84 RM500 JETTING

[RED ALERT]

Would the Mikuni PowerJet kit work Ok on this carb? they have the fitting already cast into them.

[holeshot buddy]

johhny o is on the money you need a leaner needle jet for sure
reset needle to middle and install leaner needle jet
i would have to check what i ran in them in the past
the one i have now runs a 40mm roundslide but thats another story

[Lozza]

Would the Mikuni PowerJet kit work Ok on this carb? they have the fitting already cast into them.

   that would work a treat

[POM]

Update:
spent a further couple of hrs last saturday with this jetting issue.....fitted needle jet 2 sizes smaller and set the needle at middle......improvement!!.....lowered needle to lowest...more improvement but not right......with the temp at 35degs and 800mts above sea level, I sorta gave up as it seemed a pointless excercise to get a good setting at  that extreme temp and altitude...... i suppose a leaner needle will be the next step.....but!!!...temp or not, the settings are now so far lean from standard its causing me concern that there might be somthing else wrong with it other than jetting........any thoughts??......and oh yeah!!.....it was starting to detonate after 10 mins of good flogging...even though its had a real nice squish and combustion chamber volume job done on it.

[Lozza]

Have you looked at the cylinder head, piston crown and plug? Can you post a pic? How long did you continue to ride after the deto set in?

[holeshot buddy]

how is your timing

[POM]

I sorta called it a day after it started to detonate...and i never got round to doin a plug check.....the timing is food for thought.....iv never checked it since i had the bike (10yrs) might have a look at that this weekend.....hopefully the weather will be cooler which should make things easyier..

[KTMaico]

P.S. or you could try the mikuni carb guys t.d. hatrick in townsville  they will answer all your questions 07 4771 2677, www.mikunioz.com.  The guy there sells brand new, jetted mikunis ready to bolt on and he knows EVERYTHING about these carbs

I reckon they know SFA , expensive and are a complete PITA to deal with . Ian Williams Tuning is where you can get actual answers.

POM have you thought about a plug chop? The altitude by itself not have a big effect on jetting, what it does to the air temp and pressure definatly does, which is what your suffering from. In the good old days of 2T GP racing Kyalami circuit in South Africa at 1500m required a completely different tune. Was only good for that track.

I think Lozza must have had the same experience I had with Mikunioz when I was sorting out my Mikuni Flatslide that was on my Maico 490. They would sell you anything you asked for, but would not or could not offer any advise. On the other hand, Ian from Ian williams tuning was great to talk to, sensible logical adice and was very helpful. He even asked if I would send the carb to S.A. and he would check it out for me. I would only use Ian Williams now for Mikuni parts and accessories.

I still think it would be quicker, cheaper and less frustrating to get your bike to a good bike tuner.

Kevin

[Lozza]

The plug has the answers, cooler temps will lean out the mixture further

[POM]

Iv checked the plug and it looks real white....bit scary.....I must be mistaken here as i could have sworn this bike was running rich at certain throttle openings,the timing was slightly advanced..i fixed that.
After some further thought about the jetting in this bike, it came to me that i didnt realy know what the standard jetting should be...quick read of the clymer manual (im not totally convinced of the accuracy of that book) tells me the 84 was slightly different to the 83 and 82 465... it said the following

needle= 6fm......somthing or other....it had a 6fj41 in it

pilot=40....iv been trying a 30

needle jet= r4....im down to a r 0

slide should be a 2....thats cool

main should be a 300....i was at 320

So apart from the needle jet iv set it all back to standard and im going to start again.

As the weather was crap last weekend i gave testing a miss,will have another go on sat.

[POM]

Very little improvement with the stock jetting (if any).......so last weekend i tried a different carb as an experiment.....a 38mm round slide mikuni of a yz 250...jetted to rm500 spec......much improvement...low end was smooth and predictable and good strong mid range...although it seems to have lost its top end over rev a bit....and it was running real hot and eventually detonating again....bigger main jet req i reckon.....im runnin 290...
On close inspection the slide in the original flat slide carbie was sloping about somthing shocking.......which cant be right.....or can it?

All this points me in the direction of a new flat slide carb....who's the best supplier of em?..any contact details would be appreciated.

[Stevo17]

I bought my TM38 from this guy. He has good prices on needles, jets and needle jets also.

http://www.ebay.com.au/itm/Mikuni-TM38-85-Flat-Slide-Carburetor-38mm-HP-Carb-NEW-/150684804962?pt=Motorcycles_Parts_Accessories&hash=item231583a762

[POM]

dohh!!....ebay!!!...why didnt i think of that...

[JohnnyO]

Very little improvement with the stock jetting (if any).......so last weekend i tried a different carb as an experiment.....a 38mm round slide mikuni of a yz 250...jetted to rm500 spec......much improvement...low end was smooth and predictable and good strong mid range...although it seems to have lost its top end over rev a bit....and it was running real hot and eventually detonating again....bigger main jet req i reckon.....im runnin 290...
On close inspection the slide in the original flat slide carbie was sloping about somthing shocking.......which cant be right.....or can it?

All this points me in the direction of a new flat slide carb....who's the best supplier of em?..any contact details would be appreciated.

Like I said several posts earlier, the slides wear making them hard to jet and get running properly.

[POM]

"Like I said several posts earlier, the slides wear making them hard to jet and get running properly"




No argument there!.....i might listen more carefully to the advice im asking for in future.
Anyway i will update when the new carb arrives......And I seem to be cutting it a bit fine for the first viper event at the end of april.....nothing new there i suppose.

Is everybody else's steed ready for action at monza....?