Loss of power around 5-6k RPM

[exzachtly1]

This sounds EXACTLY like my problem. I have yet to tear into the airbox, but I think I'll be starting there along with checking the valves before I tear apart my freshly rebuilt carbs.

Please do report back here if you figure out the issue! I have been ignoring the problem for a couple weeks now because we've had a run of nice weather here in Ohio. And the issue doesn't really affect normal riding, I still get pretty good power. Only really a problem when I'm really jamming on the throttle for fun

New airbox boots and clamps just arrived in the mail today. I am now also armed with a compression tester, feeler gauge, tappet tool, etc. etc. so there is some work in my future. I know that I need to get the valve adjustment done to rule that out, but I'm just taking it slow. Waiting for another paycheck so I can get new gaskets before I take things apart too.

I did try turning the ignition advancer by hand, and it didn't really "snap back" as described. I'd describe it more as "snapping forward." I turned it clockwise and after around a half turn it would snap forward (clockwise) a bit. Is that what I should expect?

[Toasty]

Do you have an inline fuel filter?

[Mr. Sinister]

Please do report back here if you figure out the issue! I have been ignoring the problem for a couple weeks now because we've had a run of nice weather here in Ohio. And the issue doesn't really affect normal riding, I still get pretty good power. Only really a problem when I'm really jamming on the throttle for fun

Will do!! I plan on tacking it one piece at a time, then testing, so I will know for sure what it was.

[exzachtly1]

Do you have an inline fuel filter?

Me? Nah, no inline filter. All stock. It is possible that the vacuum and fuel lines are NOT stock though, so the thought has crossed my mind to order some OEM hoses for those to rule that out as a potential issue.

[tom203]

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I did try turning the ignition advancer by hand, and it didn't really "snap back" as described. I'd describe it more as "snapping forward." I turned it clockwise and after around a half turn it would snap forward (clockwise) a bit. Is that what I should expect?

I erred in my prior explanation ....
Using a screwdriver to push it clockwise, the tab on advancer ( the projection that spins by the signal coils) should move easily about 30 degrees and spring back smoothly when released. The hex nut is anchored to crank.

[Toasty]

Sorry if this sounds dumb but how do you have the carb vent lines routed? They should come up out of the carb and rest on the airbox, above the fuel bowls.

[Mr. Sinister]

So my problem was caused by the lack of an air filter and airbox lid. I made a makeshift filter out of seat cushion foam, and used duct tape to make a V shaped opening in the top of the box. Bogging is gone, and the bike is running great now.

[exzachtly1]

I erred in my prior explanation ....
Using a screwdriver to push it clockwise, the tab on advancer ( the projection that spins by the signal coils) should move easily about 30 degrees and spring back smoothly when released. The hex nut is anchored to crank.

I see, I'll have to give this a shot next time I get some garage time.

Sorry if this sounds dumb but how do you have the carb vent lines routed? They should come up out of the carb and rest on the airbox, above the fuel bowls.

They are routed the way you describe. Originally there were none on there so I replaced them and made sure to route them that way.

So my problem was caused by the lack of an air filter and airbox lid. I made a makeshift filter out of seat cushion foam, and used duct tape to make a V shaped opening in the top of the box. Bogging is gone, and the bike is running great now.

Cool! Lucky that's all it was for you!

As I mentioned before I've got new boots and clamps for the airbox now so I'm gonna try that next. And valve clearances will be checked soon (want to order new gaskets before I take the valve cover off). It's also been tough to find time to get out and work on it lately. Hopefully this week.

[Mr. Sinister]

Could very well be your problem. If my bike is any indication, these bikes are very sensitive to airflow changes.

[exzachtly1]

OK, so unfortunately I am reviving this thread because the problem still exists. Since my last post I have done a few things to try to eliminate the problem, including:

• Valve adjustment. Exhaust 1 was too tight, intakes 3 and 4 were borderline (0.03mm). Those have been corrected.
• Carb sync. I did this before the valve adjustment, actually, so I need to do it again.
• Confirmed operation of the mechanical advancer on the ignition. It's working fine, the spring is fine.
• Investigated the air box - the filter was maybe a little heavily oiled so I patted it down with some paper towels. Inside the airbox I noticed there was a film of what smelled like gasoline. Not enough to be really alarmed, but definitely a little gas getting into the air box.
• There are exhaust leaks. I have noticed some light smoke coming from the exhaust connection to the headers during warm up. I think it's just normal condensation burning off, but I believe that should be coming out of the end of the exhaust, right??? And the crossover underneath has a small hole in it.
• Clamps on the intake boots are bottomed out. I believe this is probably contributing to a small air leak, leading to a creeping idle issue (that's another issue but wanted to mention here).
• Checked the compression. Getting ~135psi across all cylinders, this was done with the engine cold. I have not done a warm check yet.

The more I go through everything, I keep going back to thinking it is the carbs. I have not checked the fuel level in the bowls using the clear tube method. I'm working on getting something to do this with, and will check that soon. Could a low fuel level in the bowls cause this kind of issue?

The other thing I have not done is any electrical tests. I need to go through and check the battery voltage and voltage at the coils.

Other than this symptom and a creeping idle (creeps up to close to 2k when fully warm... I'll probably do another thread for that haha) the bike has been running great and very smooth in all other aspects.

EDIT: After reading this thread I am really beginning to suspect my air filter as well. He describes almost exactly the symptoms I am experiencing. The bike originally had an OEM filter in it that was all torn up, worn out, and barely there. I replaced it immediately. Unfortunately, as this is my first motorcycle, I did not actually drive it when it had this old filter in it so I have no basis for comparison. A friend drove it home for me when I bought it. I asked him if he experienced these symptoms at all when he drove it, and he said he didn't think so... he drove it on the highway, too. I am thinking of cleaning the filter completely, and riding it with a SUPER thin coating of oil on it... it's one of the UNI brand foam filters.

[exzachtly1]

OK guys.

OK.

Are you ready for this? Ready for what this master mechanic just figured out??

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My air filter was in backwards. Yes, backwards. I had no idea it was installed wrong all this time and after looking at the microfiche for the airbox, it struck me... so I went out, flipped it around, went for a ride and it was seriously like i have never ridden this motorcycle before. I think I was running at about half (or less) of the power this bike is capable of. Needless to say, even if I am embarrassed, I am SO FREAKIN' HAPPY!

How was it in backwards, you ask? Well, I had the skinny end jammed into the opening of the airbox... effectively cutting off air flow. the only reason I put it on this way was because that's the way it was on when I replaced it. I didn't know any better. Assumed it was right and went with it. Now that I actually look closely at the air filter housing, it is so obvious... there are indentations that match the cradle.

Now I assume I have leaned out the mixture, as I am getting a slight stumble off idle and some popping from the exhaust on decel. So I am going to richen up the mix a bit and then I should be golden... and it will be on to sorting out that creeping idle!

My only request? Please don't kick me off the forum

This thread was still very valuable to me as it prompted me to do some much needed maintenance in other areas that I'm sure are helping with the overall health of my amazing bike. I swear, before tonight, I don't think I had really ridden this thing before...