Calling all WB Mechanics!

Hey all,

Just recently the following's started happening to my GS500; when the bike warms up and hits exactly 1500 revs it makes a loud popping/knocking noise and the revs drop briefly, before climbing back up again (then the cycle happens again almost immediately.)

Anyone heard of this before/have any idea what it could be?

I've had the bike into a garage to have the valve clearances done (there was 0 clearance and they had to be adjusted and checked again)

Yesterday I balanced my carbs and gave the bike an oil and filter change but the noise still persists.

I've heard that the camshaft can 'walk' on my model of the GS500 (2001), and make a knocking sound. But I was assured by the garage that did my valves recently that this isn't the case.

If it's any use at all I'll record the sound that the bike's making/look on Youtube for an example.

Thanks in advance!

Ok, the camshaft issue will cause rattling that sounds like camchain. (I know, mine does it, the pre 05 engines were famous for this). What you have sounds like either an inlet leak or a exhaust leak.

I'd check that the headers don't have a hole in them.

Thanks for replying Jon. It's definitely not a rattling, so I can rule out the camchain/camshaft noise I guess.

I don't know much about bikes/bike mechanics atm; by headers do you mean the parts of the exhaust that come out of the engine, before they converge into one single exhaust pipe? :-?

Also, if it was an inlet leak would that be somewhere on the wide rubber hoses coming out of my carbs?

Aaaand final question: If it was either of the things that you've mentioned above, is it harmful to the bike?

Really appreciate the help!

Correct re the headers.

If it's an inlet leak, check the rubber hoses between the carbs and the engine, also check the tappings where the carb balance tubes are inserted. Both can leak.

As to harm. That's a hard one without hearing the noise and seeing the bike.

Take the plugs out and have a look at them. If they are white, I'd not run the engine too much.

That's great information, thanks.

I'll give the exhaust a good look over after work then, and the spark plugs.

As for the inlet leak I'll take a look this weekend if the weather allows! Will it be quite obvious if there is a leak somewhere?

hello once the bike is warm spray some water on the top of the pipes just to make sure that they are all firing ??
you never know :o

Hello!

Thanks for the response 8 Ball; it's only a twin, and both pipes passed the water test (luckily!).

I dragged my ex-mechanic boss outside to have a listen, and he noticed that my idle speed is a little high, so my popping noise could potentially be attributed to that. I'm gunna lower the idle after my ride home from work and see if that makes the noise less frequent.

I'll report back later!