kz750 jug/pistons on a kz700 bottom end

hey guys. I just purchased a 1984 kz700 for a real good deal. The bike was cheap but needs a lot of work. I did a compression test on the the bike and found that compression is very low on all cylinders. Ive read that the kz700 was only produced for 1 or 2 years so I figure finding a replace cylinder/set of pistons will be very difficult. On the other hand they made kz750's for many years and from what Ive heard, given the right year/model, the bottom end is essentially the same as my kz700-A1 (even the stroke is the same). So i have a few questions that I will sum up in a list and hope you guys can help me with.

1. Can I simply take a set kz750 jugs and piston and bolt them in to my kz700. will i have to make any modifications?

2. If this is possible, what year/model 750 should i look for to take the cylinder/pistons from? I would like to make this as simple as possible.

3. What kind of power difference should i see? I know the diplacment will increase but what about the compression ratio etc? Will this effect the running characteristics of the engine?

4. Ive read the cams from a kz750-L4 are the same as the cams in my kz700-A1. Is this correct?

I am planning on fully restoring to bike over winter so I am in no hurry but I would like to do as minimal work to the engine as possible to get it running/driving. I really dont want to have to split the cases or do anything major like that.

come on, someone must know.

Can't answer most of your questions as I have no direct experience. However, I have heard that there are great similarities between the 700 and 750's. Are you in Canada? The reason I ask is that the L4 was not released in the USA? If you are in the US, then you are more likely to find an L3...which has the same cams as the 700A1. The cams are the same in the 700 and the L3, R1, and a number of 750, etc. Have you checked www.Kawasaki.com and looked up each of the models? You can crosscheck parts on the exploded diagrams to see which models are identical for each part. There may be some differences between the 750 and 700...for example, the base gaskets for the KZ750R1 and KZ700A1 are not the same suggesting the jugs are not a drop-in replacement...but someone else may have personal experience with this.

Thanks for the info. Ive done some research and found that the kz700 uses the same crank as almost all kz750's after 1980. I also found that it has the same exact cases as the kz750 L3. I beginning to believe the swap should work smoothly with no major issues.

STILL if someone has done this please let me know!

Does the Bike run?

If it has been sitting it may need some oil to free up the rings.

The bike has 36xxx miles. I sprayed some dw40 in the cylinders and was only able to get about 90 psi at the best. I did also sprayed some ether in the intake and it wanted to start. The bike sat for several years.

Do you think i should put some oil directly into the cylinders?

Oil would indicate if low compression is because worn rings or valves seats. Or both. Still a job would have to be performed.

The 700cc class in the US, was imposed on the Japanese manufacturers by Harley Davidson and the US government. HD asked(and got)the Government to slap a tarif on imported bikes over 700 cc to give HD a break.

Japan responded by reducing their 750cc bikes capacity bikes to 700cc to avoid the tariff while was in effect.

Question is what Kawasaki changed to get to 700cc, the bore or the stroke, or both.?? I believe the 750 is 66mm x 54mm. If crank is same, my guess is that it changed the bore, therefore would have to be increased to accept the bigger diameter pistons.

According to my service manual the 700 has the same stroke as the 750, the only difference is the bore. I figure I have 2 choices.

A: bore the cylinders I have now over to 66mm (+2mm) and get some 750 pistons.

B: get a set of 750 cylinders and pistons.

Agree. And it makes sense, as the difference between the 650 and 750 is the bore as well.

I would look for the less complicated/expensive solution, and definetely would persue converting it to 750cc, to give the bike the natural top capacity was supposed to have.

I would consider a valve job also while the head is out.

If you are going to bore it out to a 750, I am wondering if there is an 810 kit also for the 700 like the 750? Unless you can get the 750 pistons used I can't imagine saving that much compared to the cost of a wiseco kit for the 750.

Also, what all do you need? Are you looking for jugs, pistons, heads, cams? Or just the piston kit?

I think you could use a 810 kit in a 700 the same as a 750.

I am planning on getting a set of used cylinder and pistons to keep things simple. All i need is the jugs and pistons. If i can find a piston kit for cheap i may go that route but its not likely.

I would put a little Marvel mystery oil in the cylinders and let it soak. Also low compression could be from the valve clearances being tight and hanging a valve open. also make sure you check the compression with the throttle held wide open.
Does the bike run? I would see if it could run atleast before tearing into the motor. Especially if you just want to start riding this summer then do a major job in the winter.