Lotus Elan and Lotus Elan Plus 2 Forums

Hi all.
Just need some ideas here. Just started an S2 Elan that has not run since being rebuilt by someone else. I just put the low profile carb linkage on as I was never happy with that big single spring thing. Motor in rocking and running rough like carbs are out of sync. Using a sync tool, throat 1 is showing air flow up to the 1st line while the other 3 are showing it up to almost the top of the sight glass. Now i am not able to get this to run any better by adjustment of the balance or idle screws. Open to ideas here. Thanks.

Could be an air leak through the vacuum system connection to No1 or a leaking O ring joint to the head. Could also be a twisted throttle shaft on the front carb.

cheers
Rohan

Thanks Rohan! As I was thinking about it right after I wrote the post.. I said to myself....Vacuum Leak?,,,hmmm. I should have known that right away and looked for it. But you saying it really brought it to the front of my mind. I was in a rush,I had to sell the car as I bought a JPS Esprit #45. It needs restoration but a real survivor car. I sold the Elan to one of my friends LOONY member. Under the gun as this is probably the last day I could bring it to him. I have an aluminum trailer don't like to use it in the salt. We have had unusually mild weather this December and no snow really to speak of in my area of Buffalo NY. And all the salt has pretty much been washed away by the rains. We are expecting to start getting colder temps and snow later tomorrow. Now if you have been keeping up with the news, 10 minutes down my road and where I delivered the car to, 5-8 feet of snow a few weeks ago. We only got 4 inches.

I will check it out.. Will go out to his house next Sat or the following Sat and give it a try. I will bring my new auto stethoscope.

Hi Tony
Enjoy the Esprit, they are a lot of fun. I have had my 78 S1 for almost 32 years now !
Changing the water pump on them is almost as bad as on the Elan

cheers
Rohan

I assume you checked the compression and it's okay?

Frank

Famous Frank wrote:I assume you checked the compression and it's okay?

Frank

Actually, I have not. I will however. I am assuming the guy that did this knew what he was doing. But you know what they say when you ASSUME, You make an ASS out of U and ME. (not you in this case, just me.)

Tony .......quick check for vacuum leak is to open your butain torch UN LIT and. Place it where you suspect the leak ......worst case scenario bent valve ...best set up for mixture and balance is a infr red thermometer pointed at the bend in the headers ..around 380 To 420 or so at idle .Ed

twincamman wrote:...best set up for mixture and balance is a infr red thermometer pointed at the bend in the headers ..around 380 To 420 or so at idle .Ed

Hi Ed,

Presume that is degrees F?

Been hunting the next for such a figure to get basic tune on my carbs. WIll probably have to pull the carbs and adjust throttle plates and deal with bent shafts first thou.

Thanks,

Mark

Just read your post with interest, as I have exactly the same problem!

I did find my vacuum non return valve was fitted back to front, but thought any air leaks would have had the opposite effect on the no. 1 cylinder and made it run weak ( faster) - not slower?

Haven't had chance to check for a bent spindle, so hoping that is the case?

Meantime, if you get a result, will you post a report, just so that I can plan the best course of action, for my similar issue?

Many thanks and good luck!

Phil

l10tus wrote:I did find my vacuum non return valve was fitted back to front, but thought any air leaks would have had the opposite effect on the no. 1 cylinder and made it run weak ( faster) - not slower?.........

Phil

If you have a leak in the vacuum system for the lights its is going in downstream of the throttle valve. This weakens the mixture to the point that No1 cylinder does not fire on idle producing a ricking motor and unsteady idle, The air flow measured into the No1 cylinder trumpet is low as the vacuum behind the almost closed throttle valve is low and the flow through the idle jet greatly reduced.

However having the check valve in backwards in your case should eliminate most of the potential vacuum system leaks as no flow would go through it to the engine to produce the vacuum in the headlight system - but the headlight system would not work !

cheers
Rohan

Rohan,

Thanks for that.

So, I'm hoping it's the bent shaft syndrome.

Funny how we have exactly the same problem though !

Also, should there be two non-return valves - one for the servo line and one for the lights ? (S4)

Best regards,

Phil.

I believe the original installation for the S4 with servo was just a single check valve screwed into the front no 1 intake followed by piping and then a tee that split to supply the servo and the headlight systems.

Often you find that the screw in check valve has had its internals removed and left as the hose connection and check valves have been installed in the lines.

I may be wrong as my S4 does not have a servo but this is the way I recall seeing it on cars that appeared to be original.

regards
Rohan

I tried to obtain an original brass hose connected / non return valve, but they seem to have been discontinued.

So I left it in place and have now added two inline valves, one in each line.

I haven't removed the inerds from the original one. Which I've left in place.?

Ta,
Phil.

I too thought it could be a twisted shaft. If a carb is showing different air flow between horns and it is not the engine itself ((test by swapping carbs front to back) and not a vacuum leak then I would guess either difference in the jets between the horns or a twisted shaft.

Good luck