Hi,

I own a Scrambler 400 and I would like to buy a new carb for it. The only mod on it is a dynoport pipe (torquier). I want more power throughout the powerband. Should I go with the 42mm ? The price is almost the same for the two carbs. I am afraid of having problems with the low end if I go with the 42mm... Any suggestions ???

 

Neither. The 39PWK is the way to go.

 

Yep, I'll second that opinion. Put some good reeds in it too.

 

Will it fit the stock airbox or do I have to buy a new one ?

 

It will not fit the stock air-box, my friend has a '97 Scrambler 400 and he put a 38mm Mikuni on and it wouldn't fit I don't see how it would with a 39mm, he got a clamp-on filter and took his air-box off. It works great if you don't go through deep water. You would have to find a larger intake boot to use your stock air-box

 

I spoke to a guy from polaris powersports and he told me that the 42mm fits the stock airbox with no modifications. For the 38mm, you have to buy an adapter. But my question is '' Is the 42mm only good for the very modified 400 or will it run fine with a stock engine??''

 

The 39 will fit the stock airbox, you just have to bend it downwards some. If you want to add a little extra power, get the HPD aluminum airbox and K&N filtercharger.

 

I have tested on a flow bench all 3 of the carbs listed . The 38mm and the 42 mm mikunis are the same carb . The 42 is tapered bored at the front of the carb to reach the maximum diameter of 42 mm at the very front . The venturi of the carburetor is still the same size as the 38 . In flow tests the 38 and the 42 mikunis flow identical amounts . At the same time I also flowed a 39 pwk carburetor , I am not at my notes at the moment , but as I recall the 39 mm flowed around 7% better . The 39pwk's I use will fit the stock box and use the factory choke cable . The rear of the carburetor is machined and has a special insert in it to make a nice fit to the original box .

The 39 pwk also is a little more forgiving and easier to tune in the midrange , highly modifified 400 polarises can be prone to burn downs at 30 -40 mph cruising speeds at half throttle or less . The 39 pwk seems to be easier to make fuel meter correctly and help avoid this problem .

 

HPD did not sell the 39mm until the 98 concentric drive came out because it would not fit properly, which is what I was told when I bought mine in 98. Also all the lean jetting problems were non-existant w/ the 39 vs the 38.
Jim Maloney 98 400 Scrambler
http://photos.yahoo.com/jim400scram

 

I used the 39PWK with the insert for the stock airbox and it worked great. Order one from Rick and be happy.[img]i/expressions/face-icon-small-happy.gif[/img]