Still 750 sf2 running problems

Lyndoneil

Lyndoneil

Full member
Location
Towcester uk
Oh Wise Ones.
Thought I better start a new thread, the other was getting too long
The sf is still running like a bag of shite, ticks over fine, but is pinging or knocking, pinging I reckon, hard to tell which, lazy to increase revs, but runs ok If I dare to go over 60 mph. But basically it sounds awful and on the verge of breaking down
Has a Boyer micro mk3 ignition fitted which is probably getting on.
I have checked and reset the tappets, did a compressing test both cylinders were 125-130 psi, (which isn't high, but they are very similar and I'm not intending it to be a speed machine) I've checked the carb balance with vacuum gauges which were very simular too, although in all reality it didn't seem to affect the vacuum much no matter what I turned.
I've probably totally screwed up the carb settings now!
New Boyer coil, new plugs, new copper HT leads, and new 5 ohm plug caps,
Have tested resistance on the Stators individually and together , all good 131 and 65 ish Ohms, checked all connections
I decided to strobe the ignition, the advance seems to be set at about 40 plus degrees which seems high, but for now will live with that.
Found TDC, checked several times, ran it up on the strobe and at tick over it went to full advance and as the revs increased to about 3300 ( wouldn't go higher, could be ignition or carbs) the mark remained at the full advance position may have moved slightly a degree or 2, but was fairly constant.
I tried to reset the timing to 35 degrees, but it wouldn't start, in fact I tried a few settings with no joy, possible didn't help because I was following the instructions for a 73 Triumph T120, although Boyer kindly sent me the instructions for installing the Boyer on a Laverda SF, in French. My French teacher at school told me I would regret not leaning it better, one-day.
I'm trying to get my head round it, I kind of expected the mark to be nearer the TDC at tick over and move to the advance position as the revs increased.
I no doubt are totally wrong, but it suggests to me the ignition box might have developed a fault, anyone have more idea than me?
 
Lyndoneil said:
Oh Wise Ones.
Thought I better start a new thread, the other was getting too long
The sf is still running like a bag of shite, ticks over fine, but is pinging or knocking, pinging I reckon, hard to tell which, lazy to increase revs, but runs ok If I dare to go over 60 mph. But basically it sounds awful and on the verge of breaking down
Has a Boyer micro mk3 ignition fitted which is probably getting on.
I have checked and reset the tappets, did a compressing test both cylinders were 125-130 psi, (which isn't high, but they are very similar and I'm not intending it to be a speed machine) I've checked the carb balance with vacuum gauges which were very simular too, although in all reality it didn't seem to affect the vacuum much no matter what I turned.
I've probably totally screwed up the carb settings now!
New Boyer coil, new plugs, new copper HT leads, and new 5 ohm plug caps,
Have tested resistance on the Stators individually and together , all good 131 and 65 ish Ohms, checked all connections
I decided to strobe the ignition, the advance seems to be set at about 40 plus degrees which seems high, but for now will live with that.
Found TDC, checked several times, ran it up on the strobe and at tick over it went to full advance and as the revs increased to about 3300 ( wouldn't go higher, could be ignition or carbs) the mark remained at the full advance position may have moved slightly a degree or 2, but was fairly constant.
I tried to reset the timing to 35 degrees, but it wouldn't start, in fact I tried a few settings with no joy, possible didn't help because I was following the instructions for a 73 Triumph T120, although Boyer kindly sent me the instructions for installing the Boyer on a Laverda SF, in French. My French teacher at school told me I would regret not leaning it better, one-day.
I'm trying to get my head round it, I kind of expected the mark to be nearer the TDC at tick over and move to the advance position as the revs increased.
I no doubt are totally wrong, but it suggests to me the ignition box might have developed a fault, anyone have more idea than me?
Click to expand...
I think you're right. Why not send the box to Boyer for them to test? Plenty of brit bike user comment suggests that the Mk3 ain't the best
 
It does sound like an ignition problem. Besides what Rob suggests, is there anyone nearby with either a standard points setup or another ignition system you can try fitting to determine that it is indeed ignition. 40deg at a bit over 3000 is a lot, and if has increased quickly to there from idle it will be very advanced for low revs. Retarding to 35 makes idle 5 deg after tdc (if the ignition curve is 40 deg, starting from the standard tdc static timing as Laverda had originally).
When synchronising your carbs, really the only thing to have an effect will be the cable adjusters on top of the carbs. If they don't have an effect you could have an air leak forward of the carbs, that said, an air leak will not allow it to tick over nicely as you say it does.
 
Wasn't exactly sure from your report, but it sounds like it's going to full advance way too early. It should be idling somewhere around 10 deg and slowly build from there - if the ignition curve for the Boyer has been set efficiently.

With that stuff going on I'd be very tempted to go down the Paul Marx route and refit the points!! Sounds bloody awful!
 
Forgot to say, I've checked the carb slides are equal and checked the throttle and choke cables are equal and with enough free play,
The charging system is working and the battery good.
It ticks over on full advance and basically the advance does not move from there even with rev increase.
I didn't fit the ignition, no idea how old it is, I think Boyer has moved on a few generations since the micro mk3 setup, so havent any points to refit.
Don't know anyone with a spare set of points plus distributor or ignition system to try out.
Robs is correct, I could send it to Boyer to be tested for £18, was hoping someone might be able to identify if its knackered from the symptoms, as if they test it and it comes back as being good then I'm totally foxed, or if it's bad what then? The mk4 system works with the Mk3 stator plate fitted, but that's not a particularly new ignition system, and they are not sold to work with Laverda in any case, so will be using Triumph instructions. Or their more modern systems which again are not designed to fit Laverda so might have problems fitting the Rotor and stator plate.
Or save the £18 to put towards a new Sachse system which are at least designed to fit the Laverda SF without needing to fabricate or alter parts to fit.
I must admit that the Zen like feeling of oneness with the world, that is suppose to come from owning a Laverda is so far eluding me and I'm getting to the point where I hate the sight of the f*****g beast.
 
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Grasshopper, old Chinese saying: Never give up, the promise of better times will not elude you.

Ching Kai ........ hang on that’s my name in Chinese... fuck COVID19, I give up!
 
Lyndoneil said:
It ticks over on full advance and basically the advance does not move from there even with rev increase.
Click to expand...

Lyndoneil said:
I must admit that the Zen like feeling of oneness with the world, that is suppose to come from owning a Laverda is so far eluding me and I getting to the point where I hate the sight of the f*****g beast.
Click to expand...
Absolutely not right!!!!!

I can't even imagine how nasty that must be for your poor motor - running 40 deg advance at idle!!! No wonder it bloody pings. The advance function in the Boyer box is malfunctioning. From what I understand of these systems (Sachse, Ignitech etc - and I haven't set up my Ignitech yet, so am probably wrong) you set the box to your full advance figure and the unit retards it according to your revs? Am I right that it works kinda like an auto advance in reverse - so an auto retard? Whatever - yours needs to be idling somewhere around 0-10 degrees.

Your SF will run like a clock once you sort this stuff out! Don't blame the bike. FWIW I ran my std advance unit (adjustable spring tension to control advance curve) with a magnetic pickup plate and rotor from a GS Suzuki and its little control unit for decades, with original Bosch coils - reliable as all get out. Could also modify the amount of advance by making the low-high limit hole in the advance unit smaller.
 
Are you sure your sprag wheel is located on the crank via the woodruff key ?
or is it just bunged on anywhere and giving you a false reading with timing light.......:unsure:
 
Before you spend any money, check the ignition moving the stator plate a few milimeters from your reference point in either direction.
May resolve your issue.
If that doesn't help, and you want to shell out some money for a new ignition, I'd invest in a DMC ignition rather than a Sachse.

Gerald
 
Why not ask Boyer to supply a new MkIV unit? I understand that it will replace their even older MkIII, works better (!) and complete kits seem cheap compared to any other options (Feked website list kits circa £90 for example).

Hooking up an Ignitech 'should/could' work with the Boyer inductive pickups given you're confident they are working OK. The TCIP4 is listed at €150 inc VAT (they only supply the 4 channel variant now, it supports up to 4 channels (duh!) but will work with less just fine). You'll also need their 'basic harness for Ignitech units (length 1,3 m, purchase with unit)' at €7 and 'programming cable USB-COM 2m' at €13.
Finally, there is the small matter otr P+P to the UK at €29.
Full price lists are here
Order by email to ignitech@ignitech.cz
You'll need a laptop with a USB port and load their v96 software on to it in order to programme the unit.

The above is the cheapest way of getting round the faulty Boyer box, assuming you can't get hold of a good MkIII or IV. Obviously it will require a fair amount of setup - straightforward if you're familiar with Ignitech but plenty here who can talk you through it.

Alternatively, the DMC or Sasche options are very straightforward to fit, albeit at a price. Depends how much you value your sanity I guess!!
 
I have these fitted to a Guzzi V50 . It takes the load away from the points. I've probably put about 3000 miles on them now. Left the condenser in situ as a back up. This one and its mate is for the SF when I get it rewired. Cost approximately $35 each. I also bought the brackets for them as well, probably about 100 quid by the time they landed here in UK from the States.20210616_190651.jpg20210616_190651.jpg
 
Don’t give up on the bike for the sake of a worn out ignition system! It’s basically a “consumable” part which requires replacement from time to time (they last longer than batteries and tyres but still...)
Fork out what you’re willing to spend and you’ll only regret not doing it sooner 😁
 
I chased a rough running condition for nearly a year. Turned out main issue was one of my new HT wires.
Was getting similar feelings that bike was 'getting personal'. Bike is now equal favourite to some reasonably nice superbikes of the seventies. Three thumbs up for Ignitech B.T.W. Advance curve perfect out of the box.









ignitech
 
You indicate your ignition is good ?

This may seem benign but are you using something different then the original exhaust system; something more free flowing then the original, if so, replace that orginanl 25 main jets with something like 30 or 32's perhaps even 34's - Also try running your 750 open mouth without any air filtration.

After an exhaust change I had to up my 25 jets to 32 and never could run any type of air filtration on my 30A VHB's.

Don't try and push her for any length of time under the conditions you are describing at the risk of holing a piston.

Check for air leaks around the Carb intakes or a leaking or collapsed Intake Manifold Hose. Bad engine case and Crank seals can also case this issue.

SF's are notorious for collapsing the Intake Manifold Hose. I went for a thick hydraulic hose.
 
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