Author Topic: Power loss above 7000RPM.  (Read 3525 times)

lexx790

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Power loss above 7000RPM.
« on: April 03, 2011, 05:05:13 PM »
The bike seems to be running fine apart from as the title says.
Could this be a rev limiter thing ?

Walt_M.

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Re: Power loss above 7000RPM.
« Reply #1 on: April 03, 2011, 07:52:15 PM »
Not likely. If the rev limiter is acting up you wouldn't get to 7000 rpm. I suspect the airbox, flap is closing or oil soaked filter.
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Lucky

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Re: Power loss above 7000RPM.
« Reply #2 on: April 03, 2011, 08:37:48 PM »
i'd certainly start by cutting the rev limiter wire.  they are a confirmed problem, & no particular rpm that they fail at...
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kwells

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Re: Power loss above 7000RPM.
« Reply #3 on: April 08, 2011, 01:30:51 PM »
also check the flow of your fuel petcock. And make sure the diaphram holds vacuum instead of allowing  fuel to get sucked into the vacuum line.
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lexx790

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Re: Power loss above 7000RPM.
« Reply #4 on: April 09, 2011, 04:13:50 PM »
Thanks for the suggestions, it feels more rev limiter problem as it's sounding like a misfire at higher revs, other things I would think would feel more gradual.
It pulls well from low revs but suddenly runs out of steam, put it into a higher gear of away we go again.

jasonm.

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Re: Power loss above 7000RPM.
« Reply #5 on: April 18, 2011, 08:03:12 PM »
I had the same issue. Walt is corrrect. Likely running rich from a flapper not opening enough. Easy test...take the airbox top off , loosen the 2 screws holding the flapper plunger and adjust the vaccum plunger. Slide it till it's open a bit. Then tighten the screws back down. Assemble and go for a ride.
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lexx790

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Re: Power loss above 7000RPM.
« Reply #6 on: April 18, 2011, 10:57:58 PM »
I had the same issue. Walt is corrrect. Likely running rich from a flapper not opening enough. Easy test...take the airbox top off , loosen the 2 screws holding the flapper plunger and adjust the vaccum plunger. Slide it till it's open a bit. Then tighten the screws back down. Assemble and go for a ride.

Good suggestion unfortunately UK bikes didn't have the vacuum controlled flapper.
The airbox has a flap on the inlet but it's just weighted. The bike is 3500miles away from me at the moment, so will have to wait till Thursday till I see her again. So I'll take a look at the airbox part to make sure the flapper is not jammed shut when I return home.

spectre

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Re: Power loss above 7000RPM.
« Reply #7 on: April 30, 2011, 06:40:23 PM »
I'm having the same sort of issue, when I get past about 6000 RPM, or open the throttle more than halfway, my bike bogs down, and then surges, I've adjusted the flapper, but I haven't gotten to ride it yet. but it seems weird to me that it also happens when I open the throttle more... any thoughts?
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JohnAMcG

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Re: Power loss above 7000RPM.
« Reply #8 on: April 30, 2011, 06:53:00 PM »
I'm having the same sort of issue, when I get past about 6000 RPM, or open the throttle more than halfway, my bike bogs down, and then surges, I've adjusted the flapper, but I haven't gotten to ride it yet. but it seems weird to me that it also happens when I open the throttle more... any thoughts?

I had the bog down then surge issue when I was working the kinks out on mine.  I chalked it up to accelerator pump.  With the tank and airbox off, I could pump the throttle for 5 minutes and I might eventually get a drip from one of the jets.  New diaphragm from revision, and the problem is gone.  I fixed a lot of other stuff too, but i had the rev limiter wire cut long long ago. 
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lexx790

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Re: Power loss above 7000RPM.
« Reply #9 on: April 30, 2011, 07:15:23 PM »
I took my bike to work last Thursday and on the way home, while going downhill I pulled in the clutch a twisted the throttle to way above 9000 revs, but in gear it still tops out at 7000.  ??? ??? ???

spectre

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Re: Power loss above 7000RPM.
« Reply #10 on: April 30, 2011, 07:19:42 PM »
I had the bog down then surge issue when I was working the kinks out on mine.  I chalked it up to accelerator pump.  With the tank and airbox off, I could pump the throttle for 5 minutes and I might eventually get a drip from one of the jets.  New diaphragm from revision, and the problem is gone.  I fixed a lot of other stuff too, but i had the rev limiter wire cut long long ago. 
Hmm, seems simple but obvious, I don't know why I didn't think of that,  ::) I'll take a look at it in a little bit. thanks John!
1982 yamaha vision xz550- a work in progress

Cdnlouie

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Re: Power loss above 7000RPM.
« Reply #11 on: May 08, 2011, 06:12:50 PM »
Lexx it sounds a lot like starving for fuel. If you don't get any backfiring then you are not misfiring, just running out so lean that you get a total bog.  This speaks to blockage in carb body. Check the float bowls for rust by removing a carb top and if there is rust (brown sediment) accumulation then you need a very good cleaning and a very good filter to keep the rust out in the future.  If this condition came on gradually after it had been working well then it can be rust blockage.  Not sure of your carb history but rust is the number one killer of Visions.

Lucky

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Re: Power loss above 7000RPM.
« Reply #12 on: May 08, 2011, 06:54:15 PM »
you might be wondering where all the rust comes from if the carbs are aluminum...

the tank.  the petcock 'filter' does nothing, &even with a sintered bronze filter it's still possable for rust to disolve enough in gasoline & solidify in the bowl if the carbs tend to sit between uses...
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jasonm.

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Re: Power loss above 7000RPM.
« Reply #13 on: May 19, 2011, 06:01:47 PM »
the 7000rpm thing on my '82... was too rich. The flapper on mine needed to be set open a bit from the start.  Adjust the flapper using the 2 screws on the vacuum diaphragm foot. Then take it out. It take seconds to try this.
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lexx790

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Re: Power loss above 7000RPM.
« Reply #14 on: May 19, 2011, 06:21:38 PM »
the 7000rpm thing on my '82... was too rich. The flapper on mine needed to be set open a bit from the start.  Adjust the flapper using the 2 screws on the vacuum diaphragm foot. Then take it out. It take seconds to try this.

Interesting but again as I have said before, my UK bike doesn't have any vacuum flapper. I'm going to have a look at various bits hopefully this weekend, carbs, airbox and filter etc. If I can't get it sorted I found a local garage with a dynotester who can tune carbs for bikes.

jefferson

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Re: Power loss above 7000RPM.
« Reply #15 on: July 12, 2011, 10:45:05 PM »
Check and see if your bike has the vent lines in place and run in the stock location into the hollow frame section under the battery.

Is it in all the gears that there is the power loss or just in the upper ones? Missing vent lines can cause a rich mixture and thus loss of power at higher rpms in the upper gears. Might be worth checking.

Jeff

jasonm.

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Re: Power loss above 7000RPM.
« Reply #16 on: July 13, 2011, 07:07:30 AM »
I do not understand why Yamaha would put a vacuum flapper on this side of "the pond". And not in the UK. It does help the engine run better. Your is weighted. Which will cause changes in function..up hill vs. down...ummm. The accel pump does little past7000 because you have already twisted the throttle past the usuable part. I also had a blocked accel pump. But it was a severe hesitation when I would twist the throttle moderately at most any speed. You could have something blocked in the carbs. But that would cause isues before 7000. Lastly....maybe the ignition is not advancing enough...? It's suppose to be fully advanced around 3000 or so.
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QBS

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Re: Power loss above 7000RPM.
« Reply #17 on: July 13, 2011, 01:33:26 PM »
How is the ignition made to avance?

lexx790

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Re: Power loss above 7000RPM.
« Reply #18 on: July 13, 2011, 03:20:16 PM »
I've only ridden it a couple of times lately, if it's hot and sunny I go to the beach which is just about a mile away, but the problem is still there, it's in all gears.
Not being ridden I can rev to the red line, so it''s only under load that it doesn't do it.
Fitted an XT125 rack last weekend so I still haven't pulled the tank off to look at the airbox.
I also have a spare set of carbs but have yet to clean these through, so much to do, so little time to do it.  ::)

spectre

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Re: Power loss above 7000RPM.
« Reply #19 on: July 13, 2011, 05:30:45 PM »
I've only ridden it a couple of times lately, if it's hot and sunny I go to the beach which is just about a mile away, but the problem is still there, it's in all gears.
Not being ridden I can rev to the red line, so it''s only under load that it doesn't do it.
Fitted an XT125 rack last weekend so I still haven't pulled the tank off to look at the airbox.
I also have a spare set of carbs but have yet to clean these through, so much to do, so little time to do it.  ::)
EXACT same problem with mine, it's only under load that it bogs, but mine is past 6000 :p
1982 yamaha vision xz550- a work in progress