1981 440 Invader, Making a Oval Racer.

[Flying Frenchman]

Hi Everyone, I am New to this site.  Grew up Riding these Beauties, since my Dad was a Dealer up here in Saskatchewan, Canada.  Recently became involved in hosting a Vintage Ice Oval Race, Have been doing it the last three years.  This years race is on Jan 23 2016.  I have a beautiful 81 440 invader, that has a slight bogg to it on take off.  I am also looking for any advise possible for clutching,  I have been reading that maybe the LTD clutches would be better?  Any advise on this topic would be greatly appreciated,  E ramps vs F ramps and colour of springs.... I will post pictures soon

[rminier]

 Welcome! Oval racing sounds pretty cool.
 Others on here have more experience with the best clutch ramps, etc..
 But I will discuss "The Bog".
 Assuming all is well with the carbs, the engine, crank seals, carb boots, etc...there is another thing to look at.
 Kawasaki published the center-to-center distance of the drive and driven clutches should be set at 12".
 I look at that as a good starting point. Many manufacturers used a "belt deflection" spec, also.
 You may have a good drive belt, but even the proper replacement belt may vary in length a bit, between various Companies, or even different lot numbers.
 I don't know if Kawasaki clutches are more prone to this than other brands, but they like a "tight" belt.
 One way to check belt deflection is to press down on the top of the belt, mid-way between the clutches, and measure how far down the belt deflects from a straight edge held on the belt at the top of each clutch. Using about 8 lbs. of force (about the same as holding a gallon of milk) the deflection should not be more that 1 1/4 inch.
 Another good way to check this is to keep increasing the center-to center distance between the clutches until the track just barely comes to a stop when you have run the sled on a stand.
 If the belt is too loose, it wants to try to start accelerating the sled with the belt partially up the sheaves of the drive clutch... like trying to start a car in 2nd gear.
 If your set up is slightly on the loose side, it can definitely cause a bog.
 Don't get it too tight...that has other problems. The drive belt can get a hot spot when the sled is sitting stationary and idling, and the belt can create enough drag on the clutch to make it more difficult to start it with the recoil.
 Get it so the track just barely coasts to a stop when running on a stand, and you will have that part of the equation taken care of.

[gixxer6]

rminier has a good point.  Don't mask a problem with clutching, that's just asking for trouble. 

If you have everything tuned just perfect, carbs synced, belt adjusted, idle set, crank seals fixed, no carb boot leaks, track tension set, clutches cleaned, carbs cleaned and jetted, timing checked, oil injection adjusted properly, correct plugs, airbox installed, plugs gapped, and probably a few more things that I'm not thinking of, and you want a better hole shot.  I've had very good results modifying E ramps to Aaen spec, then changing the clutch spring and weights until you get 7,900 max rpm.  Leave the secondary alone.  This gives great access to the upper power range where the 440 Invader really shines.  However, it is not fun to trail ride it like this for more than a few miles.   

[Flying Frenchman]

Thanks guys I will for sure check the belt deflection.  I will look into modifying the the Ramps

[Checkmarks]

The primary springs in K clutching vary the launch rpm.

Black primary spring and your launching around 5k.  Terrible for the trail and hard on parts, no bog (but that is arbitrary).  The varying springs all have the same ending pressure (concept).

Lock in your head the primary clutch regulates the rpm.  The secondary controls the torque or the how hp is to the ground.

The idea * the primary runs all the way to 8k, then the secondary applies available power to the ground.


Lock your rpm to shift out at the max horsepower (claimed 8k).  In a stock application anything over 8k and you lose horsepower.  The rpm Hp peak is steep and off the mark you give up very much horsepower.

Envious for your oval racing.  (name drop) Gregg Channel lives up a town from me.

[Great Jashu]

I have an oval racer I built and race. Currently building another.  Now they are both Intruders, but the stock clutching seemed to work just fine and I could get to the first corner in the first sled or two. But turning is where I had issue. But the best thing that I found to make it launch and run better out of the gate was to switch the carbs to non-power jet Mikunis. I think that extra circuit is the cause of that so called bog. Without the PJ's it launched. Those PJs were built with fuel economy in mind.... But who cares about that when racing? As far as turning, I pulled the front of the skid up with the limiter strap about 2". This is a good starting point. Then I have adjusters I can turn up to increase the ski pressure. My new sled will run with Northstar racing skis and have a lot more bite. This will cure the turning problem. On the first sled I am going to 10" carbide with stock skis and run in the trail-stock class. This will make it bite better too, as it had 6" carbides and a push I couldn't overcome.  I was sill able to finish consistently in the top 3, but that will change this year as I am going to win races.....

[Teherr]

regarding oval racing and turning.  Best think to do is to help this is pull the front of the track up 3/4".  Easy to do with invader and 80 LTD as they have straps you just shorten.  I have oval raced an invader for 3 years and it turns well. 

[Flying Frenchman]

Thank you very much everyone for the great advice.  I am running North Star skis with 10" carbides.  I have decided to change both clutches to Polaris clutches due to the ease of finding parts and the ease of fine tuning quickly.  Does the jetting change when changing to the non Power jet Mikunis and if I am changing should i try to go to 38mm

[rminier]

 Cool pictures! We look forward to some video from your helmet cam on the ice ovals.
 An old rule of thumb when switching from power jet carbs to regular Mikuni's, is to add the main jet (in the Invader's case, 150) to the power jet (120) to get the main jet size for the standard carb....which would mean a 270. Start on the safe side....maybe a 300 main, and work back down from there if a 300 is too rich.
 VM-36 vs. VM-38.....As long as the carbs are not starving the engine for air, my preference would be to go to the smaller size. My 82 SkiDoo Blizzard 9500 has peak power at 8700 RPM, and came stock with VM-36's.
  If your Invader engine is essentially stock, and still makes it's best power from 7800-8000 RPM, the VM-36's might provide slightly crisper and better response accelerating onto the straightaways, due to the slightly quicker air flow through the carb, due to the smaller venturi size, which makes for a stronger vacuum pull through the jets......it just might make jetting simpler and more consistent.
 If you find some nice VM-38's, they would certainly work, too.....there isn't that much difference between 36's and 38's.
  These are just "opinions"....perhaps some others on here can add to this.