OutdoorKing Repair Forum Forums Restoring, Customising and Modifying Tech Talk Masport 2 stroke Iron horse

Pete, the ignition timing is not the cause of it running for a few seconds then stopping (that is fairly certain to be a fuel problem), but because you are aiming to get to the bottom of how the engine works, I suggest you go through the process of checking it. The whole way around the flywheel is 360 degrees - any circle consists of 360 degrees, that is the definition of a degree of angle. You want to find how far on the outside of your flywheel coincides with the 6 degrees before TDC that is the correct ignition timing. 6 degrees, out of 360 degrees, is one part in 60, or one sixtieth of the circumference of your flywheel. One sixtieth of 502.6 mm (pi isn't exactly 3.14) is 8.4 mm, so your timing mark should be 8.4 mm clockwise from your TDC mark. When the flywheel reaches that 8.4 mm before TDC position, the points should open and the ignition should be triggered. Once you make the timing mark, it is fairly easy to check the ignition timing either by zapping your fingers as described above, or by using an ordinary xenon or neon ignition timing light.

If you have good fuel flow from your fuel pipe, the next possible cause of your problem is that the float chamber needle is sticking: it will close fully, but it won't open more than a few thousandths of an inch.

Hi Grumpy,
Thanks for those instructions i will do that.
but I thought I would have a go at getting the exhaust off.
Oh my GOD what a mission one bolt came off clean the 2nd i had to grind it off, then discovered that the exhaust is attached to the plate that the motor is attached to. so after much grunting and 6 bolts and black crap everywhere i got the motor off. It needed doing !!! I have a feeling its never been off before there is a layer of pitch black thick gritty smelly stuff almost full in the bottom half of the exhaust/muffler probably 3 inches deep the top half is only a little better only because gravity makes it fall on the bottom half.
so I'm going to set to and clean it all up and reassemble.
I'm telling you grumpy mate this was really a 2 person job for me. but I conquered the Everest of mower disassembly by myself hahaha.
Pete

The joys of owning a 2 stroke. Oil doesn't burn very well in the few milliseconds available, so it ends up as smoke and soot.

Now a good 30 year old B&S, on the other hand...

oh your a B&S man. Did you work at a factory building mowers ?

yeah the joys alright. just now carefully unclogged 2 of the 3 exhaust holes they were totally sealed i was wondering if they were supposed to be like that but someone told me there are 3.
that may explain when i did have it running for all these years why the power was diminishing.
now I'm gonna start on the muffler. I don't think the muffler bolts are stock because the head sat outside the hole that ran to the underneath, that's why i couldn't get it off because it was just spinning around and i couldn't grab the other end.
Pete

No Pete, I was in the car industry for most of the time I worked - I'm retired now. Mowers were just something more or less interesting that sometimes had to be fixed (mainly because I mostly bought garbage ones that needed some TLC). I admire the B&S formula for building cheap, reliable, repairable engines. They have been moving in a different direction lately under competitive pressure from Honda and others, gradually making their engines more complicated. They probably have no real choice, especially for the commercial engines: OHV high compression engines with variable ignition timing use much less fuel than B&S's old formula of low compression side valve engines with fixed ignition timing.

Hey Grumpy,
you must be wondering how it's going.
well after i striped it down and had to grind off one of the muffler bolts (was a piece off cake finding replacements, just coach bolts)I spent about 3 days cleaning the crud off, then decided that the body from the other mower was in better nick so i set to taking the motor off and the wheels till its was just a bare body and scrubbed her up till she looks like new, cleaned the wheels reassembled and finished at 2am this morning, was so knackered today i left it alone will have a look at connecting the fuel up and trying for a start. will let you know how it goes
Cheers mate
Pete

You've got it looking just about new, Pete. You're going to have to get it working properly to justify all this work.

Hey Grumpy
Yep she's all nice and clean, but still wont start.
just getting a cough every now and then but the engine wont carry on running
what else could it be ?
I've got a good spark
the carbys been cleaned
the exhaust ports are clean as well as muffler
I've set the spark gap
I've set the points gap
I've set the flywheel gap
there's a perfect seal in the fuel intake hose which proves the needle is sealing off
the float level is good
the governor weights and yoke are greased and assembled correctly
the magnets are good and strong
new spark plug, and even tested to make sure it's good.
fuel flow from tank is good.

but i don't know how to test if fuel is getting to the plug
any suggestions ?
I don't know what else to try.
Pete

I suggest you look at two things, Pete. First, check that the ignition timing is approximately right. I've explained how to do that in a previous post. Second, squirt a small amount of fuel into the carburetor air intake or the spark plug hole, and see if it then starts and runs briefly until it uses it up.

If it will start when you prime it in that way, then stop after just a couple of seconds, you've proved the problem is in getting fuel into the engine. If it doesn't start when you prime it, the problem is essentially spark or compression.

Um, is it possible there's an air-lock problem in the fuel-tank? (ie, not air-vented tank-cap?) I mean, if no air goes into tank through the lid, then no fuel will flow out at the bottom. I was just wondering if the primer may create enough suction to draw some fuel down, but leaves a vaccumm in the fueltank.

Seems like a good fit for the symptoms. I never did really like the idea that the float bowl was emptying in 25 seconds - most of them take a bit longer than that. It would at least be very easy to check: just take the cap off and see if it keeps running.

Hi Guys thanks for the comments about the fuel cap, I did see that on a you tube video and tried it but that was awhile ago before i was getting even a cough. so i will try that.

Grumpy: hows it going ? have you pulled your hair out yet hahaha
OK I did the TDC mark as you described but have a question.
In one post you said firing has to be before TDC so the 8.4mm mark I thought would be to the right of the TDC mark. But in another post you said it should be 8.4mm clockwise shouldn't it be Anti-clockwise ?
or have i done something wrong ?
and how do you measure .4 of a mm all my rulers don't have tiny point marks between each mm or is 8mm close enough ?
sorry to be such a bother
Pete

Hi Pete, your engine is an interesting one, so a few hassles are neither here nor there.

Your flywheel rotates clockwise, unless you have a really unusual mower. The firing mark has to reach the stationary mark before the TDC mark reaches the stationary mark - it fires 6 degrees before top dead center, not after TDC. To clarify this, just look at the flywheel and rotate it the way it normally rotates. To fire before TDC, the timing mark must get to the stationary mark before the TDC mark does. That means it has to be clockwise from the TDC mark, which means it is to the right of the TDC mark as you said. Do this a few times on the engine until you are convinced, or come back to me and tell me I'm full of prunes. Either way we'll work it out. Don't take my word for it, or you won't learn anything from this. Incidentally it is a tricky point, I always have to go through it carefully each time myself and I've been doing this a long time.

Try to get the timing mark as close as you can to the right place. You can probably manage to get it halfway between 8 and 9 mm, but 8 mm is pretty close. Whey you are really sure you are right, and have verified that is where it actually fires, try to make a nice pretty-looking permanent mark on the flywheel.

OK Grumpy I thought that it should be to the right of TDC which I have done and yep she is unusual but not as unusual as rotating anti-clockwise hahaha.
I have got my daughter to pull the cord while i hold the spark plug(was a bit nervous 1st time thought it was going to zap me like an electric fence hahaha)only thing is, is that the flywheel is rotating so fast i cant tell where it is firing in relation to the marks Ive made. If i try to spin the flywheel with my hand i'm not getting even a tickle from the plug.

so I'm starting to wonder if the coil has an intermittent failure or isn't creating enough power to create a suitably powerful spark
Pete

It's all about rotational speed Pete - it has to rotate briskly to generate a kick. The way I used to do it was to hold the flywheel with one hand and the end of the plug lead with the other, put the timing mark half an inch to the left of the stationary mark, and give it a really short but quick wrist-twist, then stop it. I'd keep adjusting the starting point a bit, and try again. With practice I'd only be whipping it a bit more than half an inch each time. Figuring out exactly where it fired in that half inch was guesswork - that difference between 8mm and 8.4mm won't ever matter unless you use a timing light later.
When you test the ignition with a spark plug, does it give a blue spark across the plug gap? If possible, you should also check it with an oversized plug gap, using a junk plug - Briggs & Stratton specify 0.060" gap for testing. If it gives a nice steady string of blue sparks when you pull the starter cord, the ignition is quite good enough to run the engine.
I may be more sensitive than you to getting zapped - the wrist flip was enough to annoy me, there's no way I'd hold a plug lead and let someone else actually pull the starter rope. That would spoil my day in a big way.

Well Grumpy that kinda settles it because the tickle i got from pulling the rope was pitiful, I tried the 0.060 gap on an old plug nothing so i closed the gap to about .50 still nothing.
I think I will have to try and find a coil somewhere, that may have been the problem all along. a dying coil.
I will let you know if i find one.
Pete

Intermittent spark might be the problem Pete - you've reported all along that you sometimes had a good spark, and sometimes none at all. I don't think it will be easy to get a Lawnboy coil in Australia, but maybe you'll be lucky, or maybe they used the same coil as some other engine. If all else fails you may be able to adapt the coil from some other engine, but as I recall the Lawnboy one was a bit weird, and as a result the design of the matching flywheel was a bit odd as well. You said earlier that the coil in your spare engine was trash.

I suggest you give the old coil a last try with the kill wire disconnected. Earlier, it seemed you were having problems with the kill wire grounding itself. To test the coil you should remove the kill wire altogether, by disconnecting it at the breaker points. If you have weak or intermittent spark with the breaker working properly, a good condenser, and no kill wire, you most likely have a bad coil.

Hi Grumpy,
I have found a guy over the north shore of Auckland who has one just waiting for a price (2nd hand)i asked him for a new lead as well just in case.

as for the kill wire I did disconnect completely it a week or so ago it didn't make any difference.
so it kinda looks like the coil is dying and your right you have a good memory i did report that the spark was on one minute off the next.
Pete

Hi Grumpy,
Got my new (2nd hand)coil and lead last night, and assembled it all this morning only bugger was the wire to the condenser had no eyelet just bare wire. but i was lucky I had 2 in my tool box.
so re-gaped the points and flywheel hooked up the fuel gave her some primes and away she went for about 1 minute or so, bit of white smoke. But the thing i cant seem to sort firstly is when it kicks over it revs up and down like when you put your foot on the accelerator in your car then take it off, continuously.
2ndly this time I'm thinking the carby needle might be sticking like you said in a previous post and it ran until the bowl was empty(also had the cap loosened).
so will take the carby off again and have a look.
How do you check for sticking needle ?
I will also double check float level supposed to be 15/16th from lip of bowl while inverted.
I feel it's getting close mate.
Pete

If it was cycling regularly, about 5 seconds per cycle, that is called hunting and is caused by the governor trying to compensate for lean mixture. You just need to adjust the mixture screw toward richer mixture - probably about a quarter turn anticlockwise. However, check your starting point: the mixture adjustment (the big black knob) should be two turns anticlockwise from all the way screwed in. Be gentle when you turn it all the way clockwise or you'll ruin it when it bottoms. Count the turns when you screw it down, and see if it is currently two turns open, or something close to that. If it has been running at two turns, you still need to open it further and retune it, in case there is some junk under it - it will probably flush itself out. With the engine running, turn it anticlockwise (that is, unscrew it) a bit and see if it stops hunting. Then adjust it for best running, and when you find that setting, make it a bit richer ( perhaps an eighth of a turn anticlockwise) but not enough to really foul it up. 2 strokes like to be a bit rich: you want it to be tending to four-stroke at high speed with no load, but you don't want it so rich that it slows down noticeably.

If you want to check the float needle, after you measure the float height, turn it back the right way up and see if the needle follows the float arm when it drops down. If the needle is sticking, the float will drop but the needle will lose contact with it instead of following it down all the way. Note Page 4-6 of the manual warns that this may happen if you don't have the spring-clip properly hooked around the float arm.

If that isn't all clear to you, just tell me and I'll try to do better.