Knocking noise

[Honeybadgerted]

I recently picked up a 98 vtr, and it has a noise I can't figure out. When started, it has a knocking noise and it backfires a little bit with partial throttle. Once warmed up, the noise goes away. It almost sounds like things knocking around in the case, but it can't be because it goes away once warmed up. I thought it might be spark knock or detonation, but I read several threads that said the compression wasn't high enough for spark knock in these motors. Not quite sure what it is, but it sounds terrible.

I did recently open her up to check valve lash and replace the automatic CCTs with manual ones from kreiger and there was nothing loose in the engine that would cause this noise that I can find. Would fuel starvation have any affect on this? When I got it it wasn't running and the carbs were dry. That is when I initially noticed it. After a few rides it didn't seem to happen as frequently or at all. After my MCCT install the carbs were dry again, and the noise was back. That's the only thing I can think of that is a constant between the times I heard the noise.

[Cadbury64]

Have you synchronised the carbs? Engines often get a bit knocky when the carbs are out of whack, and smooth out a lot when in synch.

[Honeybadgerted]

I haven't yet. I couldn't find a good write up with pictures, they all disappeared. Is it hard? I've always had 4 cylinder bikes

[Wicky]

I haven't yet. I couldn't find a good write up with pictures, they all disappeared. Is it hard? I've always had 4 cylinder bikes

Have a gander in the workshop knowledgebase section.

[Honeybadgerted]

None of the pictures show up anymore. And the service manual isn't very helpful. I'll have a go at it when I get home

[Wicky]

Follow as best you can the written description. Find a small child with ickle hands to screw in a front vacuum take off adapter. Once done add a length of hose and plug it to save the hassle doind it again at a later date.

"backfires a little bit"

Also check for airleaks in the exhaust manifold / header system gasket seals as that can create similar pulsing - knocking noise.

[Honeybadgerted]

Ok will do.

Are you saying that the air leaks can cause backfire, or sound like it? Everything is sealed up good. I double checked all hoses and clamps and re checked the block off plugs I put on the PAIR system.

[Wicky]

Airleaks in exhaust system can cuase banging on overrun plus when exhaust pulses get by a failed crush copper ring gasket in the manifold cause high frequency knocking sound. Also if vacuum hoses aren't connected properly / damaged they can lead to poor running / banging on overrun / intermittent fuelling problems (as its functoning is what allows fuel to be drawn via the fuel tap to the carbs). Basically you need to throughly and methodically go through the bike servicing inc. balancing carbs etc, it back to normal esp if you don't know what's been done to it prior.

[Stratman]

Does the knocking sound go away when you pull in the clutch lever?

[AMCQ46]

There was a PDF version of the instruction in the thread somewhere ,done by Geodude I think, the photos might still be showing in that

[MacV2]

Ah PAIRS system...I have both early & late Storms, UK bikes didn't have pairs until the F2 version. Even with all the pairs crap taken off, early cam covers & airbox, so no bunged up holes to leak, my F2 still coughs n bangs more than the early ones...I like it though...

My thought is that it's more of a fueling issue, running rich...?

[Honeybadgerted]

After playing with it, it seems like it only does it with the enrichment lever ("choke") on. Problem is, it won't stay running when cold without it. After it warms up enough to turn it off, it runs fine.

[alanfjones1411]

What revs are you idling at.I have mine idling at 1100/1200 rpm.As for the" backfiring a little bit" may be just the normal carb farts which most vtr's seem to suffer with.

[Honeybadgerted]

What revs are you idling at.I have mine idling at 1100/1200 rpm.As for the" backfiring a little bit" may be just the normal carb farts which most vtr's seem to suffer with.

Not sure, my tach doesn't work. Not sure what's wrong with it. There are no breaks in the wire between the cdi and the cluster

[MacV2]

What revs are you idling at.I have mine idling at 1100/1200 rpm.As for the" backfiring a little bit" may be just the normal carb farts which most vtr's seem to suffer with.

Not sure, my tach doesn't work. Not sure what's wrong with it. There are no breaks in the wire between the cdi and the cluster

OK, so you say it has the pairs system, is it a late model with the digi petrol gauge ? or an import early from the states or parts of europe ?

I ask as it's easy to find early clocks, late ones harder to find & more expensive... However the easy way to find if the clocks are faulty is to swap with a known working set, if thw swap set work theres your fault, if the swap set dont work you have a fault somewhere else in the system...Trouble is that that fault may be killing the tacho which then means you have two faulty sets...


Early pre facelift clocks.


Later version with digi clocks.

Is this knocking noise like a thump that you feel in the air box ? If so that will be carb fart as mentioned above.

Carb sync helps a bit on that...

Also you dont need the tach to raise the tickover...just play with the adjuster & you'll hear the revs rise & or fall.


Look through the right hand side of the frame in front of the coolant res, at rear of the front cylinder. The knurled knob with the spring is the tickover adjuster.