Gasoline in the Mag chamber?

[IDoSeaDoo]

Sooooo I've been running these Novi built carbs with rather oversized jets on my otherwise stock 96 XP. The carbs came with these jets installed, so I figured "Since the carbs have been bored, maybe they need the extra large jets to work properly". The ski started rather hard, but ran well at WOT. Anything below 1/3 throttle, and it sounds ... different, almost like it's firing every other revolution or something. The plugs did show signs of being rich, and I knew more tuning was in order, but knowing that I wasn't doing any permanent damage (i.e. running it lean) I decided to ride it a bit longer before tearing back into the carbs. Well, the last time I rode it, it started to develop this surging at WOT. I took it to mean that this was a sign of a lean condition, and therefore started to open the high needles a bit at a time. After a day of riding, the engine started to die on me, and eventually refused to start back up. Not sure why, probably fouled plugs. I towed it back to the dock but remembered to clamp the coolant inlet hose 4 min or so after we started towing. When we got back to the dock, I took out the plugs and turned it over to find that indeed I did suck some water into the motor. I blew it all out, re-installed the plugs and fired it up. The motor started and ran, but would not achieve high revs. Later that day, I came home and fired it up in the yard and noticed that while it ran, the motor was spurting this black liquid out of the square Magneto electrical connector. At first I thought it was water, but upon closer inspection, I found it to be gasoline... The MAG chamber is filling up with fuel and I am completely at a loss as to how or why... If anyone has ever heard of this, I'd be REEEEAL interested as to what to do. My first plan of action is pulling the flywheel and checking that crank seal, but even if it's bad... I still understand the physics here...

 

[Dr Honda]

Fuel in the mag housing can only get there one way... that's out the crank seal. Sounds like that engine needs to come apart, and have a full inspection. If the front is leaking, chances are the PTO is leaking too. That can cause a lean run regardless of how the carbs are set. (damage may have already been done)

 

[IDoSeaDoo]

You are right, one cylinder is at 143 or so while other is still 150. It ran like a demon at WOT, so yea, lean sounds about right... But what could cause that much gasoline to build up at the bottom of the crank? Perhaps excessive cranking? Wow, could it have been THAT rich at the bottom?? Will do a leakdown test just to see how bad and where all it's leaking. I need to make all of my caps for the test, know of any good/easy/cheap ways to build them? Thanks

 

[IDoSeaDoo]

Well, I pulled the motor out, and FINALLY built my own pressure test kit. I cut aluminum plates for the rave and carb ports. I found a local gasket supply co. and bought a sq. ft. sheet of 1/8" silicone gasket material. I cut out the gaskets for the raves, carbs and the exhaust manifold. Other gasket material simply leaked!. Working with a spray bottle of soapy water, I found that I had a MASSIVE leak around my rotary valve cover. After fixing that, I found that said cover actually had a CRACK in it, right around one of the carb. mounts. I tossed it in exchange for another I had. Pressurized the motor to 6psi and it held for like 10-15 min. I figured that was good enough. I reset my carbs to stock (142.5 main/70 pilot) needles set to spec, pop-off around 30psi. Started it within a few seconds of cranking and MAN, it sounds pissed!! I still have a bit of an exhaust leak, but will be water testing today to see if the stock carb settings will work. I've had problems with these settings in the past, but it was probably due to the leaks.

I still don't know why I had gasoline in the mag chamber: that seal was new and did not leak at all. I know b/c I took off the flywheel and douced it w/ soap water under pressure. I also found gasoline in my counterbalance shaft chamber. Fortunately I installed a drain tap on it last year and was able to refill it w/ oil.

Wish me luck guys!

 

[Minnetonka4me]

The needle and seat would have had to be stuck open....?

Also one other way gas can get into the motor...LOL I had a guy bring in his machine after he "rebuilt" the carbs....he didnt have the pulse diaphram in there and gas was being siphoned in via the pulse line. That motor started 30 times AFTER I had the carbs off before I burned off all the gas!!

 

[IDoSeaDoo]

Lol I def. have the diaphragms in there The motor actually ran well, just started hard (with the aforementioned air leaks). Here's my theory on the pool of gas: I was running racing carbs with HUGE jets, dumping loads of fuel in. The motor started, and with the excess fuel to compensate for the air leaks ran good enough. Once the parts heated up and expanded, the air leaks became smaller, in turn making the motor run rich and fouling the plugs. Once the plugs were fouled, it became hard to start, leading to longer cranking times. As I'm cranking and not starting, I'm building up a puddle of gasoline in the bottom of the motor. Once the puddle gets tall enough, it eventually touches the lip of the crank seal. As any other liquid, it makes its way past the seal with the help of any hydrostatic pressure and rotating crank. I'm not sure if there is ever a period of positive pressure in the crank case during cranking, but that would've also helped push it past the seal. Finding fuel in the CB cavity helps confirm a tall puddle of fuel in the engine.

 

[IDoSeaDoo]

Just in case anyone else has this problem, I found the cause of it in another engine I built. Turns out, one of my needles was either leaking, or otherwise stuck open. This could happen if your needle arm is bent too high. In this scenario, you can get a good, clean pop-off, but when you go to reassemble the cover on the carb, it can depress the arm and open the needle. This allows fuel to pour into the carbs, into the RV cavity, and then distribute into both of your crank chambers. This can and will cause hydrolocking and a tremendous amount of fuel to enter the engine. This is a dangerous condition as the only way to get the fuel out is to remove the plugs and crank it. It gets super messy. What's worse is you probably have to change the counterbalance oil as gasoline probably got in there as well (only on 787 engines). I hope this helps whoever reads this. It's a very perplexing problem when you don't know why it's happening.