Technical advice: Fuel problems with my carb

MCN expert Chris Dabbs is here to answer any questions you have on anything bike related.

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Q. My 1992 Honda PC800 starts well from cold, ticks over beautifully and usually pulls away smoothly on small throttle openings.

However as soon as I open the throttle wider it coughs and backfires through the carbs until I close it down again. As it gets warmer, it gets worse, although I am able to nurse it up through the gears to over 70mph, but may suddenly falter and drop back to 50-60mph.

If I need to accelerate in any gear, it may or may not respond – I simply have to try and see which makes overtaking manoeuvres quite tricky!

I have stripped and cleaned the carbs twice and spoken to several service agents but although they have all offered to “have a look” none has expressed any confidence.

Quite apart from fears of an enormous bill, I do like people who work on my bikes to show a little enthusiasm.

Allan West, Pewsey

A. It sounds like the fuel system can’t cope with the extra demands that come when you open the throttle, so you are on the right track checking over the carbs.

The PC has a vacuum fuel tap, fuel filter and fuel pump.

Try replacing the fuel filter first, if that doesn’t work a small rubber diaphragm in the vacuum fuel tap could have split making the fuel flow rate sluggish.

Finally, it could be the dreaded “intermittent” fault in the fuel pump and it could need replacing.

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Chris Dabbs

By Chris Dabbs