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Discussion Starter #1
Hi All!
I'm back with another problem for the pro's on the forum.

We have a 1976 Shadow serial # SRE26038. California Smog Car.

Problem is as follows:

After the engine warms up, thermostat opens, fan clutch engages and all is running well, the engine RPM increases quite a bit. If you shut the vehicle off and immediately re-start it, the engine idle is normal, but upon any acceleration, the idle returns to being overly high again.

This one has really stumped me, as I've tried about everything. I cannot find any vacuum leaks and both carbs are synched nicely. Passed smog beautiful, linkage is clear, unobstructed.

Any help would be appreciated!

Thank you all so much!
 

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Dale,

I'm never quite sure when/where the Solex carburettor was fitted versus the dual SUs. Which does your car have?

In any case, this could be any of several malfunctions. My first suspicion would be something with the weakner system, which involves the bimetal switch and the weakener cut-off solenoid [if your car is so equipped]. Looking here:

http://rrtechnical.info/sy/tsd2476/24.pdf

gets you the details of the 1976 emissions control system (which is intimately involved with idle speed, etc) for North American delivery cars.

Poking around the workshop manual at the rrtechnical.info site in the various versions of "Chapter U" might help you out. Even the version for the Shadow II series contains a lot of info that pertains to the earlier Shadows and has different (and often better) illustrations.

Good luck.
 

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Discussion Starter #3
Thanks so much!

Hi Brian,
Thank you kindly for the wonderful advise. I will check those areas right away and see what we can locate. I must admit, its quite an unusual problem and I've noticed the linkage is slightly out of adjustment as the idle adjustment is almost fully withdrawn (screwed outwards, not partially downwards as it should be.
 

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Discussion Starter #4
Problem Found! Hopefully?

Hi Brian,
Well, I spoke with a very competent mechanic today who specializes in UK vehicles and described the problem. When I explained how the idle changes after warm-up, and that such idle changes easily when the butterfly is touched in the slightest, he had the answer.
Apparently on SU's it is very common for the shafts/bushings to wear causing the carbs to leak. As the metal heats, tolerances change and the idle can vary tremendously, never remaining uniform. After checking the left carb, the shaft seemed solid and a quick wiggle did not alter the idle. After doing the same to the right carb, the exact opposite was found. Touching the butterfly shaft/linkage caused an immediate change in the idle and depressing and releasing caused a varied idle after the throttle linkage returned to position. I sprayed the right carb with sure-start and the idle again varied.
All in all, problem appears to be the butterfly shaft. I'm so relieved.
Now I just have to remove the carb, have it sleeved with a new bushing and hopefully we're good until the next issue arrives.
 

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Glad you found the answer. I would have thought of looking at the auto choke linkage. This gives the fast idle from cold.

SU carbs were fitted to all of the shadows. The solex carb was fitted to Corniches from around 1977/1978. also fitted to carb'd Bentley turbos

Matt.
 

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Glad you found the answer. I would have thought of looking at the auto choke linkage. This gives the fast idle from cold.

SU carbs were fitted to all of the shadows. The solex carb was fitted to Corniches from around 1977/1978. also fitted to carb'd Bentley turbos

Matt.
 
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