[Xean45]

Hey all, I'm having a real quirky problem with my Jag (actually a 81 4400 but it dropped a piston skirt and blew out the crank case, so replaced it with a 78 340cc motor).
The motor has one Mikuni carb, that feeds two cylinders. But the cylinder on the left ("driver side") is running hot and lean [reading the plugs], while the right "passenger side" is rich and wet. Any idea what's going on here? both spark good; just replaced the spark box last year.

~X8

 

[kccats]

Welcome
Sounds like one cyl is working and the other is fouled!
What is the compression

 

[Xean45]

Hmmm, So would that be looking at rings then to fix that? I'll borrow a compression tester and get back to you here. Thanks for the reply.

 

[kccats]

Pistons come with rings and gasket set comes with seals too!
Probably less that $200

 

[snowmoer]

On a motor that old, I would replace the crank seals. You said the left side is running lean and hot. That is showing you have air leaking in and leaning that side out.

 

[Xean45]

Pistons come with rings and gasket set comes with seals too!
Probably less that $200

Both cylinders tested at 130 PSI, so that seems to check out.

 

[Xean45]

On a motor that old, I would replace the crank seals. You said the left side is running lean and hot. That is showing you have air leaking in and leaning that side out.

That's an interesting thought. I though it was basically compensating for the other cylinder's lack of performance. But before I go to all that work:
1. Is there any other way anyone's hear of testing to see if a crank seal is weak/failed?
2. How would that explain the other cylinder being rich?

Thanks for the suggestion!

 

[Coolhand]

Spray the seals with carb cleaner or wd-40. If the rev up when you do that then the seal is leaking.

 

[kccats]

a bad seal would not make it rich it would make it lean!

 

[Vipertriplexxx]

Replace the plugs and check for good spark at both plugs, if the condition persists it’s most likely crank seals, there’s literally nothing else that it could be.

 

[Xean45]

Replace the plugs and check for good spark at both plugs, if the condition persists it’s most likely crank seals, there’s literally nothing else that it could be.

Well, since this seems to be the consensus, I suppose I'll look at doing seals then. I'll try that WD40 trick too to see if that works (seems cool). Ah tearing an engine apart. Good times.

 

[kccats]

Absolutely!
I have had aLOT of fun doing engines, I bet I have rebuilt 100 2 stroke engines!
I can go through one in about 2 hours!
I even did my 95 Pantara in the back of my Box truck on the way to UP to ride!

Would the lean side be the PTO and the rich side the recoil?
Do pistons and seals!

 

[Xean45]

My gosh, that's EXACTLY right! Well that puts me 100% confident that this is the issue!!! Thanks for sharing your experience with me. Question: Are any special tools required for removing the crank shaft to put new seals on it? My dad says there might be a compression fitting or something of the like that might require a special tool for removal.

Thank you!!

 

[snowmoer]

You will need to get a holder that bolts on to the flywheel to hold it in place when you remove the bolt that holds it on to the crank. Also a puller to remove it. Also a clutch puller to remove the clutch off the crank. There are video's on line where people use water or grease and a bolt to do the same thing. The cases will need to be split to do the job right.

 

[Xean45]

Alright, thanks again for the info. I'll let ya'll know how it goes.

 

[kccats]

The only thing besides pistons and gasket set is the YamaBond or the 1106 sealant
I can even look up cost for you.

 

[TheBearAk]

nothing more impressive than watching a guy tear down a Tundra on the trail. It had lost compression and it looked like just gaskets. My brother tore it down using Leatherman and a few other tools worked some magic with the piston and cut up some beer cans and the cardboard box they came in for gaskets. Put it back together and started it right up. Drove it the remaining 30 miles back to the truck.

 

[BC_Dan]

That is impressive! Beats walking, that's for sure