Differences between XJ750 maxim and Seca transmission?

I replaced an engine from a XJ750 Seca into a XJ750 maxim for a friend. Seems the gear ratios are different. The Maxim engine only ran on 3 cylinders and I found a XJ750 Seca engine, rebuilt it and installed it in the Maxim. It runs like a scalded dog but the transmission ratios seem to be geared much higher. It seems to turn a lot more RPM than I remember the Maxim engine turning. Any one have any information on this? Is it because of a possible difference in tire sizes between the Maxim and Seca?
The old engine had an excellent transmission and I don't want to get rid of it until I know for sure. I wound up rebuilding and painting the complete bike from the ground up, polishing all the exposed aluminum. It is beautiful.

Ed

 

Not sure of the differences, but I have 2 used final drives from 750 secas.

Pretty sure that is what they are call. The aluminum hub that attaches to rear wheel.

I could sell one cheap + shipping IF it will solve your problem.

 

The easy fix is to buy a 18" SECA rim for the Maxim and fit the tallest tire that won't rub the swingarm.

 

The Seca motor has hotter cams, pair that with a motor that actually runs on all cylinders. Makes a big difference.
I don't think there is a difference in the tranny or the final drive, but not sure.

 

The only difference is the 750J's outputn spur gear ratio is 1.297:1, compared to 1.361:1 for the other models.

In the rest of the 750s and also the 650s, the gear ratios, final drive ratios, middle gear ratios, etc. are all the same.

 

I rebuilt the engine and then the whole bike. It seems extremely low geared and goes through the gears as quick as you can shift them. In the highest gear, it sounds as though it need a couple more. I don't recall it being like that with the original Maxim engine.
This engine is solid mount rather than the rubber mounts that the Maxim engine had. It never occurred to me to check the transmission ratio. Considering that the engine is solid mount I expected some kind of vibration but it is extremely smooth. I noticed the other day that my friend had the engine sitting outside and the cover was blown off it. Cylinder walls are getting rusty. I originally suspected to find a hole on a piston but after getting the head off, it all looked good around the piston and cylinder wall area, but I had already rebuilt the Seca engine, so in it went. If I was savvy enough to post a picture I would like everyone to see the bike. It looks brand new.

 

Does the Seca 750 and the Maxim 750 use the same final drive, I’m trying to put a 18inch Seca rim on my Maxim.