Idle problem with Webers.

[jbcollier]

Not meant to injure, my apologies.  I'm a retired mechanic and have dealt with many. many owners who's first instinct is to start twiddling screws on the carbs when there is an issue.

 

Your issue is that the throttle plates are not seating correctly at idle, full stop.

 

The fact that the idle changes as it warms up is not indicative of any issue.  Engines idle slowly when cold and then speed up as the engine "loosens" and less of the air/fuel mix is condensing out on cold surfaces.  The fact your engine idles normally when cold -- which it shouldn't -- does not point to any particular fault, other than the throttle plates are not fully seating at idle.

 

What can cause the throttle plates to not seat correctly (hang up)?

 

- not enough slack in the throttle cable when at idle.  Just a little tight means the cable acts as a spring.  You push down and the idle is normal.  The cable isn't too tight so it doesn't lift the throttle back up when you release but it will still "hang up" again when you blip the throttle.

 

- return spring issue.  Weak, broken, or missing return spring means the internal return springs in the Webers themselves are insufficient to snap the throttle fully home.  The weight of the pedal and friction in pivots/cable/linkage cause it to, yet again, hang up.

 

- improper sync.  Someone has tried to adjust the idle using the balance adjustment.  This can cause one throttle to hold the other slightly open, giving an elevated idle.  When you push down, flex/spring tension/etc allows it seat better and the idle goes down.  Then it just hangs up again when you blip the throttle.

 

- cable issue.  Frayed/kinked/dirty cable can bind in its housing causing friction which prevents the throttle returning fully to home.  You push down... etc, etc.

 

I could go on and on with even more things I have encountered in my long career but an experienced eye will find the issue quicker than reading any long treatise.

[IamScotticus]

We can't really know you from the other side of a keyboard. 

We just try, that's all.

[IamScotticus]

3 hours ago, jbcollier said:

There are a number of things wrong in IamScotticus's photos. 

You should see the rest of the car!

That crimped lever end wasn't my doing.  I do plan to clean it up with the proper clip.

Those DCOEs aren't on the car anymore.  Next carb will probably be a DG.

Edited Sunday at 05:21 PM by IamScotticus

[wdb]

Since I'm having some issues with the new(ish) Webers on the Elan, I did some digging into rising idle. There is quite a bit to be found in google, including chapter and verse regarding throttle plate position relative to the orifices. But since you are able to return the idle to normal manually, I would tend towards a mechanical issue of some kind.

 

It could also be mixture related. My Caterham has Webers and it runs properly when warmed up, however it is a bit cantankerous when cold. Webers aren't great at cold running. The Elan starts like a dream and runs progressively more cantakerously as it warms up. I put the Colortune on it and WHOA was it running rich! I'll find out tomorrow if it starts worth a hoot...

[SENC]

21 hours ago, jbcollier said:

Your issue is that the throttle plates are not seating correctly at idle, full stop.

Agree this seems most likely. 

 

And would add to JB's list of potential culprits the plates themselves (and/or where they land).  The aluminum bodies can be worn and need a differently angled plate... or a PO may have made adjustments to the plate to try to fix something else and created an issue... or spindles slightly bent or bearings worn.

 

Also agree that going back to balance/airflow is likely to be the most efficient way to circle in on your specific problem.

 

[Davemk1]

I would be tempted to disconnect the throttle cable completely and then, with the engine cold, start it and see what it does. It sounds like it could be the cable hanging up and running it with the cable out of the picture would tell you for sure.

 

dave

[JohnnyJayhawk]

It would either confirm or deny that it had anything to do with the cable. Thank you. 

[Davemk1]

48 minutes ago, JohnnyJayhawk said:

It would either confirm or deny that it had anything to do with the cable. Thank you. 

I think so.

 

If it idles fine and as it warms the idle doesn't climb it's almost certainly the cable. If you blip the throttle by hand and then the rpm's stay high it's probably in the linkage. If the the idle speed rises when warm it's almost certainly an air leak between the carbs and the head (with the soft mounts being the most likely thing to look at).

 

If you replace the cable I would not buy a car cable. Most seem to be crap. I would get a bicycle brake cable and some "compressionless" brake cable housing. It will be much lower friction than most car cables and since the housing is compresssionless the throttle will be easier to modulate due to the housing not flexing around when the cable is under tension.

 

dave

Edited Wednesday at 02:51 PM by Davemk1

[wdb]

I keep hearing about bicycle brake cable as throttle cable and in general I agree that it sounds good. Quality bike cables have an inner liner that makes them run very very smoothly. I would caution however to make sure that the liner is made of something that will withstand underhood temperatures. The alternative isn't pretty!

 

EDIT: good bike cables are also flat wound, so no compression of the housing.

Edited Wednesday at 11:38 PM by wdb

[Davemk1]

56 minutes ago, wdb said:

I keep hearing about bicycle brake cable as throttle cable and in general I agree that it sounds good. Quality bike cables have an inner liner that makes them run very very smoothly. I would caution however to make sure that the liner is made of something that will withstand underhood temperatures. The alternative isn't pretty!

 

EDIT: good bike cables are also flat wound, so no compression of the housing.

 

 

Flat wound housing is good but it's not the same as compressionless...True compressionless is different in that the housing is not made up of a circular wound wide but instead it's made of linear wires that run axially. This makes a huge difference in both bike brakes and car throttles. Both will work well but the axial stuff is the real deal.

 

And of course the housing is teflon lined and it feels virtually frictionless.

 

I've been using it in cars for a very long time and as long you don't have the housing pressed against the exhaust you should be fine. Give it a inch or two of space and it will last nearly forever.

 

Just my 2 cents as a bike guy who's worked in the bike biz for decades.

 

dave

[toldfield]

Go here

 

https://vintagetechnologygarage.groups.io/g/sidedraft

 

Lots of great information about Webers.  Keith has pretty much reinvented the jetting and knows how to make them work.

 

Tom 

[jbcollier]

You need to be careful with compassion-less housing.  There are several kinds.  Compression-less housing for shifting is not very strong.  It will fail under load.  Compression-less housing for brakes has an extra wrapping (often kevlar) to prevent the axial wires from failing under load.  Either use regular lined brake housing -- absolutely fine for this application -- or make sure any compression-less housing is the proper stuff for brakes.

[MV8]

Morse / marine steering and shifting cables that can be 50 feet long and automotive cables for throttle (at least since the 80s) are twisted linear/axial wires ("compressionless") versus wound flat. Either is fine if the cable has enough clearance inside the housing for the degree of housing bend. Flat is often lined with nylon or teflon, and used for choke cable and lawn equipment cable housings.

 

I retrofit a morse cable to my fiero when the outerjacket became brittle in the engine bay, allowing water to rust the linear wires and causing a burr on the throttle cable. I'd already fit a morse cable shifter to replace the original cables. All the cables are between six and eight feet long. Capacity is matched based on the size of the ends. 10-32 is fine for throttle, with 1/4" a better choice for shifting feel.

 

Cable is also sold as wire rope when not bought as part of an assembly. Much simpler to buy a housing and cable made for each other and as thick as is available for a bicycle application for reduced "stretch". This is the elimination of air gaps between the wires with use and makes a bigger difference with longer cables. Load tested "pre-stretched" cable is preferred to hold a setting without eventually being too long. Thinner cable gets longer with use than thicker for the same load.

Edited yesterday at 11:31 AM by MV8