I have basically stock 88 with marginal compression. Stock carb needs a float needle/seat and maybe to be jetted. It starts fine and idles fine but seems to be rich. You have to short shift it like a diesel to keep it clean. 5th pulls hard to the top most of the time. I think it has a 340 jet, stock pipe no box lid. It likes to be very warm to run it's best.
I have a 39 keihin pwk I tried and it was seemingly even richer. Likely needs different needle/jets as it was on a TRX250R at some point.
I can get my hands on a 39 PWK that has been ported to 40.5 and has a power jet added to it. I am dumb on the power jet thingy. I can buy this carb rather cheap. I thought I read that a ported 39 to 40.5 works well for even a stock Zilla but again not sure about the power jet. I will use the Zilla for general riding. It would be cheaper to fix the Mikuni or use my 39 but I am not sure which way to go. Please chime in here. Here is a pic of the modded 39/40.5:
Not sure your level of experience tuning these but the answer is not to keep putting on new carbs. If the top end is running rich do your plug checks and lean out the main jet (going smaller in size) Just curiouos, have you checked your reeds to see what shape their in?
In the tech talk section there is an excellent write up jetting to become familiar with that does what in the carb and the steps to tune it.
I have basically stock 88 with marginal compression. Stock carb needs a float needle/seat and maybe to be jetted. It starts fine and idles fine but seems to be rich. You have to short shift it like a diesel to keep it clean. 5th pulls hard to the top most of the time. I think it has a 340 jet, stock pipe no box lid. It likes to be very warm to run it's best.
I have a 39 keihin pwk I tried and it was seemingly even richer. Likely needs different needle/jets as it was on a TRX250R at some point.
I can get my hands on a 39 PWK that has been ported to 40.5 and has a power jet added to it. I am dumb on the power jet thingy. I can buy this carb rather cheap. I thought I read that a ported 39 to 40.5 works well for even a stock Zilla but again not sure about the power jet. I will use the Zilla for general riding. It would be cheaper to fix the Mikuni or use my 39 but I am not sure which way to go. Please chime in here. Here is a pic of the modded 39/40.5:
The following is some of my experiences with power jets and Keinin carbs
The only Keihin carbs that I have found that tune the same are brand new carbs. The needle jets in all carbs elongate and get richer with mileage. With Keihin carbs you have to keep changing to different shape needles with mileage to keep the mixture the same as when the carbs were new. The bronze Keihin needles that are available for the aftermarket Keihin carbs ware the needle jet faster than the hard-anodized needles that come in the engines that use Keihin carbs as OEM. Bronze needles rubbing on a brass needle jet ware more quickly than a hard-anodized aluminum needle rubbing on a brass needle jet.
The above fact is one of the main reasons that very few guys end up with the same carb jetting specs. when they have their jetting optimized using same model and size Keihin carb on the same type of engine.
Gasoline two stroke engines should not use Power Jets UNLESS they are electronically controlled. A power jet carb that is electronically controlled, optimally jetted, and programmed correctly is superior to most conventional carbs on a high performance two-stroke. I cannot recall working on a two stroke with a conventional carb with a conventional power jet that gave the engine the correct fuel curve.
The majority of the drag racing community uses power jet carbs on methanol engines because of they cannot get enough fuel through the main jet circuit of a carb that was originally designed for gasoline. If the majority of the drag racing engine builders had the proper test equipment to better help them to understand the real fuel demands of a methanol engine, they would be doing carbs a little different.
The power jet carburetors do not flow as much air as a conventional carb because of the flow robbing tube protruding into the air stream.
Stick with the factory Mikuni and learn to tune it. They are are much better carbs than Keihins in my opinion. 340 sounds pretty small on the main. Look at your carb slide, is the black worn off? Check for a damaged reed petal. Carb probably needs a rebuild, also what are you at for cranking compression?
If you have a engine with marginal compression. You need to rebuild it and start fresh. Also get the head cut correctly It will save you a lot of time jetting. Stock heads are a mofo to get consistent and correct.
Stick with the stock carb its the easiest to maintain. Order a new needle jet ,jet needle and maybe a slide if it looks worn badly ( edges are all silver,black Anodize is all worn away).
Alright guys thanks for the input. I'm gonna pass on that carb and order parts for the stocker. I have peeped in the boot but will remove the block and check the reeds for sure..