misfire question?

[cjmeg]

Greetings.
I have an '85 Vmax, with a '96 engine, kerker 4-2-1 exhaust (I think), and Stage 7 kit with alloy tubes replacing the V-boost.
It starts easy, runs smooth, pulls fantastically through the revs and gears.
However, if I gun it hard, after it pulls like a freight train and I back it off at (around ) the speed limit, there is a (huge) flat spot when I go to put the power down again. This goes away after a short while, and is fine if I open it up again immediately.
I have changed the fuel filter, checked the fuel tank vent (OK).
Fuel lines are a soft grey rubber (stock I think).
I am suspecting the fuel pump, which operates, but as I have read here that does not mean a lot.
If I ride quietly, no issue at all.

I have waited 10 years for a V-max, and well worth the wait!
Solder wire fix was essential, as well as the earth wire mod.
15w oil and no air in the forks help, but new (progressive?) springs are next
Many thanks for the heads up in those areas..
Help? :ummm:

 

[maleko89]

Welcome!

When's the last time you sync'd your carbs?

 

[cjmeg]

Welcome!

When's the last time you sync'd your carbs?

Greetings Mark.

I have only had it for 2 months. It was owned for a long time by a Yamaha dealership, then 2 private owners.
The last one, a friend of mine, had the original engine throw a rod, so he had a 14,000mile US engine fitted and tuned, but then who knows if they had the talent to tune a VMax with no Vboost?
It starts and runs beautifully apart from this problem.
I get approx 40-45mpg on highway (180-200 km to tank)
It took me a week to work out there was no Vboost anymore- the trick was the white plug under the left sidecover was hanging in thin air . :eusa_dance:
Further research showed no butterflies, servo motor, straight alloy tubes instead.
Airbox is stock with the Y removed, PO said ran too rich with Y on..

Worth looking at syncing the carbs, Mark?

 

[maleko89]

Definitely. Since you don't have vboost you'll need something to set vacuum at the intake side of the carbs.

 

[cjmeg]

Another run tonight has me thinking..
I pulled the fuel pump down last week, after testing externally and seeing poor flow.
Diaphragm is perished but intact, but both non-return valves weren't seated properly.
Re-seated them, and fuel pump tone changed considerably, went quieter almost instantly. Output was much better also.
After a 5 minute ride, fuel pump was noisy again, flow bad again.

Riding tonight, only 2 deg. Bike loves that temp I think!

If I ride quietly, keep under 65mph the bike is smooth as silk.
If I push it hard, it misfires afterwards (but not during)
Or if I sit on over 65mph, it misfires. Open it up, fine.
Stop and idle for 10 seconds, and ride quietly no misfiring at all.

I wonder: if the fuel pump can't keep up, it would starve the front carbs first?
If so, the rear 2 would feed the animal, but not well unless opened up?

I am going to try a fuel pump, and see how I go.

Carb tune and dyno next month or 2 hopefully..

 

[cjmeg]

Well that will do it!
Replaced the stock fuel pump, with Facet Electronic pump (#FPX013).
The $#$@ thing I found out after buying it needed to be fitted vertically
All this because I didn't want to spend $400 on an OEM one :bang head:
Having said that, now it works properly!
Wheel spin in 1st, 2nd and 3rd (it is wet tonight), no hesitation anymore after winding it out!
Now all I need to do is fabricate a new coolant overflow, and mount the pump properly.
Will post some photos of the conversion..
Dyno next! :eusa_dance:

 

[cjmeg]

Arghh! :bang head::bang head::bang head:
Rode it yesterday, and worse than ever!
Road was wet, and through a corner when it misfired, I lost traction at 100km/hr, which was NOT fun.
So, did the peashooter and the shotgun this morning, finding lotsa rubbish as I went.
Also found the #3 slide was jamming (polished with 2000 grit wet/dry)

The #3 diaphragm is very thin around the edge (non-hardening gasket goo will hold it for now)
And the #3 mixture screw had no o ring.
That being said, the #2 had 2 o rings, so there you go!
Now I have a much more civilized machine, so we will see how we go next big run (have 3 kids at home today)
Guys, your various posts on how to are invaluable!
Stock fuel pump back in for now

QUESTION: with a Stage 7 kit, v-boost replaced with straight tubes, I know I can't balance all the carbs, but can I balance them left to right??

 

[Neil-3446]

With straight tubes you have to measure at the intake side of the carbs (above).

Flow master or flow meter makes the tool...maybe???

Mark can tell you for sure, most keep the stock vboost tubes for this very reason.

 

[cjmeg]

Know the tool: have a Morgan Carbtune though.
Will be buying other tool today.
Thanks Neil

 

[Neil-3446]

Know the tool: have a Morgan Carbtune though.
Will be buying other tool today.
Thanks Neil

Carbtune is a great tool...have one myself.

Just wont do what you need with open vboost or stage 7.

Morgan takes the reading below the carbs, you need something that reads on the intake (above) side.

What is your mixture????

Keep us posted!!!

Neil

 

[cjmeg]

Mixture screws out 3.5 turns,
Needles suggest Stage 7 kit through it.(get skinny at the ends - last 1/2")
The jets under the diaphragms are #150, don't know mains yet (won't pull carbs off until I know I can balance them)
Love this bike: worth a 10 year wait!
Great off the lights in the wet: wheelspin in 1st, short shift to wheelspin in second, then third. Fun,fun,fun :eusa_dance:
Just need to get on top of the fuel thing.
Looking at the 390 Holley conversion makes me think....
SLAP! Just ride it idiot!

 

[cjmeg]

Got my carb sync tool yesterday, and after 15 minutes, I have a much smoother animal!!
There was no vacuum of note in the #1 carb, left and right were out a bit.
(Only needed one in the end- they are calibrated then used each time)

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&viewitem=&item=380054025001


So to sum up: shotgun and peashooter, followed by a carb sync (thanks Mark!), gives me a new machine!
I must be getting used to it, as I now notice the lack of performance a Stage 7 kit with open tubes (no Vboost) gives in the bottom end..
Is it wrong to want more power?? :rofl_200:
Thanks for your help, peoples. Now much less scared of the Vmax carbies..

 

[cjmeg]

I have officially had enough :bang head::bang head:
How much is fuel injection again?
Thought I'd do the right thing and put the carb vent tubes back on that I took off when I cleaned and balnced the carbs.
Big mistake: instant return to misfiring :bang head::bang head:
Took them off again on the side of the road (don't ask how), bike fixed again.
You've gotta be kidding me.
Maybe the air correctors in the stage 7 kit do something different.
Either way, I cannot believe that the vent hoses would cause this :bang head::bang head:
Thought I would continue to share the story anyhow :rofl_200:

 

[MONTREALMAX]

What happened ???

It is like have the last ten pages ripped out of a good book.....

 

[cjmeg]

What happened ???

It is like have the last ten pages ripped out of a good book.....

Reading through the post you will see another greenhorn diagnosing and re (miss) diagnosing the problem.

Ultimately, the drama was the fact that this machine has a Dynajet Stage 7 kit in it, complete with v-boost completely removed, and air corrector jets fitted, so that (I believe) you don't need those carb vent tubes anymore.

(The only bit of the Stage 7) not done is the retaining of the stock airbox (no pod filters).

Anyhow, the misfire was caused by the carb vent tubes being left on.
When you gace it a fistful, it would go for it, but when you settled down, it would behave like you had fuel starvation.

Threw the vent hoses away - bewtiful bike, smooth as silk (for a feral gorilla anyhow!)

Now it's at the dyno, so we'll see how we go from here.....

 

[ipsteeler]

Have you figured out what is going on yet?
I have a stock V-Max with a 4-2 Kerker echaust and a UNI filter and i am having the same problem.
After a run it wouold seem like it is misfiring for about 30sec to 1min and then fine again.
It was happening more often before but it seem's like the more i ride it the less it is cutting out.
I would like to know what is hapening with your's so i can start a diagnosis on mine!

 

[cjmeg]

My problem (as I've said) was solved primarily by removing the four carb vent tubes (the big tubes that mount on tops of the carbs, and end up in front of the fuel tank.
The shotgun and peashooter certainly helped smoothness, and I did have a dodgy carb diaphragm also.
Balancing carbs also helped a lot (thanks Mark!)
ALSO: STAY AWAY FROM FUEL WITH ETHANOL IN IT! (Why my diaphragm was ordinary I think)

 

[Shuriken]

My problem (as I've said) was solved primarily by removing the four carb vent tubes (the big tubes that mount on tops of the carbs, and end up in front of the fuel tank.
The shotgun and peashooter certainly helped smoothness, and I did have a dodgy carb diaphragm also.
Balancing carbs also helped a lot (thanks Mark!)
ALSO: STAY AWAY FROM FUEL WITH ETHANOL IN IT! (Why my diaphragm was ordinary I think)

Not sure I'm following why removing the vent tubes would have solved your problem...

 

[cjmeg]

Not sure I'm following why removing the vent tubes would have solved your problem...

I'm not sure either, but having done all the other stuff, including taking them off, I put the vent hoses back on thinking "well they probably should be there". Within 5km my $#$%#$%# misfire was back, so on the side of the road I pulled them off, and it's been fine ever since.

Of all the dumb things, it would be good to know why.
Dynojet instructions don't mention it, I'm just glad the bike is behaving.
Now if only I could get it back from the dyno guy (2 weeks and counting)

 

[maleko89]

I missed you had stage 7. You don't use vent tubes with those unless you use velocity stacks.