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GS550E 78 big bore kit

  • Thread starter Thread starter dfgood
  • Start date Start date
If your motor needs a rebore and new pistons then the Wiseco kit is worth doing - I was assuming that you were just upgrading (Rule no. 1 - never assume anything). You will notice a performance gain, especially if your current top end is a little tired. The GS650 top end is an alternative, though I've never done it myself and I'm not sure if you could fit VM carbs rather than CVs. (That could start an argument - I'm a dyed in the wool fan of VMs where you're in total control of what goes on down below and not what is effectively a take of the old British Leyland SU carbs - the very worst of 70s British motoring design which I could rant about all day...).

As for brakes, maybe my expectations aren't as high as others but I've always found the original spec reasonable and just ride knowing what they are like. Compared with modern stuff of course there is no comparison (though the best stopper I ever had was a GT250M, all original - stop on a sixpence). Decent pads are a must - you get what you pay for. Another thing that has worked for me is an annual (or 'every now and then') 'recon' of the discs. I reckoned that with them going all shiney and polished the friction would be down and using a rotary wire brush on a little angle grinder just lightly 'de-buff' the surface. I mean lightly as you don't want to wear the disc out too quickly or create an uneven surface. Be a bit wary of the first few bites on the brakes though as it can be fierce until it beds down a bit (a bit like the brakes on your car going rusty over a weekend if you've driven through a ford on the Friday night). And braided hoses - an absolute must.

On the subject of crap brakes my mate has just restored a 1954 New Hudson autocycle. Passed its MOT but god knows how - now that is seriously deficient in the brake department. The QE2 stops quicker.

Nice looking bike by the way - like the colour and nicely polished.

Wally
 
VM carbs on the 550 are 22mm vs. 32mm for the later CV's. The CV's have the butterfly in the airflow but even so, they flow way more air than the VM's (ports in the head are larger as well) so they would be a better platform for the big bore kit in my opinion.

A big bore 550 sounds like a fun project but a little on the spendy side considering the low cost 550's go for - you will never get your money back in resale.
 
skreemer said:
ha all the pictures are gone. I'll see if Nerobro still has them and I'll try and get him to put them back up.
Click to expand...

Hi SKREEMER, any idea when we can get the photos of the 650 conversion. Would like a copy of them if that is possible.

Cheers

Don
 
The difference in size between the VMs and CVs isn't all that clear. The widest part of the CV is 32mm at the motor side of the carb, but the carb has a narrower middle section, where it is in fact quite oval in shape. The VMs, which are VM22s, are 26mm at the motor side of the carb but again with a narrower, oval centre. (I've got sets of both somewhere and ought to take some more measurements - might be interesting). It seems to me that Suzuki changed where they measured their carbs when the switched designs, possibly a marketing ploy (32s are bigger sounding than even the VM28s on a 1000). Honda did the same thing.

The obvious difference is how the 2 designs work. VMs are simple; open the throttle, the slide lifts = more fuel / air. With CVs you open the throttle, the butterflies open and as a result the slides lift. But the amount the slides lift depends on the pressure diiference caused by more air flowing through the body of the carb and this pressure is related to the draw on the airbox, or different draw if you run individual filters. This leads to all sorts of variables when swapping filters / jets etc and I've never found it easy to get CVs running sweet - might just be me as I've known others get it right (but I'm not so sure they admit to it being simple). VMs are a doddle - you have easy changes with jets and needle position and perhaps slide cutaway (ok, slide cutaway is tricky if its DIY).

I like simple 'cos I can at least pretend I understand it.

Wally
 
Suzuki_Don said:
Hi SKREEMER, any idea when we can get the photos of the 650 conversion. Would like a copy of them if that is possible.

Cheers

Don
Click to expand...

Pictures didn't do it for me. If you know how to rebuild a gs engine, you'll have no problem. I learned every step of the way and glad i did. Pretty much just remove the 550 top end and replace with the 650 top end. The hardest part for me was the grinding i had to do on the lower end to get the 650 cylinder "jug' to slide down into the mouth's of the 550 lower end.
 
hampshirehog said:
The difference in size between the VMs and CVs isn't all that clear. The widest part of the CV is 32mm at the motor side of the carb, but the carb has a narrower middle section, where it is in fact quite oval in shape. The VMs, which are VM22s, are 26mm at the motor side of the carb but again with a narrower, oval centre. (I've got sets of both somewhere and ought to take some more measurements - might be interesting). It seems to me that Suzuki changed where they measured their carbs when the switched designs, possibly a marketing ploy (32s are bigger sounding than even the VM28s on a 1000). Honda did the same thing.


Wally
Click to expand...

I agree that the difference is not as great as the listed measurements would lead one to believe. Suzuki lists the same horsepower for the VM equipped engine as the BS/CV carb engine. In actual usage though, my experience is that the CV engine is quite a bit peppier. The engine ports are clearly larger so that might have something to do with it.
 
brveagle said:
Pictures didn't do it for me. If you know how to rebuild a gs engine, you'll have no problem. I learned every step of the way and glad i did. Pretty much just remove the 550 top end and replace with the 650 top end. The hardest part for me was the grinding i had to do on the lower end to get the 650 cylinder "jug' to slide down into the mouth's of the 550 lower end.
Click to expand...

I have never rebuilt a GS engine but have rebuilt many others. Just trying to do all my research before I dish out the big bucks and start looking for a 650 top end. Its good to read your comments though and be reassured that the task is quite straightforward.

Cheers
Don
 
Thanks BRVEAGLE. Will a 4 valve cylinder head fit or is that going too far.
 
Suzuki_Don said:
Thanks BRVEAGLE. Will a 4 valve cylinder head fit or is that going too far.
Click to expand...

well there are no 4 valve per cylinder 650's...

and a 550 4 valver might mit but it's not practical as the pistons are still 2 valve.
 
VM Vs CV carbs

VM Vs CV carbs

I agree with the comments on the carbs, I had a GSX250 with CV carbs and it was such a pig to try to make those plungers and diaraghms work properly. My 550 with the VMs really are simple, and I dont mind the little bit less power.
Thanks for the brake tips, I think softer better pads may be the only answer.

Cheers

Darren
 
What about an overbore on a TSCC? My '86 550 is in need of a power boost!
 
zig06 said:
What about an overbore on a TSCC? My '86 550 is in need of a power boost!
Click to expand...

Get the jugs from a 650, overbore and when I say overbore I mean OVERBORE the hell out of it. 3mm if I remember correctly and then stuff in some TSCC 750 pistons. Of course I have no idea if it would work in real life seeing as I don't know much about those TSCC engines other than they were 4v. But the 3mm overbored 650 jugs have already been done, So I don't see why it wouldn't work.

In the end you'll have a 740cc
 
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