picking a carb and what jets to start with

blaster7

blaster7

Member
Mar 5, 2011
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Martinsburg wv
hi everyone I have a few questions, I'm looking to pick up a new carb for my new blaster I'm looking at the PJ and pwk I know the PJ is more low end torque and pwk hi end and I'm looking for more low end so I'm thinking PJ I also think that a 150 main and 50 idel would be a good starting point but not 100% sure,I've herd alot of good and bad about those oko 30mm power jet carbs but I just do not like the idea of a China carb? anyone with some good feed back let me know also I will post my engine parts below and as always Thanks in advanced.
Vito's dual stage reeds.
stock carb running 240 main and 39.5 pilot.
aluminum airbox with uni filter and no airbox lid.
stock bore trail ported cylinder with forged piston.
factory 7 full pipe kit.
adjustable timing plate.
NGK BR9ES plug.
oil injection delete running 32/1 premix.
 
With your mods you seem to be running way too lean!

Why a 9 heat range plug? It should be a b8es.

Why a 39.5 pilot? It should be a 32.5.

You should be up around a #290 main and needle on the middle clip.

Your engine should be running well with the 26mm stock carb, but you could get some more top end out of it with a 28mm.
 
Were did you here that pj is a bottomend carb an pwk is top end? The series of carb dont affect the specific powerband what so ever, its the size of the carb that sets the powerband, the pj is a good carb but the pwk in my opinion is a much better carb, the oko carbs were really good carbs about 5-6yrs ago but now i wouldn't buy one. If i were building your bike, id buy a pwk 28 and either put it on as is or have it bored to a 30mm, but if thats the carb you chose, it start with a 48 pilot an a 160 main and jet down from there, I run a original 30mm oko on my stock bore stock stroke bike, with Toomey exhaust an vf4 reeds an flotek aggressive trail port an head mod. Its at a 48 an a 152, I have a pwk 28 on my wifes an it has aggressive trail porting an head mod, LRD pipe an trenga silencer, vf3 reeds an it has a 48 an 150
 
Just reading the post again, you are looking for more low end.

The larger the carb the more low end you loose owing to the changes in velocity.

Stick with the stock carb for low end power, and choose a pipe that favours low/mids.

The available power can be moved down the pipe by installing a reed spacer block between the reeds and the cylinder as can advancing the timing up to 4 degrees.

I do believe the F7 is a high end pipe.
 
With your porting, aluminum airbox, factory 7 exhaust, etc I would go right to a 34 pj or 35 pwk. You will get plenty of low end with a 34-35 and your mods. IMO that exhaust wants the larger carb.
 
I think the pipe calls for a large carb, but I fear that the bottom end will suffer due to the slowing of the air in the Venturi at low revs.

He said that he wants more power down low, an F7. and a large carb is the wrong combination for bottom end.
blaster7 said:
I'm looking for more low end.
Click to expand...
 
I am running verry similar mods with a 32mm and have plenty of bottom end with incredible top end.. I would feel comfortable even going larger,, and like stated that pipe likes the higher revs.. Also that 240 main is to small..
 
My opinion is it really depends on your riding style an terrain, i prefer the smaller carb for loads of bottom end, i could care less about having a 70mph bike or something that pulls till it explodes, but i rarely get out of 4th gear in my area, all the woods are super tight an technical, i live in south West Pennsylvania there is mountains an lots of heavy forests, if i was down south or out west were things are more open, id be running a 35 pwk airstryker
 
OK OK I hear you guys,yeah I did not install the jets guys its what came with it I checked them when I took the carb off for cleaning I too thought they were way to small but here is the funny thing when I did a plug chop it was running a little on the rich side? maybe there off brand jets? but they do have the mikuni symbols on them,also as for the plug that's what came in it guys so I figured I'd stick a new one of those back in because I'll tell you this when I got it and took it for a test ride it seemed to run like a banshee so that's why I put another br9es in it,as far as low end and top end I do a lot of trail riding and most of the time never see 6th BTW the reason I know witch carb does witch is because on my old cr85 when I went from a pwk to a PJ it was a very big difference at least to me it was I pick up a much smother power band in the top from down low and quite a hard hit down bottom,I could run the pwk35 I have but I have no clue where to start with jets or is it the same as the pwk28? let me know guys because I have pj 's pwk's lying around from 85cc part outs lol.
 
Maybe it was showing rich because of plug. The heat range of the plug would change how the chop reads I'm sure. I don't know much about the carbs, but I have seen opinions on here do vary. Blaaster and dualstroke know their stuff but disagree on this subject as I have seen b4, but I think as 89 said it depends on what your doing
 
To get the jetting absolutely correct one must do a plug chop with the correct heat range plug.

Recently we upgraded the lads bike with a KOR ported jug and hemi rechambered head. It is married up to a low end pipe

In the shed there is a TMXX 35mm D slide Mikuni but until I get a pipe that supports it it stays on the shelf.

I am in agreeance with Dualstroke that the F7 would work so much better with a large carb but the guy states he wants more bottom end, and a F7 and a large carb is not going to provide it.

It will definatly scream at the top end, but the lows are bound to suffer.
 
I understand what you're saying, blaaster, so first thing tomorrow I will re-check the jet then stick in a br8es plug and go from there. As far as high and low end I think I'm going to go ahead and do a top end deal, and give it a try. My brother did make a good point, that when we do real deal riding we take our quads out to the power lines, and that is wide open. The only reason I was thinking low end is because around my property its all slow speed stuff, but then again I do only cruise around so it's no big deal to me.if I go with my pwk35 what jets do you guys think would be a good starting point and would it hurt to try that carb out,again guys Thanks.
 
OK guys I checked the jets again and I was miss seeing it lol,it has a main of 280 and a pilot of 32.5,now all I need to know is if I go PJ or pwk 28 what needle and what jets should I start out with also fellows I see that the cel needle are the same for 28 to 35mm? or am I missing something I thought with bigger mm it would need a longer needle,let me know guys and as always Thanks for all of your time and help.
 
also blaaster I did the plug chop on 2 br8es plugs and both look good and just a tad on the rich side witch is fine because I want it to last.
 
OK guys I've decided to go with the keihin pj28 on my trail motor but I need a little info #1 what needle is needed and let's say its a cel are all cel needles the same size for different mm carbs? to make this question simpler is a cel needle in a pwk35 the same as a cel needle in a pwk28? #2 what's a good starting point for the jets? from what I've read up on so far it looks like a 150 main and a 48 pilot is a good starting point,let me know fellows and thanks in advance.
 
any idea guys on this comment ^^^^^^^^^^ above? anything that gets me in the right direction would be of great value and help,again thanks everyone.
 
blaster7 said:
hi everyone I have blaster uestions, I'm looking to pick up a new carb for my new blaster I'm looking at the PJ and pwk I know the PJ is more low end torque and pwk hi end and I'm looking for more low end so I'm thinking PJ I also think that a 150 main and 50 idel would be a good starting point but not 100% sure,I've herd alot of good and bad about those oko 30mm power jet carbs but I just do not like the idea of a China carb? anyone with some good feed back let me know also I will post my engine parts below and as always Thanks in advanced.
Vito's dual stage reeds.
stock carb running 240 main and 39.5 pilot.
aluminum airbox with uni filter and no airbox lid.
stock bore trail ported cylinder with forged piston.
factory 7 full pipe kit.
adjustable timing plate.
NGK BR9ES plug.
oil injection delete running 32/1 premix.
Click to expand...
Can anyone tell me if its ok that i put a 34mm carb on a stock 99 blaster. I dont want to blow it up. Thanks so much
 
You wont blow it up if its jetted properly, but you prob will lose power especially on the bottom end. Start your own thread and you will get more response
 
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