Loading up

[Bill2001]

New to 2-Strokes. I understand basically what loading up is. But what is the engine's behavior like and what causes it to load up? And most importantly, what has to be done to clear the engine out?

[hodakamax]

I'll try this. Two-strokes pump the fuel/air mix through the crankcase and during bogging or long idle conditions can start to build a too rich mixture in the crankcase. Too rich of jetting can start this process also or a combination thereof. The quick cure would be to turn off the fuel supply and try to clear the crankcase by blipping the throttle until it clears. The spark plug may foul before all this happens. A leaky needle and seat can dribble fuel into the crankcase during storage and fuel can evaporate leaving the oil which makes the mixture oil rich on the next start. Symptoms of "loading up" are bogging and not being to take full throttle accompanied by heavy exhaust smoke. Kinda general but I hopes this helps!

Max

[Bullfrog]

While I can't give you technical details on "loading up", I can give you some rules-of-thumb which may increase your understanding of the situation.

1) A "loaded up" engine simply has too much fuel . . . and since the carb always provides more fuel when the engine is turning over, you have to do something which starts to bring the amount of fuel back down to what the engine really wants. So, when "loaded up" and engine running - hold the throttle wide open (promotes maximum air flow) and DO NOT fiddle with the throttle, just hold it wide open. Shut off the fuel petcock to start limiting the fuel. As the fuel level in the carb starts to drop, it will reach a point when much less(or no) fuel is being supplied by the carb . . . then the engine can consume the raw fuel which is collected in the engine . . . and it will "clean out". Burp the throttle a couple of times then turn the fuel petcock back on and get back to racing.
2) There is a strong positive correlation for loading up with piston port engines which have a) higher exhaust ports and b) larger carbs. Think Super Rat vs 100B. Or Combat Wombat vs toaster tank Wombat.
3) Simply letting the engine speed get too low while holding full throttle under load can cause "loading up" with one of those high exhaust port/large carb engines. On the trail or Cross Country events this often happens when really cooking and then a steep and very rough hill suddenly comes up and you find yourself behind the curve on downshifts and a handful of throttle trying just keep going . . . then it loads up. (see #1 for what to do)
4) Vanes added to the carb throat (both before and after the throttle slide) at the 1/2 throttle position virtually eliminated "loading up" on my piston port Combat Wombat - and the #3 description was exactly why I installed the vanes. I suspect it would do the same on a toaster tank Rat.
5) WARNING: Some folks will think this is just plain stoooopid advice. --> "Slow down. You'll go faster." Crashing takes tooooo much time. If you are going down more than once a day on the track . . . slow down and stop crashing, your full moto elapsed time will go down too. NOTE: Somehow, really fast guys seem to be able to go faster than humanly possible AND do not crash - so I am convinced even they slow down in order to go faster.

Certainly proper operation of the float valve system must be assured - also proper float level - to make sure those items aren't the cause of regular "loading" issues.

My 2 cents,
Ed

[motovate]

Very good info Ed - especially on the carb vanes. I had heard/read a few times about people having vaned carbs and how good it was but never why it was good. You cleared up a mystery for me on that one!

LBM

[Bill2001]

Very good! Now we know. Thinking it over, I suspect that I had a minor loading up incident a few days ago. Doing break-in figure-eights in a local pasture I was practicing low-rpm, wide-throttle "low end" runs when the engine started running erratically, barely idled and tended to stall. Almost as though it had a bit of water in the float bowl (my first guess). It eventually cleared up after a couple of starts. And having siezed the piston during an earlier "break in", I'm cautiously running +1 size up on the pilot and the main jet. Once the brutal Summer temps drop and the rings seat, I'll complete the jetting evaluation. I'm looking forward to the Fall-Winter-Spring riding seasons. Putting around in the pasture nd tinkering in the shop has been fun, but I wanna ride! At least I have my Hodie at long last.