Lotus Elan and Lotus Elan Plus 2 Forums

Can anybody shed any light on why someone may wish to drill a large hole in the throttle return spring cover plates. Both carbs have holes in. About 9mm Dia'. This is the small plate that has a gasket and two screws and covers the butterfly spindle and return spring etc.

I would think that this is meant to be a sealed chamber as the the spindle seal is just through the body. Could cause air vac leak. I was chasing down leaks,greasing the bearing etc and sealing the trumpets.

I have robbed a coulpe of good ones from some spare carbs. Hope that when I start it again I may have a better reading at the trumpet on that particular choke. Also re aligned the butterflys (holding up to the light etc) to get better air balance across chokes on each carb.

Mike

Some race authorities require an independent return spring on each carb and the internal throttle spring on a weber does not count as it can't be seen. Someone may have drilled thE holes so the springs could be seen by the scrutineers

Cheers
Rohan

It appears that several of the DCOE weber carbs have the hole in the plates originally, I just had a look at some of mine and some have the hole and some not but I have no idea why.
Here is a few of mine, note the 18?s have had an a modification to fit ?O? rings but do not have the holes in the plates, I also have a set of 27?s on one Elan but does not have the holes in the plates.
The 138/9 and the 151 has the hole but the DCOE 45's do not

Brian and Rohan,

Thanks for the feed back. I have two sets without and one set with. The holes look like they have been roughly drilled. This is only the very old set with low numbers.

They are all 31's.

What do you reckon about the shaft seal at that point? Potential vac' leakage. Does not matter, or conditional up on wear. ???

Mike

If it's any help I've owned my 68 +2 since it was 18 months old and it has the holes in the rear cover plates which I mislaid, so I bought 2 genuine replacements which also came with the holes. Both sets look to have had the holes stamped at the time of manufacture. Doesn't seem to have any effect on the vacuum.

Mike,
The carbs with the hole in the plates appear top be later type carbs (151/138/139) and have a air bleed system of some sort so maybe this has a bearing on whether or not it has a hole?? The holes on my carbs are not rough so seem to be original and are unlikely to have been added later.
Maybe the later carbs have better shaft seals and do not require a closed chamber.....just a thought.
RE the above post: maybe Weber only supplied the later type plates (with holes) as aftermarket parts.

Thanks for replies. Great photos Brian, thanks.

I would like to fit some 151's in the future. Has anybody obtained the adaptors to fit a Carbtune balancer to. I would be great to pick up vac at the engine side of the butterflies.

Mike

Sorry to bring an old post back from the dead but i wanted to know the reason myself so searched all over the place until i ended up at Webcon a week or so ago who said the hole aids with hot starting..... The guy couldn't give me a definitive reason why but he did say you can't buy them new without the hole and they are changed during rebuild for the new type as a matter of course.

Throttle lever housing cover plate dribbles:

? The throttle lever housing cover plate is between the two barrels and is fixed with two countersunk screws. (Figure 1 ? item 80)
a) Remove the screws and plate. A full sealing gasket should be in place. Remove it and check if the chamber is wet with fuel or shows signs of this.
b) Fuel can enter the chamber via the pump rod hole or the return spring hole. Yes I realise this should not be the case BUT do you have ANY clearance in the butterfly shaft bearing on either side of the chamber. Of course you do even if it?s only small.
c) When you are pulling 5000 to 6000 + rpm and lift off the throttle you can appreciate many inches of vacuum generated must suck from anywhere it can. Herein lies our problem. Fuel is sloshing around in our float bowl through corners and clearances around pump rod and throttle return spring hole are considerable. The vacuum pulls fuel into the chamber but there it just builds up to gradually dribble over our distributor or hot exhaust as the case may be.

Solution to throttle lever housing cover plate dribbles -

Drill a 1.5 mm ?breather hole? in the cover plate and match drill the gasket. The hole should be level with the top screw and half way to the edge to miss the housing cast edges.
The small hole stops the effect of the vacuum but also keeps the dirt out of the throttle lever chamber. Screw the plate back on for dry, dribble free motoring.

This really is an incredibly simple fix for a rather obscure problem. It took a lot of reasoning and close inspection to analyse what was actually happening but investigation is part of the problem solving. It was only after I fixed the problem that a carburetor repair person suggested that this was probably why Weber modified some plates in the 80?s with a 8 ? 10 mm hole in the middle. Unfortunately Messers Weber don?t tell everyone why they did this modification.

NOTE: Obviously all of these fuel checks are better if carried out shortly after a run so wet fuel can be seen when the carburetors are removed.



?

+1 The hole is a mod to stop carb dribbling after a run and the car is stopped.
I think this was spoken about in past posts
Alan