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#Post#: 92471--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: Richard Date: September 2, 2014, 8:59 am
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sorry to be controversial but ring bore contact will be critical
in a two stroke I would have thought, incoming gasses not being
compressed because of loss through a poorly fitting piston will
make it very difficult to start IMHO, kind regards
#Post#: 92473--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: Jackual Date: September 2, 2014, 9:12 am
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:thumbs: Not at all, let me explain, if you look at the new
rings, you will see the edge that scrapes the bore is rough,
this will do the honing work for you in a few moments when the
engine is running. The piston needs to be a good fit in the
bore, correct, crankcase compression will drop though air
leakage with a sloppy piston, causing hard starting.
#Post#: 92577--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: NoelC Date: September 5, 2014, 6:35 pm
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For what it's worth I bought a new Husqvarna chainsaw a few
years back, 65cc I think. It's always been a bastard to start
from cold even with fresh fuel. I don't use it that often so I
tend to pull the plug and give it a squirt of carb cleaner
first. It seems that's all it needs, a bit of heat to help it on
it's way.
#Post#: 92584--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: nickjaxe Date: September 6, 2014, 5:11 am
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If its been left for any lenght of time with perol in the
carb...there is a good chance that gum has formed in the
carb...jet maily....may just need a good clean...
Modern petrol with the dreaded Ethanol does not last as long as
old style petrol it also absorbs water from the atmosphere...
I fly a microlight aircraft powered by a 500cc two stroke...if
I'm not going to use it with in a week I drain out the fuel into
a sealed container,
Ethanol...the devils work......
Nick.
#Post#: 92715--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: rangerovering Date: September 11, 2014, 8:39 am
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New piston and ring are fitted, strimmer back together and tried
to start it - still no go. carb kit is ordered now (a whole £7)
as it is soaking the air filter in fuel just from pull starting.
The intention was to take pictures but general arsedness got in
the way and I haven't got any..... Its actually a very simple
system so not masses to look at.
The honing idea was abandoned after advice on here and the fact
it was making no impact on the cylinder surface - wrong tool for
the job anyway I think.
Internet opinion seemed to lie with reed valves in the carb
being the cause of fuel spitting back, also potential bad piston
ring sealing so hopefully that aspect has been covered.
#Post#: 92758--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: nickjaxe Date: September 12, 2014, 1:39 pm
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Try a little bit of mixed petrol down the plug hole then try...
#Post#: 92769--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: Jackual Date: September 12, 2014, 7:20 pm
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Think your on the right route throwing a carb kit at it, new
metering diaphragm and pump diaphragm, give the carb a good blow
out with compressed air whilst its all in bits. Check the
metering needle is in good nick, watch out under the needle
pivot, there is a tiny spring. Also check the tank pick up
filter, They do block up, easily cleaned with a compressed air
blast. If you search for your carb make and model on google,
there should be a bit of info that'll be worth looking at if
your not familiar with diaphragm carbs and how they work
:thumbs:.
Have you got good crankcase compression? (suck)
How is the cylinder compression after the new piston kit?
(squeeze)
Is there a good strong spark and is the fueling/carb set up
correct? (bang)
Is the exhaust clear?, not blocked with carbon at all (blow)
Cheers, Jack.
#Post#: 92945--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: rangerovering Date: September 19, 2014, 11:37 am
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Carb rebuild went well :thumbs:
New needle, actuator and diaphragm, fuel strainer and reed
valves. Got the thing running eventually once the hi and lo jets
were adjusted right. Picked up and ran much more cleanly and
sweeter than it did before.
So, did about half an hour cutting some verges back and then it
lost power intermittantly a couple of time and ran ok again.
Then it ran out of fuel, filled it up, got it started and off it
went again. Then 2 coughs and it wouldn't rev up, then cut out
completly. :smiley-furious:
Got fucked off with it and it was too dark so left it til today.
Initially trying to start it indicated no fuel getting in to the
cylinder. Carb off, opened it up and checked for dirt, main jet
is clear. Tried with the tank filter on and off.
Fuel is getting into the carb OK. The plug started to get wet
after some fidding but still no go. Spark is present and appears
healthy, exhaust is clear.
Unsure where to check next, it felt most like a fuel problem but
nothing obvious is standing out. Maybe a strip down is needed
again. Compression seems good too plenty power when it was
going.
:-?
cheers
#Post#: 92952--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: Jackual Date: September 19, 2014, 6:33 pm
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Hopefully something simple, First thing to look at is the plug,
I'm always dubious about them firing under compression, sure it
may fire when its out of the cylinder, under compression it may
be a different story. Try another plug, A decent brand too; NGK,
bosch, Champion ect..., Not Brisk, torch or any of these cheap
Chinese bin fodder plugs.
Also was the fuel oil mix correct?, and the carb set correct? I
always get the jets running a bit lean and the engine revving
its tits off, then back the jets out a touch till its almost
running a little rich, this ensures the engine will run sweet,
no hesitation on opening the throttle, and will not overheat
and/or ruin the engine.
If you think it has overheated, (the loosing power bit sends
alarm bells ringing for me) Have a quick look inside the engine,
whip the exhaust off and check the piston that the rings are
free in the grooves. The exhaust side of the cylinder is the
hottest part of the engine, so easy to identify if its
overheated or been run without oil with the exhaust off.
Cheers, Jack.
#Post#: 93008--------------------------------------------------
Re: Rebuilding Small 2 strokes
By: rangerovering Date: September 22, 2014, 4:18 am
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Thanks Jack didnt think about the plug going dodgy, it was a new
NGK plug when I bought the machine but may well be getting blown
out. The symptoms were the engine intermittantly bogging a few
times at full throttle then after 5 mins of this on and off it
just died completely.
Fuel is 50:1 and its decent quality petrol too (same batch has
run 2 tanks in the chainsaw no problem)
I will check the ring hasnt got stuck, would this have taken
half an hours running to show up?
Cheers
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