GT550 Carb tuning

[smoketriples]

Well, they're coming all apart again as a 160 mile trip yielded 20mpg avg and very wet black plugs. Just to make sure nothing was incorrectly machined I have another new set of mikuni 97.5 95 97.5 and 25 idles coming.

Plugs were black and wet after the trip, so it's decidedly rich, it was a high speed trip so I expect the problem is more than just off idle to 1/4.

Not entirely sure I got the pipes right in between the carbs, as I haven't found any detailed pictures, but 'guessing' they can only go one way .

Been using a gravity only pingle style with vac blocked off, original works but never shuts off, may go back to it and put a cut off valve in. It has all new rubber inside except diaphram so not sure why it doesn't shut off.

[tz375]

Did you pull the plugs after you got home to the shop or was that a plug chop at WOT? If the plugs were pulled after you rode it home, then all you are seeing is that last tootle down the street and is indicative of a rich low end jetting.

Have you checked the FUEL level? Sometimes float levels look right but the fuel level is not always where it should be. I would check that next. Do it with carbs off the bike and with a remote fuel supply.

[GTandcbr]

Is your airfilter nice and clean? I would also check choke operation as the little plungers do occasionaly stick open. Make sure the choke cable is not sticking or tangled preventing the choke closing.i had the same problem with petcock. Its possible the plunger that is attached to the inside of the diaphragm is either sticking or the little O ring on the end is worn.

[smoketriples]

tz375, that was at the end of ride, so included about 100 yards of idle/slow. It seemed right with the horrid fuel economy though....should have remembered to do a cut off and coast. Just used my calculator and it was 17.1 mpg overall mileage, US gallons, stock air box. I removed the pods last go 'round and went to stock airbox. Alan H cuffed me repeatedly around the ears (virtually) for using pods.

GTandCBR, new suzuki filters. Choke function checked just before ride, chokes are both shutting off completely. Mine is a choke lever on the carbs (VM but on a rail for the 550s).

I'm a bit mystified. Granted I know the BS carbs much better, but economy and running this badly, after running well, is frustrating. This week it will be cleaned out again and everything back to new stock genuine mikuni parts (again) to see if there is any difference.

The pipes between carbs still bother me, as I had those out, including the plastic vent Y adapters. No clew if I got those in the right place, just hoping they only fit in one !
-Eric

[GTandcbr]

I dont have the gang carbs i have a J but does this diagram help re hoses between carbs?
http://www.partzilla.com/parts/search/S ... parts.html" onclick="window.open(this.href);return false;

[smoketriples]

I dont have the gang carbs i have a J but does this diagram help re hoses between carbs?
http://www.partzilla.com/parts/search/S ... parts.html" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;

I saw that one, it's a little confusing because it only lists one as vent, but my assumption is that pipes at rear of carbs are fuel, middle (both sides) are vent, and front middle carb/right carb are vacuum.

-Eric

[GTandcbr]

http://www.alpha-sports.com/suzuki_part ... 550/07.htm" onclick="window.open(this.href);return false;" onclick="window.open(this.href);return false;
If you look at item 85 this is described as a vent. Item 86 from the center carb is described as a starter hose. As you know the right carb has no choke but receives a charge from the center carb through pipe 86.item 87 is shown as an air vent too. So to clear this up.,
Back tubes are fuel
Middle left vent
Middle right choke/starter
Front left vent
Front right vacuum.

[smoketriples]

Oh, mine are truly screwed up then....mine looks like this one from ebay:

[smoketriples]

or better pic, like this one:

[tz375]

That's easy. Thick black hose is fuel distribution.

The two tiny ones (there should be a third) are bowl overflows. and the two larger diameter clear/yellow hoses are probably vents from/to the float bowls.

The clear/yellow rising at the front from #2 looks like the vacuum to operate the OEM diaphragm petcock (petrol tap)

The black short one at the front connecting #2 to 3 is the choke (enricher) for #3.

I would pop the bowls off and check that they are all clear.

I would also re-check that the AIR passages are completely clear and that the pilot outlet and bypass are also clear. Air are usually the hardest to check. Those carbs should run just fine with good pods from K&N, Ramair, Piper etc. Just avoid cheap EMGO ones. If the problem is rich mixture, try running without a filter just as a test to see what changes.

BTW, did you clean out the exhaust pipes and baffles? Small rodents and wasps have been known to find there way into very small places - especially if the pipes were off for any length of time.

[yeadon_m]

TZ is right about the exhausts, especially GT550 centre pipes.
Many I have seen (say 4 out of 6) have had the front most baffle plate almost blocked with carbon and the motor cannot breath out!
The plate has a hole either 8mm or 10mm depending on the model and I've seen them closed up to about 3mm diameter. Chip it clear with a long handled flat blade screwdriver. Makes all the difference to the centre cylinder.
Cheers,
Mike

[smoketriples]

No baffles, but I haven't cleaned out the pipes. This bike was under water for a while and then exposed to air with water everywhere. When I took out the sris water/oil came out of the bottom end, and carbs - tank etc were full of water. Nasty ugly lake water too .

Surprisingly, once the sris were out and drained, and all the fluids changed (a couple of times), it fired right up, just had a wonky idle which led to the carb rebuild. Now the only thing good about running is the idle (and WOT).

I did pull the carbs apart again last night. One of the bowl passages was clogged (the rear one) in one bowl, and the carb needle jet for center carb was covered on the outside with lake goo, inside didn't look great either. Chokes were working correctly but individual hand activation showed one to be very 'notchy'. Pulled it out and the choke area was full of dirt, the shaft was very dirty. Cleaned all that with carb cleaner and the shaft moves easily without the notchy feeling.

Everything I can find has been blown out with compressed air again, and reassembling tonight with another new set of main and idle jets, as well as new needle jets. Going back to stock petcock as well even though mine flows like prime in all positions, just going to use an inline cutoff.

If all that has no effect, I'll be asking for tips on how to clean out exhausts

[smoketriples]

Carbs are 'rebuilt' again. Found one clogged enrichment circuit in a bowl, the floats were off by a little bit (went to a ruler vice trying to fit my calipers in there this time). Book said 27.75 from gasket surface, I assumed without gasket and without 'lip' so I'm right near 27.75 from the flat gasket surface itself.

Needle jets were scummy on the outside, inside didn't look great but not too horrible either, replaced them anyway.

One choke assembly was sticky, took it apart and cleaned everything, put a bit of grease on the shaft, it's not sticky anymore.

It has all new mikuni stock jets, original needles, slides set at spec. A bit afraid to put them back on the bike because if the problem is still there I'm at a complete loss of what to do next . Would love to find another set but GT550 carbs are so rare.

[dgoodsy]

Don't be afraid to put them on, you can only be closer! After-all you did clean out some clogging and replaced some questionable parts. If they still aren't perfect there will be more clues that you and the experts on here will be able to work with, I'm sure!

Good luck!

[GTandcbr]

Just want to confirm with you that you are setting the float height by tilting the carb forwards and setting the tang when it just touches the extended spring on the float needle valve? Some people have set float height on the upturned carb with the spring compressed. I made a tool like this one
http://s79.photobucket.com/user/petead2 ... ml?filters" onclick="window.open(this.href);return false;[user]=142386883&filters[recent]=1&sort=1&o=0
Its much easier to measure and also makes sure the floats are level.