1981 seca xj750rh rebuild

Not that I know of... surely I could find one though. Ill ask around.

 

I've heard about these, but have never found a parts shop that did it. Started wondering if it's an American thing, or just an everywhere but where I am thing.

I'm really concerned about the zero compression cylinder. If they were all low, that's one thing - could well be a poorly calibrated gauge. But NO compression? And you've done the test multiple times, and that one cylinder always reads zero?

That's pretty hard for a borked gauge to manage. Have you tried just looking in the cylinder via the spark plug hole with a flashlight? Manually turn the engine, watch the piston move up and down, see if it moves nicely.

Have you taken off the valve cover?

To have zero compression, either there's something horribly wrong (broken rod and stuck piston?) or more likely a valve is stuck open... Bent? Carbon build up?

Gotta be a pretty big gap, though, not just a valve almost-but-not-quite closing or a hinky gasket, or there'd still be some compression.

 

The combo of the two could make a big difference in the numbers. Since you've had no oil in there for a couple of months, you could be losing pressure a the rings. The 50/50 soak could unstuck the rings and reseal everything up.

 

How is the XJ oil pump? Will it get oil around effectively when cranking with the starter?

 

I'll do the soak and try again in a few days, I'll post how it goes.

Not sure about the oil pump, but I have some cases off that I would need to reseal in order to try more oil in the motor. If I can I want to avoid that as I plan to sand and polish the casings, paint the motor before I get new gaskets.

Haven't taking the valve cover off yet, that might be my next step after I soak them this week. A stuck valve did cross my mind too. hopefully its something as easy as that! Would carbon build up be relatively easy to clean up once the valve cover is off?

 

Totally not my area of expertise but generally no, you'd need to take the cylinder head off. You're just going to see the cams,buckets and shims taking the valve cover off, but you could turn the motor and watch the valve movement - measure clearances, see if one is sticking open.
Unless there's a trick to it someone more knowledgeable knows.

 

Nearly have the carbs back together but noticed all my diaphragm springs are different sizes. Not sure how it happened but does anyone know if this will be a problem? Should I just replace to be sure? Cheers

 

Kiwi Mystery Bike.
Tom, you have an array of interesting things going on. I would certainly replace the two compressed springs, in fact might as well replace all 4. Were the slides stuck on those two carbs? Confused as to what would create that...

 

Haha, and I've only scratched the surface. Yep the slides were all locked up and took some convincing to come out. The carbs were in pretty bad shape, I've replaced quite a few of the parts so I'll just add these to the list. Cheers @Stumplifter

 

Yeah, these definitely need replacing. They should, as far as I know anyways, all be the same length. This is the sort of thing that can cause really wierd and very difficult to diagnose problems later in tuning.

 

I am having the same problem with my Seca 650rj the neutral light won't come on even when in neutral. Already tried checking connections and bulb. Was wondering when using Seafoam do you suggest just mixing with oil or drain oil and pour a couple bottles of Seafoam into bike dry and let sit to try breaking up sludge then drain and put oil back in? Will Seafoam hurt clutch anything else?

 

read can put about an ounce in the oil it will clean out any sludge ride around yhen change oil and filter.although the seafoam will eveporate the sludge will end up in your filter