I just picked up a 2000 Vmax with 5k miles on it. Don't know much about these bikes other than I've wanted one for a long time. Just got to take my first real ride on it this morning. It seems to lose power about the time I hit 7k on the tach.
Losing power at High RPMs
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Seven thousand RPM's, you should be tightening your grip for the E-class ride you're about to be taking. VBoost should be close to full-open, and there should be a rush of acceleration!
What kinda-shape is the air cleaner in? And the #1 question, do-you have a Cobra 4 into 4 exhaust on it? (Fingers-crossed that you don't) I assume you've changed the spark plugs?
Use the screws by the float bowls to open the float bowl drains, those small black rubber tubes sticking-out of the carburetor brackets, below the CV carburetor diaphragm caps. Collect the runoff into a transparent container, do each carburetor 1 at a time, and see if you have any water in the gas. It should be very-apparent if you do, the water will appear to be a separate pool/'lens' of liquid, floating below the gas. Gasoline has a different specific gravity from water, water is heavier, and will migrate to the bottom of the container.
Check your fuel filter. Inspect the gas tank with a flashlight, all you should see in there on the bottom and sides is shiny, bare sheetmetal, anything-else, you need to pull the gas tank, and get it cleaned, and possibly lined/treated to seal any corrosion/pitting, after cleaning.
Seven thousand RPM's, you should be tightening your grip for the E-class ride you're about to be taking. VBoost should be close to full-open, and there should be a rush of acceleration!
What kinda-shape is the air cleaner in? And the #1 question, do-you have a Cobra 4 into 4 exhaust on it? (Fingers-crossed that you don't) I assume you've changed the spark plugs?
Use the screws by the float bowls to open the float bowl drains, those small black rubber tubes sticking-out of the carburetor brackets, below the CV carburetor diaphragm caps. Collect the runoff into a transparent container, do each carburetor 1 at a time, and see if you have any water in the gas. It should be very-apparent if you do, the water will appear to be a separate pool/'lens' of liquid, floating below the gas. Gasoline has a different specific gravity from water, water is heavier, and will migrate to the bottom of the container.
Check your fuel filter. Inspect the gas tank with a flashlight, all you should see in there on the bottom and sides is shiny, bare sheetmetal, anything-else, you need to pull the gas tank, and get it cleaned, and possibly lined/treated to seal any corrosion/pitting, after cleaning.
[email protected]
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Can you hear the v-boost servo cycling when the key is turned on before starting the bike?
Yes, it sounds like a servo doing a self check, back and forth.
Well, this is a long-shot, but where is the bike stored? Some critter(s) may have crawled-up the exhaust and made a nest, and now you've got excessive back-pressure. That will kill the top-end performance.
I'll have to check that.
Last night I found a problem with the bike during some investigation but it didn't cure the top end loss of power. The negative battery cable bolt was in about one thread and very loose. I tightened it up, but no change in engine performance. I drove it a bit more and the best way to describe the loss of power is it's like I'm hitting a rev limiter at 7-7500 rpm.
You might try Sean Morley's electrical trouble-shooting kit. It's a great benefit for tracking things down. Like Liberty Insurance, "Only-pay for-what you need."
Replace your CDI box with Sean's kit piece, and see if your troubles vanish. As the manuals say, "replace unit with one of known good operational quality."
Replace your CDI box with Sean's kit piece, and see if your troubles vanish. As the manuals say, "replace unit with one of known good operational quality."
desert_max
Well-Known Member
First of all, to quote FireMedic:
The is the way life should be on that Vmax. Hard to give you any real specifics, but falling on its face at higher RPMs, you’re likely either running out of air or fuel most likely. Somebody mentioned air cleaner, might want to take a close look at that thing. If it’s plugged it’ll be running rich and may be stinking like gas at idle or low RPMs, and will fall on his face is the revs it increase. It’s also possible that your fuel pump is going away on you and no longer has the capacity to supply the quantity of fuel needed as the revs increase.
I’m not sure I would be suspect of ignition quite yet. Poke around a bit before you start delving into those components.
The is the way life should be on that Vmax. Hard to give you any real specifics, but falling on its face at higher RPMs, you’re likely either running out of air or fuel most likely. Somebody mentioned air cleaner, might want to take a close look at that thing. If it’s plugged it’ll be running rich and may be stinking like gas at idle or low RPMs, and will fall on his face is the revs it increase. It’s also possible that your fuel pump is going away on you and no longer has the capacity to supply the quantity of fuel needed as the revs increase.
I’m not sure I would be suspect of ignition quite yet. Poke around a bit before you start delving into those components.
user 16790
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the only time I ever experienced losing power at higher rpm's turned out to be an unseated diaphragm in a carb, have you checked your diaphragms
85vmax
Well-Known Member
I've had that similar problem....right at about 6/7 k when the need for fuel increases...It hits like the rev limiter.
I had a large cut/pinhole in the fuel line on the curved horseshoe section that connects to the filter. It was underneath and never saw it.
I had a large cut/pinhole in the fuel line on the curved horseshoe section that connects to the filter. It was underneath and never saw it.
You do NOT need the OEM molded fuel line! Just use about a 7-8" length of braided fuel line, and make a big horseshoe out of it, to connect to the top of the gas tank metal hose, and the fuel filter. The big loop will keep it from kinking, if you use reinforced fuel line. You could use the clear plastic hose w/the white nylon webbing, and then it's easy to keep an eye on your fuel delivery. Use the fuel injection clamps for a 3/8"-1/2" o.d. line, instead of the traditional serrated hose clamps, and save your lines from tiny little cuts you get from those serrated clamps.
Considering that carb work was done recently, I would check up on that. Who did the rebuild? What brand of parts did they use? Did they re-install the factory jets or replace with aftermarket? Has a "jet kit" been installed? The cheap aftermarket jet/rebuild kits have very inconsistent sizing.
The reason I would suspect a carburetor issue is that rpm range is where you are transitioning to full on the main jet and the slide is fully open, or should be. Your symptoms sound like a diaphragm is not sealing properly, main jet is sized incorrectly or float level set incorrectly. Considering there was work done recently, it would be very prudent to double check unless the work was done by a known, good rebuilder/tuner.
The reason I would suspect a carburetor issue is that rpm range is where you are transitioning to full on the main jet and the slide is fully open, or should be. Your symptoms sound like a diaphragm is not sealing properly, main jet is sized incorrectly or float level set incorrectly. Considering there was work done recently, it would be very prudent to double check unless the work was done by a known, good rebuilder/tuner.
Parminio
Well-Known Member
The carb rebuild is more than likely the problem.
Ask the person who rebuilt them if he used the new brass that came with the kits or the original brass that was in the carbs. If he used the new brass, he's screwed your carbs completely up unless his kits were directly from Yamaha, which I'll bet a million dollars I don't have that they're not.
Most aftermarket kits use these ridiculously over sized needle valves for the float assembly. What happens is that they're so big that even when the float drops down and opens up the inlet it's not open enough to move enough gas.
I've got a few old valves around somewhere in my toolbox and I'll hunt them down to take a picture.
If he used any non-Yamaha kit and used the brass provided, that's your problem. Guaranteed.
Ask the person who rebuilt them if he used the new brass that came with the kits or the original brass that was in the carbs. If he used the new brass, he's screwed your carbs completely up unless his kits were directly from Yamaha, which I'll bet a million dollars I don't have that they're not.
Most aftermarket kits use these ridiculously over sized needle valves for the float assembly. What happens is that they're so big that even when the float drops down and opens up the inlet it's not open enough to move enough gas.
I've got a few old valves around somewhere in my toolbox and I'll hunt them down to take a picture.
If he used any non-Yamaha kit and used the brass provided, that's your problem. Guaranteed.
Dannymax, Sean Morley, Captain Kyle, one of those guys is gonna be able to put things right for you. Remove those carburetors and send 'em out.
That's probably what I'll do. Bike is in the shop right now getting new tires.
I found out a few things. The carb "rebuild" was done with an aftermarket kit, but only the soft parts were replaced. All the brass and jets were just "cleaned up." I can verify this as they gave me the bags of old parts, but the brass was still unopened baggies.
Traumahawk
Well-Known Member
I 2nd that. Years ago when I need the carbs on the 07 rebuilt, I sent them to Danny. I know that I could do a good job at rebuilding. I know that Danny can do a BETTER job at rebuilding the carbs.
Was it a K&L kit? I've used their stuff before and I've never-had an issue. I normally buy from a dealer, online though.
I have used K & L kits a good bit. It is the only after market kit I will use
