V-Boost rpm shift?!

[Matt-Max]

Update: checked the cylinders at idle by fondling the exhaust gases and by disconnecting ht caps from each in turn. No issues there, so I'm thinking so far so good, but a bit disconcerted by the occasional slightly louder pop through the exhaust that didn't seem to follow any pattern. Ah well, thinks me so I ride it to work...

 

[Matt-Max]

So now its blowing water but I'm unconvinced that its just coming from the breather pipe. Oh my days... could be time for an overhaul?! Is there anyone good in the North West UK?

 

[Matt-Max]

UPDATE: - Stripped off the top cover, air box etc to see if I could start piecing this one together. Having been told that there was no way the V-boost could move I figured I would look at the actual mechanism directly against the rpm. Glad to say that I wasn't just imagining it, movement started not at 5250 but after 6 with full opening coming not at 6, but just after 7. Sad to say that didn't make much difference, but then...

Looked at the carbs themselves - butterflies all operating correctly, BUT piston and needle on #3 no movement. Don't get me wrong it slides, but not of its own accord! I have to physically move it and there is no response from it to engine demand. I have removed the HT lead to the spark on the same cylinder and the lump will still run, but only just and it needs a little extra to keep it there.

Interestingly this is the cylinder which controls the V-boost signal - so fix one... hopefully fix 'em all.

SO now I have a new conundrum, why is there no life in the carb and how does that link to the HT pulse which controls the V-boost!? Is it spark, coil, cap, or carb/fuelling, valves, gasket...

ANYONE got any quick checks I can run to help eliminate problems?

 

[Fire-medic]

I don't recall what you've done to this point. If you already did it just say-so.

Did you check the slide diaphragm? Is the ribbed edge (for comfort!) of the diaphragm in the recess of the carb body properly? I've disassembled carbs before and found a careless re-assembly crimped the diaphragm out-of-place. Also, carefully-inspect the diaphragm for any holes, including rips, tears, or pinholes. Hold it up-to a light and carefully stretch the diaphragm to see if you spot any perforations.

Have you checked the intake gaskets and donuts on that cyl for leaks, by spraying some starting fluid on the airbox donuts, the carbs to VBoost manifold, and the VBoost to cyl head attachment points? Each has a gasket or a rubber piece/donut which could be interfering with your vacuum to that cyl.

Popping back is often a sign of a lean condition. A lean condition can be caused by a clogged pilot jet, or a poorly-adjusted air bleed screw, or the same, having a torn o-ring on it. The complete air bleed assembly is inexpensive, I keep a few on-hand. Part #22




When you spritz water on that exhaust header, the water should immediately vaporize. If it sizzles and drips, you have a poorly-firing cyl. Of course if you have a thermal sensing IR gun, you can get actual temperatures of each cyl, and all four should be pretty-close to one another. One or more >100 degrees difference, there's a problem. Something's causing that cyl to not fire consistently, the large temperature disparity of the exhaust header pipes is proof of that.

Checking the plugs, move that spark plug to another location, see what happens. If the 'problem' moves with the component, that's the problem component. You could do the same thing with coil wires & caps. If the plug wire conductor is green-colored, trim it back until you reach a bright, shiny metal conductor.

Just so we're speaking of the same cylinder:

 

[Matt-Max]

@Fire-medic thanks for the reply and the diagram! I have literally just returned from another poke about and checked the diaphragms on each. Three were working fine, but of those one had limited travel, inspection revealed two in good order, the limited travel was down to a carelessly refitted spring that was bent over in the head as it was off-centre. Repositioned and back in now and that is all fine.

The diaphragm in #4 is in bits. It's floating about and I'll pop a pic on soon so that folk can see and use it to help diagnose in future.

I'm confident that replacing this will go a long way to solving things, it will stop the lean run and pop back, it should shift the cylinder back to playing ball and in turn re align the V-boost... time will tell. I will try your tip for the leak checks too, as these things tend to be a combination of problems rather than just one!

Cheers chap!

 

[Matt-Max]

Photo story... add your own captions...

 

[Matt-Max]

 

[Matt-Max]

 

[Matt-Max]

QUESTION - Can I just put it all back together as it should be, or do I need to order a new assembly?

 

[Vinmax]

UPDATE: - Stripped off the top cover, air box etc to see if I could start piecing this one together. Having been told that there was no way the V-boost could move I figured I would look at the actual mechanism directly against the rpm. Glad to say that I wasn't just imagining it, movement started not at 5250 but after 6 with full opening coming not at 6, but just after 7. Sad to say that didn't make much difference, but then...

Looked at the carbs themselves - butterflies all operating correctly, BUT piston and needle on #3 no movement. Don't get me wrong it slides, but not of its own accord! I have to physically move it and there is no response from it to engine demand. I have removed the HT lead to the spark on the same cylinder and the lump will still run, but only just and it needs a little extra to keep it there.

Interestingly this is the cylinder which controls the V-boost signal - so fix one... hopefully fix 'em all.

SO now I have a new conundrum, why is there no life in the carb and how does that link to the HT pulse which controls the V-boost!? Is it spark, coil, cap, or carb/fuelling, valves, gasket...

ANYONE got any quick checks I can run to help eliminate problems?

*just throwing this in there really quick;
the Vboost in stock configuration is not supposed to come on at 5250 as you've stated. It actually starts it's actuation at 5750 so that by 6000 rpm it's opening. And it does not fully open until 8000 rpm;


V-Boost
V-Boost is a system that opens butterfly valves in the intake manifold between the 1st and 2nd and between the 3rd and 4th cylinders starting from 5,750 rpm. The valves are opened gradually to match the rising engine speed with a signal provided by the ignition system. The valves are at the full open position at 8,000 rpm. A small black box sends a computed signal to a servo motor that pulls a wire to open the butterfly valves. The V-Boost system adds 10 percent to the top power rating of the base engine.


Now with that being said, my gut feeling is that you don't really have any 'Vboost' problem at all. What I think you have going on is that your bike has a bad diaphram as you show in your pictures. You're slide is not opening properly due to the diaphram becoming disattached and you are running on only 3 cylinders once in a while. It may make it seem like it does not want to pull until higher up the rpm range.

My suggestion is to fix the diaphram first. Don't just put that mess back together because it's not going to operate properly. Fix it properly so that the engine's vacuum will pulll the slide as it was designed. Then I think you'll see that all is working properly Vboost-wise.
Once you reassemble, pull off the top airbox cover and look inside with the engine running. When you try to rev it a bit, you should see all 4 slides pull back a bit. They will pulll back evenly showing you that they all are working. The bike will not run well without the airbox lid on (if you're setup with the stock airbox). But you're doing this just to check for proper carb slide actuation.
If all looks good, then put the lid back on and go for a ride to verify that all feels normal and you have full power again, and feel the Vboost start to kick in at 6000 rpm (not 5250 by the way).



Vinnie

 

[Fire-medic]

That 'tophat' piece, the cylinder the spring fits-into/through, is part of a fastened-together slide ass'y. Buy a new diaphragm/slide ass'y. You might try supergluing things back-together, but I suspect it won't last.


Part #9
Diaphragm Assy.

1FK-14940-00-00 1FK-14940-09-00

$160.99
$124.88

https://www.ronayers.com/oemparts/a/yam/500456a5f8700209bc79313a/carburetor
I know you are in the U.K. Pricing for purposes of comparison.

 

[Matt-Max]

@Fire-medic thanks again for the excellent input and for putting me right on cylinder numbers! I'm hoping that I got the V-boost signal wrong too.. But, perhaps the lack of power until full kick in comes down in part to the inefficiency of this cylinder at the moment.

I'm currently fighting through the parts systems trying to find the right part for a Canadian 3JPR-010, but all I get is the 3JPM - do we have any number fans who can help? I need a part number and don't want to screw up as it seems to price in at £130! Can anyone help? Its a 96/97 Canadian Import.

I have 1FK1494009 as the new part number, replacing FK-14940-00. Anyone know how much it matters and how different the parts were across the variants?

 

[Fire-medic]

@Fire-medic thanks again for the excellent input and for putting me right on cylinder numbers! I'm hoping that I got the V-boost signal wrong too.. But, perhaps the lack of power until full kick in comes down in part to the inefficiency of this cylinder at the moment.

I'm currently fighting through the parts systems trying to find the right part for a Canadian 3JPR-010, but all I get is the 3JPM - do we have any number fans who can help? I need a part number and don't want to screw up as it seems to price in at £130! Can anyone help? Its a 96/97 Canadian Import.

I have 1FK1494009 as the new part number, replacing FK-14940-00. Anyone know how much it matters and how different the parts were across the variants?

ASSEMBLIES WHERE 1FK-14940-09-00 IS USED

• 1997 V-MAX 1200 (VMX12J) - Carburetor
• 1997 V-MAX 1200 (VMX12JC) - Carburetor
• 2002 V-MAX (VMX1200P) - Carburetor
• 2002 V-MAX (VMX1200PC) - Carburetor
• 2003 V-MAX (VMX1200R) - Carburetor
• 2003 V-MAX (VMX1200RC) - Carburetor
• 2003 V-MAX (VMX12R) - Carburetor
• 2003 V-MAX (VMX12RC) - Carburetor

You have to include the hyphens to use the search function on the website. You see there are also other things left-off: -00

https://www.ronayers.com/oemparts/partsearch/yamaha_motorcycle?partsearch=1fk-14940-09
I'm sure dannymax can confirm, if it's a full-power model, and I believe the Canadian models are, the diaphragms are going to be the same between Canadian and USA models.

 

[Matt-Max]

ASSEMBLIES WHERE 1FK-14940-09-00 IS USED

• 1997 V-MAX 1200 (VMX12J) - Carburetor
• 1997 V-MAX 1200 (VMX12JC) - Carburetor
• 2002 V-MAX (VMX1200P) - Carburetor
• 2002 V-MAX (VMX1200PC) - Carburetor
• 2003 V-MAX (VMX1200R) - Carburetor
• 2003 V-MAX (VMX1200RC) - Carburetor
• 2003 V-MAX (VMX12R) - Carburetor
• 2003 V-MAX (VMX12RC) - Carburetor

You have to include the hyphens to use the search function on the website. You see there are also other things left-off: -00

https://www.ronayers.com/oemparts/partsearch/yamaha_motorcycle?partsearch=1fk-14940-09
I'm sure dannymax can confirm, if it's a full-power model, and I believe the Canadian models are, the diaphragms are going to be the same between Canadian and USA models.

Excellent - many thanks. I've got to the bottom of the water issue as well now. I've taken the cap off whilst running to see if there was any sign of movement and circulation. Big no and steam rising (not just from clumsy spills) and it seems to be from the thermostat housing. I'm going to assume that this means the thermostat is gone rather than the pump itself as I presume that takes drive off the engine and would make an awful noise if it had come disengaged. I might have to check the other posts on that one... if it's not one thing...


Just checked and there's loads of good stuff on that, so coolant flush and thermostat replacement, impeller check and then I can look at the running issues. Great excuse to be in the garage!

 

[Fire-medic]

Search (on here) for low-cost replacements for the OEM thermostat, there's a Nissan part # for that. Same for the fan thermocouple.

 

[Matt-Max]

Hello All.

Ok - so diaphragm replaced. Thermostat done while I was on it to tackle the water issue. All rebuilt and back out for a quick zap on a warmed up engine.

No furious pouring of water, but maybe one or two drops just clearing out - I should have been more critical of the cleaning. But the V-Boost is still only really giving me that surging kick up the ass at 7,000rpm. I'm sure it used to feel like a wild cat at 6k. Opinions please - where does yours suddenly start ripping your arms off?