motoddrob
Hero member
- Location
- S/W Australia
Have a mate here running oem bored to 36s
What did you do to or for or with your Laverda today?
- Thread starter CLEMTOG
- Start date
Rob
Hero member
- Location
- Midlands, UK
Yep, ran my 1980 Jota with OE PHF smooth bored to 36mm back in the day.
piranha-bro2
Hero member
- Location
- Melbourne
My understanding is that 32s, 34s and 36s use thew same casting, and 38s and 40s run the same casting. My theory is that this is why 36s are prone to more slide wear than 32s because there is less metal to support them (especially at the sides of the venturi). Happy to stand corrected.
Castings differ slightly between 32 and 36mm, don't know about the 34, but maybe they're in between.
Mixing chamber/slide housing is shorter on the 32, a spacer is needed under the cap to provide full slide lift for 36mm. Shortening the slide at the top edge could be an easier alternative. Same slides for 32 and 36. I too see the 36 wearing quicker than the smaller versions.
The big challenge is re-locating the mixing chamber floor to keep the venturi centered to the flange. Bringing the floor of the mixing chamber closer to the fuel level will undoubtably require custom jetting and adjustments deviating from the standard 18mm float height.
piet
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The Sock
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- London, England
piranha-bro2
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- Location
- Melbourne
Makes sense about the centering issue, Piet.
Rob, when you say 'smooth bored' that would mean there's an insert fitted to the slide chamber that creates an uninterrupted passage through venturi (ie no deviation around the slide area). CR Keihins (round slide) literally has this insert bolted in and the slides are like an inverted bucket (22 and 41 in the diagram). Can't see how you could do that with a Dell - unless there was almost nothing supporting a closed slide.
piranha-bro2
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- Location
- Melbourne
That'll polish out Hamish!
The Sock
Hero member
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- London, England
Looks like this, Quentin.
Basically ported/blended out to 36mm.
I'll take a better piccy next time I have the tank off.
Yes Quentin,
Not at all "smooth bore". More like the bumps around the pilot passages have been smoothed out.
I did that with my PHBs as well, but seriously doubt any advantage could actually be measured.Even the humble but once omnipresent Amal Monobloc was a true smooth bore carb with a hollow slide moving over an insert in the mixing chamber.
piet
jko_78
Full member
- Location
- The ever windy Northwest of Europe
Few pages back indeed https://laverdaforum.com/threads/what-did-you-do-to-or-for-or-with-your-laverda-today.97052/page-367
short version, father bought a running bike, swapped the (working) engine with his worn out one & after a few months had holed pistons as the head had been shaved off as far as it could & it had the Ural side car on it against heavy winds.
Rebuilt later, found out about the head and other issues, then fitted with double base gasket resulting in this compression ratio which is as far as I can judge a lot more than a normal GT so I can't use the documentation for that. Father ran it with the 10s in it even after the side car was removed, and so they are still here (although replaced a few times for new ones of course). Basically have a GT engine with higher compression now. Was all ages ago so my father has a good memory doesn't remember all the details
Thanks Piet, I'll can start with the N2s then -I'm not a racy kind of rider so I'll fit those & watch what happens first also taking Marnix' advice in mind. So N2 is roughly B9 and N3 is roughly B8? ((i can imagine they are made to factory spec/definition and not to a "heat standard")Lean it out far enough and one might even NEED 10's...
Should run fine with Champion N3's/NGK 8's if carburation is correct, N2 if compression has been raised. Most SF1-3 cope quite OK with Champion N3 for tootling around, N2's should be considered forhooninghigh-speed use.
piet
A GT and high-speed seems a bit contradictory
I'll start with the N2 / B9s. What I have is basically a high compression GT engine it seems.
10s are a remnant of the sidecar history but since they work(ed) my father simply kept it like that, why change if it works. After the sidecar came off the Laverda was not used as often as as before. Just that they are hard to get it seems.
Thanks for the advice
piranha-bro2
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- Location
- Melbourne
Lee rode solo from Adelaide to Melbourne, then two up back with me as pillion. On bizarre advice he swapped his Bosch 260T2 plugs for 240T2 (eq to B9 to B8 or N2 to N3 - cool to hoy ... whoever gave the advice got it arse about ... maybe they were thinking Champion, where the numbers hot-cool go the other way). So after doing maybe 1000km, 120kph+ up a long not overly steep hill suddenly holed a piston. Moral being, you can ride safely forever if you never create the perfect conditions for the hot plug to play havoc.
piranha-bro2
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- Location
- Melbourne
Plugs sound good. Not implying that you'll definitely hole il pistone, Gerald - just pointing out that working the engine hard creates a higher risk.
The Sock
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- Location
- London, England
I've run Champions in mine for 49 years. Never liked the way it ran on NGKs
N2G gold palladium wires, I bought in a stock of them when they were being discontinued and hope I have enough to see me out.
Only time I ever had an issue was when the bike ingested a bee, which bridged the terminals and caused a misfire. Once removed, it was back to business as usual.
In September, we do a group ride with a bunch of friends on classic British machines.
3 days on the road, usually about 1000 km, 3 days in the same place visiting local sights and restaurants, and 3 days riding back home.
I'd like to take the 750 S and give my SF2 a rest. It's already run 2500 km in May down to the Amicale 750 Laverda meeting in the Southern Alps and we're setting off with my wife Corinne in a few days, probably for another 3000 km.
I much appreciate the small valve engine of the S, more perky than the SF2.
The clutch on the S was always very heavy and had become near impossible more recently. So a few weeks ago, I fitted a DAM kit which involved changing the sprocket cover for a standard one, the DAM lever not being able to operate with the kidney shaped opening originally on the S. I also took the clutch to bits to replace the old steel hub and pressure plate with a more recent alloy set up. I was sure that the heat stored by the steel was making the clutch difficult when hot. Piet convinced me not to, arguing that the steel was less wear prone than the steel. So I checked the clutch out. It seemed that one of the plates was slightly buckled, but I rebuilt it like that. A new clutch cable was fitted and I found that the clutch lever was pinched in its handlebar mount. Clutch action was much lighter after all that but, there was really a hairline adjustment between the clutch slipping when cold and dragging when hot. And it was nigh impossible to find neutral.
So, I took it all to bits again. I checked the plates but couldn't find any warpage. I'd sourced a new set of friction plates so put those in. The two rods were straight but the balls had well dented the ends and one was a bit short at something like 11.9 mm. I found two other rods in my pile of bits, one about 1 mm longer, and both not marked by the balls. More lift assured.
It's all back together now, the engine is timed and tomorrow, I'll close up the primary.
Then a once over of the SF2 before setting off.
Paul
3 days on the road, usually about 1000 km, 3 days in the same place visiting local sights and restaurants, and 3 days riding back home.
I'd like to take the 750 S and give my SF2 a rest. It's already run 2500 km in May down to the Amicale 750 Laverda meeting in the Southern Alps and we're setting off with my wife Corinne in a few days, probably for another 3000 km.
I much appreciate the small valve engine of the S, more perky than the SF2.
The clutch on the S was always very heavy and had become near impossible more recently. So a few weeks ago, I fitted a DAM kit which involved changing the sprocket cover for a standard one, the DAM lever not being able to operate with the kidney shaped opening originally on the S. I also took the clutch to bits to replace the old steel hub and pressure plate with a more recent alloy set up. I was sure that the heat stored by the steel was making the clutch difficult when hot. Piet convinced me not to, arguing that the steel was less wear prone than the steel. So I checked the clutch out. It seemed that one of the plates was slightly buckled, but I rebuilt it like that. A new clutch cable was fitted and I found that the clutch lever was pinched in its handlebar mount. Clutch action was much lighter after all that but, there was really a hairline adjustment between the clutch slipping when cold and dragging when hot. And it was nigh impossible to find neutral.
So, I took it all to bits again. I checked the plates but couldn't find any warpage. I'd sourced a new set of friction plates so put those in. The two rods were straight but the balls had well dented the ends and one was a bit short at something like 11.9 mm. I found two other rods in my pile of bits, one about 1 mm longer, and both not marked by the balls. More lift assured.
It's all back together now, the engine is timed and tomorrow, I'll close up the primary.
Then a once over of the SF2 before setting off.
Paul
Its hard to imagine how a hot grade plug has a part to play in damage to a piston in of itself, perhaps a combination? More the matter of what type of ignition in use, Inductive discharge is the most "weak" type of spark initiator, slow rise time of spark gap ionisation being the less than optimal at igniting a fuel load in compression. Contaminated plugs will defeat an inductive discharge ignition design, in worsening conditions. Included in that is the "dwell extender" designs, fix one problem ( maybe ) and get other issues.
CDI style designs have far superior rise time of arc initiation, though shorter spark duration, hence the MSD
designs in the past ( IIS long box was a multiple spark design at lower RPM, where poor fuel load ignition needed many sparks to initiate a flame front ). Most beneficial aspect of CDI is the ability to spark initiate through a fouled plug. Something an inductive discharge cannot do as a guide.
Did a lot of work on the test jigs and actual road testing in the day, my perspective and based upon many hours of same. HTH j.
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piranha-bro2
Hero member
- Location
- Melbourne
Back in the day we had to work with what the factory gave us, Jon, ie a points condenser ignition running two big Bosch coils and 40 deg full advance. A more sophisticated ignition system may have negated the tendency to burn a hole, but with the SF as it was, combining a hot plug with an enthusiastic right hand was a sure recipe for woe.
All noted Quentin, many of us speak from the hard road experiences, perspective...
BTW Bosch GT40 ( not the "electronic version" as a given, though still terrible ) with diabolical leakage inductance ( primary to secondary windings coupling ) were only fit for points, full stop, absolute rubbish. Popular with the MG mob... to their cost. j.
BTW Bosch GT40 ( not the "electronic version" as a given, though still terrible ) with diabolical leakage inductance ( primary to secondary windings coupling ) were only fit for points, full stop, absolute rubbish. Popular with the MG mob... to their cost. j.