Author Topic: Mikuni Carbs (Read 8406 times)

The_Steve_Man · « **on:** June 03, 2014, 11:50:55 AM »

With Jerry talking about Mikuni carbs I have decided to get one this fall. I have been thinking about it quite some time but I have a couple of PWKs.
I don't have the equipment to do testing so I will be asking a lot of questions. (I hope your ready Jerry lol)
I think that people buy the kiehin because there is a lot a lot of info on on jetting and setup. I have searched for jetting and setup for the TM/TMX and found very little info. I have not asked anybody because it seems they are not used as often on honda 250s.
I am not afraid to jump in and use it.
This is what I have
85 ATC250r
Stock cylinder 66.25 bore midrange port
CT pipe
Vforce2 reeds.
Going to have open filter.
Stock head with cr head gasket.

troybilt · « **Reply #1 on:** June 03, 2014, 02:09:39 PM »

If you're looking for a 39 Mikuni TMX I have one... FYI. LOL!

The_Steve_Man · « **Reply #2 on:** June 03, 2014, 02:24:42 PM »

I wouldn't mind trying it out. A friend of mine has a 39 tmx on his quad racer and loves it. I was going to buy a new one but don't know where to start on jetting and didnt know who to ask.

troybilt · « **Reply #3 on:** June 03, 2014, 03:48:23 PM »

I can send it to you to try out if you want one. They tune just like any Keihin carb, my biggest deal is I have 100's of $ in jets and needles for Keihins so it made more sense to pickup a 38 A/S for my needs.

The_Steve_Man · « **Reply #4 on:** June 03, 2014, 04:24:49 PM »

I didn't figure there was any special magic to them. I just didn't want go in blind. I don't know where to even start at. Jetting principles are the same.

I will try it out. Thanks.

Jerry Hall · « **Reply #5 on:** June 03, 2014, 04:29:58 PM »

Quote from: troybilt;35712

I can send it to you to try out if you want one. They tune just like any Keihin carb, my biggest deal is I have 100's of $ in jets and needles for Keihins so it made more sense to pickup a 38 A/S for my needs.

Every time a new style carb comes out I try to buy at least one of every tuning part for that new style of carb. 90% of it I never use, but have it if I need it in some tuning session.

After 30 to 40 years of doing this for the carbs that have been introduced during this time span, I have many cabinets full of brass. If I could sell all of this brass that I have never found a tuning need for, I could probably buy a new Corvette.

fearlessfred · « **Reply #6 on:** June 03, 2014, 06:43:00 PM »

Quote from: Jerry Hall;35714

Every time a new style carb comes out I try to buy at least one of every tuning part for that new style of carb. 90% of it I never use, but have it if I need it in some tuning session.

After 30 to 40 years of doing this for the carbs that have been introduced during this time span, I have many cabinets full of brass. If I could sell all of this brass that I have never found a tuning need for, I could probably buy a new Corvette.

You must have a lot of brass

mx250r91 · « **Reply #7 on:** June 03, 2014, 09:34:44 PM »

Your best bet might be to buy a 2001 CR250 OEM carburetor which is the year they switched from the PWK to the TMX and it's also the last year of the cylinder-reed CR engine. For $200 brand new complete carb you can't beat it and the jetting should be close off as it comes.

http://www.partzilla.com/parts/search/Honda/Motorcycle/2001/CR250R+A/CARBURETOR+%282%29/parts.html

troybilt · « **Reply #8 on:** June 04, 2014, 08:09:40 AM »

Yea when I was tuning my MX 496 Saber setup with a 41 A/S I bought every pilot, main jet, and about 15 different needles. Needless to say when I work with carbs on the R's I try to stick with the Keihin's since I have alot of brass to tune with. I do have a few jets, 5-6 for the TMX and don't mind sending it out if you want to try one out. If you like it you can buy mine or one similar and send mine back, whatever you prefer, mines just sitting here. No sense in buying one and then not liking it. This one came from Sudco and I think there is good information on their website about them. I'm sure Jerry can help get you in the ball park.

The_Steve_Man · « **Reply #9 on:** June 04, 2014, 08:59:25 AM »

I know what my pwks are like on my bike so I will have a honest comparison.
@jerry what is a starting point on jetting for my engine?

Jerry Hall · « **Reply #10 on:** June 04, 2014, 05:01:33 PM »

I have not used the TMX or the TMS on any of the 250 TRXs or ATCs I have used a lot of TM 38s bored to 41.5 on the serious 250s and big bore cylinder kits.

udontknowme · « **Reply #11 on:** April 07, 2015, 11:43:59 PM »

hey jerry you have any advice what needs done to use a TM flatslide style carb on methanol ? do the main and pilot jets go big enough or does anything need drilled out like a keihin ? can the needle and seat valve be used with a pump or what needs done in that aspect ? install a adjustable powerjet ?

hontrx265r · « **Reply #12 on:** April 08, 2015, 11:20:22 AM »

I would trust in Halls opinion as he has done more testing then anyone i know. But i still couldnt make the switch just yet. Im still holding out on my pwks just because of the familiarity with their tuning characteristics, and my vast array of parts for them.

Jerry Hall · « **Reply #13 on:** April 08, 2015, 05:56:28 PM »

Quote from: udontknowme;52821

hey jerry you have any advice what needs done to use a TM flatslide style carb on methanol ? do the main and pilot jets go big enough or does anything need drilled out like a keihin ? can the needle and seat valve be used with a pump or what needs done in that aspect ? install a adjustable powerjet ?

You will have to drill the pilot and main jets. I use to make special alcohol needles so that we did not have to use a power jet. I would have to look up the info, but the main jets would be around .115 to .130". with about .030" to .038 on the pilot and .156 to .159" on the needle jet.

With our set up we did not have to use big float bowls either. Needing to use a big float bowl is a sign that the carb is not supplying the float bowl with fuel at the same rate the engine is using fuel. If you find the reason and fix the supply problem there is no need for a huge billet float bowl!!!!!!!!!!!

We also used fuel pumps and a special float valves that are no longer made/available. Does anyone know if any one bought the tooling or the patents after the owner of gross-jet died. Gross jet float valves had two balls instead of a needle like all of the conventional float valves have? The flow rate on the gross jet was higher than that of a needle type float valve of the same orifice diameter experiencing the same fuel pressure. We could use a smaller diameter seat to hold the higher pressure that the fuel pump would generate without flooding the engine at an idle and would flow enough fuel to keep a small float bowl full of fuel if you wanted to run it wide open for a minute.

udontknowme · « **Reply #14 on:** April 08, 2015, 10:03:01 PM »

i may have to get a hold of you sometime to get this sorted out. my mikuni experience is near zero so i may need some assistance for converting these things.