4 stroke mixture,

linnix13 · #1 11-24-2009, 09:30 PM

hey there, so today i sat down and decided i want to fix my engines bogging and only running on half choke issue, my carb has an idle screw and a mixture screw, my symptoms are it boggs when i give it full throttle, and it wont run without choke(it will run but it stalls and has no power)

now my theory(please let me know if im wrong cause i am basing this on theory in my head!)

is that a 2 strokes mixture screw is life and death because if it runs lean it gets no oil, a 4 stroke has oil in the crank case so no matter what i set my screw to i will not seize the engine, is that right? am i safe to tinker with the screw without worrying about frying the rings?

also, should i turn counterclockwise or clockwise?

i turned it as far counterclockwise as i could and it made no difference, then i turned it in further and it revved higher and higher, i had to adjust my idle allot, but i stopped there and put it away because i would hate to ruin my engine, and yes i pride myself on knowing allot about engines but its better to know allot and ask questions that assume your right and wreck it, besides i wouldn't know half what i know about engines now if i never asked questions, none of us would?

anyways thanks guys,

tyrslider · #2 11-24-2009, 10:06 PM

Air fuel mixture screw is for Idle only. Usually all the way in and 1-1 1/2 turns out. In is usually lean and out is usually rich.

4 stroke or 2 stroke: 0-1/8 throttle=Idle air mixture, 1/8-1/4= Idle Jet, 1/4-2/3 (or so) = needle jet, and the rest is main jet.

You have something in your float bowl, you have an air leak and or something blocking your idle circuit. Or maybe a Sink instead of a Float. Most likely H20 in your float bowl.

Drain your float bowl 1st

linnix13 · #3 11-24-2009, 10:08 PM

Quote:

Originally Posted by tyrslider

Air fuel mixture screw is for Idle only. Usually all the way in and 1-1 1/2 turns out. In is usually lean and out is usually rich.

4 stroke or 2 stroke: 0-1/8 throttle=Idle air mixture, 1/8-1/4= Idle Jet, 1/4-2/3 (or so) = needle jet, and the rest is main jet.

You have something in your float bowl, you have an air leak and or something blocking your idle circuit. Or maybe a Sink instead of a Float. Most likely H20 in your float bowl.

Drain your float bowl 1st

way ahead of you! i took the carb apart and cleaned it and inspected for any obvious flaws, everything is perfect, it did this right outa the box brand new, so is it a jetting issue then? and so the screw i adjusted was idle only? can any damage result from messing around with it? thanks for the reply

tyrslider · #4 11-24-2009, 10:14 PM

No damage. Could run lean (Hot) at idle. Did you blow out all the passageways w compressed air? Not Likely Jets; I don't think there's any internal adj possible. Don't know though.

linnix13 · #5 11-24-2009, 10:17 PM

Quote:

Originally Posted by tyrslider

No damage. Could run lean (Hot) at idle. Did you blow out all the passageways w compressed air? Not Likely Jets; I don't think there's any internal adj possible. Don't know though.

yeah its confusing, its only when i give it 100% gas it bogs, if i give it half gas until im going then open it wide it runs great!

its not the carb i made sure nothing is dirty or clogged, i dont get it?

john_the_great · #6 11-24-2009, 10:18 PM

finding the "sweet spot" between the idle screw and the idle mixture screw on some bikes take some fiddling. You shouldn't destroy anything unless you reef on one of the screws, I've had the same problem on my Honda trail 90 and my some of my others motorcycles, the difference was though, they were old and worn out. So, I can't explain your adjustment difficulties other then the fact that these carbs are not the best in the west.

ps. maybe try a smaller idle jet?

linnix13 · #7 11-24-2009, 10:20 PM

Quote:

Originally Posted by john_the_great

finding the "sweet spot" between the idle screw and the mixture screw on some bikes take some fiddling. You shouldn't destroy anything unless you reef on one of the screws, I've had the same problem on my Honda trail 90 and my some of my others motorcycles, the difference was though, they were old and worn out. So, I can't explain your adjustment difficulties other then the fact that these carbs are not the best in the west.

ps. maybe try a smaller idle jet?

darn are they not the sickest in the south either? or the beast in the east? (what rhymes with north? lol!)

i will look into a new carb,there easy to come by, but i would like to get mine fixed if its something simple,

Bikeguy Joe · #8 11-25-2009, 09:12 AM

What kind of carb do you have on that engine? Does it have any adjustments other than the idle speed?
It sounds like it just lean on the low speed mixture.

Some screws (air bleed) make the engine richer by turning them IN.

Bikeguy Joe · #9 11-25-2009, 09:13 AM

Also, I will suggest trying to sort out the carb you have before you buy another can of worms.

**Norman** · #10 11-25-2009, 10:19 AM

is this a 4 stroke engine? Do you have the intake and exhaust valves lash set correctly? if set too tight you will burn a valve too loose it will run crappy.
When the engine is new what happens is as the valve assembly settles in they usually get tight saying it another way the clearances go away this can make it to where the lash is gone when this condition happens your in danger of burning a valve. If the valve lash goes the other way or too much lash your valve will not open far enough starving the engine for fuel.
I don't recommend tuning your engine with no load on it if you hold the throttle open and adjust the high speed jet for max speed with no load you might over rev the engine that will make it blow the rod right out of the block.