750 engine in 850 frames?

Nigeldtr · Oct 5, 2013

Hi,

I am putting a 70 750 engine back together and have a MKII 850 which also needs rebuilding :cry: . Can I put the 750 engine straight in the 850 frames while I find time for the 850 rebuild? (PS the 750 is a huge project and will be ages before I get it done).

Rohan · Oct 5, 2013

At the large lump level, 750 and 850 engines are just a bolt-in swap.
At the smaller level though, things like carbs and manifolds and exhaust pipes and exhaust nut roses are slightly different, you'd have to watch closely what goes where.

Haven't actually done this to confirm, have eyeballed the parts though.
Tell us how it goes !?

Should have asked which model of 850 too.
A Mk3 leccy start isn't going to mix with a 750 engine ??

Nigeldtr · Oct 5, 2013

I have a combat head on the 750 so I will just use the 850 carbs - hope the jetting is OK. I can swap the exhaust if necessary and will need to r- route the breather. I hope the drive sprocket, alternator etc all fits!

htown16 · Oct 5, 2013

I have a 72 750 engine in a 74 850 frame. Bolted in with no problems. All of the primary side is exactly the same. I used the 72 exhaust without the crossover pipe. One plus is you can use the oil filter. The jetting should be pretty close. You may have to go down some on the main jet. You also may need to go to a #3 slide instead of the #3.5. Do some plug chops at different throttle positions.

Nigeldtr · Oct 5, 2013

htown16 said:
I have a 72 750 engine in a 74 850 frame. Bolted in with no problems. All of the primary side is exactly the same. I used the 72 exhaust without the crossover pipe. One plus is you can use the oil filter. The jetting should be pretty close. You may have to go down some on the main jet. You also may need to go to a #3 slide instead of the #3.5. Do some plug chops at different throttle positions.

Great news - really appreciate the feeback

Flo · Oct 5, 2013

You will have to change the main jet, slide, spray tube & needle.

acotrel · Oct 5, 2013

How do you do plug chops at different throttle positions ?

Torontonian · Oct 5, 2013

Nigeldtr · Oct 5, 2013

Flo said:
You will have to change the main jet, slide, spray tube & needle.

OK I'll put the 750 carbs on

750 engine in 850 frames?

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