Quick jetting question

[Dirtscience]

Hi all,

I have read every post I can find on this forum about jetting and uncorking the BRP. I have had my BRP for about a 2 weeks. I rode for one week all pluged up and was not impressed. All my previouse experience is desert racing big 2 strokes in the ami class, I wanted a bike I could dual sport and chose the BRP. I unplugged the bike and started at a 172 main and felt a huge improvement, now I felt I could live with the pig except that I went up the mountain to about 4500 and the bike had to have a rolling start to get going again. After this I went to a 170 main and felt yet another improvement in power but now I am afraid of getting her a little too lean. The big suggestion is going to the 175 main at sea level. I live at 3500 and ride between 2500 and 7000. Does anyone think the jetting guide in the honda service manual is still accurate for the uncorked BRP? If it is correct I should apply a .92 correction factor to the 175 which gives me a 161 to 162 main. Does this sound correct? Any suggestions will be appreciated.

Thanks

Mark.

[Keo]

Mark,

If you live at 3500' you should talk to Stonewall. He lives at about the same altitude here in VA and is very helpful and knowledgeable. He is here alot, but if he doesn't see your thread, I am sure he wouldn't mind if you sent him a PM. Hope this helps.

Keo

[qadsan]

If you're riding between 2500 & 7000 feet, the only way to optimize the performance with the stock carb is to rejet when you change altitudes, but that's not always convenient.

Your best bet is to find a good compromise between everything. Try a 168 and see how it runs and then maybe go down to a 165 at the lowest if 2500 feet is your lower limit. If your low end throttle response is suffering, then try using the stock pilot jet and adjust the fuel screw. If your bike is running too lean, it will run hotter, you'll likely experience more hesitation, a loss of power and popping on deceleration. You can also verify a lean condition by properly reading your spark plug after a test run in addition to looking for the symptoms above.

[Dirtscience]

Guys,

Thanks for the replies, Rejetting at is not a problem I have a nice little jet kit I carrry with me. I have read the plug after a highway run and feel it would be a good mid to low range test. Plug is just a hair lighter than paper bag brown. Guess I need to hit the Sand wash and open her up.

Thanks.

[PeterJ]

? :smashpc:This darn computer!!!

Pilot screw on BRP adjusts fuel!

[PeterJ]

? :D

I wrote responses four times and it seems to be timing out!

BRP oppisite of two strokes on pilot screw!

[PeterJ]

? :D

Try leaning it out when you get to altitude (or should I say lean it in? :D )

[PeterJ]

? :D

Don't forget to check them valves. XR's with burnt valves are no fun! I need to go ride... :D

[smashinz2002]

The jetting chart is pretty good, I've used it for estimating jet sizes for high altitude trail riding in the mountains. The 170 is fine even at 1000', it's not too lean. Try the 155 or 160 for over 9000', works well. If you're using the competition needle, run it in the 3rd clip (middle). Also be sure you're running at least a 34mm exhaust tip, preferably the 40mm competition unit. I run the quieter 34mm in the mountains, and the above jetting, and never have starting problems. Good luck have fun!

L.L.

PS. Oh yeah, don't touch the air screw. It's fine, stock. Adjusting it properly is more involved than most people think.

[Dirtscience]

Guys,

Thanks again for all the responses. My exhaust tip is the 2 inch hole saw mod, Reason being I am putting a roof on my house now and money is a big concern. I was running the 170 yesterday up to 7000, at about 6500 when I would open her up she would hesitate in the upper RPMs, once I returned back below 6500 everything was fine again.I guess this is an indication of being rich? How often do these BRPs foul plugs? or do they? Oh yea, I adjusted the valves yesterday before my ride. The Intakes were slightly out and the exhaust were spot on.

Mark.

[PeterJ]

Back in '87... I was riding an '84 Yamaha TT600 and moved from sea level to 6500'. It ran terrible at high RPM's but O.K. down low on the first test spin. I seem to remember cutting the main jet size by 10% for starters and then dialed it in from there. It was a completely different type of carb but the rich main caused the same sick miss at high RPM. I don't remember any problems with the low end.

[Dirtscience]

Thanks PeterJ

Mark.