GT550 Carb tuning

[Alan H]

I removed the pods last go 'round and went to stock airbox. Alan H cuffed me repeatedly around the ears (virtually) for using pods.

Hopefully the ears are virtually recovered now, I thought I only cuffed once!!!
It's just that pods take a lot of messing to get carb settings right and after all, Suzuki knew what they were doing back then.
I prefer the standard airbox to at least give a chance with decent running carburation-wise.

My GT550K (separate carbs) does about 40-42 MPG (imperial gallons) running 'sensibly' and the GT550A with linked carbs does about 30, but it is tuned and I just can't go slow on it for some reason - especially through the gears!
I had had lots of carb issues in the past and they have to be scrupulously clean as even a tiny bit of crap in a jet can balls up the running. I have had the carbs in the ultrasonic cleaner then blown through every orifice before refitting the jets and after to see that the spray doesn't spit or blob and looks even. I had one jet that sprayed lopsided a tad and found the tiniest piece of 'something' between the jet and main venturi. This caused lots of grief until I finally found it. I also soaked each crankcase in diesel for a few days before running each engine (the K was a US import and hadn't run for at least 35 years) and the A hadn't run for 30 years. Turn the engine over lots by hand (barrels off) and drain the cases - my take was that the diesel would clear the bearings and soften the seals and any rust on the seal faces. Then over oil everything before starting. It seemed to work OK on both bikes anyway. Also make sure that the exhausts are clear as if there is still debris inside, it may be causing back pressure or even a complete blockage so that you need more throttle than normal at a given speed if you understand what I mean.

I also have a Suzuki service manual from 1972 that is on electronic copy. It is for ALL models at the time and is relevant for some later models. Just PM me your email addy and I'll send a copy FOC. That goes for anyone on the forum.

[Vintageman]

Getting everything back to stock is good starting point for the GT550 can run well.

Those carbs you showed from eBay, if it was a book sure the cover looks bad, but that carbs from what I can see (need to see more) didn't show white oxidation in the carb body.

How was your carb about those two little pilot holes?
On the air filter side how was the air passage to needle jet?
How was the Pilot air adjust area (inside body and screw tip itself)

inside didn't look great but not too horrible either,

If they were not smooth they were damaged. I didn't see yours, but can tell you it doesn't take much to effect the ride. Just compare those old one to the new new ones. You need bright light and couple times magnification to check quality. well you have new ones no worries.

Did you recall the size of your needle jet's. For example -P0, P2 or P4 at the end. Did you check the jet needle to see if they were OK, OEM number on them, and what clip position?

Did you check your timing yet? Measure the resistance of your plug caps (coil if you like too)? Did you check plugs are gapped to spec, correct plugs?

You may want to decoke (remove carbon) from top end. just remove head to take a look... very easy job. If you have a lot of carbon can run poor... When carb is off , exhaust is off, and head is off you can get a good look at the condition of the top end. Doesn't need to b enew just no signs of real damage. If you are not sure send some hires pics looking into exhaust port, Intake port and cylinder bore. For ports make sure piston at TDC and BDC for pics so we can see piston skirt and bore. Head dome area pic. looking into exhaust port you can see piston rings... see if they are not stuck or damaged for example

Starting stock, functionally good carb bodies, new shinny OEM jets and carb set correctly, Check oil pump setting, good usable air filter, Engine timed (good strong spark), and top end decoked. Chances are high it should run well. None if this takes that long to verify.

Don't skip any of these steps is my advise before putting carbs back on

[smoketriples]

Hmm..out of town but to catch most of these. No idea needles had numbers!! . I'm pretty sure they were original, as carb jets were untouched by screwdriver and looked to be mikuni (stampings always better than aftermarket).

They were and are on fourth down from top notch/clip wise. Timing is dead on, at least for one cylinder, it's an accent ignition.

I did already put the carbs back on, and it sounds great, revs out of gear are significantly faster to jump up and quite a bit smoother. Since it is back together I'll give it a road test before tearing them back off to look in the ports.

Right now doing a lot of little things, removed the windjammer, fitting a proper windscreen, installed baffles, lots of other delayed bits. After that, a road test to see how it does. Then I'll pull head at least even if it's running well to decarbonize, I know the pistons have quite a bit of gunk on them.

Really seems to be turning the corner running wise, never heard it sound quite so good just revving the garage.

[Vintageman]

If it is running well enjoy it. If it needs some more tweaking let us know or have fun doing it. If it's running well enough you'll know it for it will make you smile.

I have the earlier 1973 550 and runs very well, put many thousands of miles on it... have touched/renew many parts least once now, even tweaked a couple times for a bit fmore top end power, but plan to put all back to stock again, bike/I was happier stock and less fussy street rider. Sweet engine with big wide broad torque of a mid range RPM.

Maybe keep playing with pipes

Stock (sitting on the shelf for now, they do sound nice though)
3 into 3 (tried what look like Bassani's. Good mid range boost, little no pull through on top end, small outlets, very quite sounding system: Jemco? Higgsspeed? do for power charactoristics
3 into 1: Wish I could see a video of GT550 with Jemco/Omar with 3 into 1 running and/or an honest review. Just may get one and give my own review

[smoketriples]

It's running pretty good now. Too cold for a nice long road test, but a few jaunts out and other than a bit slow right out of the gate it's great. If I want to take off fast, it'll snap my head back. Slow take offs it seems to take a second right off idle, not a bog really more like a 'what...what...', then it goes fine.

Idle is good, as is running at 55 or so with throttle barely open. No more of the rough '4 stroking' when idle is cracked maintaining speed. It does run better with the stock air box on than with pods, and I'm too lazy at this point to try and tune it for the pods.

I'd really love to get the heavy stock pipes off of it, but it looks like all chambers come from UK or other Euro so shipping is a bit high. Maybe a used set will show up (for a 550, who am I kidding )