1978 Yamaha XS 750 ruff running

[phil117]

Hi, I am currently a new owner of a XS 750 after trading in a XT 600 for something more comfortable for the road(4 hours trips on a thumper are terribly uncomfortable). I love this bike but I am having several issues that are concerning me.

I recently started the bike and went to go for a quick ride on a nice day during the winter and the bike started popping and backfiring wildly and would smooth out with the choke being applied. I immediatly stopped attempting to ride and parked the bike. I though this could be a temperature issue and allowed the bike to warm for another 5 minutes and the problem was significantly reduced but there was still some popping from 1000-2500 rpm( all this mostly from the left carb but others are popping as well). I did find a small hole in the left exhaust about half way back under the foot peg which wasnt there before( my friend didnt drop the bike before this ride but almost had it sitting on its side), I think it can be repaired or I was considering ordering a 3 into 1 exhaust ( I like the design and simplicity but if this isnt a problem 300 dollars to stay in my pocket).

the other issues with the bike are random brief red lights on the dash that vanish when accelerating. (considered this to be electrical or oil pressure becoming low randomly). when changing the oil i did find small pieces of metal in the filter the size of dust I did not change the filter.

when backing the bike up there is a popping noise coming from the final drive and some resistance before the pop.

Then of course second gear is not really working (already new about this not a big deal just havent fixed it yet.)

The carb boots are worn but no cracks go all the way through the rubber. I have fixed manual petcocks and sealed off the old hoses.

I did also change the plugs about 2 months ago and i took them out for inspection after this problem and found them to be black (most likely do to the backfiring issue idk...)

any suggestions on how to fix or remedy some of my issues my biggest concern is the engine running rough the final drive isnt a huge issue. This bike being a triple is just what I have always wanted so i do not want to get rid of it i want to be able to fix these issues and countinue riding this beautiful machine.

I am a young student 22 and i do not have much knowledge of fixing these problems.

[YPVS TONE]

Regarding the rough running and popping the first thing I would do is get the valve clearances checked. I helped a mate check an old XS1100 a few weeks back with the same symptoms popping back through the inlet of no 4 cylinder. When we checked the clearance on no 4 inlet you couldn't even get a 11/2 thou feeler gauge in between the shim and camshaft. After changing the shim to put it to the required clearance it ran a great deal better with no popping. You can check the clearances yourself if you have a manual but you do need a special tool to hold the valve bucket down to remove the shim. If you have a Yamaha dealer near you perhaps see how much they would charge to do them.

[phil117]

thank you for the insight I was afraid I was going to have to check those Ill see what i can do on my own but otherwise ill check with the dealer. The bike ran great before i put it away for the season its a shame that its being plagued now.

[YPVS TONE]

It may be also that the carbs have become gummed up with stale fuel if you say it ran ok before you put it away. Did you drain the carbs before storing ? You could try draining the carb float bowls to get some fresh fuel through to see if that makes a differance. Is yours the CDI ignition model or does it stil have points ?

[phil117]

Thanks for the reply YPVS I ran the engine with the fuel off before storage and ran it once a week with the longest duration being about 4 weeks of not being ran. I believe it has a cdi its a 1978 xs 750 special which i believe has cdi ignition. I put stabilizer in however that doesn't mean much especially because it is outside under a tarp... I plan on getting a short clip together of what the bike sounds like at the moment. thanks for the replies again they are helpful. I know this model has issues with the lights being on when starting so i made sure they were off to double check it wasnt the lack of spark... I am wondering if the cam chain may need adjustment or as you had mentioned earlier the valves.

[phil117]

http://www.youtube.com/watch?v=PIF8T1HDMQ4&feature=youtu.be

This is just a sample of the low rpm clunking that i am getting while holding a higher rev a backfire will occur the popping has stopped for the time being.

[drewpy]

sounds like cam chain to me

[phil117]

I know where the adjuster is but i am not really sure how to make the adjustment

[drewpy]

usually you slacken it off and an internal spring pushes the cam blade against the chain and then tighten it up (engine off)

I strongly suggest you get a workshop manual for the bike or you'll be asking every "how do I" question going .

If you come unstuck, we'll be glad to help!

[phil117]

thank you I will be sure to look at the manual for now im cleaning the carbs super gunked up jets checking the needle and floats now.

[phil117]

after reinstalling the carbs and adjusting the tensioner the clunking noise seems to be origonating from the middle gear porsion as it is only during low rpm i believe it to be the starter motor setting down then backing off creating a hammering noise... not sure though.... i didnt get the cables hooked back up as it got dark but we shall see what i can do in the morning... the hole it the exhaust seems to have gotten bigger now the size of a quarter... I am thinking its causing low compression in that cylinder. I would like to confirm though the backfiring only occurs in the no.1 cyclinder with the hole in the exhaust.

[Airhead]

you need to balance the carbs before you can comment about rough running really...see the manual

[phil117]

fixed the problem i hope its not just temporary it would seem that the mixture was too rich with the old gas in the tank from winter storage....