OK, several of you were at the field on Friday 2 weeks ago when my 50cc started giving trouble. It starts fine, runs great to 1/2 throttle then quits, quickly. Only thing I had done was replace the carb diaphram.

I cleaned the carb, paying special attention to the little itsy screen - same problem.
I replaced the fuel lines - same result
I REPLACED the carb. Exactly the same results.
I cleaned the inline filter and checked the tank filter - same results

Today I 1) replaced the ignition battery pack, even tho it tested Ok - same result
           2)  replaced the plug - same result
           3) swapped out the entire ignition - same result

What am i missing ??????   >:(

With cowl off check movement of throttle plate.
.................. check movement of throttle arm (sometimes they slip).
Check timing (28deg. BTDC)
Check spacer block for cracks etc.

Hope this helps

throttle plate move to full extent...on both carbs.

no cracks either reed block

wouldn't timing ( no sign it's moved) affect starting as well?"

engine quits hot...

Hey Sandy. How thick is the wall of your fuel tubing. I've seen a situation like this when the tubing is too small for the engine and when you try to give it gas, it can't get it because of the restriction. just a thought....Mike

Same tubing I've been using for years - not same tubing but same roll. And standing behind engine while running it I can see the line - no "sucking" or air

It's time to go a little deeper. Check and see if there's a stuck ring or even a broken one. That would answer a lot of questions. Do a compression test on the engine. A normal two stroke cyl should have around 90 to 100 psi. below 70 is getting low. Yours may be different. Check the liner and piston.
Also make sure all the bearing are in good shape.

Unless you missed something in the fuel delivery system or ignition system your running out of stuff to check

Fuel is bad?
Had this on a. Brand new honda engine
New fuel new oil
Good luck

waverider wrote on Jul 21^st, 2014 at 3:58pm:

Fuel is bad? Had this on a. Brand new honda engine New fuel new oil Good luck

is new fuel, new oil, thanks Brian

Sandy,  Are you running a regulator for the ignition pack?  I had one that would do the exact same thing, ended up the regulator didnt do a good job with a 2 cell battery.

yup, have a regulator and am going to change that next - haven't had a chance to this week, maybe tomorrow afternoon, thanks Paul

not the regulator........................... >:( :wallbash :dead_horse :swear :crappyday :Anyone

some questions
1. when the engine dies does it sound like a lean out? or does it just stop firing? eg runs up to 1/2 throttle and then nothing just windmills???

2.  i had a thermal issue causing the bad piece of electronics to stop working and the engine just quit firing. Is there any other electronics that because of VIBRATION or THERMAL that you haven't replaced???

if it was engine internals then the engine would struggle up to half power. 
How does it respond to a throttle slam?

throttle slam to 1/2 is great.......anything above that dies, fast, no hesitation, doesn't matter if slam or creep..... hold just below the "quit" point, engine does seem to surge  :-/

new engine...

Is the throttle servo closing when you command past 1/2 throttle
Sod's law of servos???

OR
Crankshaft sensor mag pickup has it developed a funny?

OR
has the optical developed a cataract? Ie a funny

If it was the piston and or ring(s) you would be down on power below half throttle

Thanks Barry, but not the Hall sensor...then by past the voltage regulator AND the optic kill switch..... still no joy

:helpMe :Anyone :shots :bedtime :Im Happy

Gaskets leaking?

With time and normal vibration, the screws that seal the crankcase from air leaks loosen just a little and air gets into the engine through leaks in the crankcase gaskets.

waverider wrote on Jul 29^th, 2014 at 3:02am:

Gaskets leaking? With time and normal vibration, the screws that seal the crankcase from air leaks loosen just a little and air gets into the engine through leaks in the crankcase gaskets.

to ensure there is no leakage I put small run of silicone around the gaskets, both on the original and the new carb.

To clarify, at 1/2 throttle, one step before engine quits, it does "slightly" hunt or surge - next step, stop...

Hi Sandy. What engine is it exactly?

3MMTOC53

clone of a 3W

about 8 years old, never a spot of trouble till this   :violin

swapping engines........ and for the theorists, rings ordered..

If its not fuel or ignition, you have an air problem :-? :-? :-/

you'd think so, but with new plumbing, new carb, *(!@)#$ new every thing... as some have sugested, maybe ring shot and can't pull the fuel any more...don't think so because there is still ignition  ;D  :wallbash

If honing and new rings don't fix it
. Chances are the gaskets have become hardened beyond their ability to seal the engine. Dismantle the engine completely and install new gaskets. You may not be able to buy the proper gaskets, but you can buy a sheet of gasket material. Use the old gaskets or the engine castings as a pattern to cut new gaskets. Your engine will run like new again.

You might try the Russian solution
Hit the engine with a hammer
It is supposed to free up any stuck thingy

Or if you hit it hard enough
It gets you a new engine :)
Brian

carb gaskets may be a problem, but on the engine, there are no leaks evident anywhere on the block - would tired gaskets leak at least a bit of residue?  I had thought the carb gaskets would be taken care of when i swapped carbs....

The block has a front and back (!) with a central seam, and a one piece cylinder attached to the top of the block. Absolutely tight, to all appearances...

Sandy
As rpm builds crankcase pressure builds
i remember a race car engine developing so much power that the head lifted off the block!
i am not sure if the problem exists on the head side or the crancase side of the piston
or with the piston
start with honing and new rings
a dye penetrant under UV light would show up cracks.

the problem appears to be so incidious that the answer is either simple (occams razor) or very complex (sods law of engines)

if this were a sleeve valve engine , i would say junk it
but it is a simple two stroke

as I wrote check the fuel.  you would be surprised how bad fuel can cause strange things to happen....but you have done that.

as for leakage past gaskets not being evident (from the internal pressure, I would agree that that is not the cause... but you have very few options remaining...since you have replaced almost everything replaceable.

as Al suggested did you check the wet combustion chamber pressure.  two strokes are notorious for still running with very poor pressure... but being down on power.

they also are notorious for develop very strange characteristics  :-X which mystify and defy investigation

maybe Santa will be good two you and you can use the RIP solution?

good luck :)
Brian

OK guys, time for a group hug....................on the carb there is a small square plate with 4 screws and a small hole.....

in which direction does the hole point on your carb?????? Up, front, down or back.....

Away from the airstream sandy, it's supposed to stay at standard atmosphere.

Thanks Glen; yup, some say doesn't matter, some say it does..mine points back

Oh, it matters. You start getting positive air pressure in it and the engine will do all sorts of wonky things mixture wise. :o

OK -which way

---

Whichever way will keep it from being pressurized.
Thunderbolt rc even sells a "kit" that you solder a piece of tubing onto the hole, connect a piece of fuel tubing, into a film canister to ensure it stays at atmospheric pressure.

http://www.thunderboltrc.com/index.php?main_page=product_info&cPath=89_142&products_id=808

This explains everything very well :

http://www.thunderboltrc.com/tutorials/tutorial_seven.html

yup, seen the kit and heard about the phenomenum for years but never needed it.....why suddenly?

The static pressure phenomenon cause rich lean issues (depending on upright or inverted engine)...not quitting above half throttle
the hunting you describe is the engine running rich
Have you run the engine on the bench in an upright position?

in this day and age, what is the chances of, and effect of, bad gas??

Ask the people in Ikaluit
They had a winter load of bad gas about 8 years ago
Biggest issue is octane
If you add an octane booster does the engine run
Remember, the higher the octane the cooler the engine runs
Two strokes should not care too much about octane

didn't try an octane booster, but did get mix a batch of fresh fuel...... no  :swear :swear :swear difference  >:( :wallbash :dead_horse :shots :helpMe :Naaah :timetobuild :Anyone :woooweee :Oops Sorry

New idea
CDI not advancing
Any way of checking the timing?
Another is crankshaft seal leaking

timing off same amount on both engines?????

Sigh!!!! Ok I'll re-do the timing thingy

Well, we proved conclusively it's not timing, tank, voltage regulator, Tx programing, gaskets on the block, full moon or position of Ursa minor relative to star X54C766...

Cool put a carb from his DA50  :Rock on the reed blocks and today I got 2 flights on the newer of the 2 engines....so we know it's all carb  >:(

Yehhhh, my first 2 flights of the year on this plane... :Thank You Loyal Fans :Raa Raa :WEEEEE :aviater

Good to see the plane in the air after all the issues you had.  [smiley=tekst-toppie.gif]


(DA to the rescue!)

Steve Mosher wrote on Sep 7^th, 2014 at 11:00am:

(DA to the rescue!)

yup  :shots