YZ426F wont idle.

Tdubb · Dec 10, 2011

I just got this 01 YZ426F and when I'm on the gas, this thing runs great. But it does back fire every now and then, and I can't get it to idle right.

I'll turn the idle knob up, and it idles to high. It will stay running like that, but it's not right. So then I'll try and inch of the idle knob, and it just doesn't change untill all the sudden it's way to low again.

I was going to pull the carb and clean it, but someone told me I should try the LOW JET?

He said that will make it run lean, therefor causing a rough idle.

Any tips or suggestions? This guy I got the advice from is a serious rider, and I'm willing to bet he knows what he's talking about, I just like to run it by a few more people before I get into this.

Ol'89r · Dec 10, 2011

Tdubb said:
it does back fire every now and then, and I can't get it to idle right.

I was going to pull the carb and clean it, but someone told me I should try the LOW JET?
.

I think he meant the Slow Jet or otherwise known as the pilot or idle jet. It's the smallest removable jet in your carb and will clog very easily with old or dirty gas. Remove the float bowl and remove the pilot jet and the fuel screw. The pilot jet sits right next to the main jet. Make sure you can see daylight through the middle of the jet and using compressed air, blow out all of the orifices connected with the idle system. A service manual will help you figure out which jets are which.

Tight valves can also cause the bike to back fire and not idle. Make sure your valve clearance is ok.

Tdubb · Dec 14, 2011

Thanx bro, I'm going to tackle the carb on Sat. And if that don't work, maybe I'll check the valve clearence too.

It's been a while since I've had to pull a carb on a bike and never checked valve clearence. I've got the manual and it doesn't look hard, but checking the valves looks like it requires removing a lot.

I'll let you know how it goes.

Ol'89r · Dec 15, 2011

Tdubb said:
maybe I'll check the valve clearence too.

I've got the manual and it doesn't look hard, but checking the valves looks like it requires removing a lot.

I'll let you know how it goes.

If it were my bike, I would check the valves first. Tight valves can cause you a lot of problems and cost you a lot of money. If they are run too tight, it can burn the valve and also the Valve seat. You will have to replace your valves and have someone re-cut the seats. It's better to keep a constant eye on the clearance.

All you have to remove to access the valves is the Seat, Tank & shrouds and the top engine cover. Not a big deal. Changing the adjustment is a little harder and is explained in detail in your manual.

Tdubb · Dec 19, 2011

Well, I've already ran into another issue. I'm leaking coolant from were it goes into the front of the block. So I've already got everything apart, except for the top engine cover. I've got all next week off, so I'm going to dig into all that I can next week.

Thanks for the advice Ol'89r. I'm sure I'll have more questions next week.

Tdubb · Dec 23, 2011

Well, I'm glad I tried digging into the valve clearence, but what sucks is, I think I found more issues. When trying to find TDC, It looks like my cams and timing are way off.

I aligned the TDC mark on the rotor with the mark on the case. When thats done the punch marks on the cam shafts don't align where they should. I don't have time to dig into that issue right now, but I'm asuming thats my timing is off?

I assume that I can loosen the chain, pull the cams off, and just put them in the right spot? Is there anything else I need to look out for?

The guy I bought the bike from told me that the cams had just been replaced with some better ones, so does that meen the marks wont line up like the stock cams?

Tdubb · Dec 23, 2011

Since the exhaust cam and the intake cams are not in sink, is that why it backfires sometimes?

IndyMX · Dec 23, 2011

How far off are they? Can you get pictures and post them??

And more importantly, are you using a service manual?

Tdubb · Dec 23, 2011

Maybe 2 teeth on the exhaust side. I'll try and get some pics this weekend.

Tdubb · Dec 26, 2011

Well, I broke it down, and got the cams set with TDC, and the valve clearence is good.

I thought since I had the service manual, and a pretty good understanding of how an engine works that this shouldn't be that hard......and it wasn't. But I've screwed something up, cause now it wont start.

It's like I'm not getting a spark. I did replace the plug, but I did not disconnect, or even move any other electronics.

IndyMX · Dec 26, 2011

I had a similar situation on a KX250Fa couple of years ago.. No matter what I tried, it never seemed to get any better.

When I finally gave up and sent it out to someone, he reported back that the cam gear had slipped on the cam. I would have never been able to figure it out with out the proper tools. IE. a degree wheel.

As it turns out the bit that the gear bolts to is just an interference fit on the cam shaft. So, it's just held on with friction. Not the best design in my opinion, but what do I know.

He reset the cam and welded that part to the shaft so that it would never slip again.

Perhaps something like this has happened to yours.

Ol'89r · Dec 27, 2011

IndyMX said:
I had a similar situation on a KX250Fa couple of years ago.. No matter what I tried, it never seemed to get any better.

When I finally gave up and sent it out to someone, he reported back that the cam gear had slipped on the cam. I would have never been able to figure it out with out the proper tools. IE. a degree wheel.

As it turns out the bit that the gear bolts to is just an interference fit on the cam shaft. So, it's just held on with friction. Not the best design in my opinion, but what do I know.

He reset the cam and welded that part to the shaft so that it would never slip again.

Perhaps something like this has happened to yours.

This is most likely what happened. If your bike ran with the exhaust cam two teeth off and now with it set correctly it won't run, the gear has probably slipped on the cam. Or, when they changed the cams they removed the gear and pressed it on incorrectly. Like Indy said, you need a degree wheel and also a dial indicator and some knowledge of how to degree camshafts to do this. You could also remove the exhaust cam and take it to someone that has an OEM cam in stock and compare it with the OEM cam. Check the relation between the cam gear and the postion of the lobe. Like Indy said, weld the gear to the cam once it is pressed on correctly. Three small spots with a tig welder will work.

Tdubb · Jan 11, 2012

I got my bike back. The timing was off, and the carb was real dirty.

The cams in my bike are 03 cams, so I don't need to use my decomp lever. But the sprocket looks different from my manual, but my main issue was I missunderstood where the cam lobes should be at TDC. I thought they should be straight out at 9 and 3, but it's actually at 10 and 2 .

Then he pulled the carb and it needed cleaning too.

She runs like a champ now.

YZ426F wont idle.

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