power jet Vs thumb choke

[Scooterlam]

Pro,s and Con,s

[dave411]

Where would you grt a thumb choke from?

[Captain Pugwash]

Why not have both if you can.

[Scooterlam]

good point but doesn't answer the O.Q

[dave411]

OK,I would go for the thumb choke,if I could buy one.

[MickYork]

Darrel Taylor sells the thumb chokes, getting quite popular now.

Set up correctly for running purposes the Power Jet is preferred as that's what its made to do......running with the choke on shouldn't be a final solution, merely a tool to indicate whether you need more fuel or not.......plus it's good to help you start when cold.

[Warkton Tornado No.1]

More like “Theory versus Practice”

The power jet exists as a supplementary fuel feed that bypasses the traditional ‘lower’ fuel/air mixture control system by being placed in the venturi, positioned such that the vacuum to enable it to function is only available above a certain slide position.

As far as I am aware, their first use was in scooter racing with the Amal Mk II & the only means of control was via the vacuum. Various jet sizes were available.

Since then, with the incredible amount of research gained before Honda made everybody follow their preference & worship four strokes, there have been power jets controlled by various means via EGT’s, throttle positions, RPM sensors, knock sensors or whatever.

There is no doubt that power jets are an excellent concept when incorporated into the sophisticated engine management systems available to those competing within the higher levels of motor sport & that includes karting, motocross, sled racing etc.

What happens when you affix a solenoid operated power jet to a Lambretta ‘Dellorto VHB family’ carburettor? They shake to bits.

Hence the thumb controlled choke units, which utilise a low number jet size & are used for both cold starts & for the rider to operate enabling richening up when running hot.

Quite why nobody has experimented with a remote solenoid operated power jet not mounted on the carburettor or even a cable operated power jet, I don't know. Perhaps they have.

[Warrick]

I'm thinking a thumb joke would be nice.. You would like to think you could getting the jetting right and not to need a power jet.. I could be wrong

[Scooterlam]

All the time we rely on sucking fuel thru straws., there is always going to be a compromise.
Big enough to to meet the flat out demands will kill the ability to accelerate.
In my case I'm just being ultra picky I could just up the main. . I should leave it alone and build something else.

Having said that, i fancy a power jet and maybe a thumb operated power jet is the future.

[dave411]

Does anyone know how to get hold of Mr Taylor?Tried e mail and his Faceache account,no joy.

[hullygully]

some of the Silhouettes from Scunny bunny land can give you better access to Mr Taylor
as previous have said get your main jet right, then if you want to go power jet I believe the power jet & new main total the existing main jet size , ie you come down 25% on your new main.
the thumb choke's about £45-ish but feels better starting & is a lot safer if needing to cool engine down @ speed

[Warkton Tornado No.1]

Most people that are interested in the technical advances that may be available with such an old, odd two stroke design inherent with the Lambretta would always try & keep in mind reliability.

That has to be why some of you are giving consideration to being able to sacrifice ultimate power for reliability by being able to ‘richen up’ as exhaust/cylinder head temperatures reach the zone where it’s fair to say that the piston is likely to suffer.

I doubt many people (having read this far!) will disagree that ‘adding fuel’ is just one way of avoiding disaster. It may well be the best, but, for example, further retardation of the ignition, may be another.

What I’m striving to say, is that ideally any action taken should ideally be automatic. It should not rely on the rider keeping one eye on the temperature. It’s bad enough having one hand hovering over the clutch all the time!

I believe that with the Mychron range of Data-loggers, for example, that it is possible to actuate whatever you want when a certain pre-set temperature is reached. So an EGT probe reaching 700°C, say, might allow the Data-logger to operate whatever richening device you place your trust in.

Has anybody on this Forum used, or considered using, their electronic monitoring devices to do anything along these lines?

I am interested in this technology, but mine is biased toward the track, if ever I get back to it.

However, there are more pro-active rider/tuners on this Forum that I will gladly lend a Mychron III along with a choice of 12 volt solenoids if they wish to research & experiment the feasibility of an automatic ‘Fail safe’ set up. My preference would be that an EGT probe be utilised, properly mounted in the down pipe as I believe this to be the most re-active means of ascertaining temperature. I may even have an EGT probe suitable.

PM me if you want to consider this option.

[Eden]

Most people that are interested in the technical advances that may be available with such an old, odd two stroke design inherent with the Lambretta would always try & keep in mind reliability.

That has to be why some of you are giving consideration to being able to sacrifice ultimate power for reliability by being able to ‘richen up’ as exhaust/cylinder head temperatures reach the zone where it’s fair to say that the piston is likely to suffer.

I doubt many people (having read this far!) will disagree that ‘adding fuel’ is just one way of avoiding disaster. It may well be the best, but, for example, further retardation of the ignition, may be another.

What I’m striving to say, is that ideally any action taken should ideally be automatic. It should not rely on the rider keeping one eye on the temperature. It’s bad enough having one hand hovering over the clutch all the time!

I believe that with the Mychron range of Data-loggers, for example, that it is possible to actuate whatever you want when a certain pre-set temperature is reached. So an EGT probe reaching 700°C, say, might allow the Data-logger to operate whatever richening device you place your trust in.

Has anybody on this Forum used, or considered using, their electronic monitoring devices to do anything along these lines?

I am interested in this technology, but mine is biased toward the track, if ever I get back to it.

However, there are more pro-active rider/tuners on this Forum that I will gladly lend a Mychron III along with a choice of 12 volt solenoids if they wish to research & experiment the feasibility of an automatic ‘Fail safe’ set up. My preference would be that an EGT probe be utilised, properly mounted in the down pipe as I believe this to be the most re-active means of ascertaining temperature. I may even have an EGT probe suitable.

PM me if you want to consider this option.

The gamma unit has the facility to operate a solenoid, I just haven't got round to trying it yet.


PM sent

[Warkton Tornado No.1]

PM replied to.