Terrot MT1 Motorcycle restoration project

[911hillclimber]

New piston is exactly as the original piston, and as the engine has, last year, run once or twice on the Dellorto for several minutes but would not start ever when you wanted it to do so...
The piston only goes in one way.

Decision to buy it was wrong, hindsight and all that, but there are bikes as this one on you tube that demonstrate starting on 2nd or 3rd kick and simply tick over for ever or ride away.

Albeit when new, customers would expect it to start on the kick surely?

Will keep chipping away, feel closer than ever before.

[911hillclimber]

Can't imagine too many people are interested any more, but a short update.

Left the bike alone as it was/is just a real pain.
Had a few hours messing about fine tuning ( ) all the variables, fuel mixture and timing.

Got it to run sort of, but seem to have the mixture close to right, but still it protests.

On the original carb now, adjusted the needle to give a weak as possible mix and set the float to 'just' get the fuel puddle 'just' at the rim of the venturie.
I think this must be right as there is an easy to see small hole drilled that puddles when the float is at the level, the hole is exactly at the same height as the venturie tube top.

It ran for quite some time, and is a far more reliable to fire, but the running is about 1 minute and then peeters-out for no reason.
Most noticeable is the singular reluctance to 'throttle' when it has run.
No matter what the carb piston position it runs at one speed, no fast/slow as if you were using the twist grip to rev the engine, just one speed!

I've moved the ignition timing all over the place.
The spec for the magneto is 5mm piston drop BTDC, most 2 strokes are 3mm, but tried 6mm and it started quite well, have tried mmm to 0mm (ie TDC) the latter was a fatigue mistake.
It seems to tolerate almost any angle you choose within reason, and 6mm seems to be the best of a bad bunch.

Decided to give myself this weekend to try other stabs-in-the-dark and will advertise it as a starter/non runner for £1800 and see it go.

Just had enough now, time to move on. Tempted to try ebay in UK and certainly France too.
I'm keen to get going on the little Peugeot moped in the shed, but for sure I'll get that engine done before I touch anything else.

A change is as good as a rest.
Pity, a nice looking little 50's bike.

[jjeffries]

Ignorant question, from one who knows little of two-stroke engines: does this have a reed valve(s) to pull the mixture in and let the exhaust out? John

[911hillclimber]

Not at all John, the carb is really simple.

Just a float (adjustable height, critical) a needle jet like an SU carb in a round vertical slide piston, again very SU carb design, just very small.

Carb bore is 22mm max, 17mm minimum.
The needle can be adjusted in 1mm steps to penetrate the needle tube to change the mixture.
The position of the float and the jet is crucial as I now know.

Just one main jet with a 0.34mm dia in it. The engine is killed by the blunt end of the needle coming to rest on the main jet blocking it and the fuel delivery off, there is no engine kill switch.

It is this stark simplicity that makes is so infuriating I can't get it to run. I have now managed to get the thing to start quite reliably but not run properly.

The fact that opening and closing the carb does not change the revs the engine runs at is another mystery to me.
Can't find another carb anywhere in France, people in UK have never heard of the make Terrot, so spares are zero.

[Nine One One]

Is the carb actually getting enough fuel delivery? You haven’t changed the diameter of the fuel pipe, put a bend or kink it is. Sounds like its getting fuel initially and then no more and just dies?
Ian

[911hillclimber]

Now....
You do make an interesting point!
I have on the engine stand a small bottle with a fuel tube that has an S bend in it.
The bottle is obviously above the carb, but not by much.
Time to try something different tomorrow I think.

The flow into an empty float bowl is slow...

Hope you have spotted something.

[911hillclimber]

9-1-1:
Your suggestion has improved things, it runs a bit longer before stopping!

I am now in the leaning-out exercise which is a challenge.

Float now in the right place but with the needle at the weakest height it stiff eventually gets too rich and dies.
Still no throttle effect when open/closing the needle slide.
That must signify something?

[Nine One One]

When I had a Honda SS50 years ago (in my youth! - 5 speed at that, followed by a FS1E) one of the tricks was to cut the top off the plastic top of the throttle slide by a few millimetre which would allow more fuel in on full throttle. (and shape the bottom).Think you had to cut down the spring that fitted inside the slide as well to allow more movement.
Something is wrong with the needle valve that controls the fuel flow when you open the throttle. Is the needle valve sticking or too thick for where it slides in and out of the chamber. Its definately fuel related. Have you tried testing the fuel flow with the carb in bits as to how much is actually getting through to the engine at various levels? You could try reverse fed fuel pressure where the fuel would normally exit, and send it back up the other way to see what is actually going through the needle valve at various throttle positions?

It was these things you cut down............https://www.ebay.com/p/1611859509

Not trying to teach anyone to suck eggs, but you might have done this already??

https://www.fixyourdirtbike.com/fix/how ... rb-tuning/

https://www.howtomotorcyclerepair.com/h ... e-cutaway/

And this argument of another forum........


https://yamahaclub.com/forums/topic/405 ... g-2stroke/

If all else fails stick a lawn mower carburettor on it??

http://www.ipspower.com/images/document ... ressed.pdf




You need to get the the bloody thing running so you can then start on your exotic wood and table post

[911hillclimber]

Ha!
The wood bit is relaxation from this stupid engine I can't figure out!

The carb is almost to simple, but the tapered needle is raised with the piston. It is trapped in the brass piston by a simple round disc clipped to the top of the needle and the return spring.
This way the needle has a degree of freedom to align (ish) concentrically to the needle tube which has the main (only) jet screwed into the base of it.

The brass piston is shaped much as you describe and is shaped as it left the factory.

To get the engine to fire the piston is raised to some degree manually (normally by the twist grip of course) and you kick start it.
9 times out of 10 it will fire and run seemingly rich to my ear. My previous experience of 2 strokes are Lambrettas which are no more complicated than this engine.

Once it runs, revs somewhat erratic the engine will not 'throttle' by the twist grip.
After about 1 minute the engine will die of it's own accord.
Removing the plug (quite hot by now) shows a real whetting of the plug tip, over fueling . Removing the crank case drain plug will release about 1/2 a thimble full of petroil, so the bottom end is also flooding to some degree.
The engine does not need choke (a sliding plate that blocks over the inlet to the carb).

All points to too much fuel.
I have the needle as extended as I can and the float j u s t so to get fuel just to the top of the needle tube top.
If I change the float level (5 points of adjustment) I can starve or flood the engine.

I have tried a new 50 to 80cc scooter carb from China. This has a smaller bre than the original but is a general carb found on a lot of Chinese scooters.
This carb is no better than the original.
I also have a Dellorto Chinese rip-off , same bore as the original and this is no better. I have 'adjusted' the main jet hole to the same diameter (and have tried larger and smaller jet diameters).
This carb is a far more temperamental starter and will not actually run.

In all the 3 carbs the original has worked best. I think the tube for the needle is worn to much and the current needle diameter still allows far too much fuel to be drawn in when the engine is running.

I plan to make my own needle soon much fatter than the current 2.5mm dia needle, possibly 2.8mm

Thank you for all your help, I need some help on this thing.

[Ashley James]

Amac became Amal and is English I believe. There are two components to the mixture. The slide or piston and the needle. At lower speeds the cutaway of the slide controls the mixture, the needle at full speed. A bit like an SU, but you control its position, not engine vacuum.

Trouble is I’ve forgotten the finer details. Somewhere I have a Tuning For Speed by Phil Irving, which is very helpful, so I’ll see if I can find it.

[911hillclimber]

Thank you Ashley.

This carb is stock as a stone, everything is clean and clear so it really should simply work?
Any wearing parts are now restored except for the tube the needle goes into, I think that is oval.

Tempted to try a sleeve into the end of it and drill back to a some size, but getting the drills, getting the hole right seems difficult, making a fatter needle seems easier as the machining is all external surfaces.
Tedious!

[Winston Teague]

Im intriguied by that slide, it looks home made. Is the end shown in the photo the top or bottom? could we see a picture of the cutaway please? My (limited) knowledge is that Amac were also available in Britain. Have you talked to Chris Williams at Autocycle Engineering in Netherton? W

[911hillclimber]

When I got the bike I stripped the carb apart and found somebody in France had filed the 'roundness' of the piston!
The piston was very barrel shaped, not a true cylinder, but the sloping slot was true (where the needle comes through).

I bought a piece of cold drawn brass who's dia was the same as the carb body bore and machined the 'barrel' piston true to the same size as the internal bore of the new tube. I sweated the two together with soft solder so I now have a true cylindrical piston running nicely in the carb body bore. See pics.

Thus the piston is dimensionally the same as the original.
The opening of the tapered slot faces incoming air.

Never heard of the gent in Netherton, but they are just 5 miles from me! Will contact them to see if they have any parts.

I have asked AMAL about this carb, and they have no knowledge of the carb at all, so no spares, in fact they were far from helpful, not a British bike!
No idea why anyone would have attacked the piston in this way, what is to be gained from filing the thing? The carb body bore is perfect!

Original piston after cleaning:



Repairs:

[Nine One One]

Graham,
Filing the bottom of the barrel changes the tick over or idle air volume going into the carb. So if its been filed off before, someone had the same problems as you are having now!

One of the articles I sent you had this ‘modification’ included in it. Not sure if filing away those bits also changes the air volume drawn in further up the throttle position?

https://www.howtomotorcyclerepair.com/h ... e-cutaway/

Its in this article here..........the shape you have looks like it will weaken the mixture, according to that article, especially since your ‘arch’ cutaway is quite steep in comparison to those shown in the pictures on that article?

Whether the carb is also running rich or flooding the whole system as a result of these modifications maybe your issue?



Ian

[911hillclimber]

The cut away at the bottom of the piston is an interesting area.
I read the article but thought it more about fine tuning than getting the engine to run.

During all my frantic kick starting the piston is not at a single stable position.
It has only fired by pulling the piston up and down during the plunge of the kick lever.
Holding thepiston, say 20% open does very little to aide a fire.
When running the piston needs to be held open at least above 1/2 way or fully open.

When the engine dies of its own accord the plug will be wet or very wet,
I would wash the plug in brake cleaner befor re fitting for the next attempt.

I'll have another think about what you think, the article and how The piston was.
Some YouTube vids I've seen on these bikes show engines that fire almost instantly, tick over and Rev willingly.
The exhaust note is heavy, not crisp and the exhaust port gets wet with petoil.