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Anyone have S/C on RX-1 riding 10k-13k feet? Tuning Help?

Colorado Yamaha

Colorado Yamaha

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Sep 4, 2005
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117
Location
Colorado Springs
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USA
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2010 Nytro MTX - MCX
I've been working out some bugs on carb settings/adjustments ~ still having issues. Anyone riding at this elevation, willing to share information? Hammer, MPI & TJ's all have been helping, doing testing currently, but still not right. Thanks, Derek
 

I ride Cooke City MT (7600-10,00+). I have about 300 miles on now with no problems. What are you needing info on exactly? I'm running 127.5 mains, needle in stock position, 25 pilots, with the screw 2 3/4 turns out and floats at 14.5mm. I'm a bit lean at idle (low 13s) but hit mid 12s at part throttle and high 11s to low 12s at WFO on the A/F meter.

Jim
 
S/C TUNING

JIM: Why such a variation from what MPI recomends for jetting @ 6-8 feet I realize your climbing to 10k but 25 pilots @ 2+ turns on fuel screw?Mpi recommends stocks pilots and #2 needle position with 3/4 on screws, any info and experience on this is appreciated
 
Blgs: what I have: 17.5 pilots, 127.5 mains and had Troy at TJ's double check the above and everything else - the floats, fuel screws, etc., and I'm still having a slight - what I would say mirrors a miss at idle to about 20 mph, you can feel and hear it. I'm getting 9 lbs. boost above 11k feet and 9900 max rpm's, running 50/50 leaded 116 MO race and 91 pump fuel.

If I run WOT and either let off fairly quick or fast, the motor stalls or the power starts to fall off and I have to milk the throttle to have the motor come back. MPI says its the floats but they've been checked - since I ride at 11.5k to 13k, do I need to go up more than 14-15mm? Are there some other settings I don't know about? I'm checking the carbs for any possible leaks this weekend, looking for any help. Derek
 
RX-Boy, I am running what MPI recomended on the phone except for the screw settings and mains. MPI recommended a starting point of; 130 mains, stock needle settings, stock pilot settings (my carbs had 25s so I assumed they were stock since the mains were with 135s). I started with these settings and had serious lean at idle (18s to 19s) on the A/F. With the 130 mains I was getting 9s for WFO readings so I adjusted the pilot screws out and dropped a size on the mains.

Derek, what are you A/F readings at idle, part throttle, WFO and when you quickly let off the throttle? I don't have the problem you are experiencing when letting off. Mine will drop to high 10s and then recover quickly. I'm guessing that you actually have a lean pop at that speed and are going way rich when letting off the throttle. For fuel; I'm running 50/50 91 prem and VP 110 race.

Jim
 
It sounds like a lean spot to me too, but you are likely going even leaner when chopping the throttle not richer. Almost any motor will go lean during a throttle chop.

If your problems occur from idle to 20 mph that is the range of your fuel screws and pilots. It seems to me that if Blgs is running 25's and 2+ turns then your 17.5's and 3/4's turn are to lean.

Do you have an AF gauge? If not get one. It will make your life much easier.
 
Jim ~ no A/F on the sled, guess MPI didn't think it needed one? Spray25 ~ thanks for the info, I'll be changing the pilots and adjust the fuel "again" and look into the A/F. Have you or Jim put in a BOV?, heard that helped fix the flooding problem on many T's and S/C's.
 
Just a thought but you might try 22.5 pilots. Jim is topping out at 10,000 feet with 25's and you are going as high as 13,000 feet. It is just a guess but I would think 22.5's would get you real close. I would go somewhere near 2 turns out on the fuel screws for starters.

Yes I put a BOV on my Bender turbo. I was not having a flooding issue, but I was having some pretty good turbo stacking. I have a rear mount and I think stacking is a bigger issue for rear mounts. The BOV cured the stacking. Ask Jonny Rocket to email you some pics of his install. It turned out good.
 
I do not have a BOV on my Stage 1 SC. SuperAbe posted on here recomending a wideband A/F meter, water temp and blower oil temp. I am running the A/F from MPI along with their multifunction guage which has time, water temp, blower oil temp, and voltage output. The multifunction guage also has RPMs but I haven't figured out which wire I ned to connect it to.

Ray, as for the lean theory when chopping the throttle; my A/F actually shows a drop in Air to Fuel. When I let off it will drop into the 10s which is rich.
 
Spray25 ~ thanks for the help, that's great. Jim ~ Abe did this install himself and said nothing about an A/F, it was early last year & I have all the other gauges. MPI is so damn busy "reportedly", I was told Mac or Abe would call me, weeks ago, but no luck. I guess this is what happens when you want to be first with something new. Sigh ...
 
BlgsRX-1mtn said:
Ray, as for the lean theory when chopping the throttle; my A/F actually shows a drop in Air to Fuel. When I let off it will drop into the 10s which is rich.
Click to expand...

Interesting :itchy: maybe a temporary over pressure in the float bowls like the MCX guys were experiencing?
 
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