copied from an earlier post....
Ok, I will chime in and give my 2 cents worth. I have over 10 years of experience messing with the 350s and have have found out (mostly the hard way) what works well for my riding style. I am on a tight military budget so most parts I use are either fabbed or bought used from Ebay. Not everyone will agree on the best mods, or good mods so use whatever you like. These are my personal suggestions and opinions. Hows that for a disclaimer! LOL
1. Air Box Mods. The factory airbox, snorkle and tail light box. Great for keeping out dirt, mud, rain ect., but extremely air flow restrictive especially in hopped up machines where you need increased air flow. There are alot of posted pictures of dual snorkle mods, each a little different and all fix the restrictive problem. Probably best bang for the $15 spent!
2. Air Filters. Hot debate topic with different views, all require proper oiling and regular cleanings, especially in a dusty enviroments.
In box, Factory foam filter--probably the best filtering but most restrictive becuase of the metal screen cage inside. Dual stage, Uni foam filters--most commonly used, great flow and good filtration. K&N filters-- most air flow but least filtering even with the optional outer precharger covers. most expensive also.
(No box) pod filters--again, debatable, you may lose power by removing the box because of the two stroke pulsewave/resonance, loosing the box makes access to the carb much easier, the filter is exposed the elements and needs to be covered when not in use, does not like water covered trails!
3. Carbs--again 32mm(stock)is too small for hopped up engines but fine for stockers. If you want your
Engine for torque(hard launches, steep climbing, ect) stay small 34-36MM, if you want your Engine to rev high and really pull on top end, go big 38,39MM, +. Ofcourse you will want a port job and an exhaust pipe to match, rev or torque.
The more modern flat slide type carbs give a better throttle responce. I prefer Keihin over Mikuni, but that is just me.
4. Exhaust pipes-- Stock works well and is the quietest but is restrictive when hopped up. DG, PowerPros and Bills are some that I have tried, and all give good gains. The DG silencer(or lack there of) is horribly loud and has to be swapped out ASAP. Again, some have been tuned/designed for rev or torque.
5. Reeds--Stock are steel and very trust worthy but restrictive on built engines. Boysene makes replacement fiberglass reed pedals for the stock cage in either rev or torque pretty cheap. Also most 250R, CR250, and pilot reed cages will fit in the 350. I prefer the 4 pedal Cr250 cages(best flow). I also use a straightened neck boysene Rad Valve, G-3 and Delta V Force reeds, all with increased power and throttle response over stockers. There has been some verified cases of the V force cage getting sucked into the engines. I don't recall if they were version 1,2, or 3. I have used my version 2 for 5 years with no problems, yet. Knock on wood.
6. Clutches--Again another topic of debate, Salisburys(stock) good ol reliable but a lower engagement boggs the Engine for racing. 94C-great all round clutch, draw backs are its not really tuneable. 102C- great for racing because you can adjust engagement and different areas of the powerband by changing springs or cam arms. Draw backs-expensive, without the dustcover can wear parts quickly. HRD & Alt--good simple design clutch(very similar to the 94C) except you can adjust puck wieghts for tuning, priced between the 102 and 94. Drawbacks tends to tear up the "D" slot on the cover and possibly has ties to Pilot main bearing failures, none know on 350s yet.
7. Porting-- The heart and sole of the Engine, can be mild to full race(wild). If not done correctly, you can ruin an Engine. It needs to be done by a knowledgable person, not a shadetree(like me). You can take a dremel and clean up casting flaws and other imperfections inside the jug, polish up the exhaust port and make better flow thru the Engine(better power) but avoid changing the size and shape of the openings. That is the timing and could spell disaster. There are alot of articles written on porting work so if you want to do it, better do the homework.
8. The little tricks-- here are just a few I use. The stock head gasket is actually three layers. I use only 1 which bumps up the compression some. Always use a quailty synthetic oil at 40 or 32:1 with fresh premium gas. Run a liq cooled head and radiator to help control heat especially with a built up Engine. I use an EGT and a water temp guage to help monitor things. Run .190 aluminium rims and lighter weight tires if not in rough/rocky areas, less kenetic mass.
Theres a good start of info to absorb and I am sure other will add to the list too. I am sure I have forgot things too. Good luck,
Gary
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