Mikuni makes a host of TM style carbs that have an accelerator pump on them.

Since Mechanical carbs are directly opperated by the rider, at low rpm when a rider opens the throttle wide open, there is a drop in velocity and suction in the venturi of the carb. This drop in suction will reduce the ability for fuel to be sucked out of the float bowl and hence you have a lean condition for a split second.

You can change needles or nozzles to try and compensate but then at partial throttle openings, you are too rich.

Carb companies designed a pump as you open the throttle is will give an "extra squirt" of fuel for a short time and cancels this lean condition without having to resort to settling between too rich and too lean.



Main reason why companies don't install them on pitbikes is normally pitbikes come with smallish carbs which don't have this issue but when you install a bigger carb to try and make big power, you then have your carb issues.



Companies would rather have a good all around running engine vs something that just makes a bunch of power.

 

so are they worth the money?

 

so are they worth the money?

Depends on the build you do. The biggest problem is trying to get them to fit on the engine and the chassis because the carb bodies themselves are bigger along with all the mechanical crap attached to them.



I used TM32's on alot of my out door bikes with out accellerator pumps but, that's also with big engines.

 

well would it be worth it for my bike? haha

 

I wouldn't do it although I know Hack and others on this forum have had great success with the TM28 with the pumper carb.



It's up to you, but just like anything. It's not perfect and will require some messin with.

 

Yea they work great but they are so big in size your gonna have a problem fitting them under most frames.

 

Yea they work great but they are so big in size your gonna have a problem fitting them under most frames.

He has a YX top end on a 70 chassis, so it may clear.

 

yea it might, there are 2 different tm28-1 carbs, the stock ones out of mikuni are 28mm bore then the ones off some of the drz250 bikes are the same carb bored to 31mm.

 

Not only is there a problem with making them fit in the chassis but also making a bracket to support such a huge carb so that it doesn't tear the spigot off the manifold.