I have a 94 FLTCU and was experiencing an intermittent issue where fuel would pour out of the air cleaner and flood the motor after (very) hard acceleration. The first time it happened, I realized what was going on and turned of the gas valve. It finally fired once most the fuel was gone and ran great until it ran out of gas in the carb. I used this valve on/off method to ride it all the way home without incident.

The next day, everything was fine. I had it happen several times since then, and it always happens after I really stand on the throttle. If I just ride it straight it rarely (if ever) happens.

I was convinced it was a float issue, so I pulled the carb and cleaned everything out. I figured it was debris or buildup in the valve seat or something. So here's my question:

As I got ready to reassemble the breather i noticed that the rear "breather screw" (the hollowed out bolt that holds the back plate on) seemed to be the source of some oil/fuel type mixture. In other words, the back plate wetness seemed to originate at that place.

I'm not familiar with these breather screws and what they are doing exactly. Is this a sign of a bigger problem? I know just about enough to be dangerous.

Thanks for any help or insights!

 

Just an update: I still don't understand the breather screws and what they are doing, but I'm going to go ahead and reassemble the air cleaner and ride the bike a while to see if the problem continues. Cleaning the carb certainly couldn't have hurt, I'm just not convinced it was the whole problem. Time will tell....

 

What did the float valve look like? I would replace it, its 16 years old. Did you check to see if your float height was set correctly? If you had to turn the petcock off and on to control flooding it is a float/float valve issue.

 

Yeah, like I said I was thinking float issue too, but the only weird thing was that it was intermittent. It could go for weeks without happening. The only fairly consistent pattern I noticed is when I really got into the throttle and ran it out. In other words, wide open through all the gears.

The motor has been reworked with new jugs and a racing cam of some sort, all before I bought it. I don't know all the specs, but it's not stock. The bike has 77,000 miles on it with about 6000 of that on the new motor (or top end or whatever). I'm sure the carb has been reworked a time or two, in fact I think it was rejetted a couple of years ago. Anyway, none of that explains the behavior exactly. Why does it only happen when I run it wide open? Is it because I'm emptying the bowl and the floats are sticking down or the float valve is not seating properly? If it's a seating issue, why doesn't it happen all the time?

Float issues were what I was assuming hence the carb cleanout. As far as how things looked, they looked a little gummed up or "tarnished", but again, I know about enough to be dangerous. I just cleaned it up, dried it out, and put it back together. I didn't really want to mess with too much of it (yet) because the bike runs awesome about 98% of the time (especially if I behave myself).

One last thing: none of this answers the wetness around the rear breather bolt. Is that normal? The front breather bolt is bone dry. Ironically, the spark plugs are just the opposite. The front plug is a bit rich and the rear plug bone dry. I wish I understood all this stuff better, but heck, I'm learning!

Thanks for the reply.

 

When you are hard on the throttle the bike is using the most fuel then you chop the throttle, kinda like having a garden hose on full then trying to stop the flow suddenly. The float valve may be damaged/worn out and my only seal intermittently. As far as the breather bolts they are there to vent the crankcase into the a/c, a pcv system. That can be changed if I remember correctly to vent from the case directly to the atmosphere, bypassing the heads and the a/c but it has been a long time since I worked on a evo.

 

Thanks for the reply and the information. That makes sense. Now that I cleaned it out I'm going to ride it a bit and see how it behaves. If it keeps acting up I'll probably just take it in to a shop and have them go through the carb, replace what is necessary, etc.

 

Just one more comment on this deal, the reason it appeared the fuel was coming out of the air cleaner was because at some point someone decided not to replace the overflow fuel line. From the way the overflow looks you would think that it would just drip down on the motor, but as liquid so often does it somehow ended up dripping from the bottom of the cleaner cover giving the illusion it was coming from inside. This perception even alarmed the mechanic when he saw it.

This is what was throwing me off a bit, as simple as it sounds. After reassembling the carb, it overflowed once for some reason, but all the fuel simply dripped out on the ground (far better than on the chrome, my leg, and other stuff that's important). I disassembled and reassembled everything again, assuming--rightly--that I had made some mistake along the way, and it ran fine. I took it out and ran it hard and it gave no trouble at all.

Now this could be coincidence, or it could be fixed. Time will tell. That's the trouble with intermittent issues. Thanks again for your thoughts @qtrracer and the explanation of the breather tubes, it's good to know what's happening there. Ride on!