GS750 850 upgrade

[doctorgonzo]

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

HA!
Well, that trashes that idea. I knew the 850 was heavier, but didn't think the 750 was. That's what I get for thinking.

I'm rolling the idea of a cafe or GP build around in my head, so trying to come up with ideas for getting max horsepower out of one of the smaller engines. Obviously the 750 is a deadend. Also looking for a use for my set of stock 1000 pistoins.

[TheCafeKid]

HA!
Well, that trashes that idea. I knew the 850 was heavier, but didn't think the 750 was. That's what I get for thinking.

I'm rolling the idea of a cafe or GP build around in my head, so trying to come up with ideas for getting max horsepower out of one of the smaller engines. Obviously the 750 is a deadend. Also looking for a use for my set of stock 1000 pistoins.

If you're making a cafe the 750 isn't a dead end. But I would think the only use your going to find for your stock 1000 pistons is gonna be in a stock 1000 motor. Maybe punch out an 850....but why do that when you won't gain the CR increase...

[doctorgonzo]

If you're making a cafe the 750 isn't a dead end. But I would think the only use your going to find for your stock 1000 pistons is gonna be in a stock 1000 motor. Maybe punch out an 850....but why do that when you won't gain the CR increase...

Yeah, no real reason to punch out an 850 when it's a heavier engine than the 1000. As you said, I'd just do the mods to make a 1000 engine fit.

[boingk]

If you're looking for a performance increase then use the tried and true methods.

1) Exhaust and pod setup - cheapest and easiest, make sure you tune carbies well though or you will end up with less horsepower.

2) Carbies - get some smoothbores to suit. Once they're set up they'll decimate all.

3) Head shave - Bump that compression ratio up a tad. 20 thou off is a safe bet.

4) Mild cam - often referred to as a 'Stage 1' cam, these will give an increase in performance while retaining most of the stock usability and reliability.

If you do all of that you'll be the envy of many bike owners, not to mention have a well-sorted machine that'll have quite a few more ponies than stock. Nothing to challenge 'modern' bikes, mind you, but definitely enough to surprise people. I would agree, however, that the best option is probably just going to a 1000 engine, especially if your bores are scored. All the work mentioned above, plus the boring/pistons/rings you'll need for your current unit, would probably run in excess of a 1000 engine and almost certainly not give you as much horsepower.

Summary? If you're after power, go a larger engine. If you want to get the most out of the engine you have, do numbers one to four and write back to us.

Cheers mate - boingk

[doctorgonzo]

I have a fairly built 1000 engine in my G. I just see a lot of 750s come around cheap, so seeing what the limitations of that engine were as far as using stock parts from a larger engine. I had no idea it was so heavy (the engine), which basically makes a 750 build (for me) need to look in the direction of a full engine replace. 750 is a little big for what I want to do anyway, how heavy is the 550 engine.. anybody?

[hampshirehog]

If you're building a cafe racer I'd stick with the 750 and do whatever mods you can / want to with the motor. The 750 has the BIG advantage of having a kickstart - in my book a must have for a pukka cafe job.

[doctorgonzo]

If you're building a cafe racer I'd stick with the 750 and do whatever mods you can / want to with the motor. The 750 has the BIG advantage of having a kickstart - in my book a must have for a pukka cafe job.

Interesting, know nothing about the 550 so didn't know their is no kickstart model, or the don't date to the kickstart days. I agree on the kickstart. This WHOLE line of thinking may be out the window though if the guy near me with an 1100E for sale for $400 hasn't aready moved it (and it isn't a rusted out hulk). My plan was to hack up a smaller bike, but that's a deal I can't refuse.

[Beaver]

If you're looking for a performance increase then use the tried and true methods.

1) Exhaust and pod setup - cheapest and easiest, make sure you tune carbies well though or you will end up with less horsepower.

Done

2) Carbies - get some smoothbores to suit. Once they're set up they'll decimate all.

Which ones?

4) Mild cam - often referred to as a 'Stage 1' cam, these will give an increase in performance while retaining most of the stock usability and reliability.

From where?

I need something to keep me busy over the winter

[hampshirehog]

Interesting, know nothing about the 550 so didn't know their is no kickstart model, or the don't date to the kickstart days. I agree on the kickstart. This WHOLE line of thinking may be out the window though if the guy near me with an 1100E for sale for $400 hasn't aready moved it (and it isn't a rusted out hulk). My plan was to hack up a smaller bike, but that's a deal I can't refuse.

The earlier 550s did have kickstarts (plus the bonus of 6 gears - all years) and they can make great cafe racers as well - just a bit less power than a 750. Both 550 and 750 came with spoked wheels which is another key factor for a cafe build.

(Yeah I know some guys have made some great cafe bikes without a kicker / spoked wheels but it does make the whole job easier).

[doctorgonzo]

First, what bike...

You probably don't want smoothbores. They are very tricky on the street (and $1000 a set), RS Flatslides are less tricky, but still take getting used to (and are $800), a slightly larger carb (and an engine that can use the extra fuel) like going from a 34 mm to a 36 mm or 38 mm CVs is a better all around choice (IMO, and more in the $100 to $300 dollar range)

APE (and others) sell Web Cams, they make multiple grinds. The "least" aggressive of those just gives a little more bottom end and doesn't require other mods (like shim under bucket conversion), just maybe HD valve springs.

After that you get into things that involve major engine work, oversized valves, bigger pistons, etc...

[doctorgonzo]

The earlier 550s did have kickstarts (plus the bonus of 6 gears - all years) and they can make great cafe racers as well - just a bit less power than a 750. Both 550 and 750 came with spoked wheels which is another key factor for a cafe build.

(Yeah I know some guys have made some great cafe bikes without a kicker / spoked wheels but it does make the whole job easier).

My head is spinning for sure with all the options. A lot depends on what falls in my lap (at the right price) now that I'm actively searching. I agree on spoked wheels as well. A must on a cafe bike.

[Beaver]

First, what bike...

You probably don't want smoothbores. They are very tricky on the street (and $1000 a set), RS Flatslides are less tricky, but still take getting used to (and are $800), a slightly larger carb (and an engine that can use the extra fuel) like going from a 34 mm to a 36 mm or 38 mm CVs is a better all around choice (IMO, and more in the $100 to $300 dollar range)

APE (and others) sell Web Cams, they make multiple grinds. The "least" aggressive of those just gives a little more bottom end and doesn't require other mods (like shim under bucket conversion), just maybe HD valve springs.

After that you get into things that involve major engine work, oversized valves, bigger pistons, etc...

A '77 750 which I don't mind investing a little time and money in. I am happy to accept my limitations of patience and expertise so I am trying not to take too large a bite. I am looking at the 850 pistons and cylinders being discussed here, and like I mentioned carbs/cams. Anything that involves someone not doing me a favour and doing paid work on the engine is out of the question as wages here are too high, and everything needs to be on a DIY level.

[doctorgonzo]

A '77 750 which I don't mind investing a little time and money in. I am happy to accept my limitations of patience and expertise so I am trying not to take too large a bite. I am looking at the 850 pistons and cylinders being discussed here, and like I mentioned carbs/cams. Anything that involves someone not doing me a favour and doing paid work on the engine is out of the question as wages here are too high, and everything needs to be on a DIY level.

Not sure what all the carb options are on the older bikes (with VM carbs) other than smoothbores, which are VERY pricey. Someone will chime in I'm sure.

Pretty much everything is DIY except the machine shop work (unless you have the gear and the expertise).

[boingk]

The older rides with VM carbs will generally benefit in the top end from fitment of a slightly larger size than stock, often just from the next model up and the jetted to suit. As mentioned above, you will be able to find these commonly and relatively cheaply. If you can retrofit the CV carbs they are good for an extra horse or two, plus potential economy benefits.

As for the 4 mods I mentioned, only the head shave is a machine shop job, and its not a pricey one as far as they go. All the rest you could do by yourself with a toolkit, some new gaskets and a bit of patience. I know how it is with the DIY, I'm a student at the moment and am fairly strapped for cash. One thing though, if you haven't got a decent socket and ring-end set yet then I'd definitely invest. Most useful thing to spend your money on is often a good set of tools.

Cheers - boingk

[Coady]

Going back to my 79 GS750, I am leaning towards an 850 cylinders and pistons for simplicity and cost (ie no machining needed) and I think stock compression may be preferable as the bike was originally designed this way. Also I want to keep stock airbox and have no interest in messing with the cams as currently I really like the rideablity and amount of power as it is (anything extra is a bonus of course).

But for arguments sake and cost aside, what is the best end result, in everyday use, between a rebore of my existing 750 cylinders with an 844 wiseco kit that ups the compression, and the above? Given that in my case I will be riding 95% of the time in peak hour traffic commuting. Would the wiseco upgrade reduce the longevity of the engine and be more temperamental?