ESE's works engine tuner

[F5 Dave]

Have you polished the crank seals and the Primary drive nut?

[TZ350]

2Stroke Stuffing. Polishing crankshaft seals.

[TZ350]

Making progress, a solid 40rwhp from a 1970's 250 single.

Trying to setup the carburetor jetting from scratch is challenging. Without any petrol base line to work from it is all trial and error finding the right ignition and jet combo for methanol.

I re checked the Ignitec and trigger setup. Now the ignition timing graph is much more sensible and in line with what some other people with methanol experience have told me to expect.

But the engine has been running on at the end of a dyno pull. It just wont shut off but keeps running on. It seems to be glow plugging on NGK BR10EG's.

Enriching up results in more sever running on. I guess the richer it is, the colder it is and less of the fuel is evaporating which results in the mixture going leaner. The plug or its earth strap could also be running too hot.

More work tomorrow, slowly reducing the main jet and maybe adding a dash of Acetone to help ward of Methanol's tendency to auto ignition.

[Frits Overmars]

... the engine has been running on at the end of a dyno pull. It just wont shut off but keeps running on. It seems to be glow plugging on NGK BR10EG's.
Enriching up results in more sever running on. I guess the richer it is, the colder it is and less of the fuel is evaporating which results in the mixture going leaner. The plug or its earth strap could also be running too hot.

Enriching resulting in going leaner does not sound very likely to me. Neither does glowplugging on NGK 10-plugs, although I cannot exclude it.
Bringing coolant close to the plug threads has solved some problems in the Aprilia racing engines. Increasing the coolant circulation speed and lowering its temperature should help. And you might try a surface discharge plug; that would definitely exclude glowplugging.

But I rather suspect you are experiencing HCCI: Homogeneous Charge Compression Ignition. Lowering the compression ratio (how high is it now?) could give a clue. It may decrease engine power but increase your knowledge.
One way of inducing HCCI is pre-heating the combustible mixture using EGR, which normally stands for Exhaust Gas Recirculation, but in two-strokes comes down to Exhaus Gas Retention. From a certain rpm onward the blowdown time.area becomes insufficient and exhaust gas that has not had the time to leave the premises heats up the fresh mixture. Too small an end cone restrictor or silencer could be a culprit as well.
If you are willing to sacrifice a piston, you can file 1 mm off the edge that controls the exhaust timing while avoiding to touch the parts of the edge that control the transfer timing. This will increase the blowdown angle.area sufficiently to give an indication whether that was the problem.

[Vannik]

Enriching up results in more sever running on. I guess the richer it is, the colder it is and less of the fuel is evaporating which results in the mixture going leaner.

This usually means the float bowl runs empty sooner. How sure are you that you have a big enough feed to the bowl?

[Frits Overmars]

This usually means the float bowl runs empty sooner. How sure are you that you have a big enough feed to the bowl?

Didn't think of that. Makes sense; thank you Neels.
Now that you remind me, restricting the flow to the float bowl used to be a trick in the 100cc direct-drive kart era to automatically lean the mixture when running WOT on the straight, to wring some extra revs out of the engine. Quite risky....

[wobbly]

Frits , TeeZee's thing is aircooled , that is the real reason for the jungle juice.
I found years ago that when really pushing an aircooled and using rich mixtures to keep the cylinder cool , an 11 plug was needed.
Never thought of a surface discharge - would probably work well with dual Ignitech CDI into the Crane coil.
Also had the issue Neels came up with , the only way to keep the bowl full was to use a 4.5mm Dellorto methanol specific float valve.
And yes Frits , the drivers back then were well versed in running very lean at WOT then semi choking the carb for the last 1/3 of the straights.

[Grumph]

Frits , TeeZee's thing is aircooled , that is the real reason for the jungle juice.
I found years ago that when really pushing an aircooled and using rich mixtures to keep the cylinder cool , an 11 plug was needed.
Never thought of a surface discharge - would probably work well with dual Ignitech CDI into the Crane coil.
Also had the issue Neels came up with , the only way to keep the bowl full was to use a 4.5mm Dellorto methanol specific float valve.
And yes Frits , the drivers back then were well versed in running very lean at WOT then semi choking the carb for the last 1/3 of the straights.

Those were the days when you could pick out a top 100 driver in the bar by the short fingers...

[TZ350]

I rather suspect you are experiencing HCCI: Homogeneous Charge Compression Ignition. Lowering the compression ratio (how high is it now?) could give a clue. It may decrease engine power but increase your knowledge.
One way of inducing HCCI is pre-heating the combustible mixture using EGR, which normally stands for Exhaust Gas Recirculation, but in two-strokes comes down to Exhaus Gas Retention. From a certain rpm onward the blowdown time.area becomes insufficient and exhaust gas that has not had the time to leave the premises heats up the fresh mixture. Too small an end cone restrictor or silencer could be a culprit as well.

HCCI sounds possible. Single Ex opens 80 deg ATDC and is 72% wide. Not keen on going any more than that. Maybe time for that triple exhaust port modification I have in mind. A very cunning plan. The end cone restrictor is 32mm sure looks big enough but I will re visit that.

From memory, the compression ratio is 14:1 swept on a 70mm bore, 45% squish at 0.9mm clearance.

[TZ350]

Enriching up results in more sever running on. I guess the richer it is, the colder it is and less of the fuel is evaporating which results in the mixture going leaner. The plug or its earth strap could also be running too hot.

This usually means the float bowl runs empty sooner. How sure are you that you have a big enough feed to the bowl?

That sounds very likely, Thanks.

Also had the issue Neels came up with , the only way to keep the bowl full was to use a 4.5mm Dellorto methanol specific float valve.

Cant manage 4.5mm but was able to drill a standard Mikuni out to 3.5 and modify it for improved flow through the valve itself (hopefully).

[pete376403]

That sound very likely, Thanks.



Cant manage 4.5mm but was able to drill a standard Mikuni out to 3.5 and modify it for improved flow through the valve itself (hopefully).

The float valve holder in the 38mm Mikuni round slide carb on my jawa speedway bike had a horizontal cut (1 - 1.5mm wide) just below where the float valve seated. Allowed the fuel (Methanol) straight into the bowl as soon as the valve was of its seat, rather than having to get past the sides of the valve.

[Grumph]

Mk1 Amal concentric alcohol float bowls have the same thing - a slot just up from the needle seat about 2mm deep and around 1/3 of the circumference of the needle housing. They also have large 3 sided float needles running in a bore about 9mm ID, Actual bore of the orifice is probably 4mm.

If all else fails you could always pressure feed the carb. It violates KISS - but if it works...

[wobbly]

3.5mm is too small even if its modified , and I never could get drilled seats to seal.
The Dellorto seat is the same sort of shape - you can modify the carb body to use that.

[husaberg]

Pretty sure Neil made a lake injector they had no float bowl. pre 1970 so legit for class

or here is an aussuie moded concentric on an alcohol hardlet classic racer with a concentric amal with a flat bowl off a strongberg carb from a valiant.


the other mod that might help
https://thunderproducts.com/product/...bowl-extender/


Also make sure your needle jet is big enough as per one of the first posts in the tread

.

This is Thomas a Vietnamese race mechanic, you know that place where they have all those hot 50's and 125's are big bikes.

Thomas, ESE's Race Team's Tuner is fettling number 9. adjusting the port timing for Taupo.

Its hard to see but he has taped a degree wheel to the magneto flywheel so he can mark out the exhaust port height he wants.

None of this raise the port 3.5mm for a gazillion HP nonsense. He knows what timing he needs and sets the crank position there before marking the port and then doing the hells death port job that we all dream of.

You should see him setting up a carb. Talk about pain staking, he starts with a main jet so big the bike floods at about half throttle (apparently this proves the oriface of the needle/needle jet combo is big enough) and then he slowly step by step works back until it runs clean.

Most people start at the bottom with a carb and work up, He starts at the top and works backwards.

Never seen him blow one up. But then he is intelligent with the throttle and does not ring its neck when the engine is in distress.

Boy o Boy am I Looking forward to Taupo.

.

[Flettner]

At the two minute seventeen second mark, 350 Bighorn with Lake Injector, E85. The only day I got it to run nice, won its class. I still have the Lake Injector under the bench somewhere. I moved on to electronic injection after this, all hidden inside, no one knew.
https://youtu.be/7CSXHo3jLVc