Gt550 idle issues
Posted: Tue Jul 19, 2022 8:40 am
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.
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.
