High idle Weber external springs

[Bilbo]

Hi All

 

HELP

 

The cars been off the road a few weeks since the sprint at MIRA. Mostly as I have been on a 7 day working week.

 

The throttle stuck all day at MIRA and despite fitting new external springs I can not get the idle fixed.

 

Basically the throttle, without a throttle cable fitted, will not idle below 1200 rpm unless I push the leavers back. Then it ticks over fine on 600 rpm. It seems the accelerator pump springs are holding it open. I tried changing the length of the external springs by bending back the 90 deg at the top and re-bending it , that has lowered it to 1000 rpm. The carbs are in balance so that's not the problem. Also the internal springs are removed.

 

Its the Caterham two springs in the middle option. I am unable to fit alternative springs at the outward side of the slave carb as the Weber Alpha throttle position sensor fits. Fit just the slave carb external spring its mega worse to the extent of no engine the revs go so high. I have always found the 2nd spring is a bit naff, normally mod the shape and length a bit anyway.

 

Still it's been working fine for 6000 miles so should be Ok now. If I take the springs off it opens the butterflies say 15 degrees. Assume this is the accelerator pump springs, had these out everything seems fine. Also no play in the linkage.

 

Any ideas I run out of them, this is unusual as I have not been stuck before when fixing them.

 

Given up at present as I have run out of external springs playing with the overall length trying to get more force out of them.

 

Why Caterham have never provided two spring fixing points to the "Y" bracket that holds the springs bets me. The second spring fits to the same point as the first one so without some mod to the second spring it snags on the other. Think a mod is in order ❗

 

All this nice weather and its stuck with no MOT in the garage aqs it has been since MIRA !!! Mutter Mutter...

 

 

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

[Chelspeed]

I have always thought the watchspring type springs that Caterham sell are a bit naff. The second one sold for competition in particular.

 

You really want to convert to a couple of simple coil wound tension springs, simple, cheap and very little to go wrong, I suppose they might break but they wont ever get jammed or catch on each other or anything else.

 

Now you just need to think how to fit them. Normally as you say they go on the outboard end of each carb. You could do this on one but not the other due to the throttle pot. What about the outboard end of the front carb and the centre link from the slave carb?

 

Make up small brackets off a couple of the cam cover bolts to anchor the other end of the springs. For the front carb, undo the nut from the free end of the carb and replace the washer with a bit of tin matching the washer at one end but with an arm approx 1.5 inch long to take the carb end of the spring. For the carb with the throttle pot can you attach the spring to something on the linkage in the centre? Difficult to say without looking at the linkage. If not can you do the same as above but still drive the throttle pot or does it get in the way?

[Bilbo]

Hi Chelspeed

 

Thanks for the reply seems Weber Guru's are getting a bit thin on the ground with all the fuel injection ❗

 

I thought you would reply to this... well an alternative at the end of the slave carb is properly not impossible, but it will need to be a bracket. Its not really a throttle pot in the true sense i.e. no pot, more just a potentiometer.

 

Thinking where to get a coil wound tension spring leaves me a bit dead tonight very very long HOT day. Now knowing you have already done this ideas 🤔. Seems the length verses resistance is important.

 

The downside to springs at the other end is you putting the butterfly linkage in tension over its length. If something jams it could twist as it would act as a lever, even a good few thou will upset the carbs.

 

As there is some resistance to the throttle going all the way back I think a strip downs in order. Its been fine since the last rebuild until MIRA or perhaps until the engine was out after Curborough, so I think some investigations needed.

 

First pull both the accelerator pumps out again see if that cures it.

 

Oh well now know what I am doing Saturday or as I am working Sunday perhaps one evening as well, if I can get home early.

 

Works taking up too much time at present ☹️. Still it pays for the toys

 

 

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

[StewartG]

sounds to me like the butterflies may not be centred in the barrels or the spindles may be bent.

[Bilbo]

Hi StewartG

 

Now why did you point out the one thing that was worrying me

 

Well as you say its the most likely call as there are some thrust washers behind the spindle end nuts and washers may be one of these has had it or lost its tension. However when you look down the barrels everything looks fine. Still that a bit hard to do with them in still the car, so looks may be deceiving. They have done over 50,000 miles now.

 

So its a full strip this weekend if not sooner ❗ not a pleasent sight some would say

 

Thanks for the reply.

 

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

[Bilbo]

Hi All

 

Think I may have found the fault.

 

Seems the balance adjustment screw for the slave carb has worn a slight hole in the linkage from the master carb that has the throttle cable, where the balance adjustment screw presses onto it.

 

Its been a slight dent for ages now its a hole. The carbs when they returns back no longer go clean into the hole. If I push the linkage back the screw goes into the hole. So it seems the linkage has become misaligned.

 

A temporary solution is to increase the diameter of the hole. Then adjustment screw will not stick.

 

Long term change the linkage.

 

Still they do still seem a bit sticky at the near closed position so it may not be the whole story. Could be a bit of build up on the butterfly bars from fuel deposits.

 

The accelerator fuel pump bars have polish marks so they also might be sticking a bit. This must be causing wear in their barrels so may be the carbs are reaching are reaching their sell by date.

 

 

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

[dmc]

At that mileage the spindle bearings probably gone stiff.

the internal spring (the one that shuts the throttle)

can break and jam the throttle so can the plate that retains it.

 

 

[Bilbo]

HI dcm

 

No internal springs.

 

The Master carb is defiantly stiffer at the closed position than the slave. But just a tad.

 

Carbs off tomorrow with a few parts being picked up b the wife. Whilst I strip it/them out, give her the full list when its out.

 

New link arm, lock washers plus new mounting rubbers etc. New springs for the accelerator pump might be an idea. The throttle/link arm is in stock locally at Sanspeed. As you say bearings might be a good idea. Having removed the end nuts and he throttle/link arm wear seems nill other than said above. I think its just the wear in the throttle/link arm thats the problem now its out its been wearing off center.

 

I know this seems to be taking ages but I am rather busy at present and only have Saturday off this weekend.

 

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

[Bilbo]

Hi All

 

Well took the Carbs off to day the Primary Carb butterflies were sticking a bit open. I Forgotten what a pain it is getting the carbs off with the engine in place.

 

I have also changed the spindle bearings on that carb. They seemed just a bit stiff. Getting the screws out of the butterflies was a bit of a pain. Could not get any new ones. Put the old ones back with some locktite, think I put some superglue on the exposed threads just to be safe. Last thing I want is one to work loose.

 

Any recommendations for something better 🤔

 

The holes in the butterflies are a bit bigger than the screws so you need to seat the butterflies the tighten the screws. Takes a while to get it just right.

 

Replaced the throttle linkage on that carb. The hole where the balance screw pushes onto the linkage was about half way through the bar.

 

Getting the end nuts right a REAL pain tighten them slightly unevenly and the butterflies stick again. Then again the Haynes Weber manual does not say how tight but it must be tighter than I have them at present. Anything over just a little more than finger tight makes them stick.

 

Thoughts anyone 🤔

 

I think its just a case of a bit of trial and error plus patience getting the tension the same each end.

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

 

Edited by - bilbo on 4 Aug 2002 09:41:01

[Bilbo]

Hi All

 

Well just an update carbs are back on but not fully tightened. Setting the butterflies up proved to be a case of getting them positioned then tightening the end nuts. Then re-centring the butterflies. Took 3 goes before I was happy with them.

 

The Haynes manual talks about tightening the end nuts then fitting the butterflies. Thats not a good idea as its not possible to centre the spindle accurately. The above is a lot easier.

 

As to fixing the butterfly screws the Haynes manual say use a Weber peening tool or locktite. This I have interpreted as bugger the screw thread so it will not come loose. I used locktite and distorted the threads just a touch. Read the latter as tap blunt screw driver on threads to flatten a part of 2 threads next to the butterflies.

 

I must say loosing one of these I find a little worrying to say the least. ❗

 

The master carb spindle is still stiffer than the slave but no where near as bad and its not sticking now. Could be just the new bearings.

 

1988 200 bhp, 146 ft lbs, 1700cc Cosworth BD? with Brooklands and Clamshell wings, Freestyle Motorsport suspension. Q 979 CGY

 

 

Edited by - Bilbo on 4 Aug 2002 19:48:19