Need help! Bike is terrible over 4k rpm

[Rosholm]

Hi, I am a new vmax owner from Sweden. Sorry if my English is not perfekt!

I bought the bike a week ago and it run perfekt on the 200km I drove it home. It was a dream! The best bike I ever ridden!

When I got home I cleaned the air filters because they looked really dirty and the crankcase breathing tube vas cracked so I replace it. Now the bike hardly won't rev past 4k at WOT. The idle is perfekt and I can start it without choke every time.
It runs perfekt up to 4k with good power.

The bike has a stage 7 kit and full exhaust. I have bench papers from the previous owner. 115rwhp with a nice curve so the carb settings should be fine.

I have changed the fuelfilter, checked for leaks with startgas and drained the bowls. Everything looked good.

I planning on removing the carbs and doing a ful clean but I don't have a sync tool so I must get me one first.

Any other ideas I can try before cleaning the carbs?

 

[Traumahawk]

First of all welcome to the forum. I wonder if a bit of dirt was knocked into the PAJ1 or even where the air correctors go, when the filters were removed?

I would suggest doing a "Shotgun" and that should help clear out PAJ1 and 2, and other small passages.

Here is a website that details it. http://vmax.lvlhead.com/tips/shotgun.htm

 

[Dragmaxster]

I highly recommend this one
http://www.carbtune.com/

 

[thor_eyerdhal]

Don't trust dyno curve regarding carb settings!
One circuit can be well tuned and another one not...

115 rwhp is not terrific with Stage7 and full exhaust.

If you can always start your engine without choke (in sweden!) , so it is not well tuned, idle setting is way too rich

 

[Dragmaxster]

You would need to take off the jet block from underneath the bowls and clean the 2 jets inside. Also check your floatbowl heights before putting your bowls back on. You can also "bench sync" with a drill bit for syncing.
A few times i have just bench synced and they did not not even need a carb sync.

 

[Hellboy]

Don't trust dyno curve regarding carb settings!
One circuit can be well tuned and another one not...

115 rwhp is not terrific with Stage7 and full exhaust.

If you can always start your engine without choke (in sweden!) , so it is not well tuned, idle setting is way too rich

It is the middle of summer in Sweden, It's not always cold there. That wouldn't be a factor.

If it ran before you cleaned a dirty air filter and not runs up to 4k it sounds like it is too lean and not getting enough fuel to rev high. Cleaning a very dirty air filter would allow much better airflow but the same fuel flow which in turn would create a more lean mixture which could cause your symptoms. Have you actually ridden the bike since the air filter clean? If you just cleaned it and then tried running it with the airbox cover off then my bike does exactly what you are describing, I just wrote about it not long ago. Put the airbox cover back on and try it if that is the case.

Matt

 

[Traumahawk]

It is the middle of summer in Sweden, It's not always cold there. That wouldn't be a factor.

If it ran before you cleaned a dirty air filter and not runs up to 4k it sounds like it is too lean and not getting enough fuel to rev high. Cleaning a very dirty air filter would allow much better airflow but the same fuel flow which in turn would create a more lean mixture which could cause your symptoms. Have you actually ridden the bike since the air filter clean? If you just cleaned it and then tried running it with the airbox cover off then my bike does exactly what you are describing, I just wrote about it not long ago. Put the airbox cover back on and try it if that is the case.

Matt

Its stage 7....so it should have the pod filters and air correctors in the carbs.

 

[Dragmaxster]

What did you clean the filters with? I assume they are individual K&N's and if you used the red K&N filter cleaner and did not let them dry properly it is possible that it has clogged an air jet. What do the plugs look like?
Hope it helps.

 

[Rosholm]

Like you say I have k&n filters and I have driven about 50km after the clean.
Thank you all for all the help. I will do a full carb clean soon and do the bench sync for start and see how it goes after that. I dont like not knowing the carb setup anyway.

 

[sdt354]

+1 to all the above. Also change your fuel filter. Make sure the vacuum line to the MAP sensor is connected and the advance is working. And welcome to the forum.
Steve-o

 

[Hellboy]

Its stage 7....so it should have the pod filters and air correctors in the carbs.

Don't know how I skipped the stage 7 part???

 

[Traumahawk]

Don't know how I skipped the stage 7 part???

LOL....it happens. Just like me copying the wrong plug numbers...

 

[Rosholm]

+1 to all the above. Also change your fuel filter. Make sure the vacuum line to the MAP sensor is connected and the advance is working. And welcome to the forum.
Steve-o

Thanks!
I´ve changed the fuel filter. Where is the map sensor and what do you mean with advance?

 

[Traumahawk]

Carb #2 (which is front left....but its the master carb) has a vacuum line under the "H" that runs to the vacuum advance for the TCI. Make certain that it is still hooked up, and doesnt have cracks....etc.

 

[Rosholm]

Hi again! Here comes an update.

I took of the carbs and cleaned everything good. Did the shotgun and set the af screws 2 1/2 out. Changed plugs. Two of the old ones were a little black and two locked perfect.
Now the bike runs even bettre on low rpms but still stumbles when getting to 4k.
After 6-7k it pulles hard again. Like getting kicked in the back

I have the v-boost of and the needle was at the 4 clip.

Running out of ideas here

 

[tugla]

Forth clip from blunt or pointed end of needle.... Can try dropping needle to lean it out if you mean forth from blunt or top end of needle....

Have you sync carbs on the bike? Any cracks in carb boots . Plugs all good and wires

 

[Rosholm]

Forth from blunt side. The thing is that it runned great with this setting before I cleaned the filters so I dont think its a carb tuning issue.

 

[asherc]

Ha

 

[Rosholm]

I checked that when I had the carbs off and no problem there.

 

[tugla]

check slid movement while its running and slight throttle blimp....can easily get hung up on cover install...all four should be equal..and you have the lottle oring under the diaphragm cover it didnt fall out...

4 th from blunt....and that jet. .mid say pretty rich...just my 2cents...id try three on clip even two..