Kawasaki VN750 Forum banner

1 - 20 of 22 Posts

·
Banned
Joined
·
1,620 Posts
Discussion Starter #1
I got the ear shave done today going to a single air filter. The problem is the bike runs fine in the driveway, but taking off from idle to about 1/4 throttle it sputs and putts.... to the point where I have to flick open the throttle to get it to respond. Not an issue at speed, only when taking off or at low speed is there a problem.
I like the cleaner look with no visible ears or air box. And the popping on decel is completely gone now, also seems to have a bit more power in the mid to upper rpm levels.
So what could be the issue off throttle?
 

·
The Professor
Joined
·
3,147 Posts
I got the ear shave done today going to a single air filter. The problem is the bike runs fine in the driveway, but taking off from idle to about 1/4 throttle it sputs and putts.... to the point where I have to flick open the throttle to get it to respond. Not an issue at speed, only when taking off or at low speed is there a problem.
I like the cleaner look with no visible ears or air box. And the popping on decel is completely gone now, also seems to have a bit more power in the mid to upper rpm levels.
So what could be the issue off throttle?
Try turning in the pilot screws to 2 turns.
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #3
I'm at three turns right now....
BTW- I have #42 pilot jet
#145 mqin jet
1/4" shims under needles
All emissions removed, coastered, V&H Cruzers....
 

·
Sparky!!!
Joined
·
8,697 Posts
three sounds a bit much... i am running the same set up at 2 1/4 turns, I started out at 2 1/2 turns out and had to screw them in 1/4 turn to correct the same problem you are having.
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #5
Now at two turns out and running great! It's raining right now so I haven't taken her out for a proper ride......but seems to be ok now.
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #6
Looks like I spoke too soon.......
The bike ran great until it warmed up, then the part throttle problem returned...worse than before. I am having a problem with the crankcase breather tube, looks like it might be collapsing on itself in one of the bends... I'll fix it in the AM, but could the blocked breather have anything to do with it?
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #8 (Edited)
ok....well definitely not the breather.
the bike runs great until it warms up, then begins to sputter at part throttle. idles fine and once you open the throttle past about 1/4 it runs OK.

I've tried a/f from 1/2 turn to 3 turns.....makes no difference on part throttle hesitation. I replaced the plugs with NGK iridiums and all the plugs I pulled were brown with the exception of the right rear plug....it was black.

also checked the voltage at the accesory outlet. it reads 11 volts at idle and 12 at around 2000... it maxes out around 13.5 @ 4000 rpm...
Don't think this is the problem, since the bike ran fine before the ear shave.....but who knows.
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #9
My understanding is that the a/f screw only controls idle.
The pilot is used for part throttle, then the needle kicks in with more throttle, and finally the main jet. If so, could my problem be the #42 pilot jets?
 

·
The Professor
Joined
·
3,147 Posts
My understanding is that the a/f screw only controls idle.
The pilot is used for part throttle, then the needle kicks in with more throttle, and finally the main jet. If so, could my problem be the #42 pilot jets?
The A/F mixture screw controls the pilot circuit, turning in decreases the the ammount of fuel from the pilot jet and turning out increases the the ammount of fuel.

It is a misconception that the mixture screw and pilot circuit are for idle only, Wrong!!

The pilot circuit works from idle to around 2200 rpm, at this point the pilot jet is at maximum flow and any additional fuel needed comes from the main jet.

The pilot jet is not your problem, it's either incorrect shims, diaphram not fully seated, or debris in a passage way.

What shims did you use and how many? :beerchug:
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #11
The shims were not available from the shop where I picked up the jets.....so..... I made them from some sta-kon terminals I had in the tool box. After I cut the ring off and smoothed the ends, the final height was 1/4" (+- 1/32") Yeah, it was a hack way to do it, but it looked like it would work fine....the 'hole' in the connector was just a little larger than the needle at it's head. I've never seen the proper shims for doing this, but saw someplace they are around .126" so I guessed two shims would be close to 1/4"
 

·
On His Lady Vulcan
Joined
·
1,647 Posts
The shims were not available from the shop where I picked up the jets.....so..... I made them from some sta-kon terminals I had in the tool box. After I cut the ring off and smoothed the ends, the final height was 1/4" (+- 1/32") Yeah, it was a hack way to do it, but it looked like it would work fine....the 'hole' in the connector was just a little larger than the needle at it's head. I've never seen the proper shims for doing this, but saw someplace they are around .126" so I guessed two shims would be close to 1/4"
Radio Shack has the sizes that you need.
 

·
The Professor
Joined
·
3,147 Posts
The shims were not available from the shop where I picked up the jets.....so..... I made them from some sta-kon terminals I had in the tool box. After I cut the ring off and smoothed the ends, the final height was 1/4" (+- 1/32") Yeah, it was a hack way to do it, but it looked like it would work fine....the 'hole' in the connector was just a little larger than the needle at it's head. I've never seen the proper shims for doing this, but saw someplace they are around .126" so I guessed two shims would be close to 1/4"
This is the problem!! You may have seen .126mm and not .126" The shim thickness needs to be around 1.0mm total. Standard needle shim thickness is 0.5mm and Radio Shack washers are about the same, use two per needle. :beerchug::beerchug:
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #14
oh brother....... where did i get the .126" from?!?! WOW...big difference between .25" and .04"..... 40 thousandths worth of shims makes that much difference from stock?
Well, I guess I know what I'm doing tomorrow.....
Thanks again for the help ;)
 

·
The Professor
Joined
·
3,147 Posts
With the needle set soo high you are getting fuel from the main jet before it is needed and starts to flood the engine, thats why its not a problem @ higher rpm's. ;)
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #17
The saga continues.....................
OK.....so I replaced the oversized spacers with two #4 stainless washers per carb. The total shim height is now around 1mm, give or take a couple thousandths....
That solved the problem I was having right off idle....but..... now she sputters in the 3,000~4,000 range when trying to hold the throttle steady. In other words, it wont cruise.....I can take off from a dead stop just fine now and do low speed maneuvers. BUT....now I can't cruise at say 40~60 MPH...at that point I can coast or give it the juice and it will go. Got home, pulled the tank and boots from the air cleaner to the carbs and found there was gas in them....not like a puddle, but the inside of both boots on the air cleaner side of the carbs were "wet" with fuel all around the inside almost up to the air filter......
OH... and if you choke the bike all the way on when it starts to sputter, it runs fine.
SO..... what do you think happened now?
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #18
PROBLEM SOLVED!!!!! :smiley_th

Don't know what fixed it, but here is what I did:
1. removed the petcock for inspection.... clean as a whistle
2. opened the top of the carbs and reinstalled the shims and checked the diaphragms
3. rerouted the carb vent hose
4. replaced the gas tank vent hose
5. rapped the carbs with the handle of a screwdriver
6. set a/f screws to 2 1/4

RESULT:
runs better than ever! and holy crap is this bike fast..... tons of torque and it really pulls hard even in 5th gear. used to kinda mush out around 70, but had it up to over 90 getting on the parkway and chickened out before the bike did.... :baby:
 

·
Old Truck Junkie
Joined
·
4,133 Posts
The carb vent hose is very critical. It has to be where there is none or at least the least of air pressure varience.
 

·
Banned
Joined
·
1,620 Posts
Discussion Starter #20
The carb vent hose is very critical. It has to be where there is none or at least the least of air pressure varience.
I stuck the hose inside the frame. There is a frame tube that runs under the gas tank and splits like a wishbone.... where it splits is an open hole. I looked up in the hole and it looks like it goes all the way to the tube where the handle bars and such are. Didn't look like any wind ect. would be getting in there. Seems to have worked. :beerchug:
 
1 - 20 of 22 Posts
Top