Vmax 1200 -98 Misfires

[SwedishVmax98]

Hi!

I bought this bike a month ago.

Now when the weather is hotter and the engine gets warm it starts to misfire on idle and when I drive.

It will also stall when I’m driving and stopping at a redlight, it always starts easy and I can drive further.

I have removed the carbs and dissembled them all and got them in a ultrasonic wash.

Assembled them with a rebuild kit including new jets and gaskets, needle and everything.

Once I started it there was no difference then before I did the carbs.

I have changed the spark plugs after this and got the carbs calibrated today, they were pretty much off each other.

The bike has been driven 30 000km.

I noticed today that the clip on the needle is on the third trace, but underneath the needle when I take it out, someone has placed a washer where the needle sits to the bottom in the plastic thing that moves with vacuum, is that right?

I post some picture and wants help to go further.

Can I measure the spark plug cable and coils?

Have a nice day from Sweden!

 

[Fire-medic]

Post the year of your bike under your avatar, that helps us, and will help you. From your screen name, it probably is a 1998, but put it below your avatar to help us help you. There were changes to the bike by year, and many components can be swapped among the 1985-2007 production run. For instance the 40mm front end downtubes/triple tree can be replaced by the 1993-2007 front end (43mm downtubes/triple-tree), but you also need to swap the 1993-2007 front brake discs and calipers. Other than that, it's an easy way to get a stiffer front end with better braking (298mm rotors, 4 pistons/caliper). The 1985-1992 has 2 pistons/caliper and 282mm rotors.

The flat washer on the needle is a way to richen the mixture slightly, and works on the lower rpm's.

What type of brass jets did you use? Where was the source from? The 'no-name' jet kits from ebay are not a good investment. OEM jets are preferred to avoid issues with poorly sized and machined 'no-name' jets. The K & L kits are good quality kits.



Brass jets are usually only in need of replacement if the prior owner broke-off part of the jet trying to remove it, like the pilot jet in the jet block, which is tiny. It's easy to break off one side of the head of the jet especially if you use a poorly-fitting screwdriver, and someone before you over-tightened the jet. You never know what a prior owner did, trying to get a sense of what may have been done, you could get a set of drill bits, and compare what's in your carbs with what new jets measure, via a 'go' or 'no-go' measurement.

Here is the factory manual. You have to read it from beginning to end to see the layout. The first ~64pp. are supplements for different years, then the full-service part starts. Be sure to read the Appendix, as it has torque values, cable routing, and more. Save a copy for your computer and print out one to put in a folder in your work area.

https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf

Ignition coil values.

Unscrew your spark plug wires from their caps, and where they insert into the ignition coils. See if there is any green corrosion on the spark plug wires at either end. If you find some, cut-back the spark plug wire about 1/4 inch until you have shiny wores, then clean any of the green corrosion off the spark plug cap or off the ignition coil where the wire inserts. Then screw it all together.

Take a careful look at the spark plug wires for cracks where the spark could go to ground by the spark jumping to the motor/cylinder head. Do an observation at night, in a dark area, and you can see the sparks going to ground if that's the problem.

That should get you started.

 

[99YAMAHAVMAX]

Yes you can measure the ohms of the coils and should be 3.0
From my experience most of them will crack and lose fire after getting too hot
I changed to a cop kit and that solved my problem-lots cheaper than trying to buy another coil or removing one and trying to tape it up.

 

[SwedishVmax98]

Hello!

Thanks for your replies.

I've checked the coils for cracks and did not find, also cutback the wires since there was a little green in them in the end towards the coils.

Measured up the coils and cables, the all leave the same value so they probably OK.

I measured the valve clearence and they were all in spec, 0.10mm for the intake valves and 0.25mm for the exhausts.

I also checked the timing between camshafts and crankshaft and that was fine also.

I checked the compression, and thats fine also and the same to all cylinders.

Ive noticed that when i open and close the V-boost the engine runs smoother for a while so now im thinking something with the boost does not close as it should.

I found a thing i think is something to do with alarm, is this correct?

Have a nice day!

 

[SwedishVmax98]

Yes you can measure the ohms of the coils and should be 3.0
From my experience most of them will crack and lose fire after getting too hot
I changed to a cop kit and that solved my problem-lots cheaper than trying to buy another coil or removing one and trying to tape it up.

Whats a cop kit?

 

[SwedishVmax98]

About the jets, i thinks the rebuild kit that came with the bike is some cheap noname kit, so i never changed the jets, just cleaned them with ultrasonic wash and made sure they are open.

 

[99YAMAHAVMAX]

Whats a cop kit?

http://www.exactrep.com/acatalog/212.html#SID=28

 

[SwedishVmax98]

Thank for your respond!

But what does the cop kit do?

I found a box that says Predator on it and lots of extra wires, what is this?

I saw it got something to do with the v-boost since the original wires were cut off and goes to this.

 

[Fire-medic]

Predator:
Probably a mechanism to allow you to switch between normal VBoost operation, and then switching to open butterflies all the time, or opening at a lower rpm. Have you found a 3-way switch on the left scoop, or the plastic shields by the steering head?

A coil-over-plug set replaces the traditional 4 ignition coils. They really don't do anything 'better' than a properly-operating set of OEM coils. What they are is easier to replace should an ignition coil fail. The coils behind the steering head are a pain to remove/replace.




Here's a schematic to help you deduce what's been changed from OEM.

 

[SwedishVmax98]

Thanks for your reply!

Where you describe I have a 2 way switch, and when I flip it the vboost opens so I guess you are right about what it does.

At this point I’m just trying to get the bike run smooth.

Today I used a stroboscope just to get a feeling for how the sparks are coming since it backfires.
I noticed the rear right cylinder had no spark, switches places on rear coils, tested another wire, checked the wiring diagram to understand how 3 cyl can have spark and one dead, draw air-wires from the ignition box, no difference, THEN i tried change the spark plug

Now it runs on all 4 but blacksmokes on idle, it does not matter how I adjust the mixture screw..

Any tip of a good rebuild kit for the carbs including the diaphragms?

 

[99YAMAHAVMAX]

Thanks for your reply!

Where you describe I have a 2 way switch, and when I flip it the vboost opens so I guess you are right about what it does.

At this point I’m just trying to get the bike run smooth.

Today I used a stroboscope just to get a feeling for how the sparks are coming since it backfires.
I noticed the rear right cylinder had no spark, switches places on rear coils, tested another wire, checked the wiring diagram to understand how 3 cyl can have spark and one dead, draw air-wires from the ignition box, no difference, THEN i tried change the spark plug

Now it runs on all 4 but blacksmokes on idle, it does not matter how I adjust the mixture screw..

Any tip of a good rebuild kit for the carbs including the diaphragms?

Try Exactrep in the UK.

 

[Fire-medic]

it runs on all 4 but blacksmokes on idle, it does not matter how I adjust the mixture screw..

It doesn't smoke under acceleration though? You have some smoke at idle? And no matter on how you adjust the pilot idle screws below the diaphragm caps, it still smokes? Is it smoking on one side or both sides?

You did the carburetors, or did a shop do it?

You changed a single sparkplug on the #3 cyl (RR side) and then that cyl stopped smoking, or not firing? So you found a bad plug?

One of the things that can cause smoking is worn valve seals or valve guides. The seals are relatively inexpensive. The valve guides are not.
Seal:
Seal, Valve Stem

51Y-12119-00-00

Retail Price: $5.99

Your Price: $4.54
https://www.ronayers.com/oemparts/a/yam/50045c0cf8700209bc7942ec/valve
Valve guide:
Guide, Valve 1

30X-11133-10-00

Retail Price: $75.99

Your Price: $67.30
https://www.ronayers.com/oemparts/a/yam/50045c0cf8700209bc7942ea/cylinder-head
Check the clearances of the valve guides before changing them as they are expensive.


https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf

Honestly, I think I'd take another attempt at disassembly, ultrasonic cleaning, and adjusting the carburetors before I thought about removing the cyl heads to check the valve seals and valve guides.

Use some strong wire like guitar strings to poke-out all the passageways in the carburetors. Then blow them out.

I have a thought, have you verified the proper operation of the starting enrichment lever and the connections to both the left and right banks of carburetors? If one or more of the starting enrichment pistons is stuck in the 'open' or on position, that side could be getting more fuel than it should be, and would probably be easiest to have a negative effect upon idle. Perhaps that's why you see smoking at idle.

Here's an example of the starting enrichment lever finger-followers at one enrichment piston not properly adjusted. The enrichment piston on the left is fully-open/on; the upper-right one is stuck nearly-closed. Note the bottom one is also opened/on.



The example I showed is for an enrichment piston being nearly-closed, and not opening to provide enrichment for that engine cylinder. In that case, there would probably be an issue in starting because not all cylinders were enriched. The problem I was describing is for an enrichment piston (one or more) being stuck open/on and not closed as in the picture. You get the idea.

 

[SwedishVmax98]

It doesn't smoke under acceleration though? You have some smoke at idle? And no matter on how you adjust the pilot idle screws below the diaphragm caps, it still smokes? Is it smoking on one side or both sides?

You did the carburetors, or did a shop do it?

You changed a single sparkplug on the #3 cyl (RR side) and then that cyl stopped smoking, or not firing? So you found a bad plug?

One of the things that can cause smoking is worn valve seals or valve guides. The seals are relatively inexpensive. The valve guides are not.
Seal:
Seal, Valve Stem

51Y-12119-00-00

Retail Price: $5.99

Your Price: $4.54
https://www.ronayers.com/oemparts/a/yam/50045c0cf8700209bc7942ec/valve
Valve guide:
Guide, Valve 1

30X-11133-10-00

Retail Price: $75.99

Your Price: $67.30
https://www.ronayers.com/oemparts/a/yam/50045c0cf8700209bc7942ea/cylinder-head
Check the clearances of the valve guides before changing them as they are expensive.

View attachment 89871
https://dn790009.ca.archive.org/0/i...ice-manual/yamahavmaxvmx12-service-manual.pdf
View attachment 89872
Honestly, I think I'd take another attempt at disassembly, ultrasonic cleaning, and adjusting the carburetors before I thought about removing the cyl heads to check the valve seals and valve guides.

Use some strong wire like guitar strings to poke-out all the passageways in the carburetors. Then blow them out.

I have a thought, have you verified the proper operation of the starting enrichment lever and the connections to both the left and right banks of carburetors? If one or more of the starting enrichment pistons is stuck in the 'open' or on position, that side could be getting more fuel than it should be, and would probably be easiest to have a negative effect upon idle. Perhaps that's why you see smoking at idle.

Here's an example of the starting enrichment lever finger-followers at one enrichment piston not properly adjusted. The enrichment piston on the left is fully-open/on; the upper-right one is stuck nearly-closed. Note the bottom one is also opened/on.

View attachment 89873View attachment 89874

The example I showed is for an enrichment piston being nearly-closed, and not opening to provide enrichment for that engine cylinder. In that case, there would probably be an issue in starting because not all cylinders were enriched. The problem I was describing is for an enrichment piston (one or more) being stuck open/on and not closed as in the picture. You get the idea.

Thanks for your reply and good thoughts!

The plug RR just happend to die, and it took a few hours before I noticed that.

So now I got spark on all cylinders.

It blacksmokes from both exhaust, just on idle and when I rev it up when I stand still, I can’t see any smoke while riding if I look back.

I can’t get it to stop smoke on idle by adjusting the mixture screw under the diaphragms.

I’m now going to my bike to take out the needles and adjusting the clips from #3 to to #1 just to see if it smokes less and I can get difference by adjusting the idle mixture screws.

I also going to check proper adjustments for the choke levers.

Have a nice day!

 

[SwedishVmax98]

Bor i changed the needle clip to pos 1, so the needle is as low as possible.

Now it don’t smokes on idle.

At first it started I had no spark right front, changed the plug and it has spark, by that time right rear stops to spark, changed the wire to a loose and it starts to sparks.

I think there’s a problem in the ignition unit that does not want to spark all 4?

Now with a loose wire to rear right it has spark but very inconsistent.