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Gents, I'm in need of some options regarding a rough idle I've been dealing with on my 93 GL1500. Here's a little history that might help in formulating any diagnostic opinions you guys have.



- Purchased the bike earlier this summer. During the test ride it ran smooth at idle and during low RPM acceleration. Purchased on started the 400 mile drive home.

- About100 miles into the ride I came to a stop and bike began idling very rough and had choppy acceleration at low RPMs.

- During the remainder of the ride I ran through an entire can of Sea Foam. No change in the problem.

- The day after I got home I changed the fuel filter and thought I had fixed the problem but after about 30 minutes of riding the rough idle returned (when the bike hot).

- Went to the dealer. They concluded that the carbs needed overhaul.Becuase I didn't want to drop the ~$650 for the overhaul, they offered me a "heavy duty" fuel additivesold by Yamaha ($20 for the bottle...ouch! but still cheaper than an overhaul). You burn the entire bottle in one tankful then you have to change the oil.

- Beforetrying the additive I got the bike good and warm so it was idling rough.Filled the tank and put in the additive. After about 20 minutes of riding the roughness completely disappeared. Thought I had the problem licked!

- However, after about 400 miles of riding the roughness began to GRADUALLY return.

- I tried the additive again and the exact same scenario happen. Smoothed out and then roughness gradually began to return.



Has anyone else experienced something like this? Does it sound like the carbs? Any idea why it smooths out and then gradually begins idling rough again?
 

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I know it does not explain why the additive cured it temporarily but I bet it needs the vacuum lines replaced.
 

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Busdriver
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I'd also pull the spark plugs and check for fouling.
Could be the additives are temporarily cleaning the plugs up, and once your back to straight gasoline in your tank the plugs get oil fouled again.
Are you having to top up the engine oil? Is there any signs of smoke from the tailpipes?
Also a possibility of incorrect plugs (heat range).

Also check your air filter, and while you have it out check the carb slides for any restriction. They should both move freely with a finger. If you feel any resistance or grit spray them with a little WD40 and work them till they are smooh throughout their travel.

Keep at it and let us know.
 

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I haven't checked for rust but wouldn't it be caught by the fuel filter? When I chnaged the filter the old one was clean.:?
 

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What grade fuel are you using, it's possible that the additives have an ingredient which improves the octane quality of your fuel. The fact that the problem goes away after the additive is added would suggest that your problem is purely fuel related. Perhaps there is a quantity of water in your fuel tank and by keeping it topped up the water content is not being 'used'. Many fuel additives have methyl hydrate as an ingredient, this is commonly used by boaters as their boats are prone to condensation, for removing or shall we say making the water content palatable to the engine so it doesn't quit on you. You could siphon off the fuel and separate any crud and fit a suitable filter. Or just add a half cup full of Meths to your full tank of gas and see what happens!!
 

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Piaggio MP3, was 02 GL1800
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Fine rust dust is so small, it will go right through any fuel line filter you can find.

IF, the fuel tank has rust in it, that must be taken care of.

I would drain the tank, and inspect it closely looking for sediments, rust, or water lurking in your fuel.

The vacuum lines can deal you a world of misery, check them all for being tight and still flexible. The main one, and easiest to get to, is the one between the middle and rear, left side cylinders. It makes a very sharp 180 degree turn. I had to snip 3/8 inch off mine and slip it back on.
 
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