QuestionHi Mark, I have a 78 GS550 which has just returned to the road after 4 years. Did all the usual cleaned out carbs/jets set floats set timing new plugs points fresh petrol, but have a problem. The bike starts and idles fine but when you blip the throttle hard from idle it completely dies. if you rev it normally it goes up to about 5000 revs the again dies. (fully warmed up)
There is no backfiring or spitting, no noises and no smoke. It is fitted with the original Mikuni slide carbs which have been jetted up from 80 to 92.5 (running ok last time on road) it has pod airfilters and non standard silencers.
I have synched the carbs with vaccum gauges but noticed the readings all seemed a bit low ?. Also, the plugs are brown which I think is ok. I would really appreciate your views,I'm just out of ideas. Many thanks in advance, John.
sideshowzak@hotmail.com
AnswerHi John,
From the descriptiuon provided I suspect the carburetors may need more thoroughly cleaned and/or the air-fuel mixtures need corrected.
The description explains the work that was performed, but lacks details of the work. For example...
How badly was the carburetors varnished?
Was any carb parts replaced?
Why was float levels adjusted?
Why was larger jets installed?
What was performance like with old carb jets and settings? What were the vacuum readings of the synchronization?
What is cylinder compression?
Are valve clearances within service limits?
Was carb changes and adjustments performed one change at a time?
Spark plug chop performed?
Do you have the Service Manual?
Also, if you provide me with the average warm air temperature and the elevation of your environment, I can do the math and get the jetting baseline correct.
I need to know the answers to the above questions to help you diagnose and correct the problem(s).
Respectfully,
Mark Shively
