HelloI have a question regarding a 74' Yamaha TX500. I have just had it serviced (its been sitting for 25 years). Carbs rebuilt, one new (used new) ignition coil, and a cleaned gas tank. The bike runs fairly well, but I'm having two problems. First, when the bike gets good and warm, it idles to 4000 and wont come down for quite some time, and when it does it stalls. Second, there is white smoke with a gassy smell, quite a bit of it, coming from the cylinder head/crankcase breather tube located on the left side, top, and back of the engine (routed down under the bike). Any ideas?
The idle problem is a lean fuel mix caused by an air leak in the intake system. Bad gaskets /seals on the intake manifold, bad valves, bad piston rings, loose spark plugs, and bad head gasket are all things that can lean the fuel/air mix. The smoke indicates a need for new rings. I would have the cylinders bored then install new pistons and rings. Now finish the top end work by getting a valve job. You should get a liquid fuel tank liner to eliminate any rust problems in the future. Also, install an in-line fuel filter.
Google “ kreem fuel tank liner “ or go to www.http://www.4secondsflat.com/Fuel_Tank_Sealer.html
My complements on the well cleaned carbs. Do the work mentioned above an you will effectively have a new engine.
A “very helpful” rating for this answer? Thanks!
I'm not sure it needed new rings quite yet Tombones49...The smoke is coming from the breather tube...that can be caused by a few things (some of which you mentioned) but sometimes if I bike has been sitting for that long it just needs to be run for a bit to get rid of all the vapor and **** thats been sitting in there so long. Mine smoked for 2 hours solid when I first got it (sitting since at least 1995) and it stopped smoking and runs like a champ now. The main thing on a TX500 (XS500) is that they valves are set to the correct gap. These bikes had a LOT of head gasket issues due to overheating and valve train problems. Just another point of view. Because parts are harder to find for this bike and cost a fortune.
Man! That answer is from a year and a half ago. Running the engine can either hurt or help. If the rings are frozen then some of the cylinder pressure can go to the crankcase and out the breather. If they free up then great! If they don't, then the cylinder can seize and score the cylinder wall. The safe thing is to do as I had suggested. I agree that rings can come free, but I prefer pulling the cylinder and freeing them up by hand. That way I know they are ALL free and the condition of the pistons and cylinder as well. Yes, parts can be hard to find and are certainly overpriced. Best wishes, Tombones49.
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