Kawasaki VN750 Forum banner

1 - 20 of 42 Posts

·
Premium Member
Joined
·
335 Posts
Discussion Starter #1
My 2006 750 Vulcan, having sat idle for a number of years, would not go above 50 mph.
I had intended to leave the bike stock but when faced with the task of removing the carbs to clean, I elected to do the full ear shave.

I cleaned the carbs thoroughly and the bike seemed to run well after reassembly though I suspected lean but didn't get around to a plug chop until yesterday. One new plug in each cylinder and snow-white and bone dry, looking like they had just come out of the box and never been in an engine. Also, the engine has been running a little bit on the hot side with the temp needle just to the right of the little white temp symbol but never into the red zone.

Having read as much as I can find on this forum, I've decided to take out the 132 stock main and put in a 135 main and leave the pilot stock 38. A 40 pilot seems to me to be to big a jump in size.


Any suggestions?

Should I go with a 138 main instead of a 135?

Am I safe on the low end from being too lean with the stock 38?

If I keep the stock 38, how many turns out on the idle screws should I go to avoid being too lean on the low end?

I appreciate all the good contributors to this forum..... a wealth of information, invaluable for the maintenance of the 750V.
 

·
Registered
Joined
·
730 Posts
that's exactly what I did after putting the previously recommended 142/42 in there (far far far too rich!)

I now run 138/38, which runs great. I am constantly trying to tune the idle mix screws to eliminate the burbling/popping on decel, but it doesn't bother me too much, I just haven't gotten it dialed in perfect yet
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #3 (Edited)
that's exactly what I did after putting the previously recommended 142/42 in there (far far far too rich!)

I now run 138/38, which runs great. I am constantly trying to tune the idle mix screws to eliminate the burbling/popping on decel, but it doesn't bother me too much, I just haven't gotten it dialed in perfect yet
I was hoping to hear from you. I've read your posts on the subject and was wondering if you had gotten around to doing it.

Therefore, I shall go with the 138 instead of the 135 and leave the stock 38. You likely have saved me a third-time carb removal.

Thankyou!

Wish they made a 39 pilot. Might be just right on the low end, but perhaps the screw adjustment will suffice.

Thanks again! :)
 

·
Registered
Joined
·
7,663 Posts
These carbs get onto the main jet pretty early, maybe 2500-2800rpm.

Looks like a good plan, just read the plugs again after you jet.

Curious about what air filters you went with?
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #5
These carbs get onto the main jet pretty early, maybe 2500-2800rpm.
Oh!, Good to know. So the 38 pilot only matters below that, so shouldn't be a problem for scorching anything. Right?

Looks like a good plan, just read the plugs again after you jet.
I hope so! Yep, will do.

Curious about what air filters you went with?
K&Ns conical, right on the carbs.

You were another whom I had hoped to hear from.

Thank you!
 

·
FREEBIRDS MC CENTRAL NY
Joined
·
16,076 Posts
What I exhaust?

Sent from my Z899VL using Tapatalk
 
  • Like
Reactions: roadpouring

·
Registered
Joined
·
730 Posts
ooh wait I re-read my signature and remembered that I did 135, not 138. Then again, 138 vs 135 isn't much, but stock was 132 in mine. I went up one size to 135. 138 would probably be fine, tbh

also worth mentioning that I have one needle shim on each needle, so my overall mix is up one size at the very top of the carb, but is slightly advanced due to the shim as well.
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #9
ooh wait I re-read my signature and remembered that I did 135, not 138. Then again, 138 vs 135 isn't much, but stock was 132 in mine. I went up one size to 135. 138 would probably be fine, tbh
I've got both on their way by mail.

So, to be clear, you're using the 135 and it's running great. Right?

Did you test any plugs after the earshave and before you did any jetting?

I'm just wondering if it's possible that mine is running more lean than yours was and if I need to go with the 138.

But the 135 would suit me. Better mpg and I'm not looking for more power.

Thanks for comin' back to let me know about your 135!
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #10
also worth mentioning that I have one needle shim on each needle, so my overall mix is up one size at the very top of the carb, but is slightly advanced due to the shim as well.

Thanks for that, too.

I have the shims, so I could do it.

Could you describe to me the difference that the shim would make if I were to use it?

In his thread, "Tuning (jetting) Keihin Carbs for the VN 750", Hexadecimus said that "....shims often cause more trouble than good" and that "Shims were the sole cause of poor idle and hot start problems..." on two of his VN750s.

*shrug* So I don't know, I'm listening to you guys and weighing things out.

Thanks much!
 

·
Registered
Joined
·
730 Posts
My idle is rock solid at 1100, and I've done the coil pickup clearance mod and have an AGM battery, so mine starts really well.

I've heard it's best for engines with little bottom-end torque to richen the bottom end of the mix to make it a little easier to feed torque to the clutch on takeoff. I've never experimented with taking them out, but I think it gets the revs up off the line a little bit. Maybe it roughens the transition a little bit, too, but it's nothing I can't handle. I have strong engine braking and good torque off the line, so I've more or less left it as is.
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #12
My idle is rock solid at 1100, and I've done the coil pickup clearance mod and have an AGM battery, so mine starts really well.

I've heard it's best for engines with little bottom-end torque to richen the bottom end of the mix to make it a little easier to feed torque to the clutch on takeoff. I've never experimented with taking them out, but I think it gets the revs up off the line a little bit. Maybe it roughens the transition a little bit, too, but it's nothing I can't handle. I have strong engine braking and good torque off the line, so I've more or less left it as is.
My idle is good too and starts great. I have the AGM battery but haven't done the coil mod yet.

I removed my carbs yesterday evening and my new jets came today. I hope to get it back together in a couple of hours.

Out of curiosity, I attempted to get a perspective on the main jet hole sizes. Not perfect measurement but enough for my need.

I can put a .051" drill bit shank through the #132 with no wiggle and not forcing it in. It just slides nicely through.

I can't get a .055" drill bit shank through the #138, so guessing if the #138 is .053" or .054", then the #135 is .052" or .053".

I may have some other various diameter wires for the measurement but that covered the range of number drills at that approximate diameter. Not important enough to pursue it, but that gives me an idea of the hair's diameter difference in those three sizes.

One of the hairs of my head measures exactly .001".



I'm not gonna' tell ya' which one. :)
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #13
Okay, read HexaD's thread yet again and found that the jet numbers correspond to 100ths of millimeters. There are 25.4 millimeters in one inch.

So, a #132 converted to 1000ths of an inch would be 1.32 ÷ 25.4 = .052" diameter hole

#135 = 1.35 ÷ 25.4 = .053 diameter hole

#138 = 1.38 ÷ 25.4 = .054

#140 = 1.40 ÷ 25.4 = .055

#142 = 1.42 ÷ 25.4 = .056

So basically the jet hole diameters progress by one thousandth of an inch .001 per number change. That's some close metering.

This squares with my drill bit test estimates.

But I've been wrong before.
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #14 (Edited)
HexaD recommends a 5% increase in jet size to compensate for the earshave, if I've understood correctly.

So, #132 stock jet has a .052" diameter hole.

.052 x .05 = .0026

.052 + .0026 = .0546 which corresponds to a #38- #40 jet size.

So, I put in a #138 main jet, left the stock #38 pilot jet and opened the screws to 3 1/2 turns.

Starts good, idles good, progresses smoothly up to 6000 rpm parked.

It's all back together but I haven't ridden yet. Perhaps tomorrow and do a plug chop.

Went with the #138 instead of the #135 to distance it from a too lean/hot situation.

I'm just semi-educatedly guessing and playing with it here and hopefully will understand it more by and by. I've got a set of #135s if I need to cut back.... and shims as well.

Any comments are welcome
 

·
FREEBIRDS MC CENTRAL NY
Joined
·
16,076 Posts
That's it, we're calling him HexaD from now on

Sent from my Z899VL using Tapatalk
 
  • Like
Reactions: roadpouring

·
Premium Member
Joined
·
335 Posts
Discussion Starter #16
So, I contracted a bad cold after the jet change and didn't get to try it out for a week or so.
It ran great but the plugs are still white and the temp needle is still stayin just to the right of the Mayflower.
I'm gonna put 40 pilots and 140 mains in tomorrow or the next day and see if it'll bring the temp down and brown the plugs.

I live at 900ft above sea level and ride probably from 300ft to 1200ft at times.
 

·
Registered
Joined
·
132 Posts
after the ear shave I used 140/40 jets with two shims on each carb ,the bike ran great at high speed but was hell to hot start so took out one shim and went for 138/40 ,runs ok and starts hot ok but needs to be turned right out as far as can go with mixture screw to get plugs good colour also did the pick up mod which helps hot starts..i may go back to 140/40 and try that but each bike seems to differ. I have stock exhausts but someone has tampered with them because its a lot louder than norm I think.
 
  • Like
Reactions: roadpouring

·
Registered
Joined
·
7,663 Posts
I don't think elevation comes into play with fuel mixture until around 5000ft+.

Have you tried shimming the needles yet?

Are you doing a plug chop reading, or just a general plug read? Just wondering if you're actually seeing anything from the pilot jet.
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #19
Thanks for the feedback, Jethro.
My 40 pilots are expected in the mail today, so... we'll see how it goes.

With the 38/138, 2 1/2 turn set up that I have now, hot starts are no problem. I barely twist the throttle, hit the starter and starts right up.
It starts cold just fine with choke and gradually turning back.

It'll be interesting to see if and how that changes with the 40/140 set up.
 

·
Premium Member
Joined
·
335 Posts
Discussion Starter #20
I don't think elevation comes into play with fuel mixture until around 5000ft+.

Have you tried shimming the needles yet?

Are you doing a plug chop reading, or just a general plug read? Just wondering if you're actually seeing anything from the pilot jet.
I ran with one shim on each needle for 34 miles yesterday and didn't seem to be any different than without the shims, but someone more experienced might be able to notice something.

Plug chops have rendered no color change on the plugs. They remain snow white no matter what I do.
So, I assume the pilot is as lean as the mains.
At this point I'll forgo the trouble of plug chops and just go with the general plug read til I see change.

Thanks!
 
1 - 20 of 42 Posts
Top