Vmax fuel pump questions

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Smallz700r

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Hey guys, my 92 vmax coughs at low rpm but really starts cutting out at high rpm, only time it runs decent is when I hold it at about 15% throttle and let it slowly build up! It really starts cutting out if I’m in 5th gear going about 50 mph and hammer throttle…When I turn key on I can hear vboost cycle, but I also hear fuel pump clicking for about 10 seconds or more sometimes… do you think my problems in my coils, fuel pump or carbs?
 

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Parminio

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do you think my problems in my coils, fuel pump or carbs?
Yes.

Could be any of them. Could be something else entirely. You have to investigate each. I would start with pulling the plugs to see what they look like. That can tell you a lot. Make sure to note which plug came from each cylinder so that you know which coil / carb you may have issues with.
 

Smallz700r

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Yes.

Could be any of them. Could be something else entirely. You have to investigate each. I would start with pulling the plugs to see what they look like. That can tell you a lot. Make sure to note which plug came from each cylinder so that you know which coil / carb you may have issues with.
Okay, I replaced all 4 spark plugs with NGK's, but never looked at them as I just figured they needed replacing,... Is the fuel pump a pain to get out of bike? I would just throw some spark plug wires at it, but not sure on what to buy, bikes all stock besides slip ons.
 
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DreamV4

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read manual pump specs. Testing pump takes probably 5 min. w/o removing it. Disconnect hose, attach another one to pump into measuring cup. Connect jumper wire.
 
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MaxMidnight

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Okay, I replaced all 4 spark plugs with NGK's, but never looked at them as I just figured they needed replacing, and new battery for the hell of it.... Is the fuel pump a pain to get out of bike? I would just throw some spark plug wires at it, but not sure on what to buy, bikes all stock besides slip ons.

If you 'throw' parts at the problem then eventually you will strike lucky and find what is causing the issue.
The only down side is the time and money you will need to spend to arrive at that point.

Is this a new problem and if so have you done anything recently to the bike?
Does the problem change if it is on choke?

When it starts to play up can this be reproduced statically (i.e. no load) and is it all cylinders that are similarly affected? If it one or two cylinders then you need to establish which ones they are and identify what is causing the problem.

If it affecting all cylinders then I would suspect it is a fuel/ carb related issue.

Start with the basics; is the fuel tank breather clear and if the air and fuel filters haven't been replaced since the ark last floated, change them.
Whilst you are checking the air filter start the motor and check that the throttle slides all rise at the same time.
If not done recently synchronise the carbs.
Check for kinks or 'soft' fuel hoses which may indicate and internal collapse.
Drain each float chamber into a suitable receptacle and check for crud.

I've not found a specification for how much fuel the pump should deliver so a check to see it is pumping is as much as you can do.
It is possible to dismantle the pump and check that the contacts/ diaphragm and one way valve are all OK.
 

Smallz700r

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If you 'throw' parts at the problem then eventually you will strike lucky and find what is causing the issue.
The only down side is the time and money you will need to spend to arrive at that point.

Is this a new problem and if so have you done anything recently to the bike?
Does the problem change if it is on choke?

When it starts to play up can this be reproduced statically (i.e. no load) and is it all cylinders that are similarly affected? If it one or two cylinders then you need to establish which ones they are and identify what is causing the problem.

If it affecting all cylinders then I would suspect it is a fuel/ carb related issue.

Start with the basics; is the fuel tank breather clear and if the air and fuel filters haven't been replaced since the ark last floated, change them.
Whilst you are checking the air filter start the motor and check that the throttle slides all rise at the same time.
If not done recently synchronise the carbs.
Check for kinks or 'soft' fuel hoses which may indicate and internal collapse.
Drain each float chamber into a suitable receptacle and check for crud.

I've not found a specification for how much fuel the pump should deliver so a check to see it is pumping is as much as you can do.
It is possible to dismantle the pump and check that the contacts/ diaphragm and one way valve are all OK.
Just got home and went for very short ride to see if it ran better with choke on, and it ran substantially better! Actually got to feel the top end power without it cutting in and out as much! Its starts completely cutting out around 8-9k RPM!! But it obviously made it idle higher as well, so that means its the carbs? Just ordered a clymer manual off ebay should be here this week! thanks
 
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patate657

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I found that I had a premature issue with the fuel pump shutting off and wanting me to switch to reserve. With still about a gallon on board....... Which brings up a question. How much gas is still in the tank when you're supposed to switch over?
 

Smallz700r

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If you 'throw' parts at the problem then eventually you will strike lucky and find what is causing the issue.
The only down side is the time and money you will need to spend to arrive at that point.

Is this a new problem and if so have you done anything recently to the bike?
Does the problem change if it is on choke?

When it starts to play up can this be reproduced statically (i.e. no load) and is it all cylinders that are similarly affected? If it one or two cylinders then you need to establish which ones they are and identify what is causing the problem.

If it affecting all cylinders then I would suspect it is a fuel/ carb related issue.

Start with the basics; is the fuel tank breather clear and if the air and fuel filters haven't been replaced since the ark last floated, change them.
Whilst you are checking the air filter start the motor and check that the throttle slides all rise at the same time.
If not done recently synchronise the carbs.
Check for kinks or 'soft' fuel hoses which may indicate and internal collapse.
Drain each float chamber into a suitable receptacle and check for crud.

I've not found a specification for how much fuel the pump should deliver so a check to see it is pumping is as much as you can do.
It is possible to dismantle the pump and check that the contacts/ diaphragm and one way valve are all OK.
Replaced dirty fuel filter with a NAPA one also! Fuel hoses and breather hose seem fine. Spits and sputters a bit around 3-5k RPM and badly over 8k RPM. I drained carb bowls into cups a couple months ago and two of carbs had a bit sediment...
 

Smallz700r

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I found that I had a premature issue with the fuel pump shutting off and wanting me to switch to reserve. With still about a gallon on board....... Which brings up a question. How much gas is still in the tank when you're supposed to switch over?
Not much id say half a gallon to a full gallon. About two months ago I was on the road and was switching to reserve and the bike cut off and died on the side of the road, could it of been because the battery was dead?
 
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Smallz700r

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Bike idles great id say, but at idle, when putting your hand over the right side slip on you can feel the exhaust smacking your hand hard, and the left side is like coughing or choking... No smacks of exhaust to your hand on the left side pipe at all if that even matters....
 

patate657

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Bike idles great id say, but at idle, when putting your hand over the right side slip on you can feel the exhaust smacking your hand hard, and the left side is like coughing or choking... No smacks of exhaust to your hand on the left side pipe at all if that even matters....
Are you running the bike with the air box off. My bike did some wierd $h--t with the air box off.
 

Smallz700r

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Idles great no choke
 

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patate657

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Most people don't even try to read service manual. It is not a case "I read it but couldn't understand", it is a case "I don't want to read it".
I have a few manuals, even one that is pretty good on a Kindle app here on the PC. Very good pictures. But nothings is as good as getting info from you guys that have had hands-on experience. I'll be first to admit it.... :)
 

Smallz700r

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Are you running the bike with the air box off. My bike did some wierd $h--t with the air box off.
Air box is always on, I’m at a loss… I just wish I knew what part was bad, might just take it in to local shop for diagnosis…
 

VMAXXIMUM

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I found that I had a premature issue with the fuel pump shutting off and wanting me to switch to reserve. With still about a gallon on board....... Which brings up a question. How much gas is still in the tank when you're supposed to switch over?
The light comes on when you have about .8 of a gallon remaining.
 

02GF74

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at idle, when putting your hand over the right side slip on you can feel the exhaust smacking your hand hard, and the left side is like coughing or choking... No smacks of exhaust to your hand on the left side pipe at all if that even matters....
I'd say it does matter, if carbs are balanced and engine is running correctly, why would one pair of cylinders behave differently?

Probably can rule out any fuel pump problem since it supplies petrol to all 4 cylinders.

Have you checked float levels?
Also pull off a lead to plug, fit a plug if you have a spare or remove from the engine and see how good the spark is and if consistent.

Somebody may have asked this but had it started doing this recently, if so, wad anything changed?
Has the bike been standing unused for a few months?

Checked the plungers for enrichment circuit return when choke is off.
 

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