High Altitude carb adjustments?

[rotaxrule1]

Hi Guys,

I was chatting with a local mechanic today, he mentioned that I can tune up my machines to better match my altitude (makes sense). I just didnt know if it was safe on these tempermental machines, so I didnt really think about it.

According to the spec sheet for high altitude (BTW, what is considered high altitude?), the GSX calls for almost 10 steps down from the factory (which I currently have). Has anyone messed much with the jets? Or should I leave well enough alone? The only one I am trying to tune better is my GSX, since it is having a bit of sluggish performance up top.

Anyone have any input on this? I am a little hesitant to lean anything out that I have (including my ATVs) unless I am absolutely sure it is safe. (my plugs on the GSX are a tad on the rich side, but not bad)

-Brandon

 

[Dr Honda]

I jet carbs all the time. (mostly for motorcycles) But, it's all the same. But... the nice thing about the regulator carbs are that they can handle altitude changes better than a regular "float" style carb.

So... yes... if you have less O2 per volume... you need less fuel too.

The big question is... when the engine is warm... and you mash the throttle down... does the engine stutter? (does it need to clear out) If yes... then drop the main jet a little. If no... then leave it alone.

Secondly... are you fouling plugs? Then same as above.


Now... as far as "What is high altitude?".... normally I'd say 4000', but I seem to remember seeing 6000' on the boat high altitude kits. BUT... your book should say.

BTW... that's a nice info. What book is that?

 

[rotaxrule1]

Cool, yeah I want to be absolutely sure before making any changes, especially leaning out. This issue is just part of the same troubleshooting process I have been doing on my GSX to get it to run better. I recall you helping me with a few pointers on another thread, but I basically have ran through the throttle response tests and have come up with awesome low end response. But mid to top is just slow and sluggish.

It does not cut out, or appear to load up at all, it just is "ok" and never reaches 6800 RPM, stays around 6450-6500. I investigated the timing issue, and still have that possibility in the back of my mind. But man there is alot of work involved in testing that.

The page shown came from the dealer mechanic I talked to, he just printed it for me. If you would like, I can scan it into a PDF and send it to you. Let me know if you want, and ill be glad to do that.

-Brandon

 

[rotaxrule1]

I should elaborate on the mid to top end. Most of the time it gets through mid to top end "ok". But depending on the load, maybe through turns, etc. It will bog on midrange for a minute (reminds me of my old 95 GTX with the 650) and consistently never tops 6500 RPM.

Just feels like it can run better, especially when I hop on my GTX that runs circles around it. I also am going to play with the raves a little more and retest them. Notice that page recommends raves turned all the way in for my altitude, which my GTX is currently set that way and I didnt notice previously. (Trying that on the GSX next)

-Brandon