Author Topic: What is a good carb for a moderately built 250R (Read 13706 times)

nick20555 · « **on:** May 27, 2016, 08:52:53 PM »

New to the forum here. I will put a thread up on my 86 250R soon but in the mean time, I am looking for some info. So while working on my R that I bought last week, I found that the carb bowl was cracked and the corner actually broke off when I disassembled it. I figure it will be just a much to get a new carb as it is to replace this broken bowl and a few other parts that are in bad shape on it. It already has a Curtis sparks exhaust, uni air filter, outerwears cover to replace the lid (in the mail), and unknown engine work (was told its been worked on but I don't know for sure. I will find out soon enough). I'll probably get it ported and rechamber the head soon and maybe add some more stuff and potential big bore in the long run. So my question is, what is a good carb for these future mods I'm looking to do? I'd rather only have to buy a carb once, not one now and another later. I do a lot of woods riding. I'll also need some jetting suggestions with whatever carb I go with as well if you guys can help.

Burns363R · « **Reply #1 on:** May 27, 2016, 10:23:32 PM »

38 air striker is a great all around carb. I have run it on 290cc motors up to my 363. i think its probably one of the most favorite out there.

nick20555 · « **Reply #2 on:** May 27, 2016, 11:49:23 PM »

When looking, it seemed like the 38 air striker was pretty common but my concern with going that much bigger on a carb is power down low. I do woods riding so low to mid power would be nice but I don't mind some of that power up top as well. Really my goal eventually is to be able to get a stock or piped 450 in a drag but be able to use that power on the trails as well.

jcs003 · « **Reply #3 on:** May 28, 2016, 01:37:24 AM »

the 38 A/S is the a very versatile carb and will adapt to engine changes easily. for example, adding a big bore, port work or pipe change.

john

2ndmoto · « **Reply #4 on:** May 28, 2016, 01:52:50 AM »

What are you doing with the bike? If you are doing MX or dunes, 38AS is a good choice. If you are doing hare scrambles, tight trails, then look at a 35AS. The 35 will work better in the lower rpm range, plus it can be bored if you need a bit more. Should be able to find either used, for around $100-120.

thesmith87250r · « **Reply #5 on:** May 28, 2016, 01:56:16 AM »

Like said a 38 a/s will be a great carb an will work well goin up in motor size for a future build

broken1 · « **Reply #6 on:** May 28, 2016, 02:54:01 AM »

The Air Stryker series of Keihin's are PWK's which are more of a mid to top end carb. The smaller PWK's will give better throttle response in the mid but sacrifice some top end power. If you want more grunt you could go with a bigger PJ but they have a combined choke & idle circuit which can give you problems plus they don't pull up top like a PWK. Another option is the Mikuni TMX. I never tried one but hear there as good or better than a PJ down low & a PWK up top. The 38TMX is the carb I'm going to get for my wife's R since it get's riden in the woods mostly.

thesmith87250r · « **Reply #7 on:** May 28, 2016, 05:25:47 AM »

I have a tmx carb if interested maybe 2 of them. Pm me

nick20555 · « **Reply #8 on:** May 28, 2016, 09:40:34 AM »

I do some woods riding and ride around on back roads as well so I'd like a good well rounded carb. Having a good mid range would be best. I'd like some down low for the woods but I'd still like to hit the highs for the back roads or when the trails open up.

2SMOKE · « **Reply #9 on:** May 28, 2016, 09:48:38 AM »

I ride woods, fields, and seasonal roads and really like my 38 A/S on my 310

Aceman · « **Reply #10 on:** May 28, 2016, 10:19:59 AM »

I used to have a 36 pj on my 310, it worked great in the woods. I switched it out for a 38mm pwk air stryker when I switched to mostly all dune riding.

christph · « **Reply #11 on:** May 28, 2016, 06:00:56 PM »

I've used Keihin 38 A/S in the past, but on my most recent build I tried the Mikuni 38 TMX and love it. Being a flat slide it is supposed to have better throttle response and top end. I've found it to be a great performer all around. It doesn't have all the hoses the A/S does either, which I find annoying. Does a small carburetor really need 5 vent hoses? The TMX is also much narrower than the A/S, around 70mm, so you might have to use a reed spacer. Before I bought it I read comments that Mikunis are harder to adjust and more temperamental than Keihins. Not true. The jets are actually easier to change. The drain plug at the bottom of the float bowl actually holds the bowl in place, whereas with the Keihin has 4 phillips screws. I got mine at Niche Cycle Supply. Good prices and fast shipping.

http://www.nichecycle.com/ncs/mikuni/carburetors/tm38-27-mikuni-tmx38-flatslide-carburetor-44mm-by-mikuni.html

nick20555 · « **Reply #12 on:** May 28, 2016, 08:06:06 PM »

Not sure which to choose. Good info on both the tmx and A/S

Skeans1 · « **Reply #13 on:** May 28, 2016, 09:23:46 PM »

On the zillas we ran tm38 bored to 41 or 42.5 and they were easy to jet if you put a pwk you couldn't jet them.

RIDE-RED 350r · « **Reply #14 on:** May 29, 2016, 09:11:02 AM »

I've run the 38AS on an OEM cyl with nothing but bolt-on mods and I was very pleased with it. It ran very strong, including down low, and responded predictably to jetting changes. I ran that same carb on my trike when I did a 350 big bore and it worked well on that too. I have since swapped to a 41.2mm PWK on the 350 as it is a better fit to the build theme and so far have been pleased with that choice. Not to say the 38AS didn't perform well on the big bore, it did. I just feel that the 41.2 is a better fit in that situation.

The 38AS carb works very well on alot of different applications. Hard to go wrong if you choose one.

Another alternative you might consider is the 39mm PWK. Not being an AS type carb, it will be easier to bore out should you end up with a big bore cylinder and decide you want more carb down the line. Carb boring is cheaper than a whole new carb. I initially asked Eddie Sanders if he could bore my old 38AS and he said while it can be done, it can be a real pain due to the vanes in the venturi. He recommended I trade in my 38AS for the ESR bored 41.2 standard PWK so that's what I did.