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1985 Yamaha XT600 problems


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I have a 1985 Yamaha XT600 I bought from my uncle. He hadn’t ran it for 4 or 5 years and it was stored before then. I cleaned out the fuel tank and bought a new petcock. I cleaned the carburetor with carburetor cleaner, cleaned out the airbox and bought a K&N air filter. I changed the oil with Yamalube and oil filter and bought a new NGK spark plug. When the motor is cold it will start on the 4th or 5th kick and die unless I hold the throttle a little. When the motor is warm it will start on the 1st or 2nd kick and idle by itself but it seems to be sporadic. Idle will range from 1100rpm-2100rpm. I have ridden it 4 or 5 times and it has a lot of power and acceleration and after it has been ran and is just sitting, it will idle around 2000rpm and sometimes drop to around 1400rpm. When I’m riding it I can hear the exhaust popping and the bike jerks a little like its missing unless I really get on the throttle. The exhaust pops at idle too and I can hear it backfiring at the carburetor/airbox joint.

any suggestions, ideas?🙂

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I think you've got the YDLS carb that came on the 550. It's a dual carb but only one has a pilot jet, the other is only a main and uses the same bowl for both.

On the left side of the carb is a round cover with a big depression in it. It's held on by two phillips head screws.

There is a spring, diaphragm under this cover and a "button" looking thing when you remove it, held on by another screw. It's very well possible that the diaphragm is ripped or rotted and is causing a funny vacuum leak. If this is the case, order a new one ($30? from Yamaha?) and replace everything that comes with it.

If it's not ripped, clean that assembly just like you would any other carb part, soak the metal parts in carb cleaner and possibly wash the rubber parts with soapy water.

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yes it is the dual carb. the first time i cleaned the carb i opened the diaphram and looked at it and there was nothing wrong with it. the second time i actually took the diaphram out and looked inside. the screw holding the "button looking thing" was already stripped so when i finally got the screw out i couldnt get the "button" out.

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Yeah, mine was stripped too, it wasn't stripped when I started, but about 1/3 or so of a turn later it was. I got it out by putting the carb in a vise and then used a chisel and hammer to extract it. Just put the chisel on the right side of the screw head at roughly a 30 degree angle and give it a whack with a hammer at a 90 degrees, like you're trying to unscrew it. It will come out.

Left hand drill bits would probably work too, but I don't have those.

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I've got the 84 version of this bike. I've had a similar issue. what I did to rectify it was I merely disabled that 2nd carb, since it didnt work properly anyhow, and also got REALLY obsessive about cleaning in the carb, which helped.

another thing I did, was adjust the pilot screw out to 2.25 turns, which helped a LOT on my bike. before you adjust it though, remove the pilot screw and clean everything in that area well first as it may be partially clogged. been there and done that before. NOT Fun to have clogged jets be your issue.

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I found the solution to the stripped screw. Use a #1 phillips screw driver out of a jeweler's set of screw drivers. Even though a #1 out of my tool box looked like it fit, it didn't want to turn, just strip. The problem, at least for me, was I can't get enough of a grip to get the screw out with the jeweler's set. So I used a pair of vice grips on the shaft of the screw driver and pushed down (carb was on a work bench) as hard as I could to keep the screw driver in place. Once broken free it was no problem to get it out the rest of the way.

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I never play around on stripped screws. out comes my dremel and they get a nice clean flathead slot, EVERY time. with the right bit in a 1/4" drive ratchet, you can both put pressure, AND leverage on the screw then, and it usually comes right on out.

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I didn't think of that, I probably have a #1 1/4 drive bit. It was an improvised solution, due to how small the area you have to work in is and how close the you'd be to messing something up, something expensive, a dremel wouldn't be a good choice. It's slightly larger than a nickel. That's why I used a chisel on the screw on the first carb.

However, I might still be concerned that even a 1/4" drive bit might be too intolerant and would strip. I had that happen on a #3 head on the magneto cover on my XT, I ended up welding a section of metal to it to use like a handle which eventually broke it free, there was simply no room to work in that tiny little area. Since it's magnesium not steel (screw was steel), I was going to try everything I could think of before I'd drill and tap it.

This carb, IIRC, is zinc, same situation except they don't make left hand bits that small and I'm not even sure if they make screw extractors that small. It's a 4mmX0.5? on that carb screw.

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