January 27, 2011
What would make my old motorcycle stumble, like it is running out of gas?
I have a 82 suzuki gs450, which is somewhat like L? W runs out of gas? Used during the trip. I think some people call it stumbles. It can not go faster than 65 km / h in sixth Transition. I know it should go faster. I think it is in the carburetor, which I cleaned, but maybe I did not clean it good enough? Perhaps it is needs new jets? It's really clean inside by the way. Any help is welcome.
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Comments on What would make my old motorcycle stumble, like it is running out of gas?
Sounds like you either have clogged jets (easily cleaned with a tin peice of wire and carb cleaner), improper air/fuel mixture, or it may be a spark, or timing problem. Check your plugs, maybe a fouled plug or improper gap could cause this too, but it does sound more like a fuel issue. I'd check the plugs first because its easier than pulling the carbs when troubleshooting.
(just a note, the comment below mine is only for idle adjustment, its going to have little, to no effect while the throttle is opened up. Your idle jets in your carbs have no effect on a bikes performance when the main jet and secondaries are in use.)
You probably need to adjust you're fuel/air mixture, it's a screw on the carb (and if you've just cleaned it inside and out you already know where it is.)
With the engine WARM.
Adjust your idle speed till the bike starts with the least effort, but without the engine "racing".
(you'll know what idle speed is right, it'll sound good!)
If you're idle speed is ok, then adjust the mix screw clockwise by 1/8 turn and listen fofr any change in the engine revs.
If no change, or it gets slower, then put it back and try 1/8 turn anti-clockwise.
If the engine revs faster then repeat adjustent in the direction you where turning it by increments of about 1/8 turn.When your mix is optimal, the engine will idle fastest.
(note, you may have to lower the idle speed if the bike "races" while you're doing this.)
This is the "old-fashioned" way of doing it, It's worked well for me for 30 years.
Just to add: If you have not completely disassembled the carb, removed all the jets and blown out the passageways in the body with compressed air you really can't be certain that it is truly clean. These are a type of carb known as CV for Constant Velocity. The name isn't critical but they do employ a diaphragm [part #5] as part of the throttle slide. If one of these diaphragms has an air leak it can affect your running at speed in the way you describe. They are expensive so you will want to inspect them before ordering any replacements.
Inspect the throttle slide diaphragms for rips of tears.
Make sure the carb tops are sealing – when the diaphragms get old, they expand making it close to impossible to install the carb tops.