Lotus Elan

Hard to start hot? Stalls easily....Carb issue?

PostPost by: tedtaylor » Tue Mar 12, 2013 2:16 am

Looking for some direction. '71 Elan S4 with Stromberg carbs, federal cross over tubes blocked off, still has throttle body. I pulled distributor, set point gap, timing to 9 degrees BTDC. Car starts cold using choke....takes a long time to warm up and won't run without choke on until up to full operating temp. Idles rough, but steady. Runs great, good acceleration, but after awhile, i'll be at a stop and letting clutch out and it stalls unless i use high revs on take off. Then i can't get it started again....just cranks over without firing. After awhile, it will start up and the whole scenario starts over again.

Car has been sitting since last year not run. Gas coming through filter. Mechanical fuel pump. Vacuum lines all checked, no leaks found. Pistons move freely up and down in carb and oil in dashpot. I get a fair share of blowby coming into breather where i get some oil dripping out of breather. Everything I look at leads me to believe its a carb issue. Would a minor rebuild kit do the trick? I would have thought if it ran OK last year, nothing should be wrong in the settings ?

Any suggestions on pinpointing why it's not running consistently? I fear to drive more than a couple blocks from home for fear of having to push it home (again). Thanks
TED
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PostPost by: 69S4 » Tue Mar 12, 2013 7:37 am

I've had very similar hot starting characteristics on my 69 Stromberg S4 that were 80% solved with a complete carb rebuild - including needles, jets, seals, calibrating temp compensators etc. The starting problem is down to the carbs flooding - I could see fuel dripping out of the rear one on one won't start session. Just don't do what I did and rebuild one of the choke mechanisms backwards. It may start hot now but it wouldn't cold start in the winter before I managed to work out what I'd done :oops:
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PostPost by: peterexpart » Tue Mar 12, 2013 9:17 am

You could try checking the Float Hight (17mm from Carb body highest point of Float with Carb Inverted) or it could be that the Float Valve is sticking and causing the Carbs to flood when hot !!
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PostPost by: oldelanman » Tue Mar 12, 2013 10:02 am

In cold damp weather conditions carb icing can also be a problem with Strombergs. In my experience it affects the rear carb where ice forms around the air valve causing it to stick open so cylinders 3 and 4 cut out when you back off the throttle and the engine runs very rough and eventually stalls. The ice quickly melts but the engine is reluctant to restart because plugs 3 and 4 are fouled - I found it necessary to pull the plugs and clean them up to get going again.
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PostPost by: tedtaylor » Fri Mar 15, 2013 11:32 pm

actually i did a little more diagnosis (fiddling around) and a couple things to report:
1) when idling, if i pull the choke out slowly, the revs increase. When the choke is pulled out too far, the engine bogs down and stalls.
2) hesitation. when at a stop, with low rev take off and push gas pedal down, it hesitates.
3) after running at operating temp and shut off.....it won't start.

so, does this indicate a fuel starvation issue rather than a fuel flooding issue? That would help me go to the issue at heart and focus upon one aspect of the carb setup.
thanks
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PostPost by: 69S4 » Sat Mar 16, 2013 7:45 am

I think you're going to have to poke around a bit more and check a few bits. Regarding symptom one, it suggests that the fast idle mechanism and the cold start enrichment (choke) are working as they should - presumably you were doing this test when the car was hot. From the sound of that (to me anyway) I'd guess you're dealing with a flooding / running rich issue rather than the opposite - if it was weak you'd be able to compensate with the choke when it was hot

To begin with I'd suggest taking the tops off the carbs and checking both the diaphragms for tears / pinholes etc. Be careful when you lift the top part initially as the diaphragm edges often stick in the locating groove and you can end up causing a tear rather than just checking for an existing one. You can also check the state of the needles. When I had symptoms like yours the core problem was that one of the needles had broken - not the needle part but where it fixes into the piston. The bias spring had broken and the needle was jammed about 3mm higher than it should have been so that carb was running very rich. I only noticed that by holding both pistons up side by side. Have a look and check whether both needle / piston assemblies look the same.

Others will be along with more sensible suggestions shortly! :lol:
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PostPost by: Quart Meg Miles » Sat Mar 16, 2013 11:38 am

A Colortune plug will confirm whether you are running lean or rich and a pair would show one carb against the other (and a set of four, ?98 at www.carbtune.co.uk to see every cylinder). It was the only way I could set up a Sprint engine to hot start though your problem sounds different. It's a great diagnostic tool and clears all the speculation.
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PostPost by: oldelanman » Sun Mar 17, 2013 5:51 pm

tedtaylor wrote:actually i did a little more diagnosis (fiddling around) and a couple things to report:
1) when idling, if i pull the choke out slowly, the revs increase. When the choke is pulled out too far, the engine bogs down and stalls.
2) hesitation. when at a stop, with low rev take off and push gas pedal down, it hesitates.
3) after running at operating temp and shut off.....it won't start.

so, does this indicate a fuel starvation issue rather than a fuel flooding issue? That would help me go to the issue at heart and focus upon one aspect of the carb setup.
thanks


Ted,
You said earlier that the car has not been used for a while, I assume that it was running OK before that ? If so then maybe you aren't looking for a carb set-up problem but rather for something resulting from the lack of use - sticking float valves, sluggish air valves, sticking temperature compensators or even partially siezed distributor advance.

I know you said that you've checked the air valves already but I would suggest you also check that they rise/fall at the same rate - with the air box removed, take out the dampers and lift both air valves fully, release them simultaneously and check they fall at the same rate. Also what oil are you using in the dashpots ? If it's too thin the air valve won't be damped enough and the mixture will be too weak when you open the throttle.

Take off the temperature compensators and check that the plastic valves are fully closed when cold. Heat them gently in a water bath and they should open (at the same time if adjusted correctly) and close fully as they cool down - I had one which stuck open. Make sure you refit them with both of the seals on the stem.

If you don't find a problem with either of the above then I would check the float valves are not sticking and, as suggested earlier, take the opportunity to check/adjust the float height as well.

Good luck...
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PostPost by: RogerFrench » Sun Mar 17, 2013 8:27 pm

Your symptoms sound a bit like those I had with my Europa TC, and that I posted here ( http://www.lotuselan.net/forums/engine-exhaust-cooling-f39/engine-cutting-out-low-speed-t25880.html ) a bit back.

I could have sworn the problem was carburation, but it turned out to be electrical, specifically a "dry Joint" on the main feed from the starter solenoid (thick brown wire). Some of the times it could carry a full current, sometimes not. When it got hot, not!
While the engine was running, with revs up, the alternator supplied all the juice necessary, but when revs dropped, the resistance in the joint was enough so the engine cut out - particularly when the radiator cooling fan was running. It would carry enough current to operate the starter solenoid, which made it doubly frustrating to track down. I found it eventually when I discovered the joint was very hot!

Now, I'm not saying you have the same issue, but just maybe....
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PostPost by: tedtaylor » Sun Mar 17, 2013 10:31 pm

all good suggestions, thank you. Actually my brown wire was loose on the solinoid too, tightened that. My carbs do NOT have temp compesators, but rather a manual choke. I don't have the plastic side pieces i think is referred to as the temp compensators. Also, when i said it ran fine before, i actually don't know that for certain since i just bought the car last month. I only assumed it was running correctly last year. I'll be tinkering, checking and adjusting some more before i actually take a rebuild under consideration. hopeing that it may just be sticking and needing a good run in. I'll check on those suggestions as mentioned about. Thanks again.
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PostPost by: oldelanman » Mon Mar 18, 2013 8:06 am

tedtaylor wrote:all good suggestions, thank you. Actually my brown wire was loose on the solinoid too, tightened that. My carbs do NOT have temp compesators, but rather a manual choke. I don't have the plastic side pieces i think is referred to as the temp compensators. Also, when i said it ran fine before, i actually don't know that for certain since i just bought the car last month. I only assumed it was running correctly last year. I'll be tinkering, checking and adjusting some more before i actually take a rebuild under consideration. hopeing that it may just be sticking and needing a good run in. I'll check on those suggestions as mentioned about. Thanks again.


Hi Ted,
I'm surprised that you don't have temperature compensators - perhaps the previous owner of your car removed them when ditching the crossover tubes etc ? I must admit that I have never seen the federal set-up in the flesh so to speak but the workshop manual shows a compensator fitted and I've always thought - probably wrongly - that it was necessary in all applications. I don't recall ever seeing a picture of a Stromberg that did not have it fitted but I could well be mistaken and I'm sure someone will correct me if I'm wrong.
Regarding the choke, again from the workshop manual, I thought the federal set-up used one on the front carb only - is that what you have ? And do you still have the throttle by-pass valves fitted or were they removed with the cross-over tubes ? Maybe if you post a couple of pictures of what you have others who have removed the federal set-up will be able to offer advice.

Edit:- There are several pictures in this thread of engines with the emission set-up and they all appear to have temperature compensators so looks like yours have been removed. Maybe that's part of the cause of your problems.
elan-photos-f18/elan-engine-bays-stock-modified-restored-and-26r-t21231.html
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PostPost by: tedtaylor » Tue Mar 19, 2013 5:10 pm

OK, here at two pictures (side shots) of my Strombergs. I checked that long thread on engine bays and the vast majority were Weber setups with only a couple Stromberg setups. And from those shots, they had the temp sensor side plastic parts. As you can see, mine do NOT have that. Also, my choke cable, although attached to the right carb, hook up both carbs with the rod running between them, so what ever adjustment is made to the butterfly/throttle opening, is done to both carbs simultaneously.
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strombergs 002.jpg and
strombergs 001.jpg and
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PostPost by: collins_dan » Tue Mar 19, 2013 6:06 pm

Those are not the standard 175 strombergs used on elans, so you may have a tough time getting advice on here for them. Mine used to be impossible to start hot, so rebuilt (seals, float level...same needles) and they have been fine ever since. The only other things I changed at the same time was to insulate the fuel line and to get a fuel pressure regulator (electric fuel pump), as pressure from the pump was way too high. I think that may have been the culprit. Just to look at yours, the thackery washers are cranked down way too much, so I suspect a rebuild is needed regardless. Good Luck, Dan
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PostPost by: oldelanman » Tue Mar 19, 2013 7:33 pm

Those carbs are almost certainly not the originals - they are a different version of the 175 CD probably from some other car. Possibly they were fitted as a simple way to get rid of all the emission bits and pieces. Without the temperature compensators I don't know if they will work satisfactorily on the twin cam engine and they may well have the wrong needles in as well. If it were me I would try to get hold of a pair of the correct carbs (non-emission preferably) and also a standard balance pipe/adaptor block assembly while you're at it, rather than spend money on rebuilding the ones you have only to find that they don't work.
Good luck......
Attachments
Carburettor mounting 002.jpg and
175CD-2 (non-emission)
strombergs 001(a).jpg
175CD
strombergs 001(a).jpg (72.04 KiB) Viewed 2497 times
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PostPost by: oldelanman » Tue Mar 19, 2013 7:48 pm

Sorry Dan, didn't intend to repeat what you'd said - you posted while I was composing my reply. At least we are of the same mind :wink:
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