Extra Spooge - theory

[Goat]

After track practice last week, I stopped by a buddy to check up on his RMX250 project.
He was kind enough to point out that my pipe looked too spoogie. I blew him off, since I do run a bit on the gooey side. But when I washed the kdx, I realized it was definitely a bit more than normal.
Theory: I had lost my fuel cap vent tube, before hitting the track. It was one of those stubby ones with the anodized nipple check valve ball in it.
I think it was maybe restricting air into tank which might have been limiting fuel flow to the carb. So now that more is dumping in there I am probably slightly too rich and get a bit more spooge.
What do you think?

I have RB PWK AS carb w/ 150-38 jets.

When I was looking up a new vent tube several folks had complaints that if the ball isn’t working right it can starve or completely stop fuel flow to the carb.

Do most of you just run open tube for fuel cap vent?

[doakley]

I’ve heard the same report on those little stubby vents. I run a straight hose tucked into the stem. I do have a one way valve in the hose at the end that tucks into the stem so I don’t dump gas out of the tank when I tip over. Never had a problem.

[bufftester]

I've only ever run straight hose, tucked in the stem. More fuel dumps out the carb overflow when I dump it than out that vent hose

[Goat]

I think it’s time to try a straight tube and jet down to 148. I’d hate to think I’m relying on a vent valve for carb flow. ... even though it does run well.

[Molly's 70]

I run the factory cap & vent tube.

[Goat]

Thanks, I am convinced to forgoe the cute little stubby.
PS. My AS carb pretty much flows like faucet, when I go down. Seems like I can crash at just the right angle to turn empty the wing tanks.

[MoonStomper]

My vent hose has a one way valve thing in it with an arrow that shows direction of flow - I've never dumped fuel out of it. I solved the carb vent dump issue by putting a loop coil into the lower (bottom float bowl) vent hose. That seems to prevent gas dumps when I lay her down most of the time.

[Goat]

Intersting. I'll give that a whirl. ty

[bufftester]

Only possible issue with coiling your carb overflow is that when you do dump it the fuel has to go somewhere, the overflows keep it from pooling at your reed block and letting a bunch of raw fuel into the bottom end. Of course you'd have to be down a while to have issues likely.

[Goat]

That seems concerning. Maybe a little puddle isn’t so bad. After all

[MoonStomper]

So far the coiled bowl vent tube hasn't created any issues, but I don't just leave it lying there when I dump it (probably have bigger issues to deal with if that happens anyway!). The coil has definitely has solved issues with pouring out fuel each time. Never had issues restarting after either.

[Goat]

I finally repacked my silencer. Seems I should have invested in $10 wash plug, some time ago.

[Goat]

So anyway. I have done 3 things:
1. Straight rubber hose for tank vent cap.
2. New plug
3. Repack Silencer.
My spooge is back to normal flow, or maybe a
little less than normal.
Would y’all please let me know if this looks normal to you?
This pic is spooge after normal day. About 6 hours in the woods so est 3-4 hours of hard riding, between 200 and 1800 ft elevation. Bike running great, by seat of the pant eval.

[KDXGarage]

That is too much.

Take the pipe off and clean it out. Lean it out a little.

[MoonStomper]

Too much drool for me, but I'm curious what premix you are running - or rather, what is your premix's flash point? When I switched to Yamalube 2S (very low FP), my spooge production mostly ceased. Never spits or drools - minimal smoke and runs great. I am running the OEM pipe, and recently rebuilt my stock carb using stock jets, etc. I am running the BR8EIX plug.

My theory is the KDX when run on trails, more completely burns a premix oil with the lower FP. However, if you aren't running in the woods but are running MX or a lot of WOT - the higher FP premixes would burn more completely and may be preferred (as would the higher octane to avoid detonation).

If you are running higher than ROM 90 octane fuel, this also delays the combustion and lowers the temps which burns even less oil and sends more spooge out the exhaust. My bike runs on the 90, non-ethanol and mostly in the woods - so a lot of 1/8 to 1/2 throttle with some WOT here and there. I think a lot of folks make a mistake of running the high-end/high dollar brand premix along with higher than factory recommended octane fuels thinking they are doing extra diligence for the longevity of their motor, when in reality a lower flash point pre-mix combined with 90 octane runs better and produces less smoke and spooge.

If you are running higher compression like my son's KTM 144SX, it makes sense - but not on a lightly modified KDX trail bike.

Keep in mind, the service manuals are written with the severe service user in mind. The service intervals and other recommendations always lean toward overkill to protect against failure.

[KDXGarage]

Ah, Slash 8 in your signature. Spending money on the KDX does not seem so bad after all. :-)

[Goofaroo]

I agree with Moonstomper. I’m lucky to be able to get 87 octane ethanol free gas but it varies by area. Just buy the lowest octane you can without ethanol.

I don’t think I have seen the mix ratio you are using in this thread. If you’re at 32:1 or even 40:1 try 50:1. A decent synthetic oil is ideal but dino oil will work. I have found that synthetic will create less smoke and spooge than dino.

Just a thought. If you’re already running 50:1 you may have other issues. Dirty air filter? Lugging the engine?
Rider skill and habits can certainly have an effect as well as jetting. If all else fails fall back to factory specs on jetting as a baseline if you haven’t already. Both of my KDXs are at factory jetting and run great. I ride primarily at around 1100ft altitude but both bikes run pretty well, idle well, and start easily even at 10,000ft.

Obviously low compression could also contribute to your problem.

[Goat]

I am running 32:1 yamalube 2R.
92 octane (ethanol)
Best I can get local is 87 octane (ethanol free). I thought 92 would be better.
I have RB 36mm (150 MJ, 38 PJ, DEK clip 2). RB came pre-jetted at 152/42 clip 3. I don’t think a stock 160/48 would be good for me but am open to suggestion.
Compression 151 (last checked in Feb 2020).
My spooge is similar at MX track or hard gnar. I ride both.
I’ll throw in the 148 MJ, and see what that looks like this weekend. Just a little concerned I maybe heading toward too lean.

[Goat]

PS. The bike runs like a raped ape. And has never fouled a plug. This is picture of plug after 24 mi enduro race (3 laps / 45 min ea).
Note this is my avg plug. Not a WOT plug chop.

[KDXGarage]

I might try a different needle. Try to do some test runs where you can limit the throttle range.

For example, my 1994 was a bit rich from 1/8 - 1/4 throttle, so I changed to a thicker needle as suggested by Jeff Fredette. It helped it out.