Idle problem with Webers.

[JohnnyJayhawk]

When I start it up it idles just great. As the engine warms up, the RPM's get higher and higher. After 10 to 15 minutes my idle is up over 3,000. I can, with my hand, move the linkage that is up by the carbs, and can get it to go back down to where it should be. It acts like the spring isn't strong enough to seat the throttle linkage back to full off. Blipping the throttle pedal has no effect. The idle stays high. I have checked for vacuum leaks, but it doesn't appear to have any. Any suggestions? The carbs are on a 1,720cc Ford Kent Crossflow.

[wdb]

I have a twincam but as far as I can see from staring at pictures the crossflow should have a similar return spring at the carbs. Ray sells them at rdent.com. 

 

 

EDIT: you might also want to ensure that the choke mechanisms are returning fully. 

Edited April 24 by wdb

[JohnnyJayhawk]

Do you think that the spring gets weak as it heats up?

 

[wdb]

The spring will lose tension over time, but the timeframe is years or decades, not minutes. I'd be more suspicious of the carbs themselves, or the mounts. I just redid the mounts on my Elan and I was astonished at how worn out the stuff was. But then everything on that poor old thing is worn out...

[MV8]

I've seen many examples where a tension spring was added to the linkage at the carbs. How it's done varies. Post pics of your linkage if you need a suggestion on how to do this.

 

Generally, most all types of carbs have a spring on the butterfly shaft and a tension or compression spring in the linkage.

 

Most older cables are not plastic lined and require periodic lubrication. The cable should have some slack in it (i.e., the cable should not pull the throttle pedal up to the travel stop). Similarly, full throttle at the pedal should have a slight amount of slack at the carb linkage to reduce cable fatigue.

Edited April 25 by MV8

[IamScotticus]

Dumping fuel?

[jbcollier]

Are you experienced with balancing and syncing carbs?

[JohnnyJayhawk]

They work great until the engine gets warm and then the idle just keeps climbing. Car runs great until then. 

[IamScotticus]

On 4/24/2025 at 10:45 AM, JohnnyJayhawk said:

I can, with my hand, move the linkage that is up by the carbs, and can get it to go back down to where it should be

When you do this, does the idle go down to normal?  You don't say.  I understand the link doesn't stay there, but you don't say that this changes the idle.

[IamScotticus]

This is your idle speed adjustment screw.  As you climb up, and have the chokes off, turn this screw to adjust the idle speed. 

You likely need a full rebalance and idle adjustment, but this is a start.

 

Don't forget you have fuel filter screens under the brass caps.

Edited Sunday at 01:41 AM by IamScotticus

[JohnnyJayhawk]

Yes. When we move it by hand up by the carbs the idle goes down to normal and stays there until you push on the throttle with your foot then it takes off again. 

[IamScotticus]

Looks like cable, throttle and linkage stuff.  These Xflow cars are all thirty years and older.  All the joints, cables, etc are gumming up.  I have heard of the throttle pedal pivot being a problem and if you unhook the cable and try moving it you may be surprised how stiff it can be.  It could possibly be rubbing on the steering shaft  if LHD.

 

Check our your pedal and cable.

[jbcollier]

I think you have an issue that would be easily solved by someone familiar with multi-carb set-ups.  And, that you are not that person.  It is not hard, and it is easy to learn given the right instruction.  But, if you don't know what you are doing, it is so easy to make it worse.  Find a shop or local mechanic that is knowledgeable and ask them to show you what's wrong and how to do a basic balance and sync.

[JohnnyJayhawk]

It has nothing to do with the balance and sync of the carbs. The balance and sync have nothing to do with the idle slowly gaining RPM's as the engine warms up. But thank you for your comments. 

[MV8]

10 hours ago, IamScotticus said:

Looks like cable, throttle and linkage stuff.  These Xflow cars are all thirty years and older.  All the joints, cables, etc are gumming up.  I have heard of the throttle pedal pivot being a problem and if you unhook the cable and try moving it you may be surprised how stiff it can be.  It could possibly be rubbing on the steering shaft  if LHD.

 

Check our your pedal and cable.

I'm shocked at how close they put the pedal arm to the steering shaft.

[jbcollier]

The idle slowly gaining while it warms up is due to the simple fact that friction and mixture requirements change as the engine heats up.

 

Your issue could be caused by a number of issues ranging from insufficient freeplay in the throttle cable to someone having tried to adjust the idle speed using the balance screw.

[jbcollier]

There are a number of things wrong in IamScotticus's photos.  But, they are not photos from JohnnyJayhawk's car so of little use is figuring out what is actually up.

[IamScotticus]

9 minutes ago, MV8 said:

I'm shocked at how close they put the pedal arm to the steering shaft.

The armature is actually bent around the shaft with a papers width clearance.  My pedal is stiff, and I thought was rubbing,  but it's in the axis.

Edited Sunday at 02:25 PM by IamScotticus

[MV8]

Hello, it's a forum! I think Johnny's had about all the help he can stomach for now. Place your bets! Discuss among'st yourselves.

[JohnnyJayhawk]

I was really hoping that this had happened to someone else out there in 7 land and could let me know what they did to fix it. I have owned an Elan, two Europa's and now this Caterham. Multiple Healy's' MG's, Triumph's etc.. I'm not a stranger to British cars with dual carbs. This one does have me baffled though. So your comments are welcome but some of the suggestions are just like you didn't read my explanation of what was going on. Also the dig that I don't know what I'm doing really hurt. 🤕