SF jetting to compensate for unleaded after 20 years out of action

piranha-bro2

piranha-bro2

Hero member
Location
Melbourne
Ciao
Have read a few posts on rejetting for unleaded after searching our forum and it seems things have changed since I last tuned/jetted an SF.

On a twin that last ran on Super leaded 20 years ago (in Oz), it's now clear that the overall state of the jetting is too rich. I also know from a BP PDF that unleaded reads black on plugs (none of the lovely tans and greys I'm familiar with), so joy looking at plug colour?

On std original jetting the SF in question generally runs well, but has already fouled a plug, runs only around 1 turn out on the pilots and splutters from 3/4-full throttle ... all confirming that everything has to be leaned off for unleaded (running 98 premium unleaded). Does anyone have any numbers on jetting for a stock SF1? It also seems to be giving poor fuel econ - though no odo or speedo makes confirmation of that difficult.

Currently 60 pilots (thinking drop to 55?), 140 mains (drop to 130?). Will I also need to drop the K2 needles a notch? Will it run safely on 95? Haven't even considered a 'valve saver' - waste of time?? Has done 500-odd km and valve clearances are unchanged (if slightly wider on exhaust from carbon under seats).

Lastly, will it be of benefit to go hotter in plugs from NGK B9ES to B8ES? I've never had an issue on leaded or lead replacement with B9ES's but on a stock motor maybe 8's are a better option in light of slower burning with unleaded.

Grazie tante
Quentin
 
Hi Quentin,

first of all: before you re-jet the carbs, make sure they have been ulatrasonic cleaned and new seals/gaskets have been used everywhere. Also the needle, needle jet and all jets need to be replaced. The needle scraps against the needle jet when opened and that causes wear on both of them. Make sure the choke sliders run evenly up and down and that they completely seal and their O-rings are not hardened or even broken. Now you need to set float-levels to the right adjustment and afterwards sync the carbs.

If that is all done and the results on the bike are still the same, you can start changing jets and needles. Everything else would just mislead you due to wrong settings or worn parts.

a general jetting list can be found here: http://www.laverdamania.net/carbgb.htm

cheers and good luck  ;)
 
Hi, Quentin.
Why not use the B8ES as in the NGK list?
http://www.ngk.de/nc/en/product-finder/produktfinder/MOTORRAEDER/ZUENDKERZEN/LAVERDA/SF2-10%252C%2520SF3/B8ES/7625/
Never had them foul or any other issues.
Take into consideration if your bike runs with air filter or velocity stacks. They need even bigger
main jets, about 10 points higher for the start.
Could you give us the link to the BP pdf? Would be interesting for many of us, because the
question of reading with unleaded comes up from time to time.

hth
Ernesto

 
cut out the guess work, seat of the arse feeling and unreadable plug colours and go to the dyno.
I am doing this after 35 years of owning TOG (and thinking that I know more about 1200 jetting than most) in the next few weeks, you do need to cut all the crap occasionally and get on with it.
Clem
 
Have found after a fair amount of time on the dyno that the factory quoted jetting sizes generally work out a bit large for modern petrol. Still get the occasional Slater Jota in with 165 mains in it.. :o My theory is modern fuel is a lot "thinner" than the good stuff of old and passes through the jets faster.


  Keith
 
That's the same theory the local Ducati bloke has,so I went from 65 idle jets,std, to 62 in my Pantah.The bloody weird thing is it ended up running best on 3 1/2 turns out on the front and 2 on the back.You can waste a hell of a lot of time fing about with jetting
 
Why has nobody said "Be really careful leaning off the mixture on an SF unless you want holes in your pistons." - or was I imagining things for all those years?

H.
 
Howdy Quentin,

By yourself some shares in NGK  ;) Try the 8,s and see if she fouls.
Im running a 73 and 72 sf,s both on 8,s poppin around town does foul them,
but out in the hills/track on a fang they are fine.

Both bikes will run no probs on 91/95 unleaded as they are a soft state of tune.
Running same jetting as you , needle on leanest setting.

Like to run a drum of rf100 octane every now and then  ;) dont they love it.

Jota i have not happy at all unless on bp98 , pinks its head off otherwise.
In short, fuel from servos is shit and stale now days  >:D sits underground
in tanks wayyyy to long , find a local servo that you know turns over a lot of fuel  ::)
Hooksey.
 
Try and get hold of some BP Ultimate if you can!
I use it on my bike all the time and some of the 'problems' have disappeared.

Interesting that it is a high density fuel which MAY well mimic the older fuels and mean your jets are the correct size after all:

BP Ultimate Main Benefits
High octane rating (98 Octane)
High density fuel ? can give better fuel economy
Contains additive that cleans and protects the engine
Low Sulphur levels reduce engine wear and potentially reduces maintenance costs
Lower benzene, sulphur and lower aromatics reduces exhaust emissions.
 
I think I said in a thread a couple of years ago:

When Perth first came out with a choice of fuels in the servo's I did a small comparison test.
Price difference between 92 octane and 98 octane was about 5%.
Mileage improvement from a tankful was about 25% (Jaguar 4.2lt) and 20% (Mitsubishi 2.6lt).

A no-brainer, really.
Plus it keeps the engine and exhaust cleaner.
Just a pity that they don't sell the good stuff here in Malta.

Dale
 
As usual, some great info and advice from you mob - and a mix of ideas, which is great. I'm no greenhorn to carb tuning and worked on Lavs for a living when Super was the fuel we used, so hadn't come up against the 'black plug syndrome' until I got this guy's SF1 back on the road. Bike is relatively low mileage, so carb and needle/needle jet wear not an issue (and won't affect full throttle) - choke plungers and float levels were the first place i looked. Dyno work sounds great if I had access and the owner had the financial resources - I used one for years in the Perth workshop I spannered in - was the only dyno in Western Oz back then. Taken on board your 'thinner fuel' advice, Keith - seems consistent with my theories.

The 3/4 to full throttle splutters to me are a dead giveaway of an oversize main, so will see what 135s do. May drop the needle a notch as well and try 55 idles. Bike runs Uni foam filters in the cutaway original airbox. I've been running it on the Shell eq of Ultimate, but might see how the BP good gear goes - I am a fan of Ultimate.

As for plugs, I've always run B9s but have also run high comp for many years in my own SF - prefer colder to hotter and the quickest way to hole a piston on an SF is run it on too hot a plug on high speed runs - not sure about jetting and holed pistons. Will see how B8s work.

Not surprised the Pantah wanted unmatched mixture Fr & Rr - the tendency on a 270/90 motor is for one side to run 'lazy' at idle due to the shorter interval to the 'trailing' piston - this is quite pronounced in my 270 SFC crank. Seems more pronounced the heavier the crank or longer the stroke.

Will report back ...

Thanks again.
Quentin
 
if the Uni filter is oil soaked, wash it out thoroughly, do not re-oil it and take the bike for a run
will be a huge improvement

you can actually use a Uni-Filter as a rev limiter in standard form, kicks in at approx 6,000 rpm on a triple
 
Interesting comment re my Pantah and twisted twins,One cylinder running lazy is exactly how I should have described it to a T.
 
Vince said:
Interesting comment re my Pantah and twisted twins,One cylinder running lazy is exactly how I should have described it to a T.
Click to expand...

That has less to do with the firing order and is more likely caused by the totally different shapes of the inlet ports. How a carbureted Ducati twin is supposed to make equal power from both cylinders has always been a bit of a mystery to me, may even partially explain their appetite for big ends...
  I have as far as I can tell got equal bang out of both pipes on the little twisted twin.


        Keith 
 
laverdakeith said:
That has less to do with the firing order and is more likely caused by the totally different shapes of the inlet ports. How a carbureted Ducati twin is supposed to make equal power from both cylinders has always been a bit of a mystery to me, may even partially explain their appetite for big ends...
  I have as far as I can tell got equal bang out of both pipes on the little twisted twin.


        Keith
Click to expand...
Only noticeable on my SFC twisted crank at idle. But clearly a 'lazy' cylinder issue. Will run perfectly on each cylinder individually but reconnect the other plug and the lazy side has to be pulled down on the idle speed screw. Might be quite different on short stroke big bore motors with very light crankshafts.
 
redax5 said:
if the Uni filter is oil soaked, wash it out thoroughly, do not re-oil it and take the bike for a run
will be a huge improvement

you can actually use a Uni-Filter as a rev limiter in standard form, kicks in at approx 6,000 rpm on a triple
Click to expand...
Well, that is surprising ... thought they were pretty open breathers (running one decent size unit for each carb) but taken on board. I've removed as much filter oil as poss, but they may well be the culprit from what you've seen, Red.

When it's back in one piece (crank rebuild Mk11!) I'll put it to the test. I must say i had considered it a possibility but assumed I was looking at a modern fuel issue. Thing is, it will rev, but only at 3/4 throttle.
 
You must log in or register to reply here.
Back
Top