Originally Posted by 2bold2getold
From my experience in trips to CO mountains ( 8k ft - 13k ft ) every summer for 30+ yrs. In the 70s and 80s on the old trials and enduro bikes, carbs required dropping the main jet size quite a bit. With the newer bikes with the CV (vacuum) carbs not so much. Each bike is different...KLX300 with CV carb needed a much smaller main jet. Don't remember exactly how much but was supprised how much it took. KLR with CV carb needed very little reduction, 150 to 148. DR350 with CV carb none. And really ran great. All had "opened" air boxes. XR650R with non CV carb went from 150 to 125 main. Don't know how much air box mod will help. You could lean idle fuel screw ( turn in ), might help idle but probably won't effect mid and high rpms much. Some people have reported no problems at altitude. I haven't had my TA up there yet ( next summer
), so I'm also interested to hear what jetting and mods the Colorado TA guys are running. If you're not getting knock or hot running, lower octain gas might help. Hard to tell with the alcohol blend gas we have now. Try to find non blend gas. Makes 3 to 5 mpg difference in my car. Not much way around some loss of power though, short of a turbo.
I haven't played with the mixture but think it is running quite lean already as I get around 50mpg with pillion and full luggage. Might be worth looking at though! I'm in South America at the moment so god knows what blend the TA is getting. When we rode through Colorado, I always used the lowest octane available - think it might have been 83/85 but seemed to run fine.
Originally Posted by mas335
Have you checked your air filter lately, is it dirty? Rather than modifiy the air box you might try a less restricted air filter element. I'm not a big fan of K&N filters but that might help or better yet do the "Ladder" air filter mod that has been discussed in the past.
Without going into details you basically remove all the paper from the filter frame and replace it with a UNI filter or like I did replace it with the foam element from a NX125 filter. It will breath much easier.
The mod is not something that you can easily do, especially without a dremel tool but you only need to modify the filter frame once and then you have a washable foam filter.
See post 11484-11490 http://www.advrider.com/forums/showt...r#post16069437
I'm not a fan of K&N either but I like the idea of the foam filter mod. I'll see if I can source the bits required and report back. Thanks for the link!
Originally Posted by mgorman
I had always heard the CV's weren't as finicky as normal carbs but I've never
been above 7000 feet to know the difference. Has the slide ever been drilled? Some people drill the slides with a slightly larger hole to aide in throttle response and performance. I wonder if too big of a hole may have been drilled that would cause the slide to not have enough vaccume to raise it?
If it weren't such a pain to drain the TA tank, I'd try it on that bike too.
I've got a set of carbs from a '93 Transalp but I am using the vacuum sliders from the original '87 carb which are made of plastic instead of metal so maybe that has something to do with it. I don't think it has been modified apart from that though.