GS550 shifting issues 1977 & 1978

[Chuck78]

I have an old gs650 4:1 header already, & will get the proper exhaust gaskets. I should have just ordered a gs650 complete gasket set, it appears that the only thing that could be much different may be the clutch cover vs a 77 550.

I think the salvage yard still has the bs32's, and there is another 650 there now but probably in lesser condition. I have a set of 88-89 gsx600f katana flatslide mikuni carbs, bst31's, that could be used with modified stock intakes and some port matching, and a set of 90-96/7 600 katana bst33 slingshot flatslides that are almost the same as the bst34's that boontonmike used on his 673cc 550 with mixed &matched intake boots. Not sure which to use. I can try out boontonmike's jetting w/stage 3 jet kit & adjust, so that I can have an excellent baseline starting point, but so would be the stock carbs with a couple of jet sizes larger.

I already have the dual K&N filters that fit either set of the Katana 600 carbs. I'm sure they have a better response and are lighter, but the BS32 is going to be the easiest, as it was already optimized for a similar set up by Suzuki.about the same price for the stage 3 kit and 4 rebuild kits (could just order 2 o-rings per carb from suzuki if needle&seat are good) as it is to buy a rack of bs32's, $30 in o-rings, and a set of pods. Probably more, as she won't want uni pods and I won't let her run any more EMGO's...

[Chuck78]

The squish needs to be between .035" and .040". I think i ended up at .038" using gasket material from the Auto parts store.

RC-2382 is the K&N part number. The spacing is correct yes.

And yeah chuck, if you compare the two plates side by side, you will see the differences. Interesting that the part nums are the same as the marks are clearly different. Mine is an '82 model and still used the mechanical advance. I haven't tried running it ever with the 550 advance unit. Wonder what change it would have. Hmm...

By squish, are you referring to the quench height between the bottom of the head to the top of the piston? as in the distance the edge of the piston is below the deck + the compressed head gasket thickness? I remember geeking out about the quench distance on a 406 small block chevy I built 11 years ago... .035-.050" on those, around .038-.043 was best it has been said. For water cooled sbc v8's

[Chuck78]

I believe the actual advancer on the 650 when maxed out has a total advance of around 40 degrees, if I recall what someone else posted, where the 550 is around 34 or 36 degrees. The 550 timing will run slightly cooler, the 650 timing I would think would need a slightly richer mixture, which may be why you are a good with stock 650 jetting. the more advance I believe would make more power on the top end. correct me if I'm wrong.


what was the thickness of the stock base gasket? did you have too much quench height? Or not enough? I may have this 650 head slightly milled to clean it up when I have it at the cylinder head shop getting a performance valve job.

[Chuck78]

And yeah chuck, if you compare the two plates side by side, you will see the differences. Interesting that the part nums are the same as the marks are clearly different.

I'm still really confused on this, & I believe what you are referring to are the actual timing marks on the advancer assembly with the spring loaded weights/arms that rotate on an eccentric bushing to advance the center rotor, not the fixed mark reference plate that shows top dead center with a timing light. No?

These advancers?:



Or the reference plate for the advancers? Is this not the same for both 550&550 w/673 top?



We have a Dyna S that was going to go in, and the ignition pickup's rotor fits the dyna we have, and there is another factory advancer of a different manufacturer that fits the other Dyna rotor. One is N-D, the other slips my mind.

[Sci85]

Yeah Chuck,the top pic comparing the timing marks is what I was referring to.

Yes, squish and quench refer to the same thing. IIRC, with the stock base gasket the squish or quench was too little. I've been on the road this week so I have not looked at my notes from the build. I will see if I can find them but I'm kinda a scatter brain and write stuff all over the place lol. If I dig it up, I'll post what the stock numbers where.

If you don't mill the head, then I can find the gasket thickness I used and tha will take the guess work out for you. If you decide to mill the head, then you are gonna have to take your own measurements and figure out what base gasket thickness you are gonna need.

[tkent02]

I believe the actual advancer on the 650 when maxed out has a total advance of around 40 degrees, if I recall what someone else posted, where the 550 is around 34 or 36 degrees. The 550 timing will run slightly cooler, the 650 timing I would think would need a slightly richer mixture, which may be why you are a good with stock 650 jetting. the more advance I believe would make more power on the top end. correct me if I'm wrong.


what was the thickness of the stock base gasket? did you have too much quench height? Or not enough? I may have this 650 head slightly milled to clean it up when I have it at the cylinder head shop getting a performance valve job.

They are maxed out on advance all the time, you almost never ride these little bikes below 3,400 RPM or whatever it is where the advance hits maximum. If you adjust the timing so the max advance is 40, it will just be a few degrees more advanced at idle, probably no big deal. You can also alter the advance mechanism so it moves a little farther, probably not that hard to get the same range as the 650 unit. Only talking a few degrees more. Slightly bigger springs will slow the advance a little should that be necessary.

I don't have the 650's ignition system, just going to go with the 550 one and see what I can get it to do.

I like points ignitions anyway, and I have a lifetime supply of points and condensers.

[tkent02]

Even lower than I thought, 17 degrees under 1,500 RPM, 37 degrees over 2,500 RPM for the 550.