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Only runs with choke

  • Thread starter Thread starter tcarr
  • Start date Start date
T

tcarr

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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?
 
Running with the standard air filter?

Sorry - just spotted it's your first post - welcome aboard the good ship GSR.
 
Ya, I forgot to mention that. Yes, standard air filter.

And thanks for the welcome.
 
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.
 
Greetings and Salutations!!

Greetings and Salutations!!

Hi Mr. tcarr,

You carbs must be properly cleaned. You'll find complete guides on my little website. You have a 30 year old motorcycle that probably needs 20 years worth of maintenance. If you do all of the required maintenance properly, without skipping steps or taking shortcuts, you and your bike will be insanely happy. Now let's roll up our sleeves and get started. Pay very close attention to the information in the links below.

Let me dump a TON of information on you and share some GS lovin'. :D

I just stopped by to welcome you to the forum in my own, special way.
big_hi.gif


If there's anything you'd like to know about the Suzuki GS model bikes, and most others actually, you've come to the right place. There's a lot of knowledge and experience here in the community. Come on in and let me say "HOoooowwwDY!"....
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Here is your very own magical, mystical, mythical, mind-expanding "mega-welcome". Please take notice of the "Top 10 Common Issues", "Top 15 Tips For GS Happiness", the Carb Cleanup Series, and the Stator Papers. All of these tasks must be addressed in order to have a safe, reliable machine. This is what NOT to do: Top 10 Newbie Mistakes. Now let me roll out the welcome mat for you...

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Please click here for your mega-welcome, chock full of tips, suggestions, links to vendors, and other information. Then feel free to visit my little BikeCliff website where I've been collecting the wisdom of this generous community. Don't forget, we like pictures! Not you, your bike! :D

Thanks for joining us. Keep us informed. I will put you on my prayer list.

Thank you for your indulgence,

BassCliff
 
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. :D

.
 
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.
 
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.
 
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.
 
What happens when you take the "choke" off? :-k

If the engine slows down and dies, it might be a simple matter of raising the idle.
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.
 
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?
 
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
07.gif
 
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?
 
DON'T LOSE THE SPRING. :eek:

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

.
 
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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.
 
Okay, I got the idle adjustment screw problem fixed, and everything was peachy until I did a carb sync. When I synced the carbs (they were pretty far off) it raised my idle speed so much that when I have the idle speed screw out all the way I'm idling at about 3000 rpms. I'm guessing that means the adjustment screws on the carbs are off... even though I have them set to what was recommended here. (3/4ths turn out on fuel screws on bottom and 1 1/2 turns out on the air screws on top) are those the right settings for the VM carbs?
 
The fuel and air screw setting from Steve are correct

It is possible that you overadjusted your sync - try taking them down (clockwise) a 1/2 turn each and see what happens
 
tcarr said:
Thank you so much Steve, wish I knew a way to repay you.
Click to expand...
Now that you mention it, there is a way to repay. :-k

Get your bike running correctly, get some pictures of it and post them here. :D



tcarr said:
Okay, I got the idle adjustment screw problem fixed, and everything was peachy until I did a carb sync. When I synced the carbs (they were pretty far off) it raised my idle speed so much that when I have the idle speed screw out all the way I'm idling at about 3000 rpms. I'm guessing that means the adjustment screws on the carbs are off... even though I have them set to what was recommended here. (3/4ths turn out on fuel screws on bottom and 1 1/2 turns out on the air screws on top) are those the right settings for the VM carbs?
Click to expand...
Those are the correct setting for where to start with the VM carbs. Once the bike is warmed up, slowly turn each of the air screws (the ones on the sides), listening for highest idle speed.

Your high idle speed might be because there is not enough slack in the throttle cable. Try loosening the cable at the carb mount or at the handgrip to see if that helps.

.
 
I finally took some time tonight to take another look at it. And of course I have more questions... you all must hate me by now ;)

When I began syncing the carbs my #3 carb was about at half the vacuum of the other 3. So on final adjustment three of the carbs had the adjustment screws out rather far, while I had to turn the adjustment for #3 in (down) quite a way. As it is now #3's adjustment screw has the keeper nut almost level with the bottom of the screwdriver slot, and the other 3 there are about 4mm of clearance.

Not sure I explained that very well, if you need I can post pictures of it. The only thing that seems different about that carb (other than that adjustment) is the float looks better than the others - the others look somewhat discolored while that one looks like it may have been replaced at some point.

I checked the throttle cable and that seems to be strange too. I can't feel any slack at the hand grip but I can see slack in the cable where it connects to the carburetor (on both cables) when I'm idling high I can twist the throttle forward and lower the speed so long as I apply a slight pressure to it, but it doesn't seem to be putting any pressure on the throttle at the carbs in it's resting position.
 
When you did your bench synch do you recall if the adjuster screw contacted the plate at all?

Is there enough room for you to capture a decent picture of this setup in the bike?
 
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