Gt550 idle issues

[Kevgt550]

Hey guys. First post here, but I’ve been on here a ton looking for resources. Wanted to throw my story out and see if anyone has some suggestions. Bike was running for a year, a little rough but i just wanted to get my first bike on the road. It’s a 77 gt550 US model, basically all original other than maintenance items.

The carbs were done with the best kit i could find, but it has #98 main Jets on all 3 and did before as well (the only thing out of spec as far as i know, should be 95L&R, 97.5C)
Pilots have been cleaned and are the original #25.
float height: about 15.75mm as best i could.
I thought issue was the slide height which i never changed, just brought up the throttle adjustment screw until it idled before.
Now the clearance is 1mm on the side going into the engine.
I did have an issue with the choke jet and cleaned that out and it is good now. After bringing the slide height to spec it starts and runs better than i have ever had it, but it seems to be too lean. Messing with the air screws only helped it die quicker.
Reason i say it is too lean is that after about a minute it will slowly lose RPM until it cuts off the engine, or when i brought the throttle screw up just a tiny bit, it slowly gained RPM until about 2k RPM then stopped about there, all while the throttle was not touched and screw not moved. And this was with a warmed up engine.
Also: Spark plugs are new, tested the firing of the plug wires and they fire Consistently. After some running, plugs are a light brown and dry.
My current instinct is telling me to try a #27.5 pilot jet. Reason I’m not worried about the main Jets being a bit different is that the idle is what gives me issues. I want to see if anyone has some wisdom. I’ll try to attach the specs to reference.
I would take it to a good mechanic at this point but i have no clue if any of them are any better than me on my guessing game hunt, since i have not found someone well versed on 2 stroke triples around me by chicago. I’m young but very mechanically inclined, I just don’t have the experience, never rode a motorcycle until this one, never seen another one of these, most of the resources are on UK bikes, and i have no idea what a 2 stroke 3 cylinder should sound or feel like when perfected.
Good news is: it was free after sitting in my grandpas garage for 20 years.

[karl pa]

Welcome to the forum.
I am not very good with carburation, others are much better than I am. couple thoughts I have are, many don't like rebuild kits, they use mukuni jets. Another suspect is air leaks on carb boots, you can spray carb cleaner on boots and carbs while running and see if engine rpm changes.
Are you running stock airbox with good filter? Pods filters can give lean issues with jetting.
Is timing set correctly?

[dollydog]

if it's been sitting for 20 years i'd suspect the crank seals being a tad hard
cheers, dd.

[Kevgt550]

To Karl, it has all stock air box and new filters. Timing is good. I did not suspect a boot leak but i will be using your tip to check that.

Dolly dog, I don’t doubt that you’re right, sitting is never good. I did have it running for a year just fine so I’m hoping it’s not an internal issue. If i need to pull the motor to do crank seals, then selling might have to be an option with how much i would spend for an engine refresh. Trying to cover all other bases first

Thank you both for the replies

[Harrymail]

There is a member on the forum called Teazer who I am sure is in Chicago. He may be able to help you. He's certainly very knowledgeable with 2 strokes

Paul

[Cliff56]

Check your float height. Should be 25.8mm.

[Cliff56]

http://www.3cyl.com/mraxl/gt/manuals/su ... /cover.htm

[Cliff56]

https://www.oldjapanesebikes.com/mraxl_ ... les/page-9

[Kevgt550]

Check your float height. Should be 25.8mm.

Either i read incorrectly as 15.75 and set it to 15.75mm or i mistyped. I do know i had my manual right next to me. So i did not believe the float was a problem, will investigate this again though, and thank you for some good links!

[Kevgt550]

There is a member on the forum called Teazer who I am sure is in Chicago. He may be able to help you. He's certainly very knowledgeable with 2 strokes

Paul

Thank you Paul, I’ve been addressing other issues that popped up, but once I’m back to working on the idle, if i can’t figure it out I will look to see if teazer does work on these. Thanks!