Newbie jetting questions

Piranha Brother 2 said:
And now I can forget Dells and enjoy the FCRs.
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With two separate mixture adjusters for this area. Far more precise adjustment requiring careful study of the guidelines. I bought my FCR39s from someone who swapped them for 32mm because an expert told him the bike wouldn't run cleanly because they were too big.
Dells in good condition should pull cleanly all the way. It seems that different fuels coming into use more and more are making challenges, especially in the small opening transition area. How will we adjust them for when the only fuel available is electrons?
 
Another thread about throttle slides made me wonder. Perhaps the guys at the Dellorto factory had a tendency to use slides with a bit too much cutaway, causing the mixture to be too lean for the first bit of throttle opening.

To cure the hesitation just off idle, it might be worth trying a 'richer' slide with less cutaway. 60/2 was mentioned as the correct slide for Lav triples. Has anyone tried 50/2 slides?

Rather than buying a new set of slides just to see what they do, I remember reading in an old engine tuning book (don't recall which one) that it's possible to experiment with reduced cutaway by adding a bit of material to the edge of the cutaway opening. The example given was to build up the edge of a brass slide with soft solder and file it back to a smooth edge with the desired cutaway opening. If the slide is made from some alloy that is difficult to solder, then maybe a bit of auto body filler would do the trick. Perhaps even a piece of thin plastic cut to shape and glued to the inside of the slide with hot melt glue. The latter two are my own ideas. I dunno if they'll stick in place long enough for a decent road test.

Obviously it's possible to reduce the cutaway by filing a bit off the bottom of the slide so it sits lower in the carb. But that will also drop the jet needle down, so you'd need to compensate for that. And filing the slide down isn't reversible, whereas the above methods are.

Just food for thought ...

 
I filed the 2mm off slide on my Husky Automatic and it made the bike 100% easier to ride, before doing that it would not run off the pipe and this had it only running at max acceleration and then Automatically changing up a gear. Huge fun till you arrived at tough track.
 
Liquid metal holds about the best of anything and could be done. However the fear of anything like that going down the manifold is a bit scary. Borrowing some to try if it was possible would be ideal. Triples seem to be fine with 60 slides though.
 
I've got some hard-chromed bronze slides I made when I rebored my worn out 36mm dells. Unfortunately I made them with 70 cutaways as that's what i'd had in the SF1 for years. Ran OK but better with 60s. Once I get a certain moto on the road I'm going to machine up some detachable inserts with different cutaways that can be screwed onto the slides.

Slides will last forever so may as well make them usable - I'll sell them eventually (the carbies and slides that is).
 
I was never partial for carburetor accelerator pumps on a European Motorcycle. Jap bikes like the 900k and the GSW-R liked pumps.

As far as jetting goes - Take your moped for a hard ride  - If she dies and leans out put in a larger main jet before you melt pistons.

If she bogs and floods, blacking the plugs, lean out out the main jet.

The exhaust system plays an important part - You have to jet your carbs by feel !

Fuck them CV Air flow Gauges just set the sliders evenly say using a screw driver octagon attachment to seat the slides constant, ensure the throttle cables are tight (Slap your throttle and listen so that each carb slide falls at the same time) then adjust each carb with the same adjustments to obtain your goal - Guaranteed each carb will flow equally.
 
Laverda SF said:
I was never partial for carburetor accelerator pumps on a European Motorcycle. Jap bikes like the 900k and the GSW-R liked pumps.

As far as jetting goes - Take your moped for a hard ride  - If she dies and leans out put in a larger main jet before you melt pistons.

If she bogs and floods, blacking the plugs, lean out out the main jet.

The exhaust system plays an important part - You have to jet your carbs by feel !

Fuck them CV Air flow Gauges just set the sliders evenly say using a screw driver octagon attachment to seat the slides constant, ensure the throttle cables are tight (Slap your throttle and listen so that each carb slide falls at the same time) then adjust each carb with the same adjustments to obtain your goal - Guaranteed each carb will flow equally.
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A very different story on a triple, Ron.
 
Thanks for all the suggestions and proposals.

I started again with the mixture screws. 1.5 turns out, tweaked for "better idle", then an extra 8th to quarter turn richer.  Honestly couldn't make it work any better - still pretty fluffy picking up from idle.  I also did what LaverdaSF suggested and watched/listened that the throttles snap back with one 'snap', which they do.

I sort of suspect ignition timing - so have been reading all threads and manuals on how to time up a Witt 90s era ignition, as far as I can tell it's working fine - it was definitely advancing, hopping around the TDC mark (marking verified with TDC + dial gauge)at idle and advancing when revved up. Now I've read-up, need to re-connect the strobe and see where it is at 3000rpm.  tomorrow...

First time today I had both a bled clutch and a running engine so tried that in the shed. It works fine but all the action is right by the handlebar, feels like it needs bleeding more but I've done everything I know to bleed it.  Maybe the m/c needs a rebuild kit? I read yet more threads here about that and took the triangular cover off the right cover and about a liter of oil poured out.  Whoops, lots to learn about this engine - and of course that cover doesn't reveal the clutch slave anyway. I'll drain the rest of the oil and take the big sprocket cover off. Gives me another chance to examine the drain plug and try a longer one.

Meanwhile I still haven't got it registered so plenty of time to mess around.

-Richard
 
Something we used to talk about a lot but not lately is leaking choke plungers, make sure there isn't one hanging up a bit, or the rubber divot on its bottom isn't allowing it to not seal completely
 
Vince said:
Something we used to talk about a lot but not lately is leaking choke plungers, make sure there isn't one hanging up a bit, or the rubber divot on its bottom isn't allowing it to not seal completely
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Thanks Vince - I've replaced the rubber seals on top where the cable enters, adjusted the cables so they're all similar - and then watched them all rise and fall before I reattached the airbox rubbers.  Not sure about the "rubber divot on its bottom" - is that part of the plunger or the bore it sits in?  Not sure what you mean.  I did replace all the o'rings/seals on the jets in the float bowl too.



 
There are 2 cables connected to these carbs, the main throttle cable, and a smaller choke cable, that comes out of that 3 way to one cable connecter on the backbone of the bike frame, you need to use a slotted screwdriver to remove it from the carb at the side. They need equal Freeplay, off it fully down and at the bottom of the metal plunger, there is a rubber seal attached. Years of use result in a divot, sometimes it gets damaged or goes hard and that allows the choke to stay on a touch affecting the way the carb runs.
 
ok, sounds like a pretty likely scenario - I didn't spot any rubber seal at the base of the plungers so maybe they've vanished over the years. Or were lost in a previous rebuild - need to study the PHF diagram again.  Thanks Vince.

-Richard
 
Forget what Ron said about hearing the slides hit down together on the stop screws, it is only relevant to 750s. Your carb rack has the slides hanging from a rack which itself has the idle stop screw, hence the need for vacuum gauge synch.
 
Tippie said:
...only relevant to 750s. Your carb rack has the slides hanging from a rack which itself has the idle stop screw, hence the need for vacuum gauge synch.
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Okay, i did balance them with the gauges and haven't touched the linkage since.  Only problem was it ran badly with the gauges, but well enough to balance I think. yeah makes sense what you're saying about the single stop-screw, I tried it with the screw backed-off but not relevant when the screw is engaged.
 
An interesting couple of days with this bike - I've got a few questions that are definitely off the "jetting questions" topic but I'll put them here for now.

I lost some oil when i took off the right-side cover plate - so I drained the oil altogether to flush it one more time (I reckon the oil I received it with had been in there about 17 years, so there's some catching up to be done 🙄). You may recall my previous worry about the drain-plug not torquing up, so this time I experimentally poked a M14x1.5 tap up the hole, fingertip force only, and oh f...., about 4 threads-worth of aluminium swarf came back out with it. Looking up the hole with lights and mirrors it looks like almost a smooth, threadless tube with maybe 2 threads at the top of the bore. I've got a longer plug on order as Clem suggested but I reckon it might be beyond that.

So I've been studying how to do TimeSerts - they seem to be the method that removes the least material and I figure it's expensive but worth a stab given it's engine out otherwise and I really (really!) would like to ride this thing a bit before I get too medieval with engines out etc. If anybody's got more good advice (thanks to Piet and others for advice already) on doing re-threading on Laverda sumps, I'd be grateful. Maybe we need a new mattress so I can lean the bike on the old one...

Chain and sprockets - the bike currently has a 630 chain with a completely loose/buggered master-link so I cut that off today. The front/rear sprockets are 16/37 (carefully counted..). I'll get a 530 chain and new sprockets but what gearing is stock and/or recommended for street use only. Was 19/40 standard on a Series2 180?

Clutch, I rebuilt the (PS15, is that original?) clutch Master and it's better but still the action is too close to the bar - therefore got the covers off and dismantled the slave today. The hose is ancient so I'll replace that and the piston seal - where is the o'ring that people replace in the slave - does that sit in the nose of the piston? I didn't have one. Any good threads on slave reconditioning, haven't found one yet?

There's more (like I said, interesting days) but I'll leave it there.

Thanks as always,

Richard
 
19/40 works well. I've tried shorter hearing but it just seems too busy at highway speeds.
O-ring is in a groove in the cover. Make sure you get a brake fluid proof replacement.
New forum software works a lot better on a phone. 👍
 
Hello Paul,

I do believe that Green Bible and Laverdamania’s standard settings are identical.

Gijs van Dijk renewed my carbs, i could check the receipts. However, i found these ‘standard’ settings to be too rich, so i simply lowered the needles to the highest slots. A bit of work mind you, not a easy as with my SF by far. 🥴

Haven’t had the time to ride the bike yet, mainly due to winter and road salt. So can’t judge any results yet.

However, my SF’s rideability bettered quite a bit

Jilles
 

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