Question about S Dual Fire Ignition System-Motorcycle

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I have an uncontrollable high idle problem on only one side of my 1978 BMW R100/7. Everything checks out. No air leaks, new plugs, rebuilt carbs, adjusted valves, good compression. The only thing left is the electronics. Could a bad electronic ignition system cause high idle on one side?

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Do you have like TPS sensor or IAC sensor.

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I can't get my saw to idle down,i have adjusted my jets and nothing i'm doing is helping.Do you think i have an air leak.Idon't really know to remove the carburetor. thank you

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Had carbs rebuilt on my 1975 Yamaha Xs 650 now the left side cylnder fires infrequently and backfires loudly with new plugs. could this be a timing issue?

If it's just one cyl, then I doubt its timing.
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Oct 12, 2010 | 1978 Yamaha XS 650 E

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Idles very high

It could be sucking air from the right side crankshaft seal, where the generator is. Or it could have an air leak at the crankcase center gasket, or carburetor intake manifold. I have found that spraying WD-40 around the suspected areas (with the engine running) helps to locate air leaks because the idle speed will change noticeably when the WD-40 hits it.
Also check that the carburetor slide isn't hanging up inside the carburetor and that your throttle cable is routed correctly and has at least some free-play at the twist grip.

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I have a 1978 R80/7 BMW motorcycle with Bing diaphram carbs that have been rebuilt with new parts. It will start and run but only if I almost completely cover the carb inlets. I will not run with the choke...

it could be that you have a vacuum leak between the cylinder and the carb that is leaning out your fuel, check the connection between the the two. to confirm that there is a vacuum leak spray some brake cleaner or any flammable gas on the connection between the two and if the revs go up, you found the problem... hope that helps

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1978 Suzuki GS 1000 revs up on its own.

Hi and welcome to FixYa,

To my understanding, an air leak would be anywhere before the carbs; the air box  cover, the the 4 coupling rubber tubes or even the air filter itself.  Although an air leak in any of these areas would not cause an intermittent high idle. Air leak here would cause a lean mix and/or a flat spot while accelerating.  

On the other hand, a vacuum leak could cause high idle. Vacuum leak would be after the carbs and on any of the coupling to the intake ports of the engine or how they are fitted. In some versions, there are balancer nipples that have interconnecting rubber hoses and/or a vacuum line to the fuel cut-off valve that couls also have a hole or tear. It must be noted that the high idle because of a vacuum leak is consistent.

Intermittent high idle would often be mechanical or almost always on the throttle system. Common causes are:
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  • pinched, kinked or sharp bended cable housing;
  • forced or irregular routing of the cable;
  • it must also be pointed that sticking sliders (inside the carbs) can cause irregular (high) idle.
Good luck and thank you for asking FixYa.

Aug 06, 2009 | 1978 Suzuki GS 750 E

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High idle on start up with choke off.

This sounds like an air leak is making the fuel/air mixture too lean. Any air leaks between the carb and the head will lean the mixture. Old, hard and cracked rubber manifold parts are the usual culprits. Old gaskets and "O" ring seals can leak air also. A bad head gasket seal happens at times also, as does an exhaust valve not fully seating. Air leaks are the idle speed problem.

A different problem is likely present in the carbs and that is what is causing the rich fuel smell. The carbs must be balanced. Example > If three of four carbs are perfectly balanced and one carb is not, then the 3 are "driving" the 4th carb. This will cause gas to spit into the air cleaner from the "bad" carb and can cause a backfire or two. Special vacuum gauges are needed to balance the carbs. Also be aware the carbs must be scycronizsed as well. The slides on all four carbs must lift at exactly the same time when the throttle is cracked.

Go to the site below where you can see a parts diagram for your specific bike. You will select the actual brand, year, model, etc., once you go to the site. Part numbers and prices are also shown. You can order parts from this site. In the event no price is shown on a particular part, the part is not in stock.

I don't get paid for my answers but I do take pride in them, and I am only trying to help. So if you will, > > A “very helpful” rating for these answers? Thanks!

Jun 14, 2009 | 1977 Suzuki GS 750

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