Another newbie with a silly carb question.

[Anonymous]

Ok, so I have read at length about GS carbs and it interests me. I just picked up an 86' GS550ES. I was unaware it had dual carbs, opposed to the quad carb setups of the Yamaha and Kawasaki 550's I've owned. This makes my life easier when it comes to vacuum synchronization, so all is well. My question is, will this thing carburate smoothly with the stock jetting? It has the stock exhaust and air box/filter set-up. I'm in Chicago and am a competent mechanic, but am curious if I should just be looking at new pilot and main jets as it seems wickedly lean. It has 6100 miles and is very clean and fresh. If, after fully warming, I give it a handful of throttle, it hesistates pretty noticeably before really accelerating. Additionally, is it just a by-product of the dual carbs that it seems breathless in the upper RPM range, above 9500?
I know 80's bikes were all this way to some extent(lean), but my Seca's would get down the road smoothly, and really seemed to like the revs.
The carbs were professionally rebuilt by a dealer earlier this year, but I will be checking the balance none the less to ensure that I don't have what appears to be a common tuning issue, imbalance. Hopefully I won't have to tear into the carbs, but am already somewhat resigned this will become necessary.
Thanks, and I look forward to using this site for future insight on projects as they come up.

[Anonymous]

You don't say if it has the stock pipes or not. If it doesn't, a couple steps up on the main jet will help, and even if it has the stock exhaust, it wouldn't hurt to go up a step. Try cleaning the carbs and tank first

[earlfor]

Re: Another newbie with a silly carb question.

9500 rpm is beyond engine limits. Hope you enjoy walking. :-) :-)

Earl

[quote="PJD"]
Additionally, is it just a by-product of the dual carbs that it seems breathless in the upper RPM range, above 9500?

[Anonymous]

Re: Another newbie with a silly carb question.

[quote="earlfor"]9500 rpm is beyond engine limits. Hope you enjoy walking. :-) :-)

Earl

Additionally, is it just a by-product of the dual carbs that it seems breathless in the upper RPM range, above 9500?

I've seen brochures listing peak HP at 10,000 rpm on the '85. Did the '86 change?

[Anonymous]

10K RPM is the upper limit, but with a 18 year old bike (I have the 86 550ESG) I don't know how hard or near that range I would push it. I rarely take mine over 8500RPM. I had a similar problem with mine. The carbs had been "professionally" done, but I discovered that they were out of synch, and that the pilot screws (4 of them) usually covered and preset at the factory, had been uncovered and were an amazing 9 turns out, causing my bike to run rich, and carbon fouling plugs. I set them to 2.5 to 3.5 turns out and now have a much better response thru the rpm range and can get off choke quicker...

On a carb note, I have noticed that they do not (or I have not found) a 'kit" for these carbs. You can get gaskets (or make your own), so my main concern is the "O" rings. I have just ordered and have still some of the "o" ring kits for the 4 carb setup, and hopefully they will fit some of my needs on the 2 carb setup on the 550ESG as well as they do on my 4 carb, pain in the ass, but I love it,1981 GS550T rebuild project.

[Kabonkie]

Don't forget to check the slides as well. Same symptom of mine. An 83 550L with dual carbs. Slides in one of the carbs was sticky. Pulled the carbs, cleaned and lubed the slides and bowls (it'd been sitting a while) and found junk in where the choke slides fit in.

Started, then balanced the carbs. Runs great now without the hesitation.

Not sure if you can check these with the carbs installed. Different bike has 4 downdraft carbs and could remove the air filter and look down on them to make sure they were working. Didn't see a way to look in thru the air box on the 550..

[Anonymous]

Re: Another newbie with a silly carb question.

[quote="earlfor"]9500 rpm is beyond engine limits. Hope you enjoy walking. :-) :-)

Earl

Additionally, is it just a by-product of the dual carbs that it seems breathless in the upper RPM range, above 9500?

Redline is listed at 10,500, and I don't push it that far often. 9,500 doesn't seem outrageous and it seems willing, just out of breath.
Thanks for the insight, time to open the carbs, after I see if a simple carb sync improves it.

[KennyJ]

My 85 550EF has a redline of 10,500, and I push it there almost everytime I ride it (you know, merging with traffic, pulling away from lights, etc). 23,000 miles and it still doesn't smoke and runs extremely smooth. Engine is stock, stock pipes carbs and aribox. My group of friends had 4 of these machines, 1 83, 1 84 and 2 85's and they all ran the same: smooth decent power, and a great hook from 8000 up to redline. So if it is breathless at upper RPM's, I am guessing you have a problem (low floats comes specifically to mind).

The jets changed each year of production. I run 37.5 pilots, but have tried 40's (altitude of 1500 feet) and they were too rich. As for mains, mine runs 97.5's on the outer cylinders, and 102.5's on the inner (I am guessing that the richer mixture combats the hotter cylinders in the center, and cools them a bit).

The slides are prone to sticking, thus that could be a problem. I clean and assemble the carbs, then once I install them (no airbox boots on), I rotate each slide with my finger until they seem to operate the smoothest, then I hook up the airbox, synch them and ride.

To get them out, pull the tank, seat, side covers, battery, and battery box (2 bolts at the bottom, and pop the fusebox off the battery box). Remove the enricher (choke) slides out each carb (front, top side, 2 cables). Then loosen the airbox/carb boots, take the 2 airbox bolts out, and pull the airbox back, remove the boots, then loosen the intake boots. Pull the carbs back, twist them down in the front, and pull out the left side. About 1/2 way out, remove the throttle cable. Good luck, its a pain in the tush!

I always replace the pilots when I am in there.

Kenny

[Anonymous]

thanks

My 85 550EF has a redline of 10,500, and I push it there almost everytime I ride it (you know, merging with traffic, pulling away from lights, etc). 23,000 miles and it still doesn't smoke and runs extremely smooth. Engine is stock, stock pipes carbs and aribox. My group of friends had 4 of these machines, 1 83, 1 84 and 2 85's and they all ran the same: smooth decent power, and a great hook from 8000 up to redline. So if it is breathless at upper RPM's, I am guessing you have a problem (low floats comes specifically to mind).

The jets changed each year of production. I run 37.5 pilots, but have tried 40's (altitude of 1500 feet) and they were too rich. As for mains, mine runs 97.5's on the outer cylinders, and 102.5's on the inner (I am guessing that the richer mixture combats the hotter cylinders in the center, and cools them a bit).

The slides are prone to sticking, thus that could be a problem. I clean and assemble the carbs, then once I install them (no airbox boots on), I rotate each slide with my finger until they seem to operate the smoothest, then I hook up the airbox, synch them and ride.

To get them out, pull the tank, seat, side covers, battery, and battery box (2 bolts at the bottom, and pop the fusebox off the battery box). Remove the enricher (choke) slides out each carb (front, top side, 2 cables). Then loosen the airbox/carb boots, take the 2 airbox bolts out, and pull the airbox back, remove the boots, then loosen the intake boots. Pull the carbs back, twist them down in the front, and pull out the left side. About 1/2 way out, remove the throttle cable. Good luck, its a pain in the tush!

I always replace the pilots when I am in there.

Kenny

Thanks Kenny and Earl. I am absolutely sure I need to have a good look at the carbs now, as much as I would rather just ride. It runs in that hinter land of acceptable, but damn, I want all it has.
I definitely am not getting a top end pull, anywhere near what the midrange has.

[Anonymous]

It is worth your trouble to take them off and have a look.

There is an excellent article on how to do this from the homepage of this site:

http://www.thegsresources.com/gs_carbrebuild.htm

It tells you everything to watch out for.

When I took my carbs out, cleaned them and replaced all the O-rings and the float bowl gaskets, here were the problems I noticed:

1. Some idiot had set the floats wrong, i.e. from the lip at the edge of the float bowl rather than at the bottom of where the gasket is supposed to go.

2. The air screws were all set differently. I reset them to 2.5 turns out as recommended here.

3. Some areas were gummed up with excess carbon buildup as a result of having the jets set too rich and from running with the choke on all the time.

4. The idle was set such that the bike would NOT idle, and so the prior owner always had the choke on, which caused the above problem

I recommend printing that article up. It is a lot of pages, but handy to have in the garage. His carbs may not be quite the same as yours, but it should be close enough that you get the idea. I found it extremely handy. With that and my Clymer manual, it was no big deal.

After I did that, the bike ran 100% better, but still not all that it could be. I'm in the process of adjusting the valve clearances and I found that 3 of the 8 valves were tigher than spec.

I suspect that I will find the carbs out of sync. also.

If that doesn't get my bike up to 100%, I give up. I'll let you know tomorrow, hehehe.

I've been told by a local mechanic that if your bike is running too lean or if the valve clearances are too tight, you could burn an exhaust valve. So it is probably a good idea to delve into it a bit.

With stock pipes, everything I've read here suggests that your stock jets are fine. (only main jets ever get changed, and those only when you put an exhaust on that alters backpressure or change to K&N pod air filters)

I'm in the northern Chicago 'burbs too, in Round Lake Beach. If you need a hand, drop me a line and I'll do what I can. (nakedsv@yahoo.com)

I just bought a tool for depressing the valve tappets and a manometer. (for syncing carbs) Our policy in the Chicagoland GS rider's group is that if one person buys the tool, he rents it to others for $5 or something until it is paid for.

If the valve clearance is off, that could cause your lack of power in the higher revs too, so you'll want to check that. I am a goddamn expert on doing that now, though I will admit that you should be prepared to spend many hours scraping off the old cam cover gasket with a razor blade...

[Anonymous]

[quote="Smaug"]It is worth your trouble to take them off and have a look.

There is an excellent article on how to do this from the homepage of this site:

http://www.thegsresources.com/gs_carbrebuild.htm

It tells you everything to watch out for.

When I took my carbs out, cleaned them and replaced all the O-rings and the float bowl gaskets, here were the problems I noticed:

quote]

Thanks for the advice Smaug. I have a vacuum sync tool as well, although I haven't looked to see if the bike has handy vacuum ports on the intakes or not. Every other 80's bike I've tuned had them, so assume it will either have a small tube to directly connect hoses to, or a threaded hole that I can thread adapters into.
Like I said earlier, the guy I bought this off of had a $400 receipt from a dealer for a rebuild, so I am really praying that just sync'ing them will do the trick, although drilling out the air/fuel mixture screws should be easy enough. I am sure this thing is going to scream when I give it what it wants, good fuel and air.