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Bike doesn't want to run past 7000rpm

Old 02-26-2013, 12:19 PM
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Bike doesn't want to run past 7000rpm

I just replaced the front cylinder head on my bike and while everything was off I adjusted the TPS and installed a new air filter. Now it runs great until you hit 7000rpm and then it starts stuttering and bogging, the revs will slowly climb but it struggles. I pulled the choke out while this was going on and it made it worse.

I'm currently thinking it might be the carb sync since it doesn't idle quite as smoothly as before and since I replaced the front cylinder head it would make sense that the carbs would have to be adjusted to match this head.

Any thoughts or insight is appreciated.
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Old 02-26-2013, 01:00 PM
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PVLIR.....sounds like the second time today..... check the vacuum line to the petcock. It goes to the fittimg on the side not the bottom,
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Old 02-26-2013, 01:38 PM
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If not PVLIR could be timing is 180 out...
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Old 02-26-2013, 03:57 PM
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Was it a new or a used head? If used did you make sure the valves were sealing well? Also how bad was your old filter? Could be that it was restricting enough air to compensate for the main jets being off.
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Old 02-26-2013, 05:36 PM
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The petcock is hooked up correctly and I popped the old air filter in and it made no difference.

If the timing was 180 degrees out wouldn't it bend the valves or am I mistaken? Either way I'll be double checking the timing.

I also noticed while running around that the idle would sometimes settle anywhere between 1100 and 1500 rpm when I'd stop at a traffic light, would that possibly be an indication of carb sync not being quite right and one cylinder fighting the other?
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Old 02-26-2013, 05:45 PM
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Originally Posted by mike21091 View Post
The petcock is hooked up correctly and I popped the old air filter in and it made no difference.

If the timing was 180 degrees out wouldn't it bend the valves or am I mistaken? Either way I'll be double checking the timing.

I also noticed while running around that the idle would sometimes settle anywhere between 1100 and 1500 rpm when I'd stop at a traffic light, would that possibly be an indication of carb sync not being quite right and one cylinder fighting the other?

idle should run around that..Mine has always run between 1100 and 1500rmp at idle w/o choke being on all being factory at least.
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Old 02-26-2013, 05:57 PM
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Originally Posted by wsharpman View Post
idle should run around that..Mine has always run between 1100 and 1500rmp at idle w/o choke being on all being factory at least.
Idle should be 1200 per the service manual.

I would double check the timing on your cam.
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Old 02-26-2013, 07:21 PM
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2nd that on the cam timing
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Old 02-26-2013, 07:32 PM
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Originally Posted by mike21091 View Post
I also noticed while running around that the idle would sometimes settle anywhere between 1100 and 1500 rpm when I'd stop at a traffic light, would that possibly be an indication of carb sync not being quite right and one cylinder fighting the other?
That is usually a sign of leanness. Either the pilots are clogged or improperly adjusted. Also a faulty TPS can cause this.
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Old 02-26-2013, 10:14 PM
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I would also check the petcock diaphragm.
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Old 02-26-2013, 10:45 PM
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Alright I checked the TPS and it was good. I'm don't think it's the jets since it was running fine before the head swap but I'm really leaning more towards timing since as I've been riding it I've noticed that at higher speeds (~6k rpm in 3rd and 4th gear) it has no power so I'll be checking the timing tomorrow.
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Old 02-27-2013, 12:14 AM
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If the timing was off it'd most likely start real hard and not run very well anywhere, not just at higher RPM's.

The guy who previously owned my bike said it ran fine on the forums then after a CCT failure and after replacing a head said it started popping and sputtering over 7K. After I bought the bike and went through the carbs the jetting was all off. Once I got the jetting sorted out now it runs great and dynoed at 9hp more than any other Superhawk I've dynoed.

What is your jetting? What pilots, needles, and mains are you running? Also make sure you didn't have some dirt or debris get into the carbs while you had them off.
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Old 02-27-2013, 09:07 AM
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As your are getting a lot of advice pointing in different directions, so lets break your problem down.

This is what you have given us:
Originally Posted by mike21091 View Post
Now it runs great until you hit 7000rpm and then it starts stuttering and bogging, the revs will slowly climb but it struggles. I pulled the choke out while this was going on and it made it worse.
As you have changed a head we do have to take the possibility of the timing being 180 into consideration.

I really don't believe this is your issue but to check this you would need to set the other cylinder to the proper TDC (as set forth in the valve adjustment sequence) then rotate the crank the proper amount of degrees to the other cylinder and see if the cams are pointing the proper direction.

We can walk you through this or just look at the manual on how to adjust the valves.

No the most likely issue would be fuel related.

Which would leave you with one of two problems. You are either going way rich or going way lean due to running out of fuel.

If it is a rich condition (which could be assumed due to things getting worse when you pull the choke out, which is actually an enrichment circuit) then for some reason your mains are all of a sudden way too big...possible but not very likely.

Which leaves going lean or running out of fuel. This can also be the reason it runs worse when you pull the choke out. The reason for this is that the fuel in the bowls is already too low and opening the circuit lowers the level even more.

This is why I have said the first place you should start is the petcock. You have already checked the vacuum line which leaves two more things to check and eliminate before going any farther.

First is the petcock all the way open? Second would be is the diaphragm damaged.

By your symptoms of running out of power and erratic idle (which could be a sign of a vacuum leak) I would disassemble the petcock and check for tears or a pin hole in the diaphragm.

Sure you can start anywhere you wish but until you are sure you have adequate fuel flow, then you are just chasing your tail IMHO
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Old 02-27-2013, 09:51 AM
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Thank you for the guidance and I'll check the petcock first and go from there.
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Old 03-01-2013, 02:22 AM
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-- ADHD version --
Timing off by 1 tooth, pilot jet clogged, carb sync way off, now much better but still has flat spot at 7k rpm.

-- Detailed Version --
Well first off I haven't checked the petcock since it wasn't hooked up backwards when I took it off and it worked fine before but I did take the carbs off and cleaned them out and found the pilot jet for the front carb was partially clogged. I also checked the timing and found that I did have the intake cam off by one tooth and that got it running somewhat better but now I synced the carbs and it's running much better except for a small flat spot at around 7k rpm but it's only momentary. I am going to sync it tomorrow again since it wasn't fully warmed up when I did it tonight but it was way off.
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Old 03-06-2013, 09:44 AM
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UPDATE!! It's running beautifully! It was cam timing all along, somehow the rear was off by a tooth and the front was off by 2 teeth. All sorted now and pulling like a banshee again!
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Old 03-06-2013, 10:14 AM
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Haha, great! Dang motor wants to be synced up like a soroity house to function well; wonder why Honda doesn't fix that .
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