Only runs with choke

[tcarr]

I have a 1977 GS550. When I bought it it ran but only at about half choke. If I opened the choke more the RPMs would drop below about 700 and it would die. I disassembled the carburetors completely and cleaned them thoroughly. I put them back on the bike and my problem is better, but I still have to choke it about 1/3rd of the way to keep it running. I've checked the rest of the fuel system: petcock, fuel lines, fuel filter, etc and made sure it's not restricting my fuel flow. I've put the fuel adjustment screws and the mixture adjustment screws at the "starting" adjustment (1 1/2 turns out for the fuel adjustment and 2 turns out for the mixture screws). I've played around with them some trying to find a better adjustment, they do affect it some but not enough.
Any ideas on where to look next?

[hampshirehog]

Running with the standard air filter?

Sorry - just spotted it's your first post - welcome aboard the good ship GSR.

[tcarr]

Ya, I forgot to mention that. Yes, standard air filter.

And thanks for the welcome.

[hampshirehog]

Have you checked the carb to head intake rubbers and their seals (O rings)? The rubbers crack and the o rings perish / split = big air leak. If they're ok (and I would strongly suggest renewing the o rings as a matter of course if you haven't already) then it will probably (= almost certainly) be blocked pilot jets. On the 550 you have 2 jets in line in each carb. The holes are tiny and get gummed up really easily.

You need to clean those carbs absolutely scrupulously and then clean them again a couple of times for good measure.

[BassCliff]

Greetings and Salutations!!

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[Steve]

Another vote here for going back and re-doing the carbs correctly.

There are a LOT of passages in the carbs that you can't see, so the only good way to clean them out is to soak the carbs. Most of us use Berryman's Carb Cleaner Dip and soak carbs of unknown quality (those that have not been used for a couple of years) for a full 24 hours. When you get the carbs out of the dip (you do one a day, keeping the bits for each carb together), assemble them with a new set of o-rings from cycleorings.com. While you are getting the o-rings for the carbs, be sure to also get the o-rings for the intake tubes, as well as the stainless bolts for the intake tubes. That whole package will set you back less than $25, and your carbs will be as good as new when you are done.

If you have the stock airbox and exhaust, your pilot fuel screws (the ones on the bottom) should be out about 3/4 turn. The pilot air screws (the ones on the side) should be about double that, or 1 1/2 turns. When the engine is warmed up, tweak the air screws for highest engine idle speed.

While the bike is down for a few days to clean the carbs, it's a perfect time to check your valve adjustment, too. With proper valve clearances and clean carbs, it will run like a NEW bike.

.

[tcarr]

Okay, I've replaced the o-rings on the boots, and while I had them off I re-dipped and re-cleaned the carbs (and replaced the o-rings - thanks for the link I was having trouble finding someone that sold them). I have the adjustment screws set to what Steve recommended as stock. It's running better but still needs some choke. My boots seem to still be in good shape - no visible cracks and still squishy like rubber should be. I still haven't gotten the carburetors synced - waiting to take it to a guy with a small motorcycle shop instead of springing for the tool myself.

Okay so, my questions are:
Is there a way to check the vacuum on those rubber boots to make sure they aren't my problem?

Could out of sync carburetors contribute to my need for choke?

And, the bike has quite a bit of vibration - need to get the valve clearances adjusted - could that be causing a need for more throttle/choking?

I've checked my compression and I'm within the range according to my shop manual. I'm also assuming I could possibly have a timing problem but I don't want to go tearing into things that might be fine just because I overlooked something here.

[cowboyup3371]

Your bike will still need choke to start up if cold for any length of time; that's normal. However, if they are out of synch you will get the vibrations you speak of. The valve adjustment will help (DO THIS BEFORE SYNCHING CARBS) but I would also check for anything loose in your frame mounts as well.

[tcarr]

Yes, I know it will still need choked to start - I understand that. I'm talking after it's warmed up - it still needs to be choked somewhat to keep it running - not as much as when I start it of course but still enough to where if I bump it with my knee it becomes a problem - not that I've done that yet but the potential is there.

[Steve]

What happens when you take the "choke" off?

If the engine slows down and dies, it might be a simple matter of raising the idle.

.

[tcarr]

It does, I'm assuming that I would use the air (top) and fuel (bottom) mixture screws on the carbs to raise the idle? I've tried to some degree to do that, but I don't seem to have enough adjustment in the screws to adjust it far enough. Of course I'm not entirely sure what I'm doing, but I have been able to raise the idle somewhat - which allows me to choke it less to keep it at idle, any tips for adjustment?

[Steve]

Use the IDLE SPEED ADJUSTER.

That would be the large knob at the TOP of the carbs, between #2 and #3.

#62 in this picture

[tcarr]

Okay, great, thank you so much! I was wondering about that knob and hadn't remembered to ask about it. If I turn the idle speed adjuster screw in the spring (#63 in the diagram) gets compressed all the way before the end of the adjuster makes contact with the plate that it pushes against... basically my screw is doing nothing and I can't get it in far enough to get it to make contact to do any good. I can see on the plate a wear mark where it used to rest. I'm guessing I could try losing the spring as a temporary fix though. How much adjustment should that screw be able to do?

[Steve]

DON'T LOSE THE SPRING.

Obviously, there is something wrong somewhere, you should be able to hold the engine at redline with that screw.

.

[tcarr]

Okay, I figured losing the spring was a bad idea. I guess I know now where my problem likely is.
Thank you so much Steve, wish I knew a way to repay you. All you guys that volunteer your expertise on these forums deserve so much.