Hey, I have an '88 FourTrax 300 with a SuperTrapp IDS2 Race Core exhaust and K&N filter and need help with deciding which main jets to get. The stock main jet is a 120, so how many sizes up should I go? The exhaust includes a larger header pipe (it's not just a slip-on). I found a guy on Angelfire that went from a stock 125 (newer TRX300 than mine) to a 128 after installing a Quiet Core version, but I'm not sure if it was just a slip-on or a complete exhaust. Then I found on a page about his snorkel that he had a 130 and went to a 132 after installing a snorkel system, which leads my to believe he went with a larger main jet than initially. Here's the link.

Now, I've finally found a place that sells main jets for the '88's VE90A carb (JetsRUs.com), or at that thinks they have some that fit. Initially they were listed as only fitting '92s and up, but I emailed them asking the difference in the carb (The VE90D was the '92 carb, so how different could it be?) and they replied by saying that the jets should actually fit and edited the listing accordingly. Here's the direct link to their page. Other companies (Dynojet, for example) have said that their '92 and up main jets explicitly won't fit, but they don't seem understand the technical differences between the carb versions (seem more like the help desk people that only read the information but don't understand the details).

Anyway, that's not really my point. The $35 jet kit they sell comes with jets that seem WAY larger than the two stock main jet sizes used, the smallest being a 135. They sell many sizes for only $2.89 each, so it seems like buying a few jets more relevantly sized would be a better idea. So that's where I'm at, what sizes should I get?

Also, is it necessary to replace the slow/pilot jet? I think the stock one is adjustable (I recall adjusting it before), so shouldn't its range cover the necessary changes? I've already moved the clip on the needle to the lowest notch, too, and it runs a bit better in mid-range.

Thanks!

 

Bump!

 

I just jetted my 98 300ex last night,
Has full aftermarket exhaust & k&n filter.
It may be bored out I am not sure.
I tried a 135 main 40 secondary, Way too rich.
Then I tried 130 and left the 40 in also raised the needle to second from bottom notch. Runs Great , Also just take you jets to a dealer they can match them up I paid $11.00 for three of them.

 

Thanks for replying! I ordered from Jet R Us a few days ago and they said their jet sizes run the same as the factory Keihin sizes. I ordered 128, 130, 132, 135, 138, and 140 main jets. A nice variety and hopefully there's a size in there that's right. I also ordered a 48 slow jet (stock is 40) since I have the stock one backed out probably five turns or so and it won't get rich enough to make it stumble. I was suggested to get a 45 and 48, but they're $6.09 each, so I just got the 48 which the guy said would probably be the best choice of the two if only buying one. Since I can screw that one in and out, it shouldn't be an issue if it's too rich. The needle's been on the bottom notch for a while, and it definitely helped in the mid-range. It's a little rich (it'll stumble slightly if I jab the throttle), but not too bad.

Anyway, thanks for the suggestion! At least there's someone out there willing to!