Lotus Elan

Weber 31's hole in return spring plate

PostPost by: miked » Sun Feb 19, 2012 7:46 pm

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 :D
Mike

Elan S4 Zetec
BSA B33
Suzuki Hustler T250
BMW rninet scrambler
Suzuki TC120R trailcat
Suzuki TC120 trailcat
Suzuki K11 super sport
User avatar
miked
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1177
Joined: 29 Sep 2003
Location: Northwest UK

PostPost by: rgh0 » Mon Feb 20, 2012 10:28 am

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
User avatar
rgh0
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 7491
Joined: 22 Sep 2003
Location: Melbourne, Australia

PostPost by: types26/36 » Mon Feb 20, 2012 4:55 pm

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 :?
Attachments
DCOE 18.JPG and
DCOE 45.JPG and
DCOE 138-139.JPG and
DCOE 151.JPG and
Brian
64 S2 Roadster
72 Sprint FHC
User avatar
types26/36
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 3655
Joined: 11 Sep 2003
Location: U.K.

PostPost by: miked » Mon Feb 20, 2012 5:01 pm

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
Mike

Elan S4 Zetec
BSA B33
Suzuki Hustler T250
BMW rninet scrambler
Suzuki TC120R trailcat
Suzuki TC120 trailcat
Suzuki K11 super sport
User avatar
miked
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1177
Joined: 29 Sep 2003
Location: Northwest UK

PostPost by: oillite » Mon Feb 20, 2012 5:21 pm

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.
oillite
First Gear
First Gear
 
Posts: 43
Joined: 03 Sep 2010
Location: East London

PostPost by: types26/36 » Mon Feb 20, 2012 5:58 pm

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.
Attachments
WEBER 151.JPG and
WEBER 139-9.JPG and
WEBER 18.JPG and
Brian
64 S2 Roadster
72 Sprint FHC
User avatar
types26/36
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 3655
Joined: 11 Sep 2003
Location: U.K.

PostPost by: miked » Tue Feb 21, 2012 2:00 pm

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 :)
Mike

Elan S4 Zetec
BSA B33
Suzuki Hustler T250
BMW rninet scrambler
Suzuki TC120R trailcat
Suzuki TC120 trailcat
Suzuki K11 super sport
User avatar
miked
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1177
Joined: 29 Sep 2003
Location: Northwest UK

PostPost by: Grizzly » Fri Sep 15, 2017 10:24 am

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.
Chris
User avatar
Grizzly
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 1958
Joined: 13 Jun 2010
Location: Cheshire/UK

PostPost by: fatboyoz » Fri Sep 15, 2017 10:46 am

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.



?
'68 S4 DHC
fatboyoz
Fourth Gear
Fourth Gear
 
Posts: 596
Joined: 04 Oct 2003
Location: Gold Coast QLD Australia

PostPost by: alan.barker » Tue Sep 19, 2017 4:06 am

+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
Alan.b Brittany 1972 elan sprint fhc Lagoon Blue 0460E
alan.barker
Coveted Fifth Gear
Coveted Fifth Gear
 
Posts: 2305
Joined: 06 Dec 2008
Location: BRITTANY FRANCE

Total Online:

Users browsing this forum: No registered users and 5 guests