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hi everyone
my 1980 sd 900 has started to backfire on the overrun on the front cylinder. now what i want to know is what is the easiest way to find out why this is happening
when its on /at power it runs faultlessly its only when i back off . in the uk there is a certain amount of bio fuel in every litre of fuel and i know that can damage the rubbers in the carbs

stuart wrote:hi everyone
my 1980 sd 900 has started to backfire on the overrun on the front cylinder. now what i want to know is what is the easiest way to find out why this is happening
when its on /at power it runs faultlessly its only when i back off . in the uk there is a certain amount of bio fuel in every litre of fuel and i know that can damage the rubbers in the carbs

Does this help?

viewtopic.php?f=26&t=4032

The ethanol may require a jetting change. We're fortunate that there are a limited number of gas stations that sell non-ethanol. And it appears there may be a trend to get rid of it altogether.

Hi Stuart - gorgeous day in Wales today, wasn't it? Shame I had to go to work............

The rubbers would be my first port of call, and then the exhaust gaskets. Have you balanced your carbs as described in BevHevSteve's article in Fuel and Carburation? Works a treat and made my SS run far more sweetly. I just need to seal the balance pipe/Conti's now to complete the loop.

May be out and about weekend after next if the weather holds, and West/Mid Wales seems a rather tempting option ........ just need an oil change before then.

Hugh

got it now its the front exhaust gasket all i need to do now is get the exhaust ring out of the head .been putting off doing it but now it needs to be done i have been squirting release fluid up between the ring and exhaust . i have the correct spanner and have been giving it a good hit with the hammer but still no joy will have to try a bit of heat and more fluid and some more taps with the hammer . :*<:
but as always anyone got any other ideas please
many thanks
stu

Stu - use heat, penetrating fluid and a •lot• of patience. I had one once that was pretty stuck, I got it over the course a 2 weeks and don't kill the fragile head threads....

well the latest on the stuck exhaust ring is it did come out with a two ft stilson. chisel and hammer . and lots of heat . no damage to the threads