Lotus Elan

Stromberg hot starting

PostPost by: 69S4 » Fri Aug 14, 2009 8:22 pm

Ever since I've owned my S4 - over 25yrs now, I've had problems with hot starting. It will start from cold instantly, with a bit of choke in the summer and full choke in the winter. It runs fine, no misfiring, backfiring etc. I get low 30's mpg and tan coloured plugs.

The hard starting has survived the engine in a knackered state and rebuilt - twice and a couple of head rebuilds on top of that. The carbs (Strombergs remember) have been rebuilt twice - new seals, jets etc without affecting it. The float levels are exactly as given in the workshop manual and the diaphrams are new.
I've replaced the fuel pump with an electric one with a pressure regulator and adjusted the pressure from firehose to zero and back to 1psi without improving the hot starting. Plugs are new B6's, timing is 10degrees btdc, points 15thou, plug leads have been carbon, copper core etc over the years without affecting anything other than my tv and the distributor was replaced only a few thousand miles ago (but made no difference)

The characteristics are that the engine will turn over (and over and over...) and occasionally one cylinder will fire - once. This throws the bendix out of mesh and I have to start again. Foot off the throttle or full throttle (or anywhere in between)makes no difference. What does work is leaving it for half an hour - slightly inconvenient if you've just stalled it in traffic. Suggestions as to what to check next gratefully received as I'm starting to run out of ideas.


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PostPost by: oldelanman » Sat Aug 15, 2009 8:08 am

Hi Stuart,

My Stromberg S4 last ran about 22 years ago but it is almost ready to fire up again after 18 months refurbing. I don't recall ever having hot start issues when it was running, the main problem was icing of the rear carb in cold damp weather as I recall.

Sounds like you've tried just about everything but here's a few things that spring to mind.

Carb temperature compensators - seals u/s, valve not seating, bi-metal spring "tired"

Carb air valves not sliding freely when hot - remove the dashpot dampers check that both valves lift and drop freely.

You could try different viscosity oil in dampers although this would be more likely to affect acceleration response than starting issues

Ignition coil breaking down when hot - there has been discussion on here on this issue and some have relocated it to cooler positions. You did not mention replacing the coil in your comprehensive list.

You have replaced the distributor was the condenser replaced also ?

Does your crankcase breather still go to the air box ? If so you could try rerouting it to a catch tank, many on here have found this improves general running performance and it may also improve hot starting if the engine is not trying to burn the oil mist which probably doesn't disperse immediately after switch off.

Hope there may be something here you haven't already thought of but I suspect over the years you've tried them all before.

Good luck. Regards,
Roger
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PostPost by: elan_fan » Sat Aug 15, 2009 8:50 am

I had hot starting problems with my stromberg Elan that I chased around for ages. Check that the bottom hose is not touching the coil, QED recommended fitting a purge pump to the manifold (which I never did). I finally took the head off in desperation as I felt that when the engine got hot it wouldn't cool prompting questions regarding the radiator sizes and types. I found a tiny problem with the head gasket and sorted it out. I know that you have said you have been re built etc but I now have no probs hot starting and the engine temp is stable on hot days with a rebuilt but standard width rad. In other words hot starting shouldn't be a problem with standerd setup. My probs were down to heat soak when hot with indicated temp of 110 plus degrees. Now runs around 95 with 78 degree stat and good standard radiator and gasket. My own probs were cooling related which the stromberg head layout seem susceptible to. They have no throttle pump and as you have said when hot you must depress the throttle fully to start. When hot mine is slighlty more reluctant to fire and takes a few seconds to catch rather than first piston up when cold. Maybe time for a cylinder leak down test and to try a different pair of carbs?

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PostPost by: 69S4 » Sat Aug 15, 2009 9:20 am

Mark, Roger, thanks for the replies. With a lot of faults I find that trying to approach it analytically eventually pays off and I've tried to think through what could be responsible for this but last night, when I wrote the post, it was more in embarassement than puzzlement.
I'd given my wife a lift to the shops and on the way back we double parked briefly to drop a couple of DVDs off. The car wouldn't restart and the road suddenly became very busy. :oops: On the way back after I eventually managed to get it going she reminded me of the time when, about 20yrs ago, she borrowed it to visit a patient (she's a GP) and it wouldn't start outside their house. I really need to get this fixed!

If you're are not having a significant problem with hot starting, at least I know that whatever is causing it is specific to my car and not a generic fault. I'm pretty certain the problem is in the fuel system but as we all know carburettor is French for leave it alone and I've tended to do this beyond checking the obvious things like float height, seals etc. The temp compensators were stuck closed for many years but are now working as they should (at least as far as I know - the main web info I could find on them related to TR6 Strombergs). It's not made any difference.

Not much I can do over the weekend as work and other things means the garage doors are shut till Monday but my subconscious get the chance to analyse the data in the background.
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PostPost by: paddy » Sat Aug 15, 2009 10:49 am

oldelanman wrote:Ignition coil breaking down when hot - there has been discussion on here on this issue and some have relocated it to cooler positions. You did not mention replacing the coil in your comprehensive list.


I wondered if there is any possibility of it being an ignition problem. Assuming it idles quite happily when hot, I think it is quite unlikely - the only thing I could think of was if it's a ballast type coil and there is a problem with the wiring or the ballast resistor that means the ignition just isn't working properly when cranking. (That is, the car would bump start easily, but because the ignition circuit is operating differently when you're cranking, it somehow goes wrong.) In any case, the usual check of just checking the spark with a loose plug attached to one of the leads would eliminate that.

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PostPost by: ppnelan » Sat Aug 15, 2009 9:24 pm

paddy wrote:...the ignition just isn't working properly when cranking.
Sounds likely - check the voltage to the coil during cranking. A bad connection can reduce it enough to stop the ignition system working, especially if it is an electronic (all or nothing) type. :wink:

I have a Stromberg Elan which has similar difficulties with hot starting. If I 'catch' it on the first 'crank' all is well, otherwise it can take a little time to get it going. :oops:

I also have a Stromberg +2 which is not as easy to start when hot as when it is cold, but is nowhere near as bad as the Elan. But, it has an alternator & not a dynamo... :?

To try to get the carbs set up properly & 'stable', I blank off the temperature compensators, re-route the head breather to a catch tank, set the needle height/mixture by the SU/Stromberg method detailed for MGs/Stags on other websites (lift air piston slightly & listen to change in engine speed to determine if mixture is rich/lean/correct), and balance the air flows. I previously set the needles flush with the bottom of the air piston but having collected a few (!) sets or carbs, it is clear that jet height and the flow 'leakage' through the carbs varies. Worn needles do not help either... :roll:

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PostPost by: johnsimister » Sat Aug 15, 2009 10:58 pm

This idea doesn't fix the root of the problem but might make it easier to overcome: replace the inertia starter with a modern pre-engaged gear-reduction starter which won't get thrown out of engagement when the engine tries to fire. You'd be able to keep it churning until it catches properly and stays running.

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PostPost by: ivor badger » Thu Aug 20, 2009 5:57 pm

I came across a similar problem on a Volvo 245 with a Stromberg. After many attempts by assorted people. The problem was the carb flooding the engine through the needle jet when stopped. If parked long enough, the petrol evaporated and the car started. So it always started cold, but not on a quick hot restart.

Check the float and needle. If you take the dashpot cover off you can see it happening.
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PostPost by: rgh0 » Sun Aug 23, 2009 12:36 pm

I have had a similar problem on various stromberg carb cars I have owned - Esprit and Saab 99 and seen it in Elans and Triumphs owned by others. Definitely relates to flooding when the engine bay is hot and worse at high ambient temperatures.

One of the reasons the S2 Esprits had a cooling fan sucking hot air out of the engine cover was to solve this problem in the US spec stromberg cars.

I only solved the problem on my S1 Esprit by changing to European Spec Dellortos.

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PostPost by: 69S4 » Sun Aug 23, 2009 1:52 pm

johnsimister wrote:This idea doesn't fix the root of the problem but might make it easier to overcome: replace the inertia starter with a modern pre-engaged gear-reduction starter which won't get thrown out of engagement when the engine tries to fire. You'd be able to keep it churning until it catches properly and stays running.

John



This is something I've been meaning to do for a while and a combination of my previous problems and your post made the decision. It does make a difference. Since I fitted it the car has always hot started but it's not a pleasant experience with the starter and the battery getting a good 20 sec workout. By contrast when it's cold it fires so fast you often can't hear the starter.

It is a bit of a brute force solution that doesn't really get to the root though. The problem definately seems to be related to flooding as you can smell petrol quite strongly at times. I fitted an electric fuel pump many years ago to give me the option of switching it off for hot starts but it doesn't seem to make any real difference.

Ivor's flooding through the needle valve observation is something I'll certainly check out but where would the excess fuel be coming from? Thermal expansion? Volatiles boiling in the float chamber? I"ve changed the needle valves twice before on these carbs without noticing any improvement. The needle valves on my motorcycle carbs seem to be quite capable of holding back a 50cm head of fuel for weeks whereas I doubt the Stromberg ones have to cope with 5cm with the pump off.

Next question though is what can be done to fix it if it does turn out to be the carbs flooding themselves. I suppose I could drain the float chambers everytime I stopped but that does seem a bit inconvenient. Yet another rebuild for the carbs is on the list already and may get done in the next week or so if I can source the parts. Any suggestions as to who to go to for Stromberg bits in the UK?


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PostPost by: Frank Howard » Sun Aug 23, 2009 3:03 pm

69S4 wrote:points 15thou

Stuart,

You might think you have them set at 15 when they are actually set at 14 or 13. I would check this with a dwell tach. It should read between 57 and 63 degrees. If it reads over 63 degrees, your points are set too close and that would account for the hard starting when hot. Good luck.
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PostPost by: elan_fan » Sun Aug 23, 2009 3:04 pm

http://www.burlen.co.uk/ for spares

regards
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PostPost by: 69S4 » Sun Aug 23, 2009 3:15 pm

Frank Howard wrote:
69S4 wrote:points 15thou

Stuart,

You might think you have them set at 15 when they are actually set at 14 or 13. I would check this with a dwell tach. It should read between 57 and 63 degrees. If it reads over 63 degrees, your points are set too close and that would account for the hard starting when hot. Good luck.



Just been looking at the ignition side now! Dwell reads 57 degrees. Came back to the computer to see what the consensus is for static timing on stromberg elans. Mine is currently 9deg btdc
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