Lotus Elan

1 3/4 SUs in place of Strombergs in S4

PostPost by: 0005K » Fri Oct 14, 2011 5:42 pm

I am rebuilding a S4 which has been off the road for 35 years. I have a guy telling me to switch to 1 3/4 SU's instead of getting the Strombergs rebuilt. I just want a good driver. Is this a good idea?
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PostPost by: Tonyw » Sat Oct 15, 2011 8:16 am

Hi,

Seems to me to be 6 of one and half a dozen of another, The Strombergs have arguably more 'bits" than can fail i.e. the diaphragm they are less well known and parts can be a problem but not insurmountable, the SU's on the other hand have been used on many vehicles are easy to get bits for and are just as easy to tune.

I am running Strombergs on my S3 out of choice and because I scored a pair of new old stock one for a good price.

Changing to SU's will make your car non standard if that matters to you and you will need to do some fettling for the choke, throttle cable and air filter etc. I cannot see why they would not work as well though.

Tonyw
Second childhood? no just an extension of my first.
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PostPost by: elancoupe » Sat Oct 15, 2011 9:36 am

elan-f15/stromberg-conversion-t503.html

Running a search for "Stromberg SU" gave 3 pages of results. :)
Mike
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PostPost by: 0005K » Sun Oct 16, 2011 10:43 pm

elancoupe & Tonyw
Thanks for the feedback. I think I'll stick with the stock Strombergs. If I've got to rebuild them anyway, and there is not much difference, why buy used SUs which also have to be rebuilt? I'm rebuilding the rest of the car pretty much stock.
It will be nice to hear it run again.....someday.

Dick
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PostPost by: Rob_LaMoreaux » Fri Dec 30, 2011 6:32 pm

A lot of people hate strombergs because they learned on SUs and then got burned because they didn't take the time to understand the difference. They blame the diaphragm on their problems when it is usually the temperature compensator burning them.

If you adjust the carb cold the engine will usually run poorly hot. If you adjust hot it will run poorly cold. This is due to the temp compensator leaning out the mixture when it gets hot.

The other issue with Elan Strombergs is that most did not have adjustable needles meaning that there was no tuning possible so after some wear in the car ran poorly.

The way I got around it was to run the adjusting nut all the way in so the compensator never opened. I also got a set of adjustable needle pistons and dropped them in, which points out an advantage of the stromberg. The SU must have the the piston matched to the carb or they don't seal well. The Stromberg diaphragm means that it always seals well.

I say, if the diaphragm is so bad why did all the Japanese motorcycle carbs use a diaphragm?

I had good luck with the Strombergs in my car once I got them right for the excessive Cam profile it had (300 degree, 0.375" lift). I even got 42MPG coming back from LOG in Wisconsin. Unfortunately the oil pickup problem did that engine in, so the spare Weber engine went in once it had John McCoy do his magic to the head.

Rob
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