CR500 and Round Slide 38 Mikuni

I have seen in other posts of using a square slide 38 mikuni on the 84 500's but has anyone used a round slide 38 mikuni and how did it work? Looking for a starting point for jetting at sea level. Trying to work around the hard starting issue's, have already changed to PVL ignition.

Thanks

If you look through the parts sheets you will notice by 1987 only the cr500 had the 40mm. The factory was using a 38 round slide on the 500xc at the end if I examine the 1987 parts sheets correctly. You probably could find the origional configuration of an 1987 xc 500 in the vintage reference section as your starting point.

I havn't done that myself I changed to a flat slide 38 out of a 2002 husky but it was because the origional carb was worn out. I kind of suspect a keihin pwk 39 would be the way to go if you had to buy something new but some work might be in order on the rubber boots. My 1983 xc500 started wonderfully even in the winter for many years and neither I nor the origional owner changed any jets. If you look through the parts sheets you will notice by 1987 only the cr500 had the 40mm. The factory was using a 38 round slide on the 500xc at the end if I examine the 1987 parts sheets correctly. The over bored 40 mm (well that is what it looks like side by side with a 40) they used when the 500 was in the silver frame didn't seem to last long as the origional equipment. You also will have to change the rubber boots on either side of the carb which might cost more than you think it ought to.

Fran

The data I have shows that engine gets a 40MM Mukuni carb.
Set up for the 40MM is: 350 main jet, AA-5 needle jet, 7DH3 needle at possition #3, 55 idel jet with idel screw 1 1/2 turns out, 2.5 slide, .7 air jet.

Here's a 38MM for my 400. Before and after PTFE coating.

Fritzco,
PTFE coating? That looks so cool. What is it?

Hi, are you able to do a photo of where to set float level from please?

that looks pretty cool

Just set the float arm parallel to gasket surface.

Here's a link to the source I used. Lots of info on thier site.
http://www.polydyn.com/performance_coatings.htm

38 is to small... 40 is the key. They also had a 42 but was to large.

Fritz,
i checked out the web site,
Did you do the carburator coating from Polydyn?
I didnt see a PTFE coating listed.

I have an 84 500cr and live in Ohio at an elevation of about 1200 feet . Went with a 38mm round slide as recomended by an old Husky dealer who had the same model back in the day .

Needle 7dh3 , 2nd clip from the top
320 Main
35 Pilot
Slide ground to about a 2.5
Timing 2.2mm BTC
2 gal. race gas mixed with 3 gal. hightest pump gas and Maxima Super M at 40:1

I also made one of the homemade power blades for the carb as was described in one of the threads on here. The bike RIPS ! No pinging / detonation , or back-popping . Throttle control is awesome especially since the power blade . The plug looks perfect . The bike can be lugged but will rev to the moon for such a long stroke monster . It will now start well hot ( wouldn't before ) but cold starts are still an issue . I ground the kicker engagement dog plate for more kicker stroke . Tried the " blowing into the vent tube till she bubbles over " trick too. Tried leaning it over until it overflows from the vent ala my old CR450R Honda . Push the kicker just past compression before wailing on it .Choke - no choke , throttle closed - throttle slightly opened . Nothing seems to consistantly help cold starting so I usually have to bump start it down a hill . It has so much compression that it often just slides the rear tire . When it turns over , I swear the bike doesn't go 2 feet and it fires right up ! I am now considering fabbing a compression release into the back of the cylinder like my buddy's 490 Maico to see if that does anything . I'm running out of ideas and getting desperate . I LOVE this bike ; power , handling , etc. make it my favorite of all time ( always loved big bores ) .I want to race it but will not go to the line with a bike that is so finicky . Maybe I'll build a roll starter like the road racers ? Leave it running all day ? I will succeed !

Hi there, Just a little addition to this thread. I rode CR 500 (82.5 year Silver mod) & 1983 White CR500`s for 4 years back in those days. As some of you may know the Silver Tank had a Large 44mm Mikuni round slide carb & was rather fierce (made for Grand Prix Racing I think) ,also wasted fuel on v.bumpy shorter tracks where not running at high revs via the o/flow tube.
The 83 was reduced to a 40mm Mikuni I ran this in MX racing and never had any trouble at all.
I`ll have to look back at what jetting & needle settings I used & add them later.
As for starting I didnt have trouble, My tecnique was the classic, H/bars on full right lock(to save hitting knee if kicked back) Then ( standing off the bike)
With right leg press kickstarter to resistance at compression then in one motion kinda spring up off your standing left foot so that you`re stood up in the air on the k/start and coming down with it with your whole weight in one nice fluid movement opening to about 3rd throttle at same time.

If First start from cold , Before turning pet/cock on .....I would turn the motor over steadily three times to get the ignition chance to spark then turn on gas , choke on & Vroom 1st or 2nd kick.
Timing was correct & every 2nd Meet the barrel had been off & piston cleaned as I used Castrol R30 pre-mix , so Spark plug was clean or new for each race meeting .

I did move onto Castrol 747 when bikes became watercooled later in 86.
Good luck with those huskys & dont kickstart without riding boots on ! Regards John

Excellent info in this thread! Thanks everybody.

Ya, Husky sure dumped that 44 quickly (only ran them on the 82.5)! I don't like them either. The 500's really work pretty well with a 40 round and good jetting. If a guy buys a 500 and it's got a 40 I'd say just run it - nostalgic, original, kinda cool. But, honestly, they can be hard to find, and the bikes run great with a 38 round. They're so much more abundant and you can get one on there easily with the air-cooled 250's intake boot (I copied the parts from my 83 250WR) and correct cable.

Ruwfo - I've never been lucky with the Mikuni flat slides, either. They've always seemed very sensitive weather.

As a lot of the pictures I see on this site these bikes have an adapter to use a generic two bolt rubber (perhaps micuni instead of generic) carb boot. I suspect those things might of kind of restricting compared with the stock rubber boot. So there may be no point of having a 40 mm carb if using that. Maybe someone who has actually held the parts side by side could comment.

Pertaining to ruwfo (and no I am not wfo just twisting enough to avoid stalling) or Husky John's post above I see what I think is the type of flat slide carb first used on the 250 somewhere around 1986. I also note that the length issue has been addressed by moving the carb to the rear instead of extending the rear of the carb to reach the air box boot. Your post is informative however I don't take it as a bad rap for flat slide or going to 38mm applications in general. I have a klein pwk 39 I intend on modifying to fit, I did a micuni like come on the modern bikes I got for cheap. Honda cr 500 Kawasaki kx 500 used a pwk 39 is my impression. Billeted intake not adapter plate.

Fran