the motor goes " bang"

[anne-marie]

hello
my seagull forty is running perfectly
excepting autumn leaves stopping the water pump sometimes,
or long grass making knots around the propellor, everything worked fine
until i noticed the carb was always leeking when the motor wasn't running.
i solved it by closing the fuel tap when i stopped
but now the motor makes a big "bang!" every minutes while running, except on slow regime
any ideas of what is going on?
when a bang happens, the motor tries to jump from the transom to the water

maybe i should clean the carb?

[Keith.P]

Definitely a problem with the carb, it's not a hard job to do and may stop your seagull going bang completely.

[anne-marie]

thank you Keith.P fort your quick answer,
i am going to do it this afternoon
but i will never did it again on the water
(i have already lost to much tools and carbs doing this! ;p)

[Hugz]

My initual thought was that the timing was too advanced with a lean fuel to air mixture. Would not the bang be a fuel burn trying to send the piston back down before it has reached the top causing the motor to come to an almost stop with only the revolutionary momentum keeping it going? Would explain why it is trying to jump off the transom. Could be worn rings too. Anyway good to overhaul carb if it is leaking.

[anne-marie]

hi guys
i cleaned my carb yesterday
it was quite clean, except some metal particles i found in it
i don't know where it comes from
i hope that's not the rings!
i looked down the carb hole while turning the wheel, the 2 rings seemed ok
maybe i'll try to run it before unsealing the block,
what if those metal chips could have been aspired in the block with the air flow?

[Hugz]

I wouldn't be pulling it apart quite yet. Have you cleaned and checked points?

[anne-marie]

what do you mean by checking points?
i'm sorry my english is quite poor....
it's sunny this morning and i am off working,
so i'm gonna try it on the water...

[Keith.P]

Hugz, was saying, have you looked at the ignition and points gap, to see if it is clean and the correct gap.

[Hugz]

If you remove the nut on top of the flywheel and corresponding pulley and plate you will see a set of points with a screw to adjust points under. These need to be cleaned and set at 20 thou. Sorry, I'm on a mobile at present so can't post pictures for a couple of days. Someone else will help. What is the engine number? (on crankcase opposite side of tiller arm.)

[anne-marie]

thanks for your advice , Hugz
i had checked those points once 2 years before, but effectively they have moved; the 2 points were touching each other
so i turned the screw in order to have a bus ticket thickness in between. i had forgotten those two little points!
i think those points touching each other was the problem, so i hope it will turn right tomorow!
(last night i had a dream; the motor was turning perfectly, making a sweet beautifull noise like "brrrrrrrrr" and the boat was going very fast, but just, well, backward...maybe there is a hidden message)

this noon, the motor was banging every 10 seconds at slow regime, so i had to lay it down the sole and row for a while.
i hope my shoulders are beautifull now !

well, just a last question, was the bus ticket thickness enough?

[Charles uk]

0.5 mm exactly!

[anne-marie]

ok i have my criterium pen 0,5 jauge
thanks you all guys
you're the best

[tambikeboy]

What number was the bus

[anne-marie]

the bus was too big for the flywheel anyway...

but i just try the motor again...
at first it doesn't start
then i realised that the ignition points wasn't 0,5mm when the cylinder was on top course, so i changed it 0,5mm at top course
then i turned the flywheel again
the motor starts first stroke
but bumping all the time like (from the lowest too the bigger speed) rrrrrBMrrrrrrBMrrrrrrrBM /rrBMrrrBMrrrBM / rBMMrBMMrBMM
i think it is time too look at the cylinder...
any advices?

[Charles uk]

The points are 0.5mm at their maximum.