Does anyone have a recipe? I'll be riding the CO national and know the elevation will be such that I should change the jetting on the bike - not that it will make a difference to me (no huge splatters for me!) but would hate to seize the bike on the loop trail or something. I will also be adding a spark arrestor (Spanish Fly) which I suppose might affect things as well. Thanks in advance, Jon
One good thing about the 300 is that it is so strong that it is very tolerant of altitude.I ride 6 to 9 thousand all the time. I am one size up on the pilot and stock needle and clip position with stock main. If I am constantly above 8 thousand I richen the airscrew a quarter turn and raise the clip one and down one on main.
So... lets assume that I was to be doing this from scratch, how exactly would I go about determining if I am rich, or lean? Surely there's a thread or article somewhere that can explain the process somewhat. I have a pretty good idea that the pilot will affect throttle response and low openings (all the time for me!!) and the main will affect WOT and mid openings will also be affected by the needle position. I tried searching PWK Jetting but never came up with much - time to troll the interwebs for more insight! Thanks in advance! If all else fails I will probably lean it out to 40/120 from the stock 45/125 and lower the needle one notch.
:eek1 Let`s assume wheels were square in the east and octagon in the midwest. If I told you to richen the pilot at colorado you would have round wheels. Best to have a small assortment of jets and a little time before the event.(P.S. The pilot jet always flows all the time. That means 99% of what you have ever read or heard is wrong.:eek1
What shape are wheels in the north, I'm from Canada!!?? I have ordered an assortment of jets and plan to have some time to play with them before the event, at 700ft elevation at home and again on Friday before the event. Some things you do have to learn and figure out for yourself - which is what I think you are trying to tell me.
All bikes can be off a little. Main 115-120 Pilot 45-52. GasGas pits should help steer you in the right direction.
The guys here have vastly more experience tuning carbs than I do, but here's my basic core dump: First, what's your baseline setting? What's your home altitude? If it's a used bike, especially, don't trust the specs to be accurate. If you haven't already, take apart the carb and figure out what jets, needle, and clip setting you are running presently. How does it work for you? Good throttle response off-idle? Does it rev out as you need it to? Is your air filter clean? Do you have a small supply of spark plugs in the proper size and range? Get an assortment of jets in the sizes close to your baseline setting, and get an extra clip or two (DAMHIK ). Increase in altitude will tend to make the engine run rich--less oxygen for the same amount of fuel. When you get to the event, as Lineaway says, take a little time to check operation. Then make a small change if you need to. After the change, use a clean plug. Warning: it's much harder to read a trials plug compared to a racing engine because you don't operate WFO. If the plug is dark and wet your setting is too rich on one or more of the circuits, especially if the engine stumbles when you change the throttle setting. If the plug is lighter than a nice cinnamon tan you may be too lean. If the bike runs hot or runs on after closing the throttle that can be a sign of leanness. Generally speaking, adjust pilot for idle, needle/clip for mid, main for larger throttle settings. They will interact to some degree but try to make one change at a time and target performance changes you want. Now is the time for guys with more trials-specific carb experience to chime in. Is there a better way to deal with circuit interaction?
The great thing about nationals is there is always factory support. I would just ask Dale what the top guys are running for the specific conditions. I would bring a range of main jets down to include a 118 and 116 main and the smaller pilots you mentioned. You will also need to tweak the air screw. Verifying Plug color and listening for detonation up a big/steep hill are good things double check after you go leaner. (a hard throttle chop near the top of the hill will also verify the air screw setting) Good luck in Co.
Thanks everyone for the great advice.... I ordered a selection of jets, and I'm looking forward to unravelling the mysteries a bit. Will post my findings after the CO round. Jon
If you are using modern pump gas it really leaves very little color on a plug. If you use race gas then you will get a little color.Much better to get a good baseline from the factory boys before you go and then ride it there to see if it is going to work. All my Gassers have run better at high altitude with a richer pilot.Less air pressure,less vacuum to pull gas through jet.Bigger jet needed to compensate.Make sure your reeds are new or close to new. That will help with jetting.
