Jgilk1

So i picked up a junk 21cc weed eater at goodwill for a few $ it still had some compression left and a tight pop but no ignition of fuel gaped plug, set needles to walbro gap.. Had spark but not consiatant ignition

Lets not fool anyone it is the cheapest of cheap off brand weed eaters.. (no clutch, bent shaft, name i never heard of)
Spent 2 hours trying to get it to fire and managed only to tear skin off my hand

Tore the thing down to the block, ring looked good no signs of extended over heating, casting looked like ... , a fins are missing, threw it back together.

set coil/flywheel gap with 2 business cards thing fired right over adjusted high needle to max rpm curve then backed off 1/16 turn

set low needle much the same till it idled and revved smoothly then set idle.

Now the motor feels torqie and laterly twists in hand much more so then 25cc mccouligh (sp) and ~21cc stihl i have previously owned

But won't even cut grass i wasn't expecting much for $2 but what am i missing?

Oil ratio is um... Well 1oz of break in oil per quart of gas (did testing in chemistry years ago there are very few differences between 2stroke and break in oil) i get light white puffs of smoke at 1/2 throttle and light transluent stream of smoke @ 3/4+ its not a smoke screen and there is no spitting fron the exhaust fuel is 87octane non ethenol...

Yep i am aware this is an rc forum not a yard epuiptment forum but if i would have to join another forum... Next yall flame less then the power equiptment forum...

Next there is experience with boats and planes on this forum thats where this is going its going on a 10' inflatable boat... Next i will need help choosing prop pitch and diameter.. Thanks for any help on either part

irocbsa

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av8tor1977

My Feedback: (6)

I think you are going to be disappointed with your project. The engine is just too small, and also, makes its meager horsepower at high rpms. It will need a very small prop because the engine only develops about 1.3 horsepower, and it does so at 7000 plus rpms. The engine has very little torque. The only way it would work would be to have some sort of a reduction setup to turn a larger prop. Even then, only 1.3 horsepower would be barely enough to move the boat. Do a web search and find some R/C boating websites. Then look at the prop size for 25cc engines. That's a popular size for R/C boats and you will be able to see what size propellers they run. You will quickly see that they would be too small to move a man sized boat of any kind. Maybe it would work for trolling, but the engine would be screaming the whole time....

AV8TOR

Jgilk1

Right i understand theory and power output and rpm... This is not a speed boat... Goal is max 5mph with out having a 20# trolling motor and 60# deep cycle battery but instead 25-30# worth of gas motor... Lets put in to perspective 3.5 hp (21#) outboard motor is $350 willl do about 12mph and with fuel tank (35#)weighs in at about 50#

my theritical math and goal of 5mph max is there... The goal of course is to after testing this is to move up to a sub 50cc motor and a 10hp build. with current transom design i can not exceed 400lb of thrust (~3.5hp)but that will be taken care of later on