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2 stroke engine running backwards

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at106
Brolly Dolly



Joined: 16 Jul 2011
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PostPosted: 16:38 - 30 Aug 2011    Post subject: 2 stroke engine running backwards Reply with quote

After i finally thought id got my suzuki ts50x ready for the road i've encountered another problem. When i start the engine and put the bike into gear it goes backwards. No matter what ive tried it wont start forwards.

At first i thought it was the timing but after putting it back to factory setting and every other setting it still runs backwards. When i kick the engine over the rotor rotates counter clockwise (which is correct) but once it starts it always spins clockwise.

Another thing which may not be associated with this is after i put the timing to the only position i hadnt tried when the engine ran there was a knocking noise from the barrel area. After i heard the noise i stopped the engine, but is the noise just due to the timing being out?

If anyone has any ideas let me know!
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P.
Red Rocket



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PostPosted: 16:47 - 30 Aug 2011    Post subject: Reply with quote

Have you built it backwards?

Can you bump start it running the correct way... Im sure 2 strokes can run backwards anyway Laughing
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at106
Brolly Dolly



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PostPosted: 16:59 - 30 Aug 2011    Post subject: Reply with quote

##Paddy## wrote:
Have you built it backwards?

Can you bump start it running the correct way... Im sure 2 strokes can run backwards anyway Laughing


I havent rebuilt the engine or gearbox (yet)

I did try bump starting it but i couldnt get it to start. 2 strokes can run backwards but it's not very practical!
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Pete.
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PostPosted: 17:04 - 30 Aug 2011    Post subject: Reply with quote

Your timing is out. Try bumping it and see what happens.

Oh - be ready on the clutch Very Happy

EDIT: actually, first-off pull the flywheel and check the woodruff key isn't sheared.
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Kickstart
The Oracle



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PostPosted: 17:06 - 30 Aug 2011    Post subject: Reply with quote

Hi

That does suggest that the timing is still out. Check that the timing marks are correct (including that the flywheel hasn't move on the crank - woodruff keys sheering off is not that unknown).

All the best

Keith
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Teflon-Mike
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PostPosted: 17:16 - 30 Aug 2011    Post subject: Reply with quote

Sounds like your timing has TOO much advance.
Kick it over, kicker turns engine the 'right' way, but kick it too slow, piston comes up, early spark lights the fire, and piston doesn't have enough momentum to over centre against expanding charge.

Hows the timing set? Are you doing it merely by points gap, or are you swinging the back-plate?

Working 'blind' without book; I would start by loosing the back plate, and closing the points; turning rotor to get poiston at TDC measured with a pencil or similar through the plug hole, NOT marks on the rotor.

Piston at TDC, I'd rotate back plate so that the points were just 'starting' to open, then back off, so they were 'just' shut....

That would give aprox ZERO advance.

THEN with timing hugely retarded, bike should start up forwards.....

Wont RUN brilliantly, but should run in the correct direction!

Then, I would start advancing the ignition, an 'nth' at a time, rotating the back plate, and starting it, until I got reverse running again..... than 'back off' an 'nth so it stars forewards again... And THEN measure the points gap with piston at TDC..... and compare THAT measurement to what the book says it ought to be.....

It's PROBABLY the way you are trying to set the timing, and I suspect it will be that the book says to set a certain points gap at TDC.... BUT if the back-plate has been shifted, then points gap alone isn't setting correct timing, becouse it could be up or down the ramp of the cam on the rotor....

Hence you need to find the correct points possition, THEN set the points gap.

If you wip the rotor off, you may find that there are timing marks on the back plate, or 'wiotness' marks where its spent most of its life clamped up, that you can use to give you a 'guide' where it ought to be.... but no garantees..... propper timing swing, as described though... old fasioned, time consuming, but garanteed way to sort it.

After swinging to get startng sorted, you can then adjust to get best throttle response and running.....

Not that I have had much practice at this, but I went to look at the rotor on my Yam yesterday, and just thought I would see if the rotor puller for my Montesa would fit..... wouldn't reach isn't long enough, annoyingly! BUT there were three in the draw..... YES I have, in quarter of a century worn out at LEAST two flywheel pullers setting points and timing, on an old two stroke!

Have fun, all gryst to the mill and good experience!
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Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'
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at106
Brolly Dolly



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PostPosted: 17:17 - 30 Aug 2011    Post subject: Reply with quote

The woodruff key is in good condition, and the rotor isn't able to move on the crankshaft.

I'll try bumping it again tomorrow and see what happens.

Also could the knocking noise be related to the timing being out?

Thanks
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Pete.
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PostPosted: 17:24 - 30 Aug 2011    Post subject: Reply with quote

Yes and it will cause a lot of damage if you run it any amount.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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at106
Brolly Dolly



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PostPosted: 17:24 - 30 Aug 2011    Post subject: Reply with quote

Teflon-Mike wrote:
Sounds like your timing has TOO much advance.
Kick it over, kicker turns engine the 'right' way, but kick it too slow, piston comes up, early spark lights the fire, and piston doesn't have enough momentum to over centre against expanding charge.

Hows the timing set? Are you doing it merely by points gap, or are you swinging the back-plate?

Working 'blind' without book; I would start by loosing the back plate, and closing the points; turning rotor to get poiston at TDC measured with a pencil or similar through the plug hole, NOT marks on the rotor.

Piston at TDC, I'd rotate back plate so that the points were just 'starting' to open, then back off, so they were 'just' shut....

That would give aprox ZERO advance.

THEN with timing hugely retarded, bike should start up forwards.....

Wont RUN brilliantly, but should run in the correct direction!

Then, I would start advancing the ignition, an 'nth' at a time, rotating the back plate, and starting it, until I got reverse running again..... than 'back off' an 'nth so it stars forewards again... And THEN measure the points gap with piston at TDC..... and compare THAT measurement to what the book says it ought to be.....

It's PROBABLY the way you are trying to set the timing, and I suspect it will be that the book says to set a certain points gap at TDC.... BUT if the back-plate has been shifted, then points gap alone isn't setting correct timing, becouse it could be up or down the ramp of the cam on the rotor....

Hence you need to find the correct points possition, THEN set the points gap.

If you wip the rotor off, you may find that there are timing marks on the back plate, or 'wiotness' marks where its spent most of its life clamped up, that you can use to give you a 'guide' where it ought to be.... but no garantees..... propper timing swing, as described though... old fasioned, time consuming, but garanteed way to sort it.

After swinging to get startng sorted, you can then adjust to get best throttle response and running.....

Not that I have had much practice at this, but I went to look at the rotor on my Yam yesterday, and just thought I would see if the rotor puller for my Montesa would fit..... wouldn't reach isn't long enough, annoyingly! BUT there were three in the draw..... YES I have, in quarter of a century worn out at LEAST two flywheel pullers setting points and timing, on an old two stroke!

Have fun, all gryst to the mill and good experience!


This bike doesnt use points as it's one of the later models. Behind the rotor there is the stator plate which has four coils. 3 for the charging circuit and one for the primary ignition. The stator plate has 3 bolts mounting it to the crankcase, if you loosen the bolts you can turn the stator plate.

On the stator i found marks where it had previously been tightened and set it to this point but it still ran backwards. So then i put it completely the opposite way hoping it would run forwards but it made no difference.
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Kickstart
The Oracle



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PostPosted: 17:34 - 30 Aug 2011    Post subject: Reply with quote

Hi

Use a strobe light to check the timing.

If you have no points then it presumably has a cdi unit (possibly built into the coil). These can fail.

All the best

Keith
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at106
Brolly Dolly



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PostPosted: 17:46 - 30 Aug 2011    Post subject: Reply with quote

Kickstart wrote:
Hi

Use a strobe light to check the timing.

If you have no points then it presumably has a cdi unit (possibly built into the coil). These can fail.

All the best

Keith


I thought about using a strobe light but i didnt as i couldnt see how it would be useful if the engine is running backwards?

Yes the CDI is built into the coil, but they're not easy to get hold of so i hope it's not.

Is there nothing internally in the engine which could cause the engine to run backwards?

Thanks
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Kickstart
The Oracle



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PostPosted: 23:00 - 30 Aug 2011    Post subject: Reply with quote

at106 wrote:

Is there nothing internally in the engine which could cause the engine to run backwards?


Nope. Possible that with the timing right it could be persuaded to run backwards by bump starting it backwards, but to actually go from being actually being turned over forwards to running backwards I would expect the timing to need to be a long way out.

A strobe light will at least confirm this, and possibly help figure out why it is out.

All the best

Keith
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Teflon-Mike
tl;dr



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PostPosted: 23:21 - 30 Aug 2011    Post subject: Reply with quote

at106 wrote:
Is there nothing internally in the engine which could cause the engine to run backwards?


Its a two stroke, it CAN run backwards becouse it completes one combustion cycle per revolution, charge controlled via holes in the cylinder wall opened and closed by the piston going up and down, makes no difference to the workings which way the crank turns.

So... No, basically, really the ONLY way that it can be made to run backwards is if you bump-start going backwards, or as described, timing is so advanced, that the piston comes up on an expanding charge without enough momentum to carry it over Top Dead Centre, and so gets blown back, and picks up enough momentum to complete the cycle running backwards,m with effectively hugely retarded ignition.

If no points, then there is still a 'trigger' somewhere on the ignition, usually an inductance coil pulsed by a lug on the rotor..... which may need looking into, but the back-plate is still out of sync with where you want the spark.

And / Or, its the CDi unit, which has an inbuilt advance curve, and rather than firing coil directly off points trigger. at LOW revs..... it fires late, by a process known as advance by retard...

Basically at higher revs you tend to want the spark earlier in the cycle.... but at low revs you want the ignition later in the cycle....

If you set your trigger pulse for low revs, you would be having to 'guess' when you want the spark ahead of the trigger signal, BUT if you set trigger pulse for where you want it at high revs, you get trigger before you want spark at low revs, so you simply set a 'delay' counter to retard it to what you want.....

Make sense?

So, if you have CDi unit, and its gone 'duff' could be its NOT delaying the timing for low rev running, and firing at the advanced high rev timing......

HOWEVER; one 'simple' thing that springs to mind; some more rudimentary CDI ignitions were either rather simple, or rather clever, depending on how you look at it.

Conventional ignition has 'something' battery, or generator of some sort providing current to 'energise' a coil, then a 'trigger' that breaks the supply to the coil, creating a field colapse and a huge reverse voltage, which provides the 'beef' to get electricity to jump the gap in the spark plug.

On a points system, trigger was the points opening.

On a CDi system, conventionally its a 'pulsar' coil, very small coil, that when a lug on the rotor passes it provides a verty small, bery bried 'pulse' of induced current, enough to be 'sensed' by a balenced electronic circuit and flip a transistor, to break the supply to the coil, mimicking the points, or, by the advance by retard method, starting a counter, that then flips a transistor and colapses the coil field...

However; on a magneto ignition, the generator is supplying a 'pulse' of electricity every time the magnets in the rotor pass the coil, being a bit clever, and saving on electronics, and wiring, using ONE WIRE from the magneto, that is supplying the current to set up the field on the coil, a CDI can simply monitor the voltage on that feed, and when it 'inverts' from a rising voltage to a decaying voltage, marking the peak of the 'pulse' from the magnet passing the coil.... trigger the field collapse, or again, start delay counter.....

This is a 'one wire' CDi ignition system, as opposed to a pulsar system that would use two wires, one for feed, one for trigger.

But there is yet another system, and that, I believe was used by Yamaha for a while, which is a 'pseudo' Cdi system, and instead of having an expensive bit of electronics, timing engine revolutions, and from a map, setting 'retard' delays, they simply had a 'duel' one wire CDi system, where there were two ignition windings, seperated on the back-plate by aproximetely 12 degrees; one provided low rev timing, other provided high rev timing, and the CDi unit simply switched between them at a pre-deturmined engine speed.....

I dont know the ignition system on your bike; BUT if you had such a duel winding CDi system, and had the wires switched so it was trying to fire from high rev winding at low rpm and low rev winding at high rpm... could explain your situation....

Running forwards, you might have 18 degrees of advance on the High Rmp winding, which would account for it it starting backwards not over centreing against burning charge....

But, running backwards your 18Deg of advance would become 18 degrees retardation, after TDC....

Not great for running at low speeds, as your low speed spark would be set something like 4 degrees advance of TDC...... but running backwards that would become 4 degrees in retard of TDC, so actually more 'advanced' than the high speed spark....

So it could still 'sort' of run nicely, backwards if you revved it! especially if the backplate had been twisted to retard the ignition, and effectively 'advanced' timing when running backwards!

Err... start with the back-plate and ignore the witness marks, see if you can retard it enough so that this start up business doesn't have it back running......

Then look at the ignition wiring and diagrams and see if anything occurs to you from ideas offered.
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'
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at106
Brolly Dolly



Joined: 16 Jul 2011
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PostPosted: 09:05 - 31 Aug 2011    Post subject: Reply with quote

Thanks for your reply! As you say my bike only has one wire coming from the ignition source coil to the cdi, and no pick up coil. So i hope it's not the CDI as they're not easy to get hold of.

I wont be able to work on it until friday now, but first i'll try bump starting it forwards and see if it will run. If it doesnt run my stator plate is similar to this https://www.google.co.uk/imgres?q=motorcycle+timing+stator&um=1&hl=en&sa=N&rlz=1T4ADRA_enGB351GB351&tbm=isch&tbnid=IQ8keym-z7XifM:&imgrefurl=https://www.scooterhelp.com/tuning/vespa.malossi210.install.html&docid=a382PlopQutEgM&w=360&h=311&ei=n-ldTpqMMMOg8QPzqLnOAw&zoom=1&iact=hc&vpx=419&vpy=259&dur=3320&hovh=209&hovw=242&tx=141&ty=87&page=1&tbnh=153&tbnw=188&start=0&ndsp=30&ved=1t:429,r:9,s:0&biw=1680&bih=794 with the yellow coil being the ignition source. Could it be that the whole stator needs turning round nearly 90 or 180 degrees?
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Teflon-Mike
tl;dr



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PostPosted: 12:28 - 31 Aug 2011    Post subject: Reply with quote

https://images.cmsnl.com/img/partslists/magneto-ts50-1987-xkh_bigsue0010fig13_4429.gif

Pic I found of TS50 Stator. Three screw attachement; you could be rotated one screw either way, but with that much extra advance or retardspark would be happening nearer BDC that TDC, probably with ports open, so I suspect engine wouldn't even run, in either direction!

Pic you linked (Use mouse right on original pics to 'copy Picture URL' then past in post, and add {img} address {/img} tags, but swap curly brakets shown for square ones, to make pic display in post) doesn't look like one shown in Suzuki Micro-Fishe; that seems to have three equipment windings, and one for the ignition, then uther gubbins I cant see inside. One in your picture seems to have four equipment windings, then for the ignition, and a 'black thing' which may be a pulsar, and possibly the CDi as well, hence one wire to coil... BUT I'm, speculating, withouty schematics for the bike.

Microfishe parts list peculiarly unhelpful; describing coil merely as Unit & Coil assembly; which may suggest CDi unit/Coil, or could just be coil with bonded HT lead!

You know... they might be a pain in the arse, needing the contacts cleaning frequently, might be a compromise between low speed sand high speed timing, they might infuriate with condensors breaking down.... BUT.... I am apreciating old fasioned points more and more these days!
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My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'
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at106
Brolly Dolly



Joined: 16 Jul 2011
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PostPosted: 15:39 - 31 Aug 2011    Post subject: Reply with quote

Teflon-Mike wrote:
[img]
Pic I found of TS50 Stator. Three screw attachement; you could be rotated one screw either way, but with that much extra advance or retardspark would be happening nearer BDC that TDC, probably with ports open, so I suspect engine wouldn't even run, in either direction!

Pic you linked (Use mouse right on original pics to 'copy Picture URL' then past in post, and add {img} address {/img} tags, but swap curly brakets shown for square ones, to make pic display in post) doesn't look like one shown in Suzuki Micro-Fishe; that seems to have three equipment windings, and one for the ignition, then uther gubbins I cant see inside. One in your picture seems to have four equipment windings, then for the ignition, and a 'black thing' which may be a pulsar, and possibly the CDi as well, hence one wire to coil... BUT I'm, speculating, withouty schematics for the bike.

Microfishe parts list peculiarly unhelpful; describing coil merely as Unit & Coil assembly; which may suggest CDi unit/Coil, or could just be coil with bonded HT lead!

You know... they might be a pain in the arse, needing the contacts cleaning frequently, might be a compromise between low speed sand high speed timing, they might infuriate with condensors breaking down.... BUT.... I am apreciating old fasioned points more and more these days!


The picture in your post is what is on my bike, the one i linked to was just to try and explain my idea of completely turning it around.

When i get time i'll try all of the suggestions and hopefully one of them will work!

I haven't run the engine much backwards ive just got it started, put it in gear and released the clutch to find the bike goes backwards.
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Pete.
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PostPosted: 16:07 - 31 Aug 2011    Post subject: Reply with quote

I bought a MBX50 once which had the wrong rotor fitted, and was firing on TDC with no advance. It would start fine and idle but had a top speed of 18mph. I had to re-time the engine by slotting the backplate.

Is your backplate mounted like in the picture with the long winding at the bottom?
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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at106
Brolly Dolly



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PostPosted: 17:37 - 31 Aug 2011    Post subject: Reply with quote

Pete. wrote:
I bought a MBX50 once which had the wrong rotor fitted, and was firing on TDC with no advance. It would start fine and idle but had a top speed of 18mph. I had to re-time the engine by slotting the backplate.

Is your backplate mounted like in the picture with the long winding at the bottom?


It's fitted exactly like the picture, and the rotor is the original.
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at106
Brolly Dolly



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PostPosted: 18:25 - 03 Sep 2011    Post subject: Reply with quote

I finally got time today to take a look at it. First i tried bump starting it but that didnt work. The engine would fire a few times but that's it. I also tried starting it and then flicking the killswitch, a couple of times it would run for a split second forwards and then cut out.

The only thing that isnt standard is the ignition source coil, but i dont think that should affect it. And would it matter if it was on the wrong way up? Although i dont think it is.
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Ed Case
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PostPosted: 18:33 - 03 Sep 2011    Post subject: Reply with quote

In days of 'yore' it was not at all unusual for some Villiers two-strokes to strike up 'backwards', interesting stuff at traffic lights. The Messerschmitt 'bubble-car' had an ignition system that catered just for this characteristic so not only did you have 4 speeds and 70mph going forwards but the same going backwards !.
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at106
Brolly Dolly



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PostPosted: 20:02 - 04 Sep 2011    Post subject: Reply with quote

Using a strobe light i found that it is sparking 180 degrees from where it should be. So am i right in thinking i should replace the cdi/coil unit?
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