KLF300 1994; Getting it to start and run smoothly

[Params_sweden]

Hi, my KLF300 Bayou 1994 from my other post can now ignite and run for a little while. It's running very rough, the idle is way off, I have to use both choke and gas to get it in a somewhat "idle" state otherwise it dies. Let's fix it

I think that the first priority is to get the idle stable, right now I can't get it to idle at all, it's either too high or too low and dying off after a few seconds. The setting of the idle screw doesn't seem to stabilize it, it's either too low or too high, if I get it between those states it's only running for a few seconds before dying. The ATV could idle and run last summer btw.

What do you think I should do next? 

/ Pär

Edited April 14, 2023 by Params_sweden

[kp3004x4]

Check for air leaks at carb connection from engine to carb even hair line cracks there you will never get it to idle. To CHK simply get wd40 and spray just a little bit right on that area if it kills it out then you have a crack hope this helps.

[Params_sweden]

Thanks, an air leak would make sense! Today I fired it up again and surprisingly it worked much better, the only difference was that I put some more gas in the tank, maybe it was almost running out yesterday... 🙈 I adjusted the idle screw a bit until I got an idle RPM that was ok, however the idle is not entirely "stable" in my opinion, nothing extreme but it's misfiring at times and acting slightly weird. Note that I find it slightly off, no extreme reving like in many recordings you can find of "bad" idle.

I sprayed CRC 5-56 at the carb rubber connection to the engine, on both sides and everywhere, it didn't affect the idle. 🤔

I'll add recordings of the idle when it's warmed up, and also a recording when I take short ride speeding up, stopping etc. Didn't think of recording the cold start and idle

Let me know what you think of the "clonk" noises etc, maybe it's to be expected?

The carb and CDI is aftermarket btw, chinese ofc

/ Pär

[Mech]

It's important to have the idle speed screw set as slow as possible while you are adjusting the idle mixture. Then after you have the idle mixture to the best setting you speed the idle up slightly to specs, or what suits you. If you have the idle speed screw wound in too far when you are adjusting the idle mixture it is adjusting the mixture with extra air being mixed in that is not intended to be there, and that causes a flat spot/hesitancy as you open the throttle.

The recommended procedure is set it to a slow speed with the speed screw and adjust the mixture, then slow it again and readjust the mixture, and keep doing that till it's slow and the mixture screw is halfway between just starting to slow from being too rich, and just starting to slow from being too lean. Then wind the speed screw in if needed. Don't readjust the mixture screw. If it doesn't like being sped up, or if it has a flat spot, there is a problem with other systems in the carb that need cleaning or adjusting.

Most bikes the idle mixture screw is quite sensitive, and a half turn can go from rich to lean. If it takes more than about a full turn, or if the mixture screw seems to need winding all in one direction without ever making it too rich or lean as we would expect, then there is a problem in the idle mixture jets or idle speed setting.

[Params_sweden]

I'll do this procedure tomorrow, thanks! Is the idle speed screw the same as the "pilot screw" in the attached screenshot from the manual?

/ Pär

[Mech]

Yes..  the pilot screw is mixture.

Edited April 14, 2023 by Mech

[Params_sweden]

Good morning I've tried to adjust the pilot screw back and forth a couple of times now when the ATV is warmed up, with some success, it starts and runs quite reliably but I think the screws are totally wrong since I didn't notice much difference when messing around with the pilot and lost count. I'll try adjusting it later today again..

I have a question though, should I have the mixture screw at the lowest point i.e. no extra gas at all? When I set it at that point I can't start the ATV at all like there's no gas going in, it's surprising to me because I though that the carb should have a "minimum idle gas" and that the screw would just add on top of that 🤔 I'm asking because I'm trying to understand if I should have the mixture screw at like a low setting or completely screwed out when initially adjusting the pilot screw.

/ Pär

Edited April 17, 2023 by Params_sweden

[Mech]

There's the pilot/mixture screw, and there's the idle speed screw. The speed screw is on the side of the carb.

The mixture screw makes it leaner when it's wound in(and richer out), and the speed screw opens the throttle when it's wound in.

Wind the speed screw in until the bike will keep running, it might have to be wound in quite a long way but eventually the bike should stay running, if it won't run with the speed screw right in then the carby is dirty or there is an air leak into the manifold or a tight valve or some other problem. If the bike will stay running then try adjusting the mixture screw trying to get it to run faster. Wind it in and out a bit and see which way it likes best, then keep winding it that way. If the revs build up(and they should), then slow it down with the speed screw, then go back to adjusting the mixture screw in and out till it's revs get as high as possible, then slow it down and adjust the mixture again.. Eventually it should end up ticking away slowly but evenly, and then you use the speed screw to get it up slightly to the recommended slightly fast idle. It doesn't need to be taken down to the very slowest possible as you do the mixture, but as slow as is possible to have a steady idle.

If it won't idle nicely after an adjustment then there's a problem and so I'd recommend pulling the carb and stripping it right down and cleaning and inspecting every jet and drilling and while it's off check the inlet for possible air leaks. Some have rubber inlets that split, and some have a gasket and some have an O ring, and some have an O ring and a gasket. If all that still doesn't get it idling nicely then checked for blocked breather hoses on the carb, tight valves, or a spark plug with too much gap.

And no, there is no "minimum idle gas" and then the idle speed screw adding to it. If you wind the idle speed screw right out the engine will stop.

[Params_sweden]

Thanks for your clarifications @Mech, I've adjusted the carb. Now the bike is starting right up and stays in a stable idle! When the motor is still cold I have to use the choke to start driving, just to get it moving, and when I slow down to a halt the first time during a "driving session" it dies *once*, I start it up again and it's working perfectly. It's always the same procedure now, probably a carb issue, but at least it's totally reliable You can notice that the carb is a bit off when stopping, the RPM goes a bit too low, and then catches up to the idle pace - when the motor is cold during the first stop this causes the motor to stop I think, because the RPM goes too low that one time.

It's a working ATV now, but I'll try to fix it so it runs perfectly

 

/ Pär