Next time just disconnect the fuel line you will hear the pump click . see if it is the same soundOriginally Posted by BaitThrower
Stuie
Next time just disconnect the fuel line you will hear the pump click . see if it is the same sound
Stuie
IF IT CAN'T EAT A WHOLE PILLY I DON'T WANT IT
Look closely at that plug again - could be a piece of the porcelian that cracked away and jammed for a minute in the bore. That would be a bad one and you may have got lucky and it got spat out the exhaust. After a can of engine tuner have a good look at the top of the piston with a decent penlight torch and if you see any indentations I'd keep a close eye on the compressions and a set of decent oars in the boat. Gaps can close and it usually hapens with rough installation of plgs where they get banged against the plughole on teh way in.
I'll do that... the noise has been there for a few trips, but it is only there every now and then and lasts for just a few seconds so its not a conitnuous noise...
Silly but check it is the correct plug for the motor as different plugs have different reach.
Definitely is the correct plug, verified by the manual and the sticker inside the cowl itself.
Running lean with air being sucked in a fuel line can generate huge combustion chamber heat and teh edges of pistons can come off along with piston skirts.. A borescope may help see it it is the piston but there would be indentations in the rest of the piston where it did a little dance
I suspect it was running lean for a trip or two because I discovered a air gap in one fo the fittings that probably got slowly worse...
You sure there was oil in the fuel and fuel was fresh?
Yes it was definitely fresh fuel and yes definitely oil... It is recommended to run at 100:1 and I rarely bring it to WOT (mostly cruise at 3/4 and nothing more. In the last few trips I have been added a bit of extra oil to the mix. so its more like 75:1 I run now... Being a single carby, I found running it at 50:1 caused quite a rough idle... and given I rarely stress the motor I decided to stick to the lower ratio.
Look at your butterflys in the carbies and see if there is any difference. Some brands still use a screw to hold on the butterfly and it wouldn't be the first to come undone and get sucked through the motor of jam in a crank bearing before getting spat out. Same for a peice of a reed valve - torch down carby to check if obvious and screws that hold reeds in place.
Will check this..
Check inside the cowl. Have had similar noises from cowl insulation rubbing on flywheel and also wiring loom etc not placed back where it should have been and rubing or blocking teh advance
Initially I thought this was the case, but I've looked and cant see anything obvious here...
The other cause which is common for the noise is the pull starter ( squeal) where it doesn't release properly , rubs etc. Have a good look at it as on other brands they can drop a circip and they then rest on teh flywheel . Not sure on a yami how they are connected. Warning that there is a spring in there that will take your finger off or a eye out so if looking be very carefull and gave a look at the parts diagrams first. Check tension on bolts that old down pull starter and if it has a electric start option check the gear is sliding up and down the input shaft cleanly and has all teeth while also springing back to where it should.
This is a possibility given the timing and occurrence of the noises I have observed in the past... I will look at that too..
Unknown noises can bring tears to the eyes but go looking for the cheapest and easiest options before pulling stuff apart to narrow it down and going to a shop and have a engineer look at aborescope is a cheap option after that.
Well I need to test a little more after resolving the above issues and see if it returns. I fish mostly estuary so never too far from land...
PS
With plugs out turn it over by hand and see if it is smooth , back and forward to see if there is any slap , chatter, flywheel side to side in case it is a crank bearing. It would have to be bad to discover it this way but easy quick check anyway.
I dont think it is this as it is smooth and chatter free and I think the flywheel runs pretty true. Again this only happens for a few seconds and only occassionally so it is harder to pin down.
Ps ya sure it was from the powerhead not the gearbox? Check the oil down there for smell ( burnt) and too many metal flakes or water in there.[/quote]
The motor is second hand and I've had it for almost 2 years. When I got it the upper shaft seals to the gearbox needed replacing so I did all that and got it all back together... Because of that I have been checking the gearbox oil regularly and there has been no signs of leaks and the gears function nice and smoothly.. The noise is definitely coming from under the cowl somewhere!
Thanks for the advice!
Ok good idea will try that
Last ones
have heard a noise similar with a faiing waterpump or incorrectly installed thermostat where the water in the head goes to steam and shoots out a squeal. Check motor temp next time with it off and back of hand on head ( should be warm but not stinling hot) and look for steam or inconsistant flow from pisser.
Check rest of fuel hose again and fittings for a vacume air leak.
Check breather on tank was open and is clear ( use your mouth through your hand and blow through the cap as sometime they get crapped up with something and when under enough vacume they "whistle "the air in. Same if cold fuel and tank then going into sun you can get a build up of pressure and vapour and a whistle out the breather.
Check the ank lift pipe in the tank is actually clear and the bottom of the tank hasn't got debri in it. low pressure conpressed air is quick check blowing back down fuel line
Ethanol fuels sometimes collapse some fuel hoses . they look perfect on the outside but collapse internally. Cause the motor to try and suck air into the fuel pipe.
Fuel filter , external or on motor can also cause a vacume / pressure situation if they are not seated right and clear.
If all the above doesn't get it you must have narowed it down somewhat.
Awesome, easy to follow advice there cormorant. Top Stuff!
yep, agree with all that, but the major problem is, what flatened the spark plug! none of those things will do that, so there is only a couple of possibilities, the plug was never gapped properly when new (maybe) it was dropped before installation and closed the gap (maybe) or (wait for it) something sinister was bouncing about on top of the piston, banged the plug flat and shot out the exhaust port (probable) what the "something" is will be anyones guess without investigation. Take your pick what option you select.
The plug had been in for a few months and had 5-6 trips under its belt, so if it was this way on initial install, I'm sure I would have had the same problem from the beginning of that plug install.
I'm leaning toward something has hit it... because it was ok at the ramp and only just started to happen as I throttled it up a little about 100m from the ramp...
Just not sure what could have hit it... if it was a piece of ring, then I should have got poor compression readings on the bottom cylinder shouldn't have I?
Anyway I will try and do a cylinder clean with engine tuner and then see if I can get a better look at the piston heads.
I don't know your motor BT but I'd think it would only take a few minutes to pull the head off and have a look. The last motor I blew up had needle rollers from the piston pin everywhere except where they were supposed to be. It showed no signs at all until it locked up when one got stuck in a port and locked the piston.
Sounds like water ingestion to me. Only takes a few drops to cause alot of damage in a small motor and there are no signs of what caused the damage when the motor is stripped down.
Tony
Check the surface of the piston directly under the spark plug, If the plug was bent inside the firing chamber it will be marked, if not it was closed before it was set into the hole. It certainly is not hard to close a gap with a bump or drop and not notice it before putting a plug in.
The squeal could also be one finger of a reed valve getting a harmonic chatter happen. This usually only occurs after a long period of no use and some of the fingers get gummed with 2 stroke oil setting.
I run surface gap plugs because they never fail due to their design. My plug in my 15 yr old motor have done thousands of hours and were put in when the motor was new. I pulled them out a month ago and they are still like new. Carbonization does not occur with these plugs too.
Jack.
I checked the surface of the suspect piston again today and can't see a thing. Did another warm compression test and pretty much 120 PSI on both cylinders...
Ran some engine tuner through it and it blew out a bit of the carbon and ran fine on the muffs otherwise.
I dont think there are surface gap plugs that corss reference to NGK BR8HS-10 plugs. I havent found any information yet anyway online.
Additionally, since I have an IR temp gun I decided to double check the head temperatures while it was running on the muffs at idle and slightly faster idle...
Reading on the cylinder cover plate (next to spark plugs) the area around top cylinder read a constant 120 degrees F and the bottom one was a fair bit lower around the 100 deg F (normal?).
I checked up the heads and this was around 125 degrees F...
The thermostat is rated to open at 118-126 degrees F so it seems its doing its job and the colling system is all in good working order... Never has been a problem... It was interesting to see the bottom cylinder runs a bit cooler though...
Just noticed my merc 2 stroke 75 doesn't have pins on end of plugs. What the?. Yesterday at high revs kept losing revs, thought it may have been tank breather hoses but no. Drained water tap lots of crap and stuff, checked cylinders and no drop in revs when removed top plug lead. Could this be the reason for drop in revs bearing in mind ran ok at high revs for minute or two before drop in revs. Bit worried about plugs
Rob
Maybe a load of shite fuel BT? Water in it, diminished octane or something?
Also just found motor only running on middle and bottom cylinder. Is it possible to be an easy fix or straight up very expensive.
Posting Permissions
Reply With Quote