650 to 550 carb swap

[waterman]

After finishing up a complete rebuild and reseal on one of my 650g, decided to look at this 82 550L that I bought last fall. It starts fine, idle great, but just never seemed to run like I thought it should. Others here had stated that a 550 ought to be as quick as a 650 considering weight increase with shaft drive, etc. This 550 would get to about 70 mph and just run out of steam.

I had pulled carbs when purchased did the usual: cleaned, new orings, reset floats, check fuel level, synched, the works. Valves are in spec, compression is nominal, some previous owner had replaced ignition with dyna s, stock coils, newer spark plug caps, new spark plugs. Stock exhaust, stock airbox, Uni foam filter, freshly cleaned and lightly oiled. Battery is fairly new and fully charged.

One curious note was that the main jets were 97.5 as opposed to stock 92.5. Didn't think this would make a great difference as many have suggested bikes are lean anyway. I figured if it ran crappy, maybe would search out a set of stock mains.

Last week went for short ride and noticed fair amount of bogging in higher rpms and started to lose power going up a long hill. On way home, dropped down to fourth gear and held wide open while it was boggy, did a plug chop. Insulators showed lean.

Today, got possessed and decided to do a carb swap with set of decently tuned 650g carbs. They will bolt right in, only concession is losing choke, no biggee, can grab choke rail from side. Figured bike ought to be rich since mains in 650 are 110. Went for a ride and wow. Starts great, warms in a hurry and seams to run nearly as strong as 650. No bogging, seams to pull great.

My question is what should I do with the 550 carbs to get them to run right. I know the simple answer is leave the 650 carbs on, but I would like to get it (650g) completely fixed and rideable (minor front end issues). I have a set of carbs from a 650E model which I have salvaged some parts from that I could possible set up but its main jets are 97.5.

I find it strange that from the 550 to 650 the main jets are 7 sizes larger. There are obviously other differences in carbs, needle jets are different, 550 have more taper. Slide springs are bigger diameter in 550, pilot air jet is larger in 650.

I know this is probably beyond what most can help with but would like to hear from some 550 experts on how they have tuned there 8 valve motors. As always, thanks in advance.

 

[Nessism]

Sounds like something is wrong with your 550 carbs. The white plugs indicate it's running lean as you already noted. You might want to go back through them, paying attention to the main circuit. Might also be a good idea to make a float level gauge, with the clear tube like the manual shows, and verify the floatbowls are properly filling.

Good luck.

 

[Suzuki_Don]

I have a set of carbs from a 650E model which I have salvaged some parts from that I could possible set up but its main jets are 97.5.

Hi Ed. I noticed that you have a set of GS650E carbs that are not on the bike. I need to find out what the ancilliary parts are that fit these carbs. There is plenty of info out there about the 650G carbs but not much on the 650E.

I have a thread going at the present time you could look at if you wanted more background. Would it be possible for you to check all the bits and settings on the GS650E carbs for me.

Main Jet:
Pilot Jet:
Main Air Jet:
Pilot Air Jet:
Starter Jet:
Needle Jet:
Needle:
Throttle Valve (butterfly):
Diaphragm Spring:

I think that's about it.

Thanks Ed in anticipation.

 

[waterman]

Give me some time, most of these bits are in my 550 carbs! Not sure if I wrote down the differences. Work and family are eating me alive. Realize that I need a vacation from both--unfortunately problems will still be here when I return. I'll see what I can come up with this weekend.

Don't want to throw another curveball but I have noticed that my 650g carbs are different from one bike to next. Nearly positive that one has had engine replaced with later 82 motor. I believe the carbs were then cobbled together with old parts. Reason I say this is the throttle plates are numbered differently and the air jets also differ. Both motors seem to run similar however. Strange.

 

[Suzuki_Don]

Give me some time, most of these bits are in my 550 carbs! Not sure if I wrote down the differences. Work and family are eating me alive. Realize that I need a vacation from both--unfortunately problems will still be here when I return. I'll see what I can come up with this weekend.

Don't want to throw another curveball but I have noticed that my 650g carbs are different from one bike to next. Nearly positive that one has had engine replaced with later 82 motor. I believe the carbs were then cobbled together with old parts. Reason I say this is the throttle plates are numbered differently and the air jets also differ. Both motors seem to run similar however. Strange.

Yes I am finding the same thing Ed. As you know I am converting my 550 to 650E specs, but I have bought a set of GS650G carbs and there seem to be some differences. If you look at my other thread you will see the "G" carbs have #135 throttle plates and the "E" model have #125. Don't know why and what the difference is.

Anyway anything you can do for me will be greatly appreciated.
Thanks. Don.