1981 Yamaha Maxim XJ650 - Sputtering? Cylinder Problem?

Hi there, Im very new to motorcycles and recently bought this bike..



I like it a lot, and think I got a pretty good deal for $1400. The guy I bought it from was kind of geeky and presumably didn't bag on it and kept it well maintained.

I'm well experienced with dirt bikes and such, but this is my first street bike. I put on about 50km on it I really got the feel of it and learning it well. However, I noticed that you need to get it to 3500+ RPMs to start to feel power (High end power???) and so I've been switching gears at around 5-6000. (Red lines at 9500). However, I noticed that sometime when doing so (even if Im cruising and not accelerating) the exhaust will almost backfire and sputter... but then I let off the gas and floor it, and it bombs off with great acceleration and no sputtering.

Im not too sure how to explain it, Im told I'd need the carbs tuned, which is supposed to be hard seeing as its a 4cyl and would be hard to get them. Anything I can do? Fuel should be new, and I haven't touched or turned anything I shouldn't have...

Today I was riding it home from a friends house playing pool, and I noticed an extreme lack of power and sputtering, so I got home and felt each pipe and the first 3 scorched my hand but the last one was warm but easily touchable.

Im led to believe one of my cylinders isn't working properly or something? I checked the plug and it sparks and its fine, put it back in and it ran like a dream. It had more power than I had ever seen, and I got a few blocks away and it stalled at a stop sign and had no intention of starting. So I had to push it home, and after about a kilometer I tried again and it fired right up and flew home, and I felt the pipe that wans't hot and it was scorching again.

So Im guessing its cutting in and out, and Im hoping you guys can helpp me diagnose whats wrong with it?

Thanks in advance!

 

First and foremost the spark plug wire "caps" (the ends that actually push onto the plugs) SCREW onto the wires and that one could simply be loose. If that's not the case, you'll need to pull the tank and check all wiring/connections to the coils, etc. Each coil fires TWO cylinders so I don't think you have an actual coil issue. As far as carb tuning, yes, it is quite possible since the bike has a 4-1 exhaust and the PO may or may not have properly retuned/rejetted the carbs to compensate. You didn't say how many miles are on it, there could be other things that need to be attended to as well like valve clearances.

 

***Totally unrelated to your issue*** I'm sure a lot of people will reply to your post in time so I'm sorta jumping on it early. Do you or anyone that reads this post know the brand of both your windshield and backrest/rack. It's a great picture and that set-up is exactly what I've been looking for (not too big).

As far as your issue, I'd definitely check the spark plug cap like bigfitz52 said, and the wire for any bare spot that may have rubbed up against metal grounding it before the spark plug. Sounds to me like a wiggeling spark plug wire short that's coming and going.

 

Thanks for the replies!

I havent really done any mechanical work, tonight I put in 10L of fresh gas and started it, let it idle for about 3 minutes and took it out, and it ran like a dream! Im really hoping the problem is solved and wont reoccur, because I want to go further than around the block without worrying about breaking down

If it happens again I'll post it along with exactly what happened...

 

Ok, so I've heard a lot out Sea Foam and wondering you guys could help me out here...

I went out an bought a bottle of Sea Foam for like $6...



Pretty sure thats the can it came in.

So from what you guys have told me, I should put in 1 oz/Gal into my tank? I believe my tanks almost 3 gal so put in 3 Ounces right in, shake it up, and ride?

Please clarify if I would be doing it right

Thanks guys!

 

3 OZ is fine the amount is not really critical. Way too much is a waste of seafoam (IMHO it won't work any better) Too little and it won't work as designed

So dump in about 3oz and enjoy your ride....

 

sounds good mate. Thanks.

By the way I just looked at my can and its not identical to the one I posted. Maybe a new 'version' of it? Or do I got the wrong crap?

http://img517.imageshack.us/my.php?image=mailgooglecom9523880kz1.jpg


Seeing as I have no spare Jerry Cans, and I just filled my bike, Im just going to take my moms measuring cup and put 2 ounces in the tank, shake it up, leave it sit for a min, start it, let it sit, and ride?