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Yamaha 90

jk030

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engine is not firing on bottom

engine is not firing on bottom cylender got good spark fuel and compression is over 100 had crank seal changed as it has less induction on bottom cylender but still the same no change wot els could cause this problem if anyone could help. thanks
 
if i remove ht lead there is n

if i remove ht lead there is no change at all to the running of the engine and the spark plug is a differant colour than the other two and the over heat buzzer has been coming on under load putting the engine in to low revs.
 
sounds like a bad coil to the

sounds like a bad coil to the bottom cylinder spark plug...could be an easy fix. why don't you swap the coil from the top cylinder to the bottom cylinder and determine if that's the problem...good Luck!
 
done that already made no chan

done that already made no change at all thnk its on the induction side someone said i might have an air leak on a gasket on the powerhead which would give poor induction. has anyone had this sort of problem before
 
how is the carb on the bottom

how is the carb on the bottom cylinder? getting fuel to it O.K.?...not a stuck float needle on that carb?
 
"if you've got good spark

"if you've got good spark and good compression,then the fuel is probably the problem. an induction side air leak would create a very lean mixture,coughing,skipping and very white spark plugs...maybe fuel related. Good luck!"
 
i have taken carb apart and cl

i have taken carb apart and cleaned out all the jets was all ok can see fuel going in through carb when you rev the engine. when i took boat out wouldnt go over 3800 rpm got no grunt when i took the air box off the carbs there was fuel in the bottom of it
 
maybe a bad reed valve on that

maybe a bad reed valve on that cylinder? are your spark plugs really clean? a fouled plug on that cylinder would do this. I've seen plugs that looked pretty good that wouldn't spark well at all under compression. I'll be very interested to learn what this problem is. maybe some of the real motor gurus on this forum can be more help than me...hope so! Good luck.
 
put new plug in no differant i

put new plug in no differant if you had poor induction then it wouldnt draw the air through the carb and suck the right amount of fuel in to cylender which could be an air leak on the centre gasket on the power head or the second ring on the piston is worn not giving good induction does anyone know if this would be the case . thanks for your help so far robert
 
with help from yamaha they tol

with help from yamaha they told us the problem the fuel pump seal has gone sucking fuel direct into the power head over fueling bottom cylender soaking the plug. thats why i must of been using a lot of fuel
 
"that's great they identif

"that's great they identified your problem and a fairly simple, inexpensive fix! good luck!
happy.gif
"
 
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