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Hey, guys. My bike seems to be 'tripping' at idle. I attached a tach and adjusted the idle speed to 1000 (done after riding for about 15 minutes). When idling, the RPM will intermittently drop to around 700 - 800, and then pick right back up to 1000. Also, while choked, the bike will seem to backfire. Not sure if it's backfiring exactly, but the exhaust will pop. Not loud pops, but it's coming from both front and rear. Hard to start the bike cold without choke.

Mods made by the previous owner:

- K&N Filter
- Partially removed baffles


Things tested and replaced by me:

- New plugs
- Cleaned carbs, new jets (180 on both front and rear)
- Checked intake lines (may stand to do this more thoroughly)


If I've left out any information, please let me know.

Hard to start cold without choke is normal. That's why it's there.
K&N flow more air than stock filters- tends to drive mixture to the lean side.
Messing with baffles - will also affect mixture.

I think your idle mix is too lean.

What would be the best next steps?

ReptarCartel wrote:What would be the best next steps?

Not being a smartass but - figure out how to adjust the idle mixture.

YouTube or Service Manual or find someone who knows how to do it.
That step is generally somewhat machine specific though it might be common to a product line.

Getting a stock air filter and putting it back in place of the K&N could go partway to making the mixture less lean.

GS_in_CO wrote:

ReptarCartel wrote:What would be the best next steps?

Not being a smartass but - figure out how to adjust the idle mixture.

LOL. Completely understand, man. I should have mentioned that I've tried adjusting the mix screws out about as far as they'll go. I just ordered an OEM filter, so I'll update here as soon as I've installed it and gone for a test run. Thanks

ReptarCartel wrote:
LOL. Completely understand, man. I should have mentioned that I've tried adjusting the mix screws out about as far as they'll go. I just ordered an OEM filter, so I'll update here as soon as I've installed it and gone for a test run. Thanks

Did the idle change for the worse and ultimately quit when you turned them in? That would tend to prove you're on the lean side already.
If you can't get it to go rich by turning them out then an additional possibility is that you have an air leak between carbs and intakes.
Or the idle passages are gummed up so adjusting has little effect.

Did it ever run right for you? If yes, what changed? How long since?

Sorry for the extremely late reply. The idle died down and nearly cut out when the screws were turned in all the way. I just replaced the filter today, and it still hasn't alleviated the issue with the popping on choke. The idle seems to be steady for the most part, but still dips occasionally. The bike hasn't run correctly since I bought it, and I'm starting to wonder what the hell the PO did to it to make it run this way. Unfortunately, he's living in London now, and I'm not sure how to get a hold of him. I'm going to see if I can go through some channels to find out what modifications he'd done to it. Until then, is there anything else I can try? I'm going to take the bike apart tomorrow and check for leaks in the intake again.

One simple thing to look for - not sure if you bike has it or not- is a vacuum tap on one of the carbs that goes to the fuel petcock.
These may not be around anymore but if the petcock was vacuum opened when original and the valve replaced the vacuum port may be open and sucking air when it should have been plugged when the petcock was changed.
Might be hard to find as it's not very big.

A trick I've heard about to find manifold leaks is to spray WD40 on the intake runners while it's running. If the idle changes it's because it's sucking combustible oil where before there was just air. Sounds a bit messy to me but can be done before disassembly.