Bolt-on Adjustable Powerjet Tube Length

[Darrell Taylor]

the exhaust used plays a part too,if it offers lots of overrev then youll see rpm enrichment play a bigger role ,i see this considerably on my 50 cc race engines revving to 14,000rpm they become a lot more dependant on fueling from the needle in the rpm area you would associate with main jet as too big on main jet might be fine at 11000 but at 14 becomes grossly rich ,,,this long term race engine development on 6 hr endurance race engines brings in a lot of data especially when theres around 40-50 bikes your looking after ,also saw many power jet brass tubes fail and snap off dropping into the motor and being throttle position dependant only delivers in that area, when your in need of enrichment lower down as in some road going roll off throttle situations dropping to say 3/4 throttle can leave you hanging lean,,

problem ive found with road going lambretta,s is that the fuelling required to be sustainable when abused on an air cooled ,fan cooled, 50,s,60s designed engine thats now up double or triple its original horsepower level ,running on lower octane fuels ,advanced ignitions,higher compression with the added twist of octane reduction when parked for a week due to water absorbtion which in turn emulsifies the 2 stroke oil held within the fuel rendering the oil near useless considerably reduces the motors resistance to failure as a result very rich fueling is employed and retarded timing and lower compression ratio,s as a measure to keep these vunerable engines alive ,when fully loaded and pushed they can burn it off but leaves them so rich at lower speeds and round town that they become horrible to ride ,you could run leaner and run a power jet option that can richen up at will by going solenoid type that you can activate but limited again to throttle position or do as i and many racers have over the years and run a thumb choke to achieve the same result as and when you need it in a safer manner at any throttle position and adjustable delivery rate thru choke jet size ,combine it with an early warning device be it cht ,egt or combination of both and it will let u know when the enrichment is needed instead of permanently running rich forever at a given throttle position only.

[Adam_Winstone]

Thanks for the additional info DT, great food for thought.

This is the first motor that I've run with a Fran Race and I've become very aware of the motor's need for plenty of fuel when it comes 'on song'. I'd started by going big on main with a fairly normal 266 atomiser and 2.5 needle shaft combo but then tried working down the main but I got to the situation where a big enough main bled over badly at lower throttle positions. I then found that I'd weakened atomiser and needle to the point that it was restricting main function. I then decided to introduce the PJ to keep it rich higher but weak lower but found that this either bled over too great a range (rather than just at high flow demands) or needed weakening off to the point that I was running weak when on song again. Somewhere along the process I introduced advance retard function and have played with that a number of times.

I did manage to check plug colour before leaving the house this morning and I'm still getting much the same plug colour (not crazy weak but I'd like to be able to get a better plug colour, going too rich and then working back) as I was previously, with PJ, with/without advance retard, different heat range plugs, etc. I'm starting to look for a constant that may be having an influence and the only things that I keep coming back with are OIL and ME!!!! I'm pretty sure it's not the oil but I might try a different type and see if a tank of different mix gives me a different result.

Ta

PS - Note to self... get it dyno'ed!!! (lol)

[Darrell Taylor]

what plug u using for chopping and are u reading it deep at base ,,,a low number like 7 or 8 will run hot and very clean giving little colour except for at the base area that on this grade sits very low and difficult to see,,a 10 will colour up more and be easier to see the base compared to a 8 that has a deeper cavity to lookdown to the base ,if you check out race type plugs like b10egv as opposed to standard br10es there generally better to read again

[drunkmunkey6969]

what plug u using for chopping and are u reading it deep at base ,,,a low number like 7 or 8 will run hot and very clean giving little colour except for at the base area that on this grade sits very low and difficult to see,,a 10 will colour up more and be easier to see the base compared to a 8 that has a deeper cavity to lookdown to the base ,if you check out race type plugs like b10egv as opposed to standard br10es there generally better to read again

Hello Mr T........nice to see you are still here!

[eden]

I can confirm that the BR10eg and BR9eg plugs are easier to read and not only easier to read, they colour up much more readily and they don't fail as often as standard type plugs. Ive been using them consistently for the last 10 years or so and have never had to change a plug due to one failing. I started using them rightly or wrongly to try and minimise the chance of buying a fake NGK as there have been so many around for so long, my thinking was that as they are not as mass market as the standard type that there was less chance of fake ones being made. Probably bollox but that line of thought lead me to a very reliable and very readable plug.

what motor are you running the fran race on Adam?

[Adam_Winstone]

Bugger, I just typed out a response and somehow lost it... something to do with Eden posting his response!

I've been running a B9ES (genuine from an NGK rep') for a number of weeks as I wondered if the previous 8 was a factor.

Couple of things from tonight's road testing, adjustments, testing...

1. My fast flow fuel tap has restrictive flow on reserve but is plenty fast enough on ON,

2. Road testing, choke tests and plug checks show that the main needs to be BIG and the clip suitably lowered (needle raised) in order for the main to deliver in a manner that reflects its true size. This has me wondering whether a change back to standard U needles might be wise, even though I know that there is plenty to support K length K needles being OK in VHSH carbs. I used standard K needles in a 32 VHSA for years, never getting on with the standard U items, however, I'm thinking that some U testing in the VHSH.

Thanks again.

Adam

[Darrell Taylor]

what plug u using for chopping and are u reading it deep at base ,,,a low number like 7 or 8 will run hot and very clean giving little colour except for at the base area that on this grade sits very low and difficult to see,,a 10 will colour up more and be easier to see the base compared to a 8 that has a deeper cavity to lookdown to the base ,if you check out race type plugs like b10egv as opposed to standard br10es there generally better to read again

Hello Mr T........nice to see you are still here!

hello Dan , thanks...keeping well i hope

[warts]

Someone posted a clip of a scooter being dyno'd, the carb was fitted with a clear float bowl. As it was run up, suddenly the fuel you could see in the bowl turned to froth.

Presumably there was less fuel being delivered as a foam under these circumstances - any chance this could be a causing a problem getting the jetting right?

Is this common? I thought it slightly odd no one commented.

[Adam_Winstone]

That was more common on solid mount carbs, which suffered this through vibration. This is commonly avoided by fitting rubber mount carbs, which mine is.

I've not seen that clip but will hunt it out at some stage.

Ta

Adam

[stokky]

By the way Adam, when use say adjustable powerjet, presume you just mean twiddling the adjuster on the top.

I'm sure a few years back when I was looking to try a power jet, that you can get some electronically controlled ones.

Worth considering ???