Jerrod's 82 Yamaha XJ-750 Maxim

Oh, and I cleaned my head up and made a discovery. It seems that at some point in the past 40 years, Someone has had some work done to this head. There has been a significant amount of material removed from each intake and exhaust port, and it definitely doesn't look to be factory work.. this is just 1 exhaust port, the intake work is much more conservative then the exhaust side. But is definitely there.. what do you guys think?

 

Here's an example of the Intake side, I suppose this could have been done at the factory, but I'm guessing these bikes were mass produced, and I just don't think Yamaha would be taking a die grinder to every head they made. But I could be wrong..

 

Intake side looks exactly like mine also '82 750 Maxim. I just did some port matching on both intake and exhaust sides. Not much but just cleanup and match the headers and carb boots.
Cheers, 50gary

 

Alright guys, for anyone that still may be paying attention to this thread. Valvestem seals are replaced, the engine is back on the Bike, the Head Gasket has been replaced, and the Head nuts have been Tourqed down in the correct sequence. Packing it in for tonight, and I'm setting the Valve timing in the A.M., so hopefully I'll be Pissing off the neighbor's by noon. I've doing SOHC Cam, and from what I've seen it's very similar just 1 more Camshaft, its rarely that simple but we'll see how it goes.

 

Did you replace the oil-feed o-rings and crush washers as well?

 

Yeah, all new everything. It sealed up just fine, But there was no change. Runs exactly the same. The stem seals were shot, but apparently that's not the reason it's down on power.

 

I talked to the P.O's brother a few days ago, and it appears I bought this thing from a complete moron. When he got new tires for it, he decided to burn the tire he was replacing off until it exploded. He said he's the guy that go's around pinging his Engine off the rev limiter, cause he thinks it sounds cool. Has me thinking I should just start looking for a new motor.

 

It takes a lot to destroy one of these motors. Never head of an XJ engine being wrecked so far.

 

I don't know why you would, Yamahas are obviously idiot proof....
Did you have your valve seats lapped and checked and clearances set?

 

There is no rev limiter on an XJ.

 

Just explaining the kinda dude he is, his older brother said they would throw party's, and would go out all drunk, and power break it until the exhaust started to glow. Apparently he thought that was just the coolest thing..

 

And my buddy did all the valve work at his shop, not positive on everything he did. But I know he set the lash to what it's supposed to be, I just didn't have the money to pay him to change the stem seals, so I did that myself.

 

It's just not right guys, it's rideable it will do 65 all day. It just has no pick up at all. My Honda is strong for a CB-750, it's up over 70hp, but this XJ should be eating it's lunch, not the other way around. But the XJ has really grown in me, its a really good feeling bike, very well balanced. But I think the dumb hillbilly I bought it from wore the motor in it out.

 

You are as illogical as he was dumb...
You should know, since you know everything else, that power is made above the piston. You've had the engine to bits, so you should also know (in fact you've told us) that the rings are good, you've had the valves done, set the cam timing, etc.
So the power producing bits are good?
Your loss of power is elsewhere - carbs or ignition timing. Try another tci - it's easy. Then maybe need to look at the carbs, it's been known to get jets fitted in the wrong place...

 

Carbs.

 

I'm inexperienced really, this is honestly a learning curve for me. I've done fuel pumps and BS like that on cars, but replacing the Camshaft and Rocker Tower's in my CB was my first time inside an Engine. And all I really learned was how to set valve timing. Now I've learned how to remove and install Valve's, but I'm far from a Mechanic. I'm learning, but there's alot more to these things then the average guy riding them around will ever realize...

 

And I will start looking into the ignition, and Carbs, what would be the result of one or multiple of the Carb Diaframs being no good?

 

Slow down.
Read.
Learn.
The Information Overload Hour
And most of all...stop jumping ahead of yourself.