Bogging at high revs

[sp1tekiller]

Buddy's Banshee he bought isn't running the greatest. It idles fine and everything, but when you start to open it up it really sounds like it's not warmed up. It's not quite what I'd call a bog, but the power just isn't there and it won't rev out like it should. It sounds like the engine is still cold and not warmed up yet. Could this be caused be old gas/oil? Tomorrow we're gonna throw a fresh tank in and change the plugs, they could be fouled I guess.

[banshee67]

check the pilots and go through all of the tuning you can do on the carb. all you can really do is trial and error. just keep fiddling

[sp1tekiller]

So it definitely sounds like a fuel related problem and not something more serious? That'll make him relieved haha.

[fastbanshee8]

Apply the choke, and see if the problem gets better, or worse, and then let us know.

[sp1tekiller]

From what I recall, it's worse.

[GrMeyer]

If it is up in the Higher RPM IE at WOT then it is the Mains.

 

see if you can list all the mods, elevation and temp. Then it will be easier to help find out if the jetting is in the area.

[F.T.W. Banshee]

could be the plug caps

[MILO]

old fuel may cause the plugs to foul, but if the plug fouled you wouldn't be idling fine either. pull the carbs & give them a good cleaning & check the reeds to see if they're cracked at all. install new plugs & fresh gas. if it still acts up, you need to work on jetting. check this out for some guidelines.

 

Carb Theory 101

Edited September 27, 2010 by MILO

[EvilBanshee]

Drop to main jet sizes and go!!!

[sp1tekiller]

Thanks for the tips guys. So you think it must be running rich? Makes sense.

[sp1tekiller]

Oh, Buddy says that he thinks the P/O ran lawnmower 2 stroke oil for premix in the last tank. Could that cause anything like this?

[banshee67]

it couldnt have been good for the cylinders but you said it seems to run rine at idle. i would say to go up a jet size in the mains

[madjimmax]

I would agree with it being to lean. Sounds like you need to do a plug chop, thats the only way to tell for sure. But just to let you know pilot jets control fuel from idle to 1/4 throttle and then the carbs switch over to the mains from 1/4 throttle to WOT. So if its bogging out at high revs that sounds like a lean condition. As stated earlier give us a list of your mods and elevation and I'm sure someone here will get you going.

[MILO]

I'm leaning towards it being rich on the needle clip position or mains. Especially if it gets worse with the choke pulled out. Go over the carb theory link so you understand what does what, do the plug chop, and adjust as needed. You need to dial in the mains before anything else. Here's a quick overview of the plug chop if you don't already know how to do it. You'll probably get better results in the jetting/exhaust board too.

 

1. Get new spark plug(s), but don't put them in yet.

2. Warm up motor to operating temp on old plugs.

3. Install new plugs.

4. Accellerate through all gears to top gear with throttle pinned.

5. When you hit the top of the top gear, hit the kill switch and

pull in the clutch.

6. Remove the spark plug(s) and ride home on the old plug(s).

7. Hold the new plug in a vise and use a hacksaw to cut the threads

away from the center electrode.

8. You should see a brown 2mm "smoke ring" at the base of the

white center electrode if the main jets are dialed in perfect.

9. if the smoke ring is darker than chocolate brown or taller

than 2mm, you're rich on the mains, but if it revs clean to full

throttle, you can leave it there and be on the rich side.

10. If the smoke ring is smaller than 2mm or lighter than chocolate

brown, you're lean on the mains, go up a size and try again.

Edited September 28, 2010 by MILO

[EvilBanshee]

it couldnt have been good for the cylinders but you said it seems to run rine at idle. i would say to go up a jet size in the mains

 

Usually its rich when it wont rev out on WOT. Lean it will rev like hell and ping and pop. Drop 2 Mains and if it fixes the problem pull the plugs and see its its burning nice(Light Brown), lean or still a tad to rich.