Lotus Elan

Stromberg carburetted s4 bogs at acceleration

PostPost by: collins_dan » Wed Nov 06, 2013 10:11 pm

I think my timing is 14 degrees, so 15 isn't too crazy. Not sure that 9 is right. I would try resetting your timing and advance back to what it was and see how it runs, then mess with carbs if needed. Dan
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PostPost by: RogerFrench » Thu Nov 07, 2013 2:15 pm

Do you have crossover tubes still? How about secondary throttles? Any leaks there?
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PostPost by: Greg Foster » Fri Nov 08, 2013 12:21 pm

Update;
I removed the tops of the carbs to look at the diaphragms and make sure they and the pistons were located properly...all in good order. I then checked again to make sure the pistons slide properly in the carb housing. All fine and back together I started the car and wanted to check the balance. While standing in front of the carbs and revving the engine I noticed the rear carb was not working, piston wasn't moving...........DUH throttle linkage was not tightened. After adjusting the balance and tightening the linkage, airbox on, went out for a spin. Mind you the needles are set in the rich position, timing at 9 degrees. Car Idles fine but when accelerating has a bog. So when the choke is set the car runs good upon acceleration...I will try setting the timing to 12or greater to test that but it seems to be more of a fuel delivery problem.......Hu!
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PostPost by: 69S4 » Fri Nov 08, 2013 12:53 pm

How far was your spin because it can take several (up to five) miles before my car is fully responsive with the chokes off / in on a cold day.

The needles shouldn't need much adjustment at all from the datum position - it's all in the profile. I think mine are only about 1/4 turn rich from that. Lots of motorcycle carbs have different clip positions for the needle to adjust mid range fueling but the Stromberg ones don't work like that - if you want to make some sort of adjustment you change the whole needle to a different profile. If you look up the profile dimensions of the various needles Lotus used in Strombergs you can see where they made things richer / weaker.
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PostPost by: Greg Foster » Fri Nov 08, 2013 11:54 pm

I will try advancing the timing to a little higher 12-14 deg. There are no crossover tubes. When I war it up before a run, I bring it up to operating temp. and then go for a spin. More on this tomorrow.
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PostPost by: oldelanman » Sat Nov 09, 2013 8:33 am

Greg,
Have you checked that your fuel cap is venting properly and your fuel pump filter isn't partially blocked ? Both could cause fuel starvation.
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PostPost by: Greg Foster » Sat Nov 09, 2013 2:23 pm

OK!!
This morning I reset the timing to 12-14 Deg. btdc and let the car warm up...... That made a substantial difference in the running of the car ! Patience, information from the forum, isolation of different aspects when changes are made and keeping track of those changes until the goal is accomplished. I feel much relieved that this could be solved. So the cars runs quite well now. I believe it has a 3.55 rear and that seems to make a difference in performance overall..... not good not bad just different than my s3 with the 3.7. Also I find the Strombergs are a smoother running carburettor than the Webers on acceleration . My favorites are still Dellortos! So thanks again everyone for helping me track various problem spots. I have learned quite a bit from the experience.
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PostPost by: [email protected] » Thu Nov 01, 2018 6:53 am

Greg Forster I understand that the new Power Valves foul the carby body and this stops the power valve from working. you have to grind the carby body of the power valve, whichever one you feel you will be most successful at doing. Please let me know how this works for you. My E-mail is [email protected]
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