Over run backfire

[Wotisname]

I bought a 1990 ST1100 in March of this year. It had been stood for about 7 years and has 129,000 miles on it. A brake rebuild, new clutch lever seals, oil change and fuel replacement and it fired up and ran quite well. After finding some insurance, it's MOT, some road tax and a new rear tire it was on the road.

The first trip was about 150 miles with my daughter and I noticed a backfire on the over-run, ie when the throttle is closed at high speed there is an explosive backfire from the left exhaust. The bike does smell a little of petrol when left on tickover.

Can anyone suggest what to look at? I'll be changing the clutch next week when a new one arrives, it slips when my right hand is a little enthusiastic.

 

[Slydynbye]

The first trip was about 150 miles with my daughter and I noticed a backfire on the over-run, ie when the throttle is closed at high speed there is an explosive backfire from the left exhaust. The bike does smell a little of petrol when left on tickover.

Can anyone suggest what to look at?

Sounds like you haven't cleaned the carb idle jets and circuits which requires them to be pulled out.
In the mean time a throttle synch would be a good step.

 

[Wotisname]

I'll try a couple of tanks of petrol with SeaFoam before pulling off the carbs. Not an easy job I think looking at where they are?

 

[SMSW]

I have no idea what the oil additives are on your side of the pond, but you might check to make sure the oil you use is not 'energy conserving'. These oils are not good for wet clutches.

Since more than a few bikes are sold after a period of decreasing use (and less maintenance) you might consider a few things for this winter....

Article - Maintenance Items Needed for a New (old) Bike | Articles

This article is the result of collaboration by Andrew Shadow, CYYJ, jfheath, Max Pete, SMSW, and SupraSabre. Igofar’s list was copied from the first link listed above. Click on the attached file. This one is V.11; in the future, any changes will be noted in the title on the first page as the...

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[kiltman]

It can backfire as a result of a poor electrical connection. Have a look at the main relay red connector, I had it also happen when my sidestand switch was on the fritz.