putting a 750 motor on a 650 frame...

So a while back i realized i needed o overhaul he top end (please excuse missing T's, my keyboard sucks). Instead, I found an engine from an 81 XJ750 that runs and only has 10,000 miles on it for a good price. The external dimensions, mounting points, and weight are identical. I'm wondering about two thing hough. An old timer across the street mentioned hat puting a bigger engine on might be too much for the frame to handle as the welds are only heliarced. is that so? and since the bore diameter is 3mm larger is was wondering if i'd need to rejet the carbs o gain full power. old timer said i shouldn't have to, but I hough i'd ask the experts. any advice?

 

I'm no expert, lol

Sounds like your planning on using carbs fron the 650, Is this correct?

 

Turltejoint has a 750 on a 650 frame. I don't think the frame is a concern. I have seen 1100s on 750 frames. The carbs are the same you will need to rejet.

Info stolen from Chacal's parts list:


NOTE: stock Hitachi XJ series carbs used the following original sizes:

#106 (XJ 750 Seca, 1984 only)
#107 (XJ700 non-X)
#110 (650 models)
#120 (all 750 models except 1984 XJ750 Seca)

NOTE: stock Hitachi XJ series carbs used the following original sizes:

#36.5 all XJ700 non-X models.
#40 all XJ650 Maxim, Midnight Maxin, and Seca (RK) models, and all XJ750 models.
#43: all 1984 XJ750 Seca and Euro/UK XJ750 models.

 

There are many threads over the past 3 years that detail successful swaps. Search Topic- - " 750 650" or "swap"
The frame will hold up, but is slightly smaller and lighter.
Keep the carbs with the motor, or move the jets for the 750 into the 650 carbs. There can be shifter issues swapping between Seca's and Maxims.
Also '81 ' s have cable type tachs, 82 and 83 are electric.
Try not to use pods. Use the oil cooler. Take pics !

Here's some "t"'s you can cut and paste - - ttttttttttttttttttt

 

ROFLMAO - :lol:

 

keeping the original 650 carbs on the bike, so i will replace the Hi jet with the proper one. the low jet is the same. both engines are `81, the new one is just a 750. thanks for the advice, now i just have to get the bike to the shop.... and i appreciate the t's, really. :wink:

ill check out those other posts about this also

 

oops... just remembered something. the new motor has the YICS stamp on it. I'm assuming that is not an issue because the YICS system is on the carb assy. not on the motor. Correct? i sure hope so.... my current carbs are non YICS.

 

YICS is on the intake ports on the head only - this will not affect your carb choice.

 

will a non YICS carb work with the YICS intake head? man im new to this.... anyway, chacal. it seems that you sell parts. reading before posting is a good deal, huh? do you have the `81 750 main jet needle, the main and pilot fuel jets, and the main and pilot air jets in stock? do i even need to replace all those? if you do have the parts i need could you PM me or otherwise let me know? gracias

 

YICS has nothing to do with the carbs. Your 650 carbs will work (as long as you re-jet to 750 specs).

 

same thing happened to my se & the whole omposition turned into an artload of rap

 

so i ve been told that i need to rework the tranny and change the oil level sender, and im looking for some info on both of those.

As far as the tranny goes, i've been told to put the 650 guts and cover on the 750. is this correct? why would i do this?

THe oil level sender is the little doohickey bolted into the oil pan right? so i should swap the sender on the 750 with the one on the 650 (750 motor/650 level sender)? and im guessing this is to alleviate any oil light problems? does anyone have the wiring diagram for this?

I also need to switch to an electric tach. does anyone have any tips on how to wire it in, or a good source for one?

any help at all is appreciated. thanks fellas!

 

Don't move the transmission, use the one that comes with the 750 engine. I'm not sure you can even interchange them.

Make sure you get the shifter with the 750. It uses a linkage. If you use the 650 shifter your shift pattern will be 1 up, 4 down, and you need Herman Munster feet to reach it.

You will need to change the main fuel jets, jet needles, and both air jets.

 

If the "cover" means the sump, the only reason you would swap is if they were different and you needed clearance to fit the 650 exhaust (this is a common issue with GSXR 7/12 motor swaps).

 

answers i was looking for thanx! switching the tranny didn't make any sense, until i reread the post i found the info in. the other person was switching just the motor and didn't hace the linkaged shift lever, so they needed to switch the 650 guts and cover to alleviate the gears being upside down. bingo... i figured out the oil level issue, it bolts right up. thanks for all the help!!

anyone have an electric tach they woulnd't mind parting with?

 

Electronic tachs get their input from the grey wire leading to the 2&3 ignition coil.

 

Actually, it's the orange wire on the 650 models (750's used the gray coil wire), but it probably doesn't make a difference..........

 

I'll face the rewiring challenge when it rears its ugly head. gotta get a tach first. ebay it is. thanks folks!