

Kane,
I may have to look into that, not sure what Redline ships the carbs with.

Thanks,
Tony

 

[jdcaples]

What is the PSI of the fuel supply to the carb?

-Jon

 

[Texas CJ7]

I have not tested the psi on the fuel supply, it is a stock mechanical pump with the three-way filter in line though so it should not be pushing so much that it would overpower and flood the bowl.

I do know that the places selling chinese built weber carbs say 3.5 psi is the proper level and a regulator is necessary for that reason. Everything I have read on the Redline's indicate that this is not an issue with the spanish made units unless running an electric pump.

I will add it to the list to check though.

Thank you,
Tony

 

[Fastatv]

Ok, Tony, I somehow misunderstood ya. I know little to nothing about Webers, didn't even know that the idle jets were changeable. I will add this tho, have you checked for vacuum leaks once it gets fully warmed up? Also, have you removed the throttle cable and applied a little pressure to try to close the throttle a little? Make any difference? Is your Weber one of the Chinese types?

 

[caveman]

Long shot but I've had it happen. I don't remember what carb it was, But it wasn't a stock carb. When it warmed up the expansion from the heat would make the throttle plate ever so slightly rub the adapter plate and would stick part way open. If so, A little filing should remedy the problem.

 

[Hedgehog]

This is seemingly repeated over and over again, but that doesn't mean its not true. I was having high idle troubles with my 2150 carbonated AMC 360. It turned out that I was getting a vacuum leak through the charcoal canister and the PCV valve. This is what you get when you mix '75 CJ technology with 82 Wagoneer tech. I'm betting that you have a vacuum leak related to one of your heat or running temperature opening valves in your emissions controls.

 

[Texas CJ7]

Hey guys,

Thanks for the ideas, haven't been able to get anything moved along on it in a few days as other issues have taken priority.

Fastatv,
The carb was made in Spain, Redline is the official American distributor for Weber in the U.S.A. They get the carbs from Weber and then set them up as conversion kits from there.

Caveman,
Interesting thought, may keep that in mind if everything else checks out.

Hedgehog,
When I first bought the jeep I had some issues with vacuum leaks (running the carter at that point) though they always seemed to stall the engine out upon deceleration. I did give it a spray down test to check for leaks when it came to temp before the initial idle setting... In combo with Caveman's thoughts I could give another leak test after driving around a bit.

Thanks,
Tony

 

[Texas CJ7]

Finally got some time in the garage yesterday and today... looks like it was a combo of heat and vacuum leak. Looks like once the engine got up to temp for a will there was enough heat soak into the adapter plates to cause a bit of a leak between the two. Tightened the pair up a bit and all seems well so far.

Thanks for the suggestions guy! Now it is time to head to a barbecue for a few beers and meat :us:.

Tony