Texas Two Step Taco

[John Murray]

It was so silly I'm almost too embarrassed to tell..

When I painted the tank I got some overspray inside it, near the filler neck. No problem I thought, the alky will just dissolve it and it will pass through the system. That was mistake number one. Number two was being so eager to get it on the dyno that I couldn't wait to get a fuel filter, so I had a couple of sessions before I fitted the filter. After sticking the piston on the lake I pulled the float bowl and found large flakes of red paint at the fuel outlet.

They say you learn from your mistakes - I now have a large screen fitted right at the tank outlet that protects everything downstream.

 

[Texasstar]

It was so silly I'm almost too embarrassed to tell..

When I painted the tank I got some overspray inside it, near the filler neck. No problem I thought, the alky will just dissolve it and it will pass through the system. That was mistake number one. Number two was being so eager to get it on the dyno that I couldn't wait to get a fuel filter, so I had a couple of sessions before I fitted the filter. After sticking the piston on the lake I pulled the float bowl and found large flakes of red paint at the fuel outlet.

They say you learn from your mistakes - I now have a large screen fitted right at the tank outlet that protects everything downstream.

I need to fit a screen on mine.


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[Texasstar]

I think once the ignition is sorted you'll find it's still a little rich. The piston issues look to have been initiated by preignition which was a result of the ignition gremlin, not the plug overheating. I think the plug damage was a result of the preignition, not the other way around. Piston crowns normally run a lot hotter on the exhaust side from the wash they get when the port opens so damage is usually more severe there. I wouldn't pay any attention to the CHT figures, there's too much latency for them to have any relevance.

Two-strokes on methanol make best power when they're getting close to being dangerously lean. The one pictured here was caused by a lean condition (due to a stupid mistake on my part) yet it ran over 150mph before it seized, so it was obviously still making some power.


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John I look at it this way. You have gone faster than anybody on a Bultaco so fast you peeled the paint off your taco. “It was still making power”

I once put a nylock on a brake stay...that was stupid.


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[Texasstar]

Here is some interesting trivia I have discovered while researching spark plugs used for methanol racing.

John says you can stick the surface gap NGK BUE in a bucket of grease and it will still fire. The Kawasaki 500 triple came with surface gap plugs back in the day. Many outboard two stroke boat motors come standard with surface gap plugs. They were originally made for WOT applications and engines that would foul plugs. The surface gap gave more area so that fouling would decrease. On one boat forum an individual said he replaced the OEM surface gap with a standard J hook spark plug and burned a hole in his piston so the surface gap was definitely designed to prevent pre detonation. They are one of the coolest running plugs out there.

I also found that the retracted gap plugs have been used for Methanol and Nitro applications. Boats, Speedway Bikes, carts, et al. Or should I say et Alky.

are retracted-gap plugs still being made? - Don Terrill’s Speed-Talk

The question comes to mind. How much nitro? Lol.

I have made two trips to Summit and have only spent 10 bucks for one NGK BUE and
a NGK-8744 resistor cap made for a solid terminal. John said they will last forever!


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[John Murray]

Here is some interesting trivia I have discovered while researching spark plugs used for methanol racing.

John says you can stick the surface gap NGK BUE in a bucket of grease and it will still fire.

I also found that the retracted gap plugs have been used for Methanol and Nitro applications. Boats, Speedway Bikes, carts, et al. Or should I say et Alky.




The question comes to mind. How much nitro?

What I meant was a sufficiently powerful ignition system will fire a surface gap plug in the grease bucket. An inductive ignition won't do it and many motorcycle CDs won't either. If you're gonna run a surface gap make sure you have an ignition that can fire it consistently. Mercury Marine pioneered this stuff and developed high energy CD systems to fire these plugs even when fouled. Mercury's 339-832757A4 coil works very well with just about any CDI.

Retracted gap plugs are very old technology and I can't think of a single reason to run them, but plenty to avoid them. They are very prone to fouling and the spark is buried in the shell so power suffers. Even with nitro I can't see any reason to use them over a S/G.

As far as I know the T/F guys mainly use conventional plugs, the electrodes of which are usually burnt off during a run.

How much nitro? How much have you got? Nitro runs very poorly in a two stroke at light loads - it's best to run it only through the main circuit and use alky or gas as a "pilot".

 

[Texasstar]

What I meant was a sufficiently powerful ignition system will fire a surface gap plug in the grease bucket. An inductive ignition won't do it and many motorcycle CDs won't either. If you're gonna run a surface gap make sure you have an ignition that can fire it consistently. Mercury Marine pioneered this stuff and developed high energy CD systems to fire these plugs even when fouled. Mercury's 339-832757A4 coil works very well with just about any CDI.

Retracted gap plugs are very old technology and I can't think of a single reason to run them, but plenty to avoid them. They are very prone to fouling and the spark is buried in the shell so power suffers. Even with nitro I can't see any reason to use them over a S/G.

As far as I know the T/F guys mainly use conventional plugs, the electrodes of which are usually burnt off during a run.

How much nitro? How much have you got? Nitro runs very poorly in a two stroke at light loads - it's best to run it only through the main circuit and use alky or gas as a "pilot".

What I meant was a sufficiently powerful ignition system will fire a surface gap plug in the grease bucket. An inductive ignition won't do it and many motorcycle CDs won't either. If you're gonna run a surface gap make sure you have an ignition that can fire it consistently. Mercury Marine pioneered this stuff and developed high energy CD systems to fire these plugs even when fouled. Mercury's 339-832757A4 coil works very well with just about any CDI.

Retracted gap plugs are very old technology and I can't think of a single reason to run them, but plenty to avoid them. They are very prone to fouling and the spark is buried in the shell so power suffers. Even with nitro I can't see any reason to use them over a S/G.

As far as I know the T/F guys mainly use conventional plugs, the electrodes of which are usually burnt off during a run.

How much nitro? How much have you got? Nitro runs very poorly in a two stroke at light loads - it's best to run it only through the main circuit and use alky or gas as a "pilot".

“Use it as a pilot” do I need to be wearing Kevlar briefs?

TF guys and BB throw them away after each run. I can’t afford to do that even with one cylinder. Fortunately the BUE is very reasonably priced. What do you think ? It sounded strong and fired quicker than with the BR10ES.


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[John Murray]

Yes, but not just Kevlar briefs

Don't get too excited by the spark plug; it won't make you any more power. They do seem to last a very long time though - I've been using the same one for years.

 

[pidjones]

I suggest Nomex briefs.

 

[Texasstar]

Yes, but not just Kevlar briefs

Don't get too excited by the spark plug; it won't make you any more power. They do seem to last a very long time though - I've been using the same one for years.

So I sat there and played with the test button testing the surface gap plug. The spark travels around in a circle. I can see how this is a big advantage over the retracted gap. If for some reason part of this plug fouls it will still fire. This is the plug for our final tune.

However, wouldn’t we want to use regular plugs to arrive at our final tune? Watching BB go through plugs like a kid in a candy store I realized something. He was using the melting of the plug tip to help him tune.


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[John Murray]

A naturally aspirated engine on alky shouldn't be melting plugs at all, and if it is it would indicate something grossly mis-configured.

 

[Texasstar]

A naturally aspirated engine on alky shouldn't be melting plugs at all, and if it is it would indicate something grossly mis-configured.

Ok a better question. How do you read the BUE plug? Just like any other plug?

 

[John Murray]

You don't. And can't to any useful degree. Tune by the torque gauge and the timeslip. A nice thing about two strokes is they give very clear indications of A/F by the sound and feel, not so much with alky but they're still there. I haven't read a plug in decades.

 

[Texasstar]

I suggest Nomex briefs.

Will do lol!


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[Texasstar]

A gift from down UNDER!!!! Ok John teach us how this dance is going to be done! The Australian Two step!


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[John Murray]

Assuming you're gonna run gas thru the low speed circuit (and I think it's worth doing) remove the line and fittings from the bowl to the front (engine side) hose tail and plug the bowl. The small gas tank should be mounted as close as possible to the carb, and the fuel level when the tank is full should be just below the bottom of the carb mounting flange. You might be able to fit a small cylindrical or rectangular section tank crosswise under the carb and in front of the float bowl, perhaps with a little re-routing of the main circuit hose.

The low speed mixture is adjusted by the needle valve in the carb near the mounting flange, it'll need an extra turn or so for a cold start then after a few seconds it can be screwed in to it's normal setting. Just screw it in till you get the best response off-idle. When you do this for the first time I'd do it without the main (alky) fuel turned on, just so you can get a feel for what this circuit does.

When the low speed is good you can turn the main tank on and set the main circuit flow with the needle valve on the float bowl. The nice thing about this is you don't even have to stop the engine to adjust it - just tweak the valve and make another pull.

You'll need to add a few degrees of advance over what you ran for gas.

Check that you have adequate fuel flow!!!!!

After a run let it idle for a bit on gas to get any remaining alky out of the engine. Good luck!



PS. you'll probably want to replace the bellmouth with something a little less agricultural - it was thrown together with whatever was laying around and I was too lazy to change it for something better..