Black oil spots from exhaust

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Black oil spots from exhaust

Postby spencers » Wed Nov 08, 2017 11:21 am

Hi, I have a 125 Deluxe with a standard 5 port 150cc conversion, std air filter (drilled), running 108 main jet, running in after 300 miles the engine seized/nipped up but then restarted straight away. I had noticed that during running in there seemed to be excess amounts of thick black oil spots coming from the exhaust/stub joint. I have handed the problem over to a friend who is experienced with working on two strokes - (Rotax used in microlights and paramotors) and , but is troubled by the amount of un-burnt oil present in the exhaust and the fact that the bore and piston seemed to be unusually un-lubricated, is this normal when running in?

On stripping down we have discovered that a new piston assembly is required but the barrel is serviceable. My friend/mechanic is concerned that the excess oil is weakening the mixture and this in turn lead to the seizure or could have contributed to it, he says that its a common misconception that greater oil/fuel mixes help lubrication when in fact they do the opposite. Could the oil pump be delivering too much oil, or is faulty.

Any ideas, anyone?
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Re: Black oil spots from exhaust

Postby Stax » Wed Nov 08, 2017 4:31 pm

I'm replying as I've noticed a distinct fall off of interest /enthusiasm in the club forum over the past few months.Could this be linked to LML ceasing trading ?.I hope this isn't indicative of a collapsing hub.With LML brand names such as 'Stella' and 'Star, a 'Supernova' perhaps?
Anyway due to the lack of any expert advice in reply to your problem may I humbly put in my twopence worth based on 32 years experience in the microlight world.
Rotax ,Cyuna ,Robin etc were the dominant 2 stroke engines used.The arrival of the big Rotax 100hp 4 stroke engines were very welcome in a world where engine seizures were not uncommon.
By the very nature of use it was quite important that the pilots had confidence in the reliability of the 2 stroke engines ,and as such much emphasis was placed on monitoring and servicing.To this end most pilots had an exhaust gas temperature gauge fitted which showed what temp the engine 'IS' ,as opposed to a useless cylinder head temp gauge which showed what the temp' WAS'.Another interesting (but alarming) feature of 2 stroke engines is the very small temperature difference between the optimal operating engine temperature and the melting point of the aluminium piston !!!!
To my knowledge ,causes of seizure could be attributed to Carburetor problems whereby the engine ran lean (higher air to fuel ratio) sometimes caused by jetting,air filter splitting ,split inlet manifold/inlet manifold gasket leaking or oil seals breaking down,also changing from mineral 2 stroke oil to synthetic would emulsify and block the fuel filter.
To eliminate unlikely causes confirm 1. you haven't changed the type/brand of 2 stroke oil,
2.The mix ratio (approx 3 percent) .Your friend is correct, reference more oil to petrol actually leans the engine.
3.The engine oil level isn't going down indicating a blown oil seal and engine oil being burnt.Excessive smoke?
Could it be that since the conversion you have been running with wrong jetting and that it was only a matter of time before it seized?
Hope my input will prompt more responses from others that really have good engineering experience.
Hope you sort it. Incidentally I'm in Portsmouth which has a few 2 stroke experts who meet up on our weekly ride out ,next time Ill elicit some advice and pass it on.
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Re: Black oil spots from exhaust

Postby mikey 69 » Wed Nov 08, 2017 5:20 pm

Have you done any plugchops To ensure jetting is right ?
Although 108 main jet sounds about right, each engine is different so you could actually be running lean thinking it is ok. Secondly air leaks can cause heat seizures, ensure all gaskets tight, head carb etc
Hope this helps
Mikey
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Re: Black oil spots from exhaust

Postby Shaunbond » Wed Nov 08, 2017 6:49 pm

108 sounds way rich to me...
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Re: Black oil spots from exhaust

Postby Shaunbond » Wed Nov 08, 2017 8:05 pm

Found my old jetting.

This is as it came out of Eddie Bullets, the guy i bought it off when 9mths old said he didnt touch it, I've no reason to disbeleive him. He only did about 700 miles.

Main jet 101
Idle 40/130
Air 140
Mixer E3
Starter 60

Ran amazingly well. Should never has traded it...
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Re: Black oil spots from exhaust

Postby rob h » Wed Nov 08, 2017 9:11 pm

I agree with your mate, too rich should mean too much oil not being burned. If you are too rich it can cause overheating, slightly rich is good for a new engine. It can run without the risk of seizure, not too hot either.
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Re: Black oil spots from exhaust

Postby spencers » Thu Nov 09, 2017 9:47 am

Hi everyone, I appreciate all the comments, will let you know what we discover in due course

Thanks
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Re: Black oil spots from exhaust

Postby hotversion » Thu Dec 21, 2017 3:20 pm

Yeah way too rich 98 main
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