Lotus Elan

Weber Jetting

PostPost by: AdrianSi » Fri May 20, 2016 9:04 pm

Hi all,

I'm sure this won't be a new one, but hoping that somebody might be able to help me with this one.

My +2 was a cancelled Federal order in '69 and factory converted to RHD before distributed to Bell & Colville on in '70.

The engine block is the original, and is identified as a Strongberg unit.

The engine is now fitted with a Weber head and 40 DOCE 31's, which may have been factory fitted, but can't be confirmed.

I've had the car for just over a year, and part of 'learning' the car has been taking the jets out and seeing what is fitted. The car runs well, bar a very slight miss at 1200rpm, that appears to be fuel based. (ignition system all new, electronic ignition module fitted).

These are the jets fitted:
imag1189.jpg and


So these seem to align to the Std +2 jets listed in the info below:
imag1236_2.jpg and


However, I was under the impression that all +2's were 'SE' spec engines?

What I haven't checked is the choke dimensions or the valve lift.

It could well be that an earlier head complete with carbs has been fitted from a non +2 during its life time, however wouldn't explain the Air correct jet size.

Ultimately I want to get hold of Sprint (or equivalent) cams and jet to suit.
1970 Elan +2
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PostPost by: mbell » Fri May 20, 2016 9:33 pm

You seem to have the correct jetting for a standard head. Have you checked what cam you have in your engine?

(no groves= STD, 1 grove = SE, two groves = Big valve)

AdrianSi wrote: I've had the car for just over a year, and part of 'learning' the car has been taking the jets out and seeing what is fitted. The car runs well, bar a very slight miss at 1200rpm, that appears to be fuel based. (ignition system all new, electronic ignition module fitted).


Does a plip on the the throttle (to engage pump jets) or very small amount of choke remove the slight miss? This will suggest if it is lean running or not.

Have you checked the fuel level in the carbs? If its too low it can delay the engagement of the main circuit and cause a lean spot as the carb transition from the idle circuit to the main circuit.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: rgh0 » Fri May 20, 2016 11:46 pm

The differences in jetting between std SE and Sprint were mainly driven the the changes to choke size i.e. 30 / 32 / 33 mm

Check you have the right choke for the jetting you select.

cheers
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PostPost by: AdrianSi » Sat May 21, 2016 8:36 am

Hi both,

Thanks for your responses. As I say, my next plan is to check the choke size and cam fitted.

The standard cam offers 105bhp from my understanding, where as the S/E had 115bhp.

I think that if the cams are a standard item i'll go straight to Sprint specs, cams, choke, jets. Does anybody have a pair of Sprint cams lurking??

The 'miss' is for a couple of hundred rpm and is slight, causes the engine to rock a little. Appears to be on cylinder number one. No amount of adjustment on the idle mixture screw cures it. Playing with the balance screw moves the miss up or down by a few hundred rpm. I've had the progression hole cover off, and the butterflies appear to be aligned.

I'll carry out some further checks.
1970 Elan +2
Factory Federal RHD
B42 Midnight Blue (Esprit S4)
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PostPost by: Verve » Sat May 21, 2016 9:08 am

Hi ,

Sounds like a servo or headlamp leak ... that`s if the plus 2 has a take off from number one inlet track ... if so , just temporarily disconnect & block off ... see if that improves matters ...

Cheers ,

Paul .
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PostPost by: AdrianSi » Sat May 21, 2016 9:15 am

Great idea Paul.

I have a feeling that it maybe servo side. On a separate niggle, I think that there is a one way valve missing from the bulkhead on the servo side.
1970 Elan +2
Factory Federal RHD
B42 Midnight Blue (Esprit S4)
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PostPost by: mbell » Sat May 21, 2016 6:25 pm

Number one take off is normally headlights. My car had a one way valve in the brass take off which I believe is standard. Brakes take vacuum from number 4.
'73 +2 130/5 RHD, now on the road and very slowly rolling though a "restoration"
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PostPost by: AdrianSi » Sun May 22, 2016 8:41 am

I'll play about with this one. The headlamp vacuum switch leaks (as with most) so I'll try clamping the line off.

The actuator is fine as I am able to clamp off the post switch line and keep the lamp pods in the down position over long periods of time.

I guess it may well be drawing a vacuum leak through the switch itself.

Thanks.
1970 Elan +2
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PostPost by: Verve » Sun May 22, 2016 8:53 am

Looks like the headlamps then ( not uncommon ) , if that is all that is hung off number one ... if number one is your sole problem that is ... easy to disconnect/block off & see if the mixture screw responds this time ...

Same applies to number 4/servo , if you have an issue there ... let us know how you get on ...

Once additional variables are removed from the equation ... & everything else is set right .... if you still have "hesitancy" on progression ... I usually find it`s just the "Progression" ( mixture/idle ) jets that just need increasing ( too weak for modern fuel ) ... another easy fix ...

Btw., I do have some Sprint cams ... but I think you would be wise to get the existing set-up running sweetly first , before adding any more variables ...

Are you taking the Elan to Castle Combe next Saturday ... we`ll be there : )

Cheers ,

Paul .
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PostPost by: AdrianSi » Mon May 23, 2016 8:03 pm

Update:
Chokes are indeed 30mm as expected. Next to check is the cams, which again I expect will turn out to be standard being as it runs and drives so well.

Tried clamping off the servo take off, and the headlamp vacuum (at the switch) but still seemed to have the very slight miss/off song. More investigations to follow there bit it is looking towards a reject and cams to suit Sprint spec. I needed a good excuse to do this.
1970 Elan +2
Factory Federal RHD
B42 Midnight Blue (Esprit S4)
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