84 RM500 JETTING

[POM]

Trying to get this bike to have a decent bottom end is proving difficult,feels a bit like the choke is on a little bit, have dropped the needle down to its leanest position which improved it considerably,put a 30 pilot in it(was 50 standard) improved it some more (wont idle now either)far from cured it though......gets worse as it gets hotter, indicating too rich
it has a massive mid/top end...........but this low end issue is hightlighting a vicious powerband when it finally comes on song......................any suggestions?

[JohnnyO]

Try going down 1 size in the needle jet as you have no adjustment left to go leaner on the needle.
Is it the std Mikuni flatslide that came out on the 500's? they are not a very good carb and even worse when the slide is worn. Some guys have good results using a new Keihin flatslide.

[POM]

as far as i know its the standard flat slide carb...and it does have some wear on the slide...not a huge amount though.....what about a leaner needle?are they available?

[JohnnyO]

as far as i know its the standard flat slide carb...and it does have some wear on the slide...not a huge amount though.....what about a leaner needle?are they available?

Very hard to get different needles and information on the needle profiles, much easier to try a smaller needle jet. Those things run eratic and are hard to jet with a worn slide and from memory the idle isn't adjustable

[POM]

Think i might just buy a new carbie ready jetted.......any suggestions on size/model?...and a decent jet spec.........
Why this has come to a head is because after spending hrs messing with this rm and thinking id got it as good as it was goin to get......i rode a yz 465 and it ripped the rm on low end smooth power......is that a fair comparison?? how do they normally compare??....or is my rm sick......?

[Viper79]

Not having ridden a RM500 I can't give you a fair comparison, but I can tell you my 465 will sail past the 500's of the start line and I am not a gun rider I can tell you!

[JohnnyO]

Think i might just buy a new carbie ready jetted.......any suggestions on size/model?...and a decent jet spec.........
Why this has come to a head is because after spending hrs messing with this rm and thinking id got it as good as it was goin to get......i rode a yz 465 and it ripped the rm on low end smooth power......is that a fair comparison?? how do they normally compare??....or is my rm sick......?

A properly jetted RM500 runs strong all the way thru the revs and should have as much or more grunt than a 465... most of them came from the factory jetted way too rich.
A mate of mine has a new 38 PWK Keihin on his 500

[Stevo17]

I have a new Mikuni flat slide on my 84 KX500 and it might be a good baseline- jetting specs as follows:

Main jet - 320
Pilot - 35
R4 needle jet
6FJ41 needle
Slide 4.0

This is very close to the stock settings apart from the needle and slide. The slides have different numbering to the old oem carbs. Hope this helps.

[maico police]

Have a talk to D Project. His RM 500 seems to pull nicely everywhere.

[D project]

I say get rid of that yellow thing and stick to the YZ's . That thing doesn't handle very well either compared to the yam's and blows head gaskets at the drop of a hat

[POM]

I say get rid of that yellow thing and stick to the YZ's . That thing doesn't handle very well either compared to the yam's and blows head gaskets at the drop of a hat

mmmm..... think i sorta asked for that....but anyway..even though the yellow piece of custard upsets the demeur of my wonderful "white and red ones" i will persist with it....just to anoy.. ... the lover of all things yellow ....mr d project!!

i also forgot to mention i was trying to jet the rm at approx 800mts above sea level.....how much difference would this make???......

[KTMaico]

My suggestion would be to take it to a good tuner and explain what you want and he should be able to set up the bike the way you want it or at least the best it can be. A good tuner with a Dyno and Carb Parts should be able to sort out your issues and change out what is worn and wrongly sized. The question then is how do you find someone that is good and knows two strokes. Best of luck.

Regards,
             Kevin

[Viper65]

suck it up pom
i reckon you are just not used to riding big bores
stick to your 250 buzzboxes

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

[D project]

Just stirring you up mate ;)Your bike sounded and ran great at Yanakie.
I found mine was rich as well when I first built it,but then I changed to the jetting spec to the one in the Motocross Action test from back in the day.
The article on the RM500's in VMX mag has the same spec's. May also be that pipe you are running, the DG ones are probably more suited to the lower rev range.

[Lozza]

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.