Keeping cool on a 36BHP Lambretta: Camb Lamb Power jet??????

[wax]

Word-up you lot.

Please see my 'Show us your ride' for the spec on my Lamby: 'Rusty 36hp Nail'

I have noticed that my EGT has started to read a little higher than it used too and i have put this down to the weather of late. It was about 12-15 degrees when i first got my engine back from JB and it read about 585 degrees at full throttle on the local dual carriage way. Now the weather has warmed up (about 20-24 degrees when i last went out, before my MOT ran out ) i recently managed a new PB of 640 degrees. Is this too hot? My plug colour is still chocolate brown and nothing has changed (although i swear this engine is getting faster!). Sitting at full throttle on a dual carriage way, covering the clutch and waiting for a seizure is not my idea of a nice ride out. So i started to think about getting one of them Cambridge lambretta power jet things. How do they work? Do you just switch a button and it stays on, or is it adjustable? Would my engine just start to splutter in the fast lane, or would i just lose a bit of top end power?

I once saw an Orange and white S type on here or LCGB (bloody luvly it was) with an old skool manual choke. Could i install one of there type set-ups instead and just add a little choke too cool the engine down a bit, without the spluttering? The choke is either on or off in standard form, so would this do what i want it to do?
Is there another temp gauge i can fit that tells you the temp of the head, not just the fluctuating exhaust gas temperature? And would an 'overall' temp be more useful to me than a EGt?
Has nayone ever fitted a water cooled head and had the original fan still cooling the barrel, with a modified cylinder cowl? Could this be a long term solution.

Any help and advice greatly recieved..........As always

Wax

[Knowledge]

Are you talking carburettors?

A power jet on a carb is not (usually) rigged as a magic cooling device that you control from the headset. It is designed to operate with the flow of air through the carb, without need for manual operation.

the theory is that if the carb does not fuel well from 50% opening to 100% opening (WOT), then by fitting a much smaller main jet, and then supplementing this with a power jet, the fueling can be cleaned-up at, say, 50% to 70%, but the same total fuel flow at 70% to WOT.

Essentially, it is designed to clean-up the higher-mid-range, rather then cool top end.

[Avantone]

The Cambridge controllable powerjet is a great solution and in racing. I believe they use it in the 2nd half of the race where the motor starts to lose a little power due to heat. On the road it means your hand can hover over the powerjet switch rather than the clutch

I think I'd try and find out why your temperature has jumped though - that's quite a difference and that powerjet may just be a sticking plaster for an undiscovered underlying issue that might end in tears later.

[soulsurfer]

My plug colour is still chocolate brown and nothing has changed (although i swear this engine is getting faster!). Sitting at full throttle on a dual carriage way, covering the clutch and waiting for a seizure is not my idea of a nice ride out.
Wax

I know what you mean about the clutch, not much fun, is it?
I'd say 640 is too hot, long term. Plug colour can vary greatly to what is deemed safe, milk chocolate, dark chocolate, coffee... all open to interpretation.

What I did notice at Lincoln and having a chat with "The Dyno Guy" (what was his name anyway?) was how the jetting on what would be considered "sorted" bikes was in fact way off the mark in some cases, most of which I noticed were lean.

This guy's job title (self titled) is "Fuelling Specialist", dyno is his business and best tool.

[DaveInPortland]

Wax, there is a cylinder head temperature (CHT) gauge available that will do the job. I used a dual EGT/CHT gauge from Westach. The needle on the left shows CHT and the right shows EGT. Very tidy.

I had a similar situation awhile back in which my CHT was consistent but EGTs were hotter than usual. Upon inspection I found I had a bit of an exhaust leak at the gasket. Once fixed my EGTs were back to normal.

Richening the mix beyond optimum will cause your engine to run hotter, not cooler.

[wax]

What effect does altering the two stroke mix have on the temperature? Will it run much hotter with 2% rather than 3%???

[soulsurfer]

What effect does altering the two stroke mix have on the temperature? Will it run much hotter with 2% rather than 3%???

No, cooler, but less lubrication. Oil lubricates, petrol cools, so you need a good balance, i.e. 3% for me (here we go... )

[J1MS]

What effect does altering the two stroke mix have on the temperature? Will it run much hotter with 2% rather than 3%???

No, cooler, but less lubrication. Oil lubricates, petrol cools, so you need a good balance, i.e. 3% for me (here we go... )

Nowt wrong with 3%.... if its a good oil it will protect the bore with its superior film strength...

[tony]

Richening the mix beyond optimum will cause your engine to run hotter, not cooler.

Really? Why?

[tony]

The Cambridge controllable powerjet is a great solution and in racing. I believe they use it in the 2nd half of the race where the motor starts to lose a little power due to heat. On the road it means your hand can hover over the powerjet switch rather than the clutch

I think I'd try and find out why your temperature has jumped though - that's quite a difference and that powerjet may just be a sticking plaster for an undiscovered underlying issue that might end in tears later.

Do you mean the Cambridge 'adjustable' power jet mate? We dont use this version in racing.