2005 500 Scrambler acting up above idle speed need help

[p5200]

I added more fresh gas it sat one day now, it's acting up again. Before cleaning out carburetor it wouldn't idle good and had gas leaks from carburetor. Now it idles pretty good but, if I increase throttle speed at a certain amount it starts missing bad. I'm going to try and post a short video. Just about ready to give up on this thing.😒  you can see reflection perking in video.

Edited February 17, 2024 by p5200

[Gwbarm]

You have cleaned the carburetor good so we know thats good now, just one thing i might mention, there is a jet down in a hole thats easy to miss when taking apart sometimes they are hard to get out, you might check that. The other thing is the mixture adjustment not the idle speed, it is in the front of carb on the bottom, sometimes there is a plug you have to take out to get to the adjusting screw. You might have done all this already, just thought i would mention it because it does still sound like fuel delivery. You could also try a new plug and check to make sure its got a good blue spark. Check all ignition wiring to make sure not corroded or loose. I couldnt see the video! I know it get frustrating at times, but too early to give up, we are here to help.

[p5200]

I 've heard a bad cam can cause this problem and common for this machine? It just seems odd for the carb and cam to mess up at the same time?

[Gwbarm]

Has this problem been previlant since you bought it or is it a new development.

[p5200]

3 minutes ago, Gwbarm said:

You have cleaned the carburetor good so we know thats good now, just one thing i might mention, there is a jet down in a hole thats easy to miss when taking apart sometimes they are hard to get out, you might check that. The other thing is the mixture adjustment not the idle speed, it is in the front of carb on the bottom, sometimes there is a plug you have to take out to get to the adjusting screw. You might have done all this already, just thought i would mention it because it does still sound like fuel delivery. You could also try a new plug and check to make sure its got a good blue spark. Check all ignition wiring to make sure not corroded or loose. I couldnt see the video! I know it get frustrating at times, but too early to give up, we are here to help.

I got the jet out you mentioned. I sprayed all jets and everything out with carb cleanen then blew it all out with air compressor. I sure do appreciate all of your help! 👍

4 minutes ago, Gwbarm said:

Has this problem been previlant since you bought it or is it a new development.

It's new development. But it does sound noisier at the valve cover area.

[p5200]

Also forgot to mention, when putting air pilot screw back in I adjusted it for 2 turns backed out per service manual.

[Mech]

The valve adjustment might have changed. If the valves have worn the rocker then adjusting them with feelers doesn't work well. The feeler doesn't allow for the wear because it just bridges across it and you end up with the feeler measurement plus the wear clearance. If the adjustment isn't right, things hammer and quickly get out of adjustment again.

There are a couple of ways of setting valves accurately. One is to use a dial gauge to measure the movement of the rocker, and the other is to check what the thread pitch is on the adjuster bolt, and then calculate how much of a turn it would take to get the correct clearance by backing out from from zero clearance. I set bike valves though by feeling the clearance and through a combination of feel and sound I know what the clearance is. Once the clearance is right, it stays right for a long time. If it's wrong it changes fast.. and that is true on most valve systems.

Other than the valves, read post #18..

 

[Gwbarm]

Yeah i figured you had done that, but just thought i would mention it, the 2 turns out sound right , but i have had to adjust some i have worked on to 2.5 to 3 turns out to get it right. You may be OK with that. Back to the noisy top end, if these are known to have premature cam wear i would do as Mech suggested and try setting the valve clearance. There could also be some cam chain noise you are hearing, what type of sound it it rattling or a thud, or click click. 

[Mech]

Most of it doesn't sound like tappets.. There are rattles and clunks..  haha.  It misses completely.   Does it run better if you open it up further P52 ?

I'd still recheck the valve clearance though. I've got the adjustment wrong before and they've gone out of adjustment in just a few minutes or riding..  It happens. And they can work tighter or looser.. Depends on the bike and how they were adjusted.

I'd also check the spark plug gap and the spark plug cap's resistance.

[p5200]

I snipped the wire going to the kill switch and right now it revs and is doing pretty good. Before I bought the machine, we had to unplug that black. We got spark 1 time and then nothing with black wire hooked up. I hooked it back later after operating kill switch a bunch of times and it then worked. I'm not positive, that was the problem I may still have a little moisture somewhere. I saw a new pull rope and handle I'm going to order and put on. I'll give it a go on the valves also, I'm sure they were probably never adjusted. I'm running it alot today just in case there is moisture still. I sure appreciate all of the help fellas! 👍

[Gwbarm]

That would be nice if it was just a partially shorted kill switch, well not nice, but better than chasing other options around.

[p5200]

Yeah, I sure hope that's what the problem is. It's a whole lot easier to get to than the carburetor. I've got my fingers crossed LOL!  🙂

[Mech]

Yeah hopefully that is it. It might just be certain revs vibrations make something wiggle and short or loose contacts. Most switches on bikes come apart pretty easy. Just do it over a big tray so you don't loose little balls or springs. Clean the contacts and check the spring is firm and springy.

[1954JF]

On 2/17/2024 at 11:48 AM, p5200 said:

I added more fresh gas it sat one day now, it's acting up again. Before cleaning out carburetor it wouldn't idle good and had gas leaks from carburetor. Now it idles pretty good but, if I increase throttle speed at a certain amount it starts missing bad. I'm going to try and post a short video. Just about ready to give up on this thing.😒  you can see reflection perking in video.

I've got a fresh idea for you so read this carefully. If your charging system is putting out too much voltage via the rectifier (bad voltage regulator) there may be a rev limiter built into the CDI unit to preserve the integrity of a very expensive part, that CDI box. When you rev up the stator produces more and the rectifier keeps things in the proper range. Use a simple DC voltage meter or (multimeter set to DC volts). Check the battery without the engine running and it should be at or a little above 12V-12.5V. If it is higher than that it is overcharged. Now start the engine and watch the volt meter. If it reads above 13.5V-14V say it goes up like 15V-17V or more then shut it down and save the brain box. These CDI ignition boxes have advanced with computers and microchips. Rectifiers can either go low or high with volts and too much can burn things up including wires and cause fires. They designed into the CDI to prevent this by limiting engine performance or revs. 

This is just a possibility that is easy to check out. I love the sound when you rev, it sounds like a deep throated two-stroke. Good luck and I hope this helped you.

 

[Gwbarm]

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