Bogging at high rpm
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Junior Member
Squid
Joined: Mar 2022
Posts: 14
Bogging at high rpm
Hello all, im scratching my head at this issue. Bike will rev up to the redline sitting in neutral with no load perfectly fine. It’ll rev fine through 1st and 2nd gear, once i start getting into higher gears any rpm above 5000 the bike will start to losing power and almost surge if i leave it at quarter throttle. Now if if flick the throttle to WOT it’ll rev up fine underload. It only seems to happen when i let it sit at about 1/4 throttle in those higher gears, ive checked vac lines and synced carbs. I have no idea what else could be causing erratic symptoms like that
Senior Member
Superstock
Joined: Sep 2013
Posts: 460
From: Costa Mesa, CA
Hello all, im scratching my head at this issue. Bike will rev up to the redline sitting in neutral with no load perfectly fine. It’ll rev fine through 1st and 2nd gear, once i start getting into higher gears any rpm above 5000 the bike will start to losing power and almost surge if i leave it at quarter throttle. Now if if flick the throttle to WOT it’ll rev up fine underload. It only seems to happen when i let it sit at about 1/4 throttle in those higher gears, ive checked vac lines and synced carbs. I have no idea what else could be causing erratic symptoms like that
I had a similar situation after changing out my ACCT's. I had a cam 180deg. out of time. Apparently not uncommon. Reset cam timing, problem solved. Another cause could be a failing Petcock diaphragm causing it to starve for fuel at higher RPM under load.
Thread Starter
Junior Member
Squid
Joined: Mar 2022
Posts: 14
A little more info might be helpful ,i.e.; was it a sudden onset, any mechanical work done prior, Etc.
I had a similar situation after changing out my ACCT's. I had a cam 180deg. out of time. Apparently not uncommon. Reset cam timing, problem solved. Another cause could be a failing Petcock diaphragm causing it to starve for fuel at higher RPM under load.
I had a similar situation after changing out my ACCT's. I had a cam 180deg. out of time. Apparently not uncommon. Reset cam timing, problem solved. Another cause could be a failing Petcock diaphragm causing it to starve for fuel at higher RPM under load.
Senior Member
Superstock
Joined: Sep 2013
Posts: 460
From: Costa Mesa, CA
I don't know what kind of "Jet Cleaning Tool" you used, but if you removed the needles or pilot jets, the stockers are both different front to back. It is not uncommon to put them in in the incorrect orientation. Don't ask how I know this. LOL I don't know if that would cause your problem. Just a thought
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Junior Member
Squid
Joined: Mar 2022
Posts: 14
I don't know what kind of "Jet Cleaning Tool" you used, but if you removed the needles or pilot jets, the stockers are both different front to back. It is not uncommon to put them in in the incorrect orientation. Don't ask how I know this. LOL I don't know if that would cause your problem. Just a thought
Retired- but not tired!
SuperBike
Joined: Aug 2010
Posts: 1,481
From: Pittsburgh
Thats not the same thing. There’s a fuel tank breather tube that routes straight down thru the frame and comes out near the oil filter. If you inadvertently pinched it while working on your carbs or jostling the fuel tank around, you can create a temporary partial vacuum inside your fuel tank. This will reduce fuel flow to your carbs. The pdf of the service manual is posted here in the tech info section. Look at page 1-24 General Info. It shows tube routing.
Thread Starter
Junior Member
Squid
Joined: Mar 2022
Posts: 14
Thats not the same thing. There’s a fuel tank breather tube that routes straight down thru the frame and comes out near the oil filter. If you inadvertently pinched it while working on your carbs or jostling the fuel tank around, you can create a temporary partial vacuum inside your fuel tank. This will reduce fuel flow to your carbs. The pdf of the service manual is posted here in the tech info section. Look at page 1-24 General Info. It shows tube routing.
Senior Member
Superstock
Joined: Sep 2013
Posts: 460
From: Costa Mesa, CA
The hole is probably the result of someone drilling the "lift " hole in the slide to install a jet kit, i.e.; Dynojet ,Etc. As long as the retainer holds the needle in place, it shouldn't be a problem. What needles are you running?
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Junior Member
Squid
Joined: Mar 2022
Posts: 14
Stock pilot jets and bike came with 180 front and 185 rear main jets, the needle clip is set at 2 above the last slot, could this issue be from the TPS sensor?
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Junior Member
Squid
Joined: Mar 2022
Posts: 14
it started running like this when i cleaned the carbs, definitely user error but I can’t seem to find the direct issue. Checked coils and wires, petcock flow and vacuum actuation, checked timing on both cylinders, everything is good, so im thinking its definitely with the slide and needles
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Junior Member
Squid
Joined: Mar 2022
Posts: 14
- I have ruled everything carb related out, I decided to run each cylinder separately. The fault consistently occurs in any high gear at 4k and up RPM and at 60-80mph, and it is isolated to the rear cylinder. What could this issue be? Im stumped ive never experienced sputtering like this and it only happens under load, the weird part is if i hold the clutch in and try to hold the throttle in that range, the engine just dies. It will not rev up when its cruising and clutch is pulled in.
Senior Member
SuperBike
Joined: Sep 2010
Posts: 1,987
From: Bisbee, AZ
The symptoms fit the cam timing being wrong. Thought someone already mentioned this, but didn’t see it when doing a quick reread of the thread. Seems very likely that is the problem. Not the first time CCTs were replaced and this same problem occurred.
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Junior Member
Squid
Joined: Mar 2022
Posts: 14
could timing be just a tooth out? Bike still has tons of power its just struggling in the high load low rpm range, i read up that if the timing was out it would have a limitation at 7k rpm, i have also checked timing and it was near perfect on the rear, also valves were just right
Senior Member
SuperBike
Joined: Sep 2010
Posts: 1,987
From: Bisbee, AZ
could timing be just a tooth out? Bike still has tons of power its just struggling in the high load low rpm range, i read up that if the timing was out it would have a limitation at 7k rpm, i have also checked timing and it was near perfect on the rear, also valves were just right
Thread Starter
Junior Member
Squid
Joined: Mar 2022
Posts: 14
After rereading this thread, I'm most likely wrong about the cam timing being 180* off. Strange problem you have. Fuel starvation to the rear carb? Float vent clogged or vent tube pinched? If this problem developed after the work you've done, seems likely it's something related.
Member
Squid
Joined: Sep 2017
Posts: 34
From: Madison, WI
You might pull out the vacuum diaphragm in the carburetor and check for small cracks where the plastic flexes. I had a similar "bogging" and that was the hard-to-find cause. Be gentle though; the diaphragm looks kind of fragile.
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