Chasing a few carb/fuel/oil issues on RN w/38's

Joined
Feb 27, 2012
Likes
131
Location
LOTO
#1
Working on a relatives ported 701 round nose with a B pipe, head, VForce reeds, MSD CDI and stock 38's. He had several issues going on last year, he says it ran good, but it was lean at times and rich at times and plugs fouled a lot. He drained the gas out of the tank last fall and it's been sitting ever since.

Step one, I pulled the plugs.

Plugs.JPG

Interesting, very different. I took the carbs off to see what jets were in it and wow full of oil !!

IMG_6071.JPG IMG_6072.JPG

What the heck, did the fuel evaporate and leave the oil? But there is so much oil that can't be it. I popped the top off the tank off and more oil.

IMG_6075.JPG

It not 100% oil, I'd guess 50/50 mix. I'm back to did the gas evaporate? He is 100% positive the fuel he drained was his normal mix 40:1 Torco oil. He used it in another ski last fall and it ran fine. He also sure no one messed with the ski, it stays in his garage all the time he's not riding it.

Next issue is the carbs, they have 140/75 jetting with a 1.5 N/S I haven't done pop off yet because of the oil. He says it fouls plugs ( BR8ES solid tip ) all time. I stuck my bore-scope in the spark plug holes and see this.

Rear

IMG_6077.PNG

Front
IMG_6078.PNG

Hard to tell but looks like a little lean with a lot of carbon? How can it foul plugs with pistons that look a little lean? Back to too much oil?? I'm not sure, I will pop the head off tomorrow. Exhaust pipe drips oil too He swears 40:1 mix every time no mistakes. I have no idea why everything is so oil fouled. 40:1 isn't that much. Torco is supposed to be pretty good oil, I thought, it's sure high $$ oil.

I'm going to clean out the entire fuel system and have him run same oil I do, Klotz Ski Craft (red stuff) 40:1. Then re-build the carbs, I'm thinking of upping the jet size up a little from the 140/70 jets that were in it because I think it should have more piston wash. Agree?? What jets and springs do the jetting experts think I should put in it?

Any other ideas would be appreciated.
Thanks
 
Joined
Feb 19, 2013
Likes
4,606
Location
Chico California
#2
Normal for the carbs to have a bunch of oil only after sitting for a while. Jetting looks good at 140/70. Check pop off and make sure it is crisp. check compression, fuel tank one way valve and and the internal fuel filter on the carbs.
 
Joined
Feb 27, 2012
Likes
131
Location
LOTO
#8
Oh, that plug. It was the rear cylinder. Engine was rebuilt 2 years ago with new Yamaha seals and held pressure great at that time according to the owner. Doesn't mean it's not leaking now, so I should check that too.
Does anyone run richer jetting in the rear cylinder of an SJ, like the Raiders jetting is set up?
 
Last edited:
Joined
Jun 12, 2011
Likes
254
Location
Southeast
#10
Oh, that plug. It was the rear cylinder. Engine was rebuilt 2 years ago with new Yamaha seals and held pressure great at that time. Doesn't mean it's not leaking now, so I should check that too.
Does anyone run richer jetting in the rear cylinder of an SJ, like the Raiders jetting is set up?
Were the seal lips packed with grease when you replaced then?
 
Joined
Feb 27, 2012
Likes
131
Location
LOTO
#11
I'm not sure, I wasn't the one that replaced them. I can ask him, are you asking if the old ones were packed full when taken out or are you asking if he packed the new ones when they were put in?
 
Joined
Jun 12, 2011
Likes
254
Location
Southeast
#12
I'm not sure, I wasn't the one that replaced them. I can ask him, are you asking if the old ones were packed full when taken out or are you asking if he packed the new ones when they were put in?
Ask him if he packed the new ones with grease. If not the seals will fail prematurely and it might explain why the rear plug looks so lean.
 
Joined
Feb 27, 2012
Likes
131
Location
LOTO
#14
Well the seals are fine, he didn't really pack them, but he "greased them up really good". I went ahead and pulled the head pipe off and pressure tested the cases. I holds 10 psi for 45 min before it dropped to 9.5 psi. I then turned it over by hand a few revolutions and it held firm at 9.5lbs So if that's not the issue, maybe a carb has a leak or the carb to manifold gasket was leaking on the rear carb. I'll rebuild the carbs and pressure test them and use a new manifold gasket.

Back to jetting Main 140's Pilot 75's 1.5 N&S with a pop off of 28-29 psi Should I change it?
I'm still bugged by the things that are opposed to each other.
Fouled plugs a lot, lots of oil dripping out of exhaust vs the piston wash doesn't look like it's rich.
 

Harbor

Site Supporter
Joined
Jun 23, 2013
Likes
1,106
Location
Stockton
#17
Is all this wetness in carbs and tank all oil ?
If yes, then something ain't adding up with that batch of fuel/oil ?

I'd flush it all out and put the ski back together and use my own fresh gas oil mix and retest how it runs..
 
Joined
Feb 27, 2012
Likes
131
Location
LOTO
#18
I'm checking the reeds too. The oil in tank is mixed with gas, hard to tell how much. I'm cleaning out tank, lines and new filter. Remember he drained the tank (as best he could). I think some of the gas evaporate giving it the extra oily look.

Question; If the check valve on the tank was good, fuel system sealed and the cap was on tight (it was) how does the gas everorate from the tank? Valve blows fine one way and not the other, I'm putting in a new one to be sure. What other symptoms occur when the check valve is bad?
 
Joined
Mar 9, 2009
Likes
446
Location
Ontario, Canada
#19
Some companies will use very dark dyes in their oil. It might only look rich due to the level of dye and manufacturer of oil. I would still clear out the tank and lines, get it all as dry as you can and start with a fresh batch of mix as Harbor said. The other concern I would have is that MSD enhancer. If you have access to a known good condition stock CDI then it would be well worth testing it comparing between that and the MSD. Also do a simple resistance value test on the coil to make sure it is not failing. The fuel shouldn't evaporate out of the tank when the system is sealing properly, even if the system let fumes out it still wouldn't be enough to empty a tank. Before dismantling the entire engine chasing possibilities check the easiest things first. Does it get fuel, does it have good compression, does it have spark. Is the fuel fresh, properly mixed with decent oil and at least 91 ethanol free. My thoughts on your carb specs are a little rich too. My ski is similar to yours but I run a 135 main and 75 pilot with about 32psi popoff and both screws at about 1 1/2 turns out. That part depends on the engine though and your knowledge of tuning.
 

maxboost

Super tuned
Joined
May 2, 2015
Likes
14
Location
Ia
#20
I had plugs that looked like that before, chased the carbs forever thinking I had one that wasn’t acting right, ended up being my crankshaft twisted between cylinders for it’s just a press fit on most cranks and caused one to run weird
 
Top Bottom