Mugello 198, Gori 50

[Delboyli150]

Not sure if this is right thread post, so apologies in hand as also posted under Carburettors'.

Hi Is anyone running or have any info on jetting on the following set up.

Mugello 198
PHBH30, Powerjet
Kytronic.

Running at moment, x4 needle 2nd clip down
Pilot 70
Av 266
Main 100
Kytronic on Dial 2 (Set up on 23 TDC,) ( Yes did retard to 17 when checked with strobe on dial 0)

All ok until I hit about 35mph, then hit flat spot as cannot go any faster?
Advice will be appreciated, beware not done any jetting before, but will be getting Dynoned when near enough about right as want to do my 100 miles running in!

[Warkton Tornado No.1]

Excuse me sticking my oar in, but a 100 main jet sounds lean though I am aware that you have a power jet to compensate. I’d hate it for you to wreck the kit through it not being rich enough!

For now, I’d advise you blank off the power jet & come back to that later.

A main jet then in the ball park area of 120-130 would be the safest to try first.

By contrast, the pilot jet of 70 should be able to come down to 50 ish.

Lastly, an X7 needle is a good one to try & seems to suit a lot of Lambretta ‘kitted’ machines.

Once you can get it running ‘somewhere near’, report back & the power jet can be discussed regarding it coming back into the equation.

I hope this helps....

[bluebob]

+1.

[Delboyli150]

Hi WT1

Thank you for that, Must admit I did thought 100 was small, so when I looked at my other scoot, set up by CS in Leeds this also had a 100, (Mugello 198, JL3, 28 Phbh, Powerjet with Augusto 6000) Running all OK but Very very thirsty getting appro 50 Miles a tank)! ( Had holed 2x pistons before this set up)

So I take it above must be set up more on the powerjet.

I Presume blanking off Powerjet just means turning dial clockwise all the way? Do you recommended changing needle straight away as well?

[Warkton Tornado No.1]

Whatever set-up CS will have applied to one scoot doesn't necessarily apply to another as I'm sure Martin of CS would agree.

Dependent upon the positioning within the venturi, the power jet only tends to come into play toward the top end of the rev range.

Theoretically, the main plus power jet sizes should add up to approximate the main jet size of a 'non-power jet' carburettor.

Characteristically, in an 'Ideal World' set-up for the maximum, two strokes tend to prefer to be richer @ the bottom end, leaning off toward the very top to allow 'over-rev' which is great if you are after maximum power & have a means of monitoring the EGT (Exhaust Gas Temperature) & enriching it on the move! That's why we see thumb operated chokes sprouting up on the top level tuned Lambrettas.

So, with an air of extreme caution as you are running in & therefore less likely to get the power jet to come into play, I suggested you dispense with the feature for the time being & adopt a more safer, conservative set-up.

As for the power jet, I don't know what type you have or if it is adjustable, nor whether you can 'dial it out' but suggest you should have some data with it or look on t'internet.

If you have an X7 needle to hand, I would also try that immediately as well.

50 miles to a tank sounds extremely thirsty if that's 'A' road riding....

[Delboyli150]

Hi WT1

Brought a x7 needle at weekend along with a box of BGM main jets, will try in the week.

[Mr G in NYC]

X2 needle gets richer sooner
X13 Slightly later
X7 Stays weaker longer

carb will deliver a rich mixture with a X13 needle
at 50% throttle than with a x7 needle.

Keep us posted on your final set up and good luck
testing and changing all out .

G.

[Delboyli150]

ok had a little play tonight and got no where, At the moment I have left the powerjet alone in case you cannot shut of completely, I changed the needle to a x7 and could not even pull away so changed back to the x4, but a 125mm in and nothing top end after say 3/4 throttle. But a 110 in same no top end, put a 105 in and same then started raining so that was the end of that!

Will ring Camlam tomorrow as opened to make sure if I turn the Powerjet fully clockwise that will shut the powerjet off completely if this is OK will put the x7 with clip on 2nd one down and see what we get!

Can anyone point me in the right direction as regards Instructions? What is the best ones out there as noticed they are all a bit different. My aim is to shut powerjet, install X7, then take out main jet and work on the first 0-1/2 throttle first.

Any advice welcome.

[Warkton Tornado No.1]

ok had a little play tonight and got no where, At the moment I have left the powerjet alone in case you cannot shut of completely, I changed the needle to a x7 and could not even pull away so changed back to the x4, but a 125mm in and nothing top end after say 3/4 throttle. But a 110 in same no top end, put a 105 in and same then started raining so that was the end of that!

Will ring Camlam tomorrow as opened to make sure if I turn the Powerjet fully clockwise that will shut the powerjet off completely if this is OK will put the x7 with clip on 2nd one down and see what we get!

Can anyone point me in the right direction as regards Instructions? What is the best ones out there as noticed they are all a bit different. My aim is to shut powerjet, install X7, then take out main jet and work on the first 0-1/2 throttle first.

Any advice welcome.

I can’t say that for certain, but believe the CamLam power jet is merely a needle valve type that fits a conical seating. Screwing in all the way should shut it off.

If you want to test that information, it’s simple to pull the feed tube from the power jet & connect another piece & blow down it.

[Delboyli150]

Hi Wt1

Will not get in garage tonight rained off!

Just a quick question, hypothetical, even if I cannot get the main jet right surly I would be able to get above 35mph? Asking in case there could be something else wrong which is not letting me get up to speed, as it is a new build.

[Warkton Tornado No.1]

Hi Wt1

Will not get in garage tonight rained off!

Just a quick question, hypothetical, even if I cannot get the main jet right surly I would be able to get above 35mph? Asking in case there could be something else wrong which is not letting me get up to speed, as it is a new build.

Whatever the jetting, before you even try to ride it, you can tell a lot about things just by revving the engine on the stand.

Generally, if the engine is lean, it will rev freely but be reluctant to ‘come back down’ to anything like idling revs.

On the other hand, if attempting to rev the engine, it has to be ‘nursed’ & feels very boggy, then it is likely to be rich.

Of course, other factors have an impact on the way the engine behaves, but it might be best to try the simple process just stated before delving further.

I hope that helps...

[Feersum Injun]

Ah... the dark arts of carb jetting!

Reading your OP and you describing the 'flat spot' I would agree the main jet is way to small, although I have no experience of the power jet you describe. On my similar set up (RT200 / JL3) I use between a 118 -122 main jet depending on time of year and riding type (town or touring). From experience that flat spot you describe is common and will disappear as you open the throttle and the main jet kicks in and you feel the engine surge. As this isn't happening on your bike it suggest the main jet is indeed too small...

A good way of setting the low - mid-range jetting (needle jet) and take the main jet out of the equation is to remove it all together! There is a good thread on here somewhere that discusses this. By removing the main jet you can ascertain at what point the the needle jet stops providing providing fuel to the engine... basically, before half throttle too weak, at full throttle too rich. Once the needle stops providing fuel the bike will just stall. The needle jet should start around quarter throttle and fade around three quarter throttle. Then there is the relationship between the size of needle jet (264, 266, 268) and the needle itself (X2, X7, X13). Cam Lam have a good guide to jetting to download off their website.

Hope I'm not telling you how to suck eggs and I'm no expert! But for what it's worth I find using an AV268 with a X13 (currently 2nd clip down) helps keep it rich enough to avoid that flat spot... good luck!

[Warkton Tornado No.1]

Ah... the dark arts of carb jetting!

There is a good thread on here somewhere that discusses this

Feersum Injun (great name!) is spot on. There are many guides available to jetting, but this is as good as any, so I hope this helps in saving any searching. (With acknowledgements to Bristol Lambretta & whoever produced the article in the first place):

http://bristollambretta.webs.com/dellorto_manual.pdf

[Delboyli150]

Update

At last stop raining!

Well I have shut off the powerjet by turning screw in clockwise fully, installed a 120 main jet and Yippie I have got 'top end' speed, this will be enough to get my 100 miles in ready for Dyno testing at CS.

It flies on acceleration (Had to keep telling myself to calm down as running in)!

It does seem a bit lean but will check spark plug next week.

Running at moment, x4 needle 2nd clip down
Pilot 70
Av 266
Main 120
Kytronic on Dial 2 (Set up on 23 TDC,) ( Yes did retard to 17 when checked with strobe on dial 0).

Thanks guys once again for all your help, will update when back from Dyno to give final setup.

[Warkton Tornado No.1]

Well done & I hope you've gained a better understanding of the principles of the carburettor & the transition from one part to another.

Personally, the reason I decided to 'juggle' with the X2, X7, X12 & X13 is that they all share the same base Ø 2.5 mm & tip Ø 1.8 mm though I suspect a lot of this Forum users do the same. They are in the same 'family' & jetting becomes a little more logical, I find.

Here's the chart (with acknowledgements to Norrie):

http://www.dellorto-carbs.co.uk/graphics/need2.jpg

[Delboyli150]

Hi WT1

To be fair propably would have had the idea by your instructions but the Powerjet was the main problem along with the Kytronic, next time I do a rebuild will leave the Powerjet and Kytronic off to start with then build it up!

thanks for all the help, much appreciated.

[Delboyli150]

Update.

Hi Guys went to dyno at weekend, nightmare for Martin, (Cheers Martin, sorry about aggro)

Final Setup
Main 125
Needle x13p2
Pilot 49
Slide 0.5 turn
Running at 19 degrees.

Outcome was not as good as the money spent to be honest.

Figures are 14.74 BHP, Max Torque 11.41, Top speed 59 mph,

Hope this helps people to make up their minds.....

[Delboyli150]

Whoops

Should read.

Slide 45
Powerjet 0.5 turns

Running at 19 degrees.

Outcome was not as good as the money spent to be honest.

Figures are 14.74 BHP, Max Torque 11.41, Top speed 59 mph,

Hope this helps people to make up their minds.....