GS750 850 upgrade

[dlanes]

I read about this and need a little guidance. What is all needed? I'm sure the carbs will have to be rejetted, but what size should I be looking for, or will I need another set of carbs? What about the bottom end? From what I read 79' gs850 is ideal. This is going to be a winter project for me.

[tkent02]

I read about this and need a little guidance. What is all needed? I'm sure the carbs will have to be rejetted, but what size should I be looking for, or will I need another set of carbs? What about the bottom end? From what I read 79' gs850 is ideal. This is going to be a winter project for me.

You need the cylinders and pistons and rings only. Jetting, heads, everything else is identical.
I have them if you want a set.

[gssuzukixxx]

tkent02,

I assume you have done this swap...did it make a big difference in power and torque? I have read that a GS750 makes about 63 HP and a 850 about 78 HP so that is substantial. Is there any issues with balance using the larger 850 pistons?

Sounds like a pretty simple and cheap upgrade.

Brian

[TheCafeKid]

Youll also need a gasket kit. From a 79 850.And a ring kit. Id suggest getting the wrist pins from the 850 pistons as well, but thats just me. I dont like mixing wear parts like that if it can be helped. Its not as cheap as you might think, you'll likely have a couple hundred into it depending on what you'll pay for parts, but its cheaper than the 750 bore kit, and you only lose .25cc per cylinder in comparison. They will not give you a compression ratio change like the bore kit will either.

[Coady]

I've read on the forum that some grinding is required to make the 850 barrels fit into the cases, as I'm interested in this upgrade too.

[TheCafeKid]

I've read on the forum that some grinding is required to make the 850 barrels fit into the cases, as I'm interested in this upgrade too.

Grinding is required only if you use the 80-81 jugs. They were a little different because of the change in the head in 80 for the emmissions required CV type carbs. If you find a set of jugs from a 79 850 they will drop right on to the 750 cases with no grinding required.

[Coady]

Grinding is required only if you use the 80-81 jugs. They were a little different because of the change in the head in 80 for the emmissions required CV type carbs. If you find a set of jugs from a 79 850 they will drop right on to the 750 cases with no grinding required.

Thanks for the info. I hadn't found a definitive answer on that.

My 750 has some vertical scratches in the cylinders - goes great (as long as I use hot plugs) but burns about a litre of oil per 1000kms and smokes a little when ridden hard and when hot.

I've been looking at these 750 cylinders and pistons on ebay as it seems a better/easier option than reboring: http://cgi.ebay.com/ebaymotors/ws/eB...K%3AMEWAX%3AIT

But is it worth holding out for 850 parts?

I'm not in a hurry to pull down the top end again but reckon I'll be keeping this bike for a while so want to get it sorted.

Sorry for hijacking your thread dlanes....

[tkent02]

But is it worth holding out for 850 parts?

I'm not in a hurry to pull down the top end again but reckon I'll be keeping this bike for a while so want to get it sorted.

Sorry for hijacking your thread dlanes....

No holding out required, I have two sets of pistons/cylinders, and one set of new Suzuki piston rings and gaskets.
Let me know if you want them.

[Coady]

No holding out required, I have two sets of pistons/cylinders, and one set of new Suzuki piston rings and gaskets.
Let me know if you want them.

Im interested. I'll send you a PM.

[cyclefvr2]

what about a cam and springs while its apart?, and atelast lapp the valves

[Coady]

what about a cam and springs while its apart?, and atelast lapp the valves

Changed the valve stem seals and measured the springs a couple of months ago, when I replaced the head gasket. That's when I saw the scored cylinders. Put it all back together and, as I said, it goes great (compression 135 - 145psi), but the oil usage is bugging me and it's impossible to read the plugs and fine tune - although I reckon I've got it pretty close.

[Detroit Diesel Man]

Great thread..having my 750 going back together i've been on the lookout for a set of 850 cylinders/pistons..maybe an upgrade late springtime if i cant find any sooner...good info here tho thanks!


DDM

[doctorgonzo]

I've been wondering just how big you could bore the 750 cylinders. If you machined them out larger could you use the sleeves from an 850 or even a 1000? I guess what I'm asking is if anyone knows the max you could bore one out to. I was thinking the other night about the crazy idea of taking that relatively light 750 engine and boring it all the way up to something in the 900's by using stock 1000 pistons. Probably not feasible... but then again maybe it is.

[Nessism]

I've been wondering just how big you could bore the 750 cylinders. If you machined them out larger could you use the sleeves from an 850 or even a 1000? I guess what I'm asking is if anyone knows the max you could bore one out to. I was thinking the other night about the crazy idea of taking that relatively light 750 engine and boring it all the way up to something in the 900's by using stock 1000 pistons. Probably not feasible... but then again maybe it is.

Just so you know, the GS1000 engine is lighter than the 750 engine so I'm not sure it's worth the hassle.

[TheCafeKid]

Just so you know, the GS1000 engine is lighter than the 750 engine so I'm not sure it's worth the hassle.

Yup, not worth the hassle. Plus, about 3mil is probably as large as you can go on the stock sleeves before they're too thin. Maybe if you used 850 jugs and punched em out etc etc. But by that point I'm just gonna find a 1000cc motor and mod the mounts on the 750 rather than mess with all that