Lotus Elan

Stromberg S4 hot start problems

PostPost by: Heuer » Sat Jun 05, 2010 2:01 pm

With the beautiful weather I have started fully enjoying the Elan. I have however discovered a problem in that starting from hot after a short stop (e.g fuel, checking a map) is problematic. The car is very reluctant to fire up even though cold start and running are perfect. It was fully checked over and serviced by Paul Matty before delivery and it was never a problem when the weather was cooler. Am I missing a trick as to how to start it? I did a forum search and found a thread where others had a similar experience but everyone seems at a loss to explain what the issue is - fooding, fuel vapourisation, distributor etc. Anyone able to offer some advice towards a long term solution as it is both a pain and embarrassing!
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PostPost by: m750rider » Sat Jun 05, 2010 3:58 pm

I can only provide my starting technique.

Cold start - use the choke, no throttle, hit the starter, adjust speed with the choke for a minute, then turn it off and drive.

Hot start - no choke, no throttle at first, after engine turns over, blip the throttle till it fires, should be very quick.

Has worked this way forever.

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PostPost by: 69S4 » Sat Jun 05, 2010 5:20 pm

Oh yes, oh yes, hot starting Strombergs. I've had a constant problem with mine since I bought the car in 1982. By constant problem I mean it WILL NOT restart when hot. If you stop for fuel you've got a 5 min time window during which it might restart but leave it for 20 mins and the only way is to either push start it or leave it until it cools down completely - usually overnight.

I think I've fixed it! After 30 yrs of problems I'm not counting three months of good hot starting as fixed but it's looking good.

Firstly, the symptoms. See if these match up with yours. It starts easily from cold, no problems whatsoever. It runs well, no misfires or any other engine problems and the usual stuff - plugs, points, condenser, timing are all in the normal range/ as they should be. The carbs are mounted properly - no air leaks from the O rings, correct gap on the washers. The diaphragms don't have any leaks and the chokes are assembled correctly. The carbs are (roughly) in balance.

When it's hot the car will run ok on the open road but is lumpy with an inconsistent idle in traffic (no black smoke though). Stop the engine and it will restart straight away but as time goes on it will get harder and harder until it won't go at all. If you've got the usual Lucas bendix starter it will usually fire on one cylinder - enough to throw the bendix out - but won't catch.

Here's what I did. Firstly if I couldn't cure it I tried to bludgeon it into submission and fitted a modern pre engaged starter and an Odyssey battery. This improved things in that it gave me a 10 mins restart window rather than five but it wasn't a cure. The core problem was that one (or both) of the carbs were flooding the engine at restart time. If you crank the engine long enough (only possible with the new starter) you could smell petrol strongly. Lifting the bonnet at this stage once I saw liquid fuel collecting under the rear carb so that was where my efforts were aimed.

A complete stripdown of both carbs and replacement of everything that had a functional role was the next task. I replaced the needle jet, spindles, seals and bushes, all O rings and diaphragms , rebuilt and recalibrated the temperature compensators and replaced both the needles and the jets with new. The jets are pressed in to the casting and have to be forcibly removed and replaced. (the exact position of the jet is important). From the hot starting perspective I found two contributory factors. First, both the needles and the jets were significantly worn. The increased gap between the two that comes from this allows more fuel through and a much richer idle mixture. On my rear carb though I found that the needle had come loose in the holder and the bias spring had pushed it up into the holder about 4-5mm, something not noticeable until I held both pistons next to each other. That was allowing a huge gap between the needle and jet when the throttle was closed so causing the even richer mixture on the rear carb.

Since the rebuild the hot starting has been transformed. It now starts every time when hot using the std Lotus technique as given in the manual. I've had one episode when it didn't go first time (when I wasn't concentrating) but it did fire up at the second attempt.

The car is much more cold blooded now though and needs choke for the first couple of miles - something it didn't need before, so I suspect less fuel is getting in via the needle / jet route as the parts now fit together proberly. Strangely it hasn't made much difference to the fuel consumption. It's still doing around 35mpg on a run.

I'm a bit surprised (actually, no I'm not!) that Matty's didn't pick up on the problem. They probably didn't run it long enough. The wear that can cause this isn't something that can be seen easily but the symptoms are obvious enough. I can't really criticise though, it only took me 30yrs to fix it. Good news is that the bits are cheap enough.
Stuart Holding
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PostPost by: Heuer » Sun Jun 06, 2010 11:25 am

Stuart

Many thanks for the full description - my car seems to suffer exactly the same symptoms so I will discuss with the ever helpful Paul Matty

Regards

David
Elan S4 DHC
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