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Dyno Tuning

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Hi all,

After going back and forth, and trying out different options of jet needle clip position, etc etc, I have decided to take the plunge and take my bike for a Dyno.

My question is: How many here have had this done and from your experience, would you say its worth it? Reason I ask, is that I have some reservations, cause obviously you can not re-create "track" conditions on a Dyno.

PS. Bike is a 2008 CRF250R .

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You wont see any changes from the needle settings unless your testing on a dyno with loadind capabilities but there are test you can do to get it close by using the highest gear and testing from lower rpms .

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You wont see any changes from the needle settings unless your testing on a dyno with loadind capabilities but there are test you can do to get it close by using the highest gear and testing from lower rpms .

Got it. So would you recommend a Dyno?

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So took the bike for a dyno. Standard settings according to my owner's manual. Jet needle clip - 2nd position, Jet needle - 42 and Main jet - 172, Pilot screw out 7/8.

Changes made. Jet needle clip - 1st position, Jet needle - same, Main jet - 158, Pilot screw - 2 1/2 turns. Bike runs slightly lean between 7000 and 9000 rpms but still a little rich @ 10 000 + rpms. Best we could set it with the time available. Main jet was changed from 172 to 168 to 165 to 162 to 160 and then to 158.

I am at about 4500 - 5000ft (1300 - 1500 metres) above sea level, temp between 26 to 32 degrees celcius. Is it possible for the main jet to have to go down THAT much?

2nd Question: What about gearing? I NEVER use 5th and very seldom use fourth gear. I run the standard gearing i.e. 13/51. May go 13/53? or 14/51?

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I have used all the way down to a 162 in modded engines @ sea levell so your probally fine .

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I have used all the way down to a 162 in modded engines @ sea levell so your probally fine .

Thanks Ron, that's good news, as I'm quite paranoid about things being 100%. Think I'm gonna try a 45 Pilot Jet and turn the pilot screw in a bit, cause it's also running a bit lean at idle and up to +/- 1/8 throttle.

Anyone got a different sprocket setup to the standard 13/51 for MX?

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Go up 3 teeth on the back.

It's not your pilot that makes it lean down low, it's your needle. If you put in the 45 it will be hard to start when hot.

You need a smaller root diameter needle. You can buy that directly from Honda.

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Go up 3 teeth on the back.

It's not your pilot that makes it lean down low, it's your needle. If you put in the 45 it will be hard to start when hot.

You need a smaller root diameter needle. You can buy that directly from Honda.

Was under the impression that the needle only starts "working" at about 1/4 throttle? On the Dyno, we had to lean out the needle as it was running rich. Am I correct in saying the a small root diameter needle will in effect be a "richer" needle?

As for the Pilot Jet - only reason I thought of going bigger is cause the Pilot Screw is current turned out 2 3/4 turns, and I read somewhere on this forum that if you have to go more than 2.5 turns out on a FCR Carb you have to go up one size on the jet? Yeah, just checked...it was posted by Eddie Sisneros.

Going up 3 teeth on the back is the same as going down 1 on the front right? MY bike has only got about 25 hours on it. I know its advisable to change all sprockets and chain together, but will I get away with changing only 1 of the sprockets on its own?

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Was under the impression that the needle only starts "working" at about 1/4 throttle? On the Dyno, we had to lean out the needle as it was running rich. Am I correct in saying the a small root diameter needle will in effect be a "richer" needle?

As for the Pilot Jet - only reason I thought of going bigger is cause the Pilot Screw is current turned out 2 3/4 turns, and I read somewhere on this forum that if you have to go more than 2.5 turns out on a FCR Carb you have to go up one size on the jet? Yeah, just checked...it was posted by Eddie Sisneros.

Going up 3 teeth on the back is the same as going down 1 on the front right? MY bike has only got about 25 hours on it. I know its advisable to change all sprockets and chain together, but will I get away with changing only 1 of the sprockets on its own?

The needle affects the entire range.

Most people only change the clip position which mostly change 1/4 to 3/4 throttle. The actual needle dimension as Jesse said above can effect the entire throttle range.

Find a needle with an earlier alphabet number. So if yours is NCYS then find a NCYR which will be a one smaller diameter with same taper and clip positions etc...

http://www.sudco.com/cat32/107.pdf

lot's to learn there.

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i think you will find that it will run lean on the track if its been set up on a dyno as like you said you cannot create the track conditions on a dyno.

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Thanks for all the input guys. Will see how it goes this weekend.

@Robm87 - Actually, when we did the dyno it ran leaner without "load". As soon as we put "load" on the engine it started running richer again.

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