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Only revs properly if idle is set in stall range

  • Thread starter Thread starter Connorjeanes
  • Start date Start date
C

Connorjeanes

Guest
Hello,

first post from me!

Ive had a GS550E for a while and the carbs have been a nightmare!

Bought from ebay as a non runner, top end rebuild, new rings, machine work on head etc.
i have a small part time custom bike shop and vapour blasting business. I do a fair amount of work on bikes but we mainly work with old British bikes this is the first transverse 4 I've worked on.

Never been able to get her to run right, first lots of issues with intermittent flooding. Float needles getting stuck in there seats. Bit of polishing sorted that and float height adjustment.

now I'm battling with a strange idle/climbing revs situation. The bike starts on choke revs fairly high. cut choke and it revs smoothly as long as the idle screw is set all the way out, at a point that causes stalling. If I set the idle screw for a good idle and then Rev the engine breifly the revs stick at what ever point it gets to and doesn't drop. I have to unscrew the idle screw all the way and it drops down and stalls if I don't give it some extra throttle.

bike rides well and has plenty of power/smooth revving with the screw all the way out you just have to keep some throttle on when waiting etc.

I can't think what this is! As I understand it a vacum leak would cause more of a wandering idle situation which doesn't fit.

Any ideas on this would be awesome!


Cheers Connor
 
Have you performed the following:

Adjusted the valves?

Completely stripped and dipped carbs?

Replaced intake boots/O-rings?

Sealed airbox?

PS: We need to know what year GS550E you have.
 
Was just coming to add that info! Don't know the exact year as it was imported into the uk and doesn't have an age related plate. Mag wheels, single disk, VM slide carbs. I've been working on the assumption it's a 1978,

i ended up up suface grinding shims myself for all the buckets, I'm pretty confident everything in the top end is good, honed the barrels (no real wear showing) new valve seats where cut and Valves lapped in. Valves and guides all looked good.

i had 2 sets of carbs, both have been stripped, ultrasoniced and vapour blasted. Best 4 carbs built up with rebuild kits. Again everything looks good slides arnt worn etc etc.

not done the air box but I think it is sealed, I'll check

intake manifolds are a bit grotty but I found some o rings and I've done the carb cleaner trick and it has not effect on revs.

buying a new set was my best guess and next move

Cheers
 
Cables routed properly?? Is there a little slack in the "pulling" cable when the throttle is off? Have you done a gauge syncing yet..that will change it a lot as far as where the idle knob has effectiveness.
 
Where are the pilot fuel screws and air screws set? Did you verify to make sure the fuel screw tips are not broke off in the carb bodies?

You need fresh carb boots and the proper O-rings. Spraying crap on them doesn't always show when there are air leaks.

Vacuum sync is important for a steady idle.

A properly sealed airbox is important.

Anytime you use "carb kit" jets they may be the wrong size and/or poorly made. Compare the numbers to those in your factory service manual to see how everything lines up.
 
When cleaning the carbs, did you do anything other than ultrasonic to clean the passages INSIDE the carbs? They are the ones that clog up and cause problems. Over on this side of "the pond", we have chemicals that work decently-well, not sure what you have available, but ultrasonic is reputed to do a good job, too.

Surface grinding the shims might be a bit ... "sketchy" at best. Did you just grind them until you had proper clearance or did you take them down to a standard size? Either way, there is no way of telling what size you have, without measuring it each time. It may have gotten you going this time, but it might prove to be a pain on the next valve adjustment. If you have notes on the new shim sizes, I would recommend having the next size down for each shim ready for your next valve adjustment.

If you have an older 550, you should have the VM carbs. They have two adjustment screws for fuel mixture. The one on the bottom is primarily for fuel, its setting will depend on whether you have stock intake and exhaust equipment. If stock airbox and exhaust, set that screw about 5/8-3/4 turn out from LIGHTLY seated. For a 4-into-1 exhaust, maybe about 7/8 turn. For individual pod filters, make it about 1 full turn. The air screws on the sides of the carbs should start just under twice the setting of the fuel screw. If they are a bit less than double, the mixture will be a bit richer, letting you start your tuning easier. Turn the air screws slowly, listening for highest idle speed.
 
I have read that the "spraying crap" doesn't work all the time, figure I'll get the boots as you suggest.

one of the 8 carbs I have had the tip of a fuel screw jammed, not using that one! All carbs are 100% free of blockages all jets are factory spec and all needles are good. Fuel screw at 7/8's air at double that.

Basically I had loads of shims all of which where really thin or thick, I needed some in the middle of the range, By putting in a thin shim that has to large a gap you can measure and work out the shim thickness that would sit you bang in the middle of correct tolerance.

so each was measured and I ground the tick ones down so they are bang on. All thicknesses are recorded.

dont have a return cable only a pull!?

Cheers
 
Connorjeanes said:
...dont have a return cable only a pull!?
Click to expand...
Again, we would need to know the year of the bike.

One clue would be the carbs that are on it. Here in the US, we had the VM carbs through the '79 model year, then switched to the BS carbs (CV type) from '80-on. You might have had the VM carbs for another year or so after we lost them. You mentioned that you had fuel screws and air screws, so that hints at the VM carbs, but the year is still in question. No VIN plate on the steering stem? The upper-right corner of the plate would have the assembly date, the lower-right corner would have the date code for the model year (it's a letter).

The VM carbs did, indeed, come with two cables, the BS carbs only had one.
 
Already provided the info

Connorjeanes said:
Was just coming to add that info! Don't know the exact year as it was imported into the uk and doesn't have an age related plate. Mag wheels, single disk, VM slide carbs. I've been working on the assumption it's a 1978,
Click to expand...
 
From the description you have either an EC or an EN ('78 or '79). It doesn't make much difference. The VM carbs had two throttle cables. If you fit a return cable, and set your idle screw where you had it before, "If I set the idle screw for a good idle and then Rev the engine breifly the revs stick at what ever point it gets to and doesn't drop.", you should find it revs up through the range, then back down again.

http://www.cmsnl.com/suzuki-gs550e-1978-c-usa-e03_model34243/partslist/BLCK0035.html#results
 
I've got a cable ordered so we will see! I figured that because it has a return Spring on the throttle mechanism this provides enough movement!?

cheers
 
Connorjeanes said:
I've got a cable ordered so we will see! I figured that because it has a return Spring on the throttle mechanism this provides enough movement!?
Click to expand...
Evidently not, or they would not have fitted the second cable.
 
Connor

Your symptoms do point to an air leak, and the carb to head boots are usually the suspects

Sounds like you have everything else done correctly so far
 
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