Jerrod's 82 Yamaha XJ-750 Maxim

Good advice, and yeah you've got some tight valves there. Big problem with using "imperial" vs. metric is that on the low side, a valve can be "in spec" using the imperial equivalent, when in fact IT'S NOT measured properly, in metric.

A set that is primarily metric is best for this, honest. I'd give you the specifics, but K-D sold out to/became Gearwrench so I don't have the part number anymore.

Those clearances are so "all over the place" that I strongly suspect your PO lied big time. Good catch.

 

Thank you, you guys are super helpful. It may be a few weeks before I'm working on it again, waiting in my service manual, and a few parts. Like a new set of intake runners becuse it appears someone attempted to do a polish job on the ones I have, which I've never heard of someone doing before. Which reminds me, what would the outcome of someone rounding off the edges on the inside of the rubber Carb boots? It looks like they tried to do a port and polish job on the intake runners. And I don't think it was a good idea...

 

I don't wanna turn the motor over 1 more revolution, until I get the new ones on it. Supposed to be here Wednesday.

 

If you mean the carburettor intake stubs be careful as the bolts can shear off when removing them.

 

Yeah, I've seen at least 4 different names for them when buying new ones. And I already have them removed, with rags in the intake port's until the new ones arrive. I'm thinking what has been done to them may have alot to do with how the bike is running. Parts like that, are the shape they are for a reason. Plus, they don't have seals, gasket sealer was used. Which to me is unexcusable, these parts are available and cheap. Using gasket sealer there was just lazy.

 

Yes should be no gasket sealer. Good they are removed with no broken bolts.

 

Figured I'd put up a few before and after's, not close to finished yet. But I think it's a pretty good start

 

I think he did too, but he knew I was fixing it up, and there was no real back and forth. But it's you guys who really pushed me to check. Thank all of you.

 

Had a fouled plug, so I replaced them today which helped it quite a bit. But this is what the brand new plugs looked like after about 5 minutes at idle. It appears my issue is in that number 2 carb. I have a friend that is a Machanic. I have to replace the starter, and then I'm hauling it to his place to dig deeper

 

I'm looking at these 30mm aftermarket carbs online, does anyone have any experience with these things? Or are aftermarket carbs more trouble then their worth?

 

All right guys, a bit of an update. I have discovered that my number 2 cylinder has low compression. Not sure if it's the valve seals, or the rings but I am about to start disassembling the top end. Going to replace all rings, and all valve seals, and will also be installing the correct shim's on reassembly. Is there anything I need to know outside of the normal everything must be reassembled in the order it was disassembled, and all parts need to be organized and labeled?

 

For example, my CB has to be reassembled dry, without any gasket sealer.. Just things like that I may not know. But could be a nightmare later on.

 

Umm....none of those plugs is indicating an acceptable fuel mixture.

 

STOP!!!!
STOP!!!!
STOP!!!

Low compression is often due to improper valve clearances, and/or stuck rings.
DO NOT take the top end apart yet.

If the bores are worn enough to equire new rings then you likely need oversize pistons, and those are only available as a custom made part anymore.

so...

STOP!!!

1. Valve clearances first.
2. Drop a tablespoon of a 50/50 mix of ATF and acetone down each sparkplug hole, and let it sit for a few days.
Run the engine for a several minutes.
Recheck compression.

 

Plus one for kmoe's advice there, don't rush taking this to bits. I would try riding it hard for at least an hour as well - you'd be surprised how this helps valves and rings bed in - when suffering from being idle as well as new. Then re measure clearances, get someone do a leakdown check as well as a compression check (assuming your valves are in spec). Slowl slowly catchee xj....

 

All my rings are fine, and all my valves are operating properly. Problem ended up being that both the Intake and Exhaust valve seals are worn out in the number 2 cylinder, it's going to a good friend of mines garage in Monday, and he's going to replace all of my seals. I could probably get the job done, but he does this kinda stuff for a living. So I figured I'm better off letting him take care of it.

 

A question I did have though, is there are these plastic sleeves that are on the cylinder studs. And they are all super brittle and coming apart. I'm sure their probably important, what are they?

 

Intake and exhaust seals worn out?
Firstly valve "seals" are there to stop oil weeping past the valve stem into the bore, they do nothing, zero zilch to affect compression.
Now, you may be meaning that your valves aren't sealing (ie closing tightly)? In which case go back up and re-read what k-moe told you, and I repeated -ride it untill it's good and hot. If you can't ride it then start it and warm it up as hot as you dare at least 4 times. Then recheck you valve gaps, and your compression. If you still have a problem then strip it, but there's mire than a good chance your issue will have gone away.

 

The engine studs are exposed to road dirt as you can see the studs if you look at the front of the cylinders. I think that's why the plastic sleeves are there. Someone said it was to stop them making a noise. Don't know if that is applicable or not.

 

Given that he mentions the plastic sleeves on the engine studs, he ignored us already and tore it down anyway.

I think seals was a typo, and he meant to write seats. In which case....I've never seen or heard of a valve seat being damaged at such low mileage, and certainly not all of the valve seats in one cylinder. It is possible though.

@Jerrod Robinson We never did hear back about the valves being adjusted. Was that done?