Super Jet 650 crank with 701 cylinders?

[davy87nj]

I've heard you can put 701 top end on a 650 lower. Is this true? whats the pros and cons of this? What needs to be done with the ebox? Can you use the same carb or do you need a bigger one? What impeller would work well with this set up? Any addtional info would be great. I cant find a good deal on a 701 but I have seen some cylinders and heads for sale I could afford.

 

[tor*p*do]

the lower case has to be clearanced (machined) for the cylinders
not a big improvement due to the restictive airflow through the 6M6 cases
CDI for a 6M6 has lower rev limit- replace with a 61x CDI or MSD
better to just get a set of 61x cases for cheap
carb will work fine with bigger jets
prop = Hooker IMHO

 

[kevbo]

I've heard you can put 701 top end on a 650 lower. Is this true? whats the pros and cons of this? What needs to be done with the ebox? Can you use the same carb or do you need a bigger one? What impeller would work well with this set up? Any addtional info would be great. I cant find a good deal on a 701 but I have seen some cylinders and heads for sale I could afford.

A cylinder, pipe, and low pitched impeller is what makes the improvement. All three are required for any meaningful gain. The rev limit must also be raised some. The 650 case is not as bad as everyone thinks, I never found a perceivable difference between a 6M6 and 61X case. I used both under the same cylinder, the 650 case ran richer for a given carb tune.

 

[rwilliamtaylor]

I'm thinking of taking the same route with my 650. What exactly needs to me machined on the 6m6 case to fit the 61x cylinder?

 

[kevbo]

The top case needs material removed to clear the cylinder sleeve. It can be done well enough with hand tools or even better on a drill press with a large rotary file.

 

[davy87nj]

Just making plans for a winter build. Trying to find a cheap 701, or at least a good core. Sad thing is, is I have a dual carb 701 in a raider, but I cant justify wasteing the couch because friends and family ride it quite often, and ive owned it since 1996, brand new old floor model. Thanks for the info. If anyone has pics of the material to be removed that would be great.

 

[rwilliamtaylor]

Just making plans for a winter build. Trying to find a cheap 701, or at least a good core. Sad thing is, is I have a dual carb 701 in a raider, but I cant justify wasteing the couch because friends and family ride it quite often, and ive owned it since 1996, brand new old floor model. Thanks for the info. If anyone has pics of the material to be removed that would be great.

Why not put your 650 in the raider for friends and family. They probably don't care about a little less grunt.

 

[vwking]

i have a good set of 6m6 cases that have already been clearenced for a 61x 701 cylinder and i also have the reed block with boyson reeds and intake manifold and 61x 701 cylinder that has a 83mm bore but needs a new bore or hone. all for sale if anyone is intrested pm me