keihin 34mm on a mostly stock blaster?

[03blasterboy]

So my buddy had to buy a new carb for a blaster he just bought, while he was looking around on ebay he found a 34 and bought it. the thing im worried about is that the quad he bought isnt ported, no bbk, and not even a redone head. The only things it has on it is an fmf and filter and some weird aluminum boyesen reed block thing. I am thinking that this thing is going to be worse then a stock carb and especially bad on the low to mid, this is where most of our riding is done too. Will it be to much for a semi stock blaster.
Thanks,
Jakob

 

[Herpderplol]

way too big for that stock

porting and a different pipe could be run with it

 

[blasterkid1998]

way too big for that stock

porting and a different pipe could be run with it

x2 on that. with that fmf and no porting the stock 26mm would be best.

 

[98blaster]

X2, way to big, I have a built engine an I use a pwk 28 bored to a 30, I also ride mostly in low to mid area, my quad chugs like a 4poke it dont bog an need clutched to get going, just hit gas an it picks back up

 

[03blasterboy]

Yeah thats what i was thinking. I will have to tell him that and maybe convince him to get something else. Do you think anyone on the forums would maybe trade a stock carb plus cash for it?

 

[Herpderplol]

make a for sale/wanted/trade thread

 

[Awk08]

and that wierd aluminum thingy is a boysen rad valve, also aimed at low/mids

 

[03blasterboy]

hmmm didnt know that i will have to tell him about the carb and rad valve. Thanks guys i will post something if he puts it up for trade/sale.

 

[amartin_72]

Try it

 

[jus_me]

Try it, with the boyesen rad valve having a smaller intake it may make up for the larger carb maybee not. I did same thing only with a 32mm (diff brand carb) and it liked it. Then i opened up the rad valve a bit then top end was better but dropped a little in bottom end. Also im looking fir a 34mm and have a few stock carbs.

 

[03blasterboy]

I told him about it today and he was a little uneasy about buying and selling on forums he said he would maybe trade for 2 stock carbs which i thought was ironic lol. im sure he will be on here tomorrow.

 

[tfaith08]

I have a rule of thumb that I go by.

For every 4hp increase due to airflow, the carb diameter should be increased by 1mm to maintain the same powerband. Increase the diameter further to aid in top-end power production, decrease for more bottom end.

For example, if you increase the displacement, have it ported, aftermarket airbox, and reeds and end up with 30hp, you should be looking at around a 29mm carb. That leaves you with either a 28 or 30mm carb. The 28 will contribute to more bottom end power, whereas the 32 would work well with top end. Of course, an aftermarket dome shape will pay off pretty well, but that won't increase the airflow requirement.

Now a 4mil stroke on a 240 with a right bend pipe and open filter with a good reed setup would probably call for 35 and up, but I don't see where anything like that was mentioned.

 

[reckless]

Where are you from im sure i have a stock carb minus spring as i was using a cr125 spring in mine, im from uk and would let it go for a pint £5 plus postage rather than it sitting with other redundant parts collecting dust

 

[03blasterboy]

It's my buddy who needs it so I will let him know.

 

[best]

I have a rule of thumb that I go by.

For every 4hp increase due to airflow, the carb diameter should be increased by 1mm to maintain the same powerband. Increase the diameter further to aid in top-end power production, decrease for more bottom end.

For example, if you increase the displacement, have it ported, aftermarket airbox, and reeds and end up with 30hp, you should be looking at around a 29mm carb. That leaves you with either a 28 or 30mm carb. The 28 will contribute to more bottom end power, whereas the 32 would work well with top end. Of course, an aftermarket dome shape will pay off pretty well, but that won't increase the airflow requirement.

Now a 4mil stroke on a 240 with a right bend pipe and open filter with a good reed setup would probably call for 35 and up, but I don't see where anything like that was mentioned.

Hmmm, my KTM 125 runs a 39mm and the DT200 makes 32hp on a 26mm.
My son's Blaster makes nearly 40hp on a 26mm. We have tried 28, 32, 34, 38 and 39mm carbs.
I don't think it is as simple as the above "rule".
It has to do with air flow, rpm and torque characteristics of the engine.
Big carbs take too much from the majority of the Blaster's powerband.
All top end power makes them too hard to ride, gotta keep some mid-range.

True enough, the port window area is larger than the carb throat area but the engine only has a fraction of the cycle to pull the mixture through that window. With a well designed intake tract the air will have more time to flow through the carb. A long narrow intake tract on either side of the carb is important for momentum, and some volume before the reed if you use a small carb. The gain is controlled mixture and throttle response in the lower half of the rpm range for minimal loss on top end.

Steve Best

 

[mlrblaster]

I would agree that a 34 would be too much for a blaster that is mostly stock. I have a 34 on my '04 but it has been stroked, BBK, dynoport right bend pipe, porting and head work done by KOR. Works well on that set up. I would stay with the 26 if I was him. I had a '92 blaster that I bought new that ended up with a LRD BBK with porting and their right bend exhaust that I ran with the stock 26 carb. It ran well enough to keep up with the 250r's I was racing with. I think if the 26 is jetted properly it should perform well on many different set ups. Just my $.02.