switching to VM-38 carb on my Invader

[Pmlecom1]

I am in the long process of re building my sled 79 Invader.  I want to switch out the Econo Jet carbs for some 38 round slide.  Any advise on where to start my jetting would be appreciated.  The cylinders ports were cleaned up a little.    Also wondering which clutch spring would work better with F ramps.  I have black and yellow!
This mostly for trail riding and making kids point at.

[rminier]

Black spring has the exact same spring rate, but is about 10 mm longer (uncompressed length). Yellow spring was stock, but many people switched to black. Only thing it changes is engagement speed. Yellow engages at approx. 3700-3800 (at least on my "79 440) and Black more like 4000-4100. After engagement the spring rate and shift pattern shouldn't be hardly any different.
  The stock econojet carbs work very well, but if you want to try standard VM-38's it would be helpful to know if you intend to trim the airbox rings to fit on the 38's and run the stock airbox, or are you going to run some type of "pod" filters?

[Pmlecom1]

I have two air boxes so was going to butcher one up to make the 38's fit.

[Macs80hp440]

Clutch Settings:  After much research and questions, I found out clutching is a personal thing.  It depends on riding style and main purpose, not to mention the main rider body weight.  These clutches are easily tuned.  I'm 270lb 6'3".  I like smooth takeaways and strong mid range, but easy to control on winding trails.  I prefer engagement around 4000rpm to avoid boggy and still not too jumpy. 

I've got two setups on my Invaders.  One Yellow spring E ramps.  One Black with F.  The yellow seems weak at startup for me, but perfect for 100lbs lighter rider.  The Black is flat out FUN for this big fella.

Don't forget to get the secondary offset correct and make sure it meets the stock 12lb setting as described in the owners manual.

I can't help you with the carb question.  I'm still trying to get one of mine tuned properly for all three phases.

[Pmlecom1]

I think I'm gona start with the black, just because of the fun factor.  First I need to replace all the bronze bushings in the rollers and ramps.  LOTS of play in there.  I was very surprised to see the bushings in the clutch cover to only have 0.010 clearance.  And the moveable sheave is 0.015.  Thinking only replacing the sheave bushing.

[kawhead]

seems like the civer bushing wears the most, smaller i guess....f ramps seems best regardless of spring

[rminier]

I will take a stab at the jetting for the 38 carbs. It is certainly up to you to start carefully so you don't run too lean and burn up a piston....and this is assuming the crank seals and rubber carb boots are all good, with no air leaks. I suspect you will wind up with a 270 or 280 main jet, but if it was me, I would start with a 300 main. I don't care if it smokes like a chimney...you can always move back down to a 290, 280...A 30 pilot jet sounds about right, but if it has an off idle bog that is not due to other things (clutches, etc.) you may need a 35 Pilot. It would be good to know what size needle jet and jet needle are in your 38 carbs currently. Both parts have a tiny stamping on them. A variety of those 2 parts could work, but it would be helpful to know. Put new plugs in the beast when you are ready to run it, and check the color often. Dark brown or black we can correct...light gray or white would really be a bad thing...

[Pmlecom1]

Hey guys I really appreciate all the hard learned wisdom.  But I am at a stand still, waiting for Wiseco
to send me some fresh pistons.  Can't wait to get this ride going! 

[Pmlecom1]

The donor sled is ZR 500.  The spec chart list the pilot at 35, needle as a Q2 and the mains are 350.  I will open them up after Christmas.  Maybe Santa will bring me some shiny aluminum this year!  I'm getting all excited!

[rminier]

I couldn't remember for sure, so I took a quick look at round slide carb dimensions. VM-36 and VM-38 carbs have the exact same dimensions for the flanges on both the airbox side and the motor (carb boot) side, so you should be able to use your stock airbox with no alterations. There are some other good posts on here about jetting you might take a look at. One recent one is under the "General Help" section from back in November entitled "Stock carb jets for invader 440"that has some good info. Good luck getting your Invader ready to ride!

[Interceptor398]

Something we all need to remember is that Kawasaki had deep pockets when all this was going on.  If they with all thier fancy stuff had felt the sleds needed 38's to compete they would have had sleds with 38's that needed them.

[invader87]

i think i have 280 mains and 30 pilots in my 78. i will pull the bowl plug and check later today if you are still working on this one.

Merry Christmas all!!

[Tory944]

I can't imagine you guys running 300 mains with 38's aren't having problems...   that's just too lean IMO.  Maybe fine as long as you aren't holding it open for more than five sec.  Unless it is 40 deg out and you ride at 7000 ft.  Running 330's and 40's in my Liquifire with perfect piston wash and plug readings (light tan).  340's and 50's in my Interceptor.  20-35 degrees.  Don't say I didn't warn you guys!

[rminier]

Yep, it's always a bit scary throwing out some guesses on jetting when someone is entering "unknown territory". My '83 Vmax service manual has a good section on finding the "rich limit" on jetting, that may be worth passing along. Of course, this is starting with a stock sled with stock jetting and the clutches in good operating condition.
 It suggests increasing the main jet size, a step at a time, and making some 100 meter (dang foreigners) accelerations....with the motor properly warmed up 1st!! Continue to increase the main jet size until the motor will no longer reach it's full shift RPM...then you know you have reached the "wall". Then back down 1 size and use piston wash and plug color to show the need to go down anymore with the jetting. As Tory pointed out...be careful at first.

[Tory944]

  Don't forget standard mics don't have a "shared" top end fuel metering system (main and econo jet).  The original econo jet 36's will run a lower main jet because they also use the econo jet as a supplement for top end fuel.