Terible rough or lumpy from 1500-2000 rpm. Please help video inside

[mvvette97]

I'm not sure what is wrong with my vmax. I have adjusted the valves, cleaned the carbs, synced the carbs, new plugs and wires. It will idle just fine and runs above 2000RPM perfect. Now driving around town is just horrible because it wants to run so rough and lumpy from 1500-2000 rpm. Once past that it will smooth out and run fine or below that is good also. It doesn't have any bog just gets super rough and lumpy sounding. Tried adjusting the mixtures screws and it helped some but not alot. Here is a video you can hear it off idle.

http://www.youtube.com/watch?v=aOZpnLj7z_M&feature=channel_video_title

 

[Rand-5107]

Is your v-boost cycling? Could it be stuck in the open position?

 

[mvvette97]

yea it cycles fine. I'm not going to say it couldn't be open a little but I really don't think it is. I have had this problem for years with this bike.

 

[SpecOps13]

I sync'd both of my VMax's at 3,000 rpm and let the idle fall where it may. Both run very smoothly in the 2,500 and up range. Both will stutter between 1,500 and some point between 2,000 and 2,500 rpms, if I run through that area very slowly.. I chalk it up to the nature of the carbs. I don't use that rpm range where the stutter is very often and usually it's time for a downshift to keep the Revs up over 2,000..:confused2: Holding a steady throttle under load at 2,000 there's just a faint stumble...

 

[mvvette97]

I pulled the carbs apart again to to have another look. The only thing I see is that those small diaphrams on the side of the carbs look really dry. What are they for?

 

[SpecOps13]

By small diaphragms, you may be talking about the circuit that richens the deceleration mixture. Keeps the bike from back firing on decel....:ummm:

 

[mvvette97]

By small diaphragms, you may be talking about the circuit that richens the deceleration mixture. Keeps the bike from back firing on decel....:ummm:

yes i think that's what they are for. They don't look the best honestly. Also this may sound stupid on my part but where is the pilot jet? I have the fuel bowls off and see the main but not the pilot.

 

[alorio1]

coaster enricher is what I have always heard people refer to them as........

 

[KJShover]

I'm just not hearing what you are. To me it sounds normal.
Your idle is not unlike mine or other's out there.

Does it when your powering through that rpm range? Or just when you slowly have the rpm's in that range.

Cause what I'm thinking is if your giving it a slow throttle increase or holding it in that area, the needle valve and a/f screws meet and overlap and give you a rich condition down low.

As you give it more throttle the a/f is a little less important as the slides start to open and the needle valves take over until they meet with the main jet. Then as even more throttle is given, the a/f, needle jet and mains will all overlap to meet the needs of the motor.


http://www.youtube.com/watch?v=VDFReKb_Vdk

 

[SpecOps13]

Look here for a parts breakdown. The jet goes up into the block like it's pointed in the picture #7, then a cover #6 screws over the opening....Had to find the picture... Find more in the stickies of the carb section, written by naughtyG.

Exactly my thoughts KJ....

 

[KJShover]

Also this may sound stupid on my part but where is the pilot jet? I have the fuel bowls off and see the main but not the pilot.

PAJ2 are under the slides. PAJ1 are at the top of each carb.

The #3 is your PAJ2 (view after popping the covers and removing the slide.) In the second picture, the green arrow is the PAJ1. If you have a stg7 or a Morley jet kit, the purple arrows would be where you put the air correctors.

 

[SpecOps13]

KJ, I think both of those are Air Jets, Think he was asking about the Fuel Jet...:confused2:
KJ, Takeover, It's Midnight here in Florida...:biglaugh: Very close anyway...

 

[mvvette97]

well I ended up pulling the carbs and took them completely apart. The pilots had just a little crud so I cleaned them up good. Put everything back togethor and adjusted the carbs and it seems alot better. It also has a lot smoother idle. The thing I think it stange is when i sync the carbs I have them perfect at idle but when I give it light throttle they don't seem to stay in sync by watching the gages. But once back to idle it's fine again. How do ya know if you ever get them right because they change depending on the RPM the engine is running. Anybody ever notice this?

 

[SpecOps13]

Like I said, I've set the carb sync on both bikes at 3,000 rpm. If your carbs are clean the idle should track fine. By doing it this way, I am pretty well assured that I'm on the money at cruise rpms. Really, you can drive yourself nuts trying to get the sync right on at all rpms... It's just not gonna happen. The carb design isn't perfect.

Happy to hear that it is running better now though...:clapping:

 

[Rusty McNeil]

As long as they are reasonably close, the "perfect synch" isn't going to matter EXCEPT at idle and just off idle when the throttle plates are practically closed, one of them being off can starve a cylinder or cause one of them to work harder than the rest...i.e.-crappy idle.......Once the plates start coming open the percentage difference in how they are synched becomes less and less a percentage of the overall opening, thereby contributing less and less to "variances" in carbs synch...Hope this makes sense...

I synched carbs for years by simply using a feeler guage and setting "static" synch with the engine off and making all the plates mechanically the same angle, after that the only difference is going to be engine variable cyl to cyl in valve condition, rings conditon, carb cleanliness etc.....

If you try to Synch at at various RPM levels you'll never get it right at all of them, the other stuff going on besides plate angle that contributes to the vac reading is changing to much from cylinder to cylinder......

In my mind, if it's firing on all cylinders at the proper idle it's good, synching it can even it out and make it idle nicer, but like I said, a tiny difference in plate angle at almost closed position can be a big thing when it's on the throttle stop but when it's open 1/4 or more that anglular difference is a tiny contibutor to the overall opening angle......

By the way, you rvideo really sounds mostly OK to me....vmax firing order is I believe basically the same goofy firing sequence as a harley times two...it's never going to sound smooth at idle...

Have you played with the a/f screws at idle to see if it "wakes up" one of the cylinders at idle?????

I use a laser temp guage on the pipe near the head to assure that a cylinder is firing,,,but this doesn't work on stock double wall pipes......

 

[alorio1]

Nothing wrong with all the above suggestions, but I just wanted to post my method of A/F screw adjusting and my thoughts about idle hanging, but keep in mind my exhaust system and jets are stock.

For me, the easiest way to set the idle mixture screws, is to run the
motor until warm and idle stable. Run each screw in, one at a time,
until the engine stumbles, back the screw out until just rich of peak
idle (idle drops again). Then run them back in to peak idle. Repeat
for each carb.
My final position is around 2.5 turns out.

Idle and off idle: Lean condition: Poor off idle throttle response, idle that flutters a little after a throttle blip then slowly returns to the idle that you've set, popping back through the carbs when the throttle is blipped.

Rich condition: Off idle response may be good unless plugs are fouled
from a way too rich mixture. After a throttle blip the motor will dive
down below set idle and will either die if way too rich or may return
to set idle if it can recover.

 

[Rusty McNeil]

Nothing wrong with all the above suggestions, but I just wanted to post my method of A/F screw adjusting and my thoughts about idle hanging, but keep in mind my exhaust system and jets are stock.

For me, the easiest way to set the idle mixture screws, is to run the
motor until warm and idle stable. Run each screw in, one at a time,
until the engine stumbles, back the screw out until just rich of peak
idle (idle drops again). Then run them back in to peak idle. Repeat
for each carb.
My final position is around 2.5 turns out.

QUOTE]

The Perfect way to assure that all cylinders are firing at idle....

Gotta make sure the Vboost butterflies are closed tho'''

 

[SpecOps13]

My carbs may just be very close to start with. I've set both bikes at 3,000 rpm, then gone to CaptainKyle's and put his gauges on at idle. The sync is always so close that there's no need to change it.. So I could set it up at idle as Rusty mentioned and it would also be good at a higher rpm....

 

[06VMAXIMUS]

I have never had any luck setting my mixture screws individually. I turn one in and it doesn't change until all the way in, then recovers immediately after I back it out a quarter turn, and doesn't increase the rpms no matter how far out I turn it! WTF?? I have tried it several times with the same results. What mods do you have Alorio1?

 

[alorio1]

06VMAXIMUS, I have COPs, R1 mod and DD clutch mod, everything else is stock. I want to get a set of Mark,s exhaust or the one Sean Morley just recently done for one member, but I hate having to rejet carbs.