Sf1 36mm PHF carb tuning

Have to agree with Tippie - if you wiggle a choke cable and it affects idle, something is definitely wrong and you are never going to get it sorted. Cables are absolutely fine - you can leave masses of freeplay in them as an overboard form of insurance - the lever will always eventually lift the choke plungers when needed. I'd be VERY suspicious of your choke system, personally, and going over it with a fine tooth comb. And I'd be putting the cables back on - but that's just me (45 years of using SFs and never had an issue with chokes or idle once they're set up properly).
 
You say left hand carb idle screw wound in all the way - you are effectively bypassing the idle circuit, you can?t have any / enough fuel going through the pilot jet.What your describing is hunting Due to poor fueling.
Re check your pilot jet and passage -is it blocked, corroded Or simply the wrong jet.Also your ?air screw? is in fact a mixture screw so undo for more fuel ,not air. Hope this helps,Jason
 
I stripped down the carbs one more time and ran them in the ultrasonic cleaner for 30 minutes, blew out all the components, I paid attention to the idle screws, these are the new Dellorto carbs and the idle screws are a two part assembly with two separate springs, a washer and an O ring. The actual ram that lifts the slide is slotted with one flat surface that passes into the carb body,  I may have had the ram not seated properly on the left carb and unable to lift the slide. I got that sorted on both carbs and made sure the slides lifted smoothly with each adjuster screw.

I removed the throttle cable / splitter and pair of throttle cables to each carb, checked and lubed everything and checked the routing from the splitter to the carb tops, all seems good. The carb slide springs are brand new stock spec, not the lighter ones.

Got it all back together and with a fuel bottle hanging from above and just one operable choke on the left carb it fired up straight away. Then I pulled the spark plugs one at a time and set the idle and fuel screw. Once both plugs were back on the idle increased significantly so I backed off each idle screw to get the idle back down to around 1500 rpm (any lower and it wants to stall).

After a couple minutes with the choke off, the idle starts to climb and holds at around 4000 rpm.  I then wind out the idle screws to drop the idle back down which it will do but then it wants to stall and I need to wind in the idle screws again and it all starts over again with idle climbing back up to 4000 rpm.

I checked the intake manifolds, which are not stock since the new style Dellorto take a rubber boot to clamp onto the carb body at the head side which then clamps onto to alloy manifold and then onto the plastic manifold spacer. The manifold spacers have O rings on both sides and I laid down a thin bead of flexible gasket sealant between all the joint faces that make up the manifold assembly. I don't think I have an air leak at the carb rubber boot to intake manifold, I sprayed WD40 around the manifolds while the engine was running and I didn't notice any change in RPM.

The bike is fitted with Witt electronic ignition and Dyna 5 ohm coils and new high tensions leads and caps.

The carb top caps have new O rings, the carb bodies are new, as are the slides (50's) so I  just can't figure out why the RPM is rising?

For the throttle to rise up to 4000 rpm would I not have to have a significant air leak at the manifold OR the slides are rising?

Maybe I need to pull the air cleaner boots and place a mirror to look into the carb intakes to see if the slides are lifting as the rpm rises?
 
Chapeau for perseverance. It's a major mystery! Are the revs rising on both cylinders? It all sounds like air getting where it shouldn't, but you've done everything right in trying to eliminate that factor.

I'm stumped to suggest anything other than putting as strobe on it and checking that it's not randomly advancing, to the point where the carbs have no effect. Prob is, at 4000 there should be close to max advance, but if you notice it advancing considerably from low revs, it could point to an issue in the Witt box - and Paul will tell you to put the points back on it!!  :o :D

You could do a lot worse than try the old points if you still have them.
 
Not sure whether this is relevant, or whether the two ignitions systems are comparable, but I had a rising revs problem on my RGS a while ago. 

When refitting the ignition after reinsulating some wires, I managed to mess up the pickup-rotor gaps, which ended up being much too small.  When the engine warmed up, the idle revs started to climb.  Can't say exactly how high, because the rev counter has a mind of its own, but it seemed at least twice the normal idle revs.  Resetting the gaps to spec cured the problem.

Tom
 
Does it smell rich when idling? Have you tried leaning it out with the pilot mixture screws ? Do the mixture screws make any difference to idle speed or smooth running? Modern fuel plays havoc with pilot circuit, they rend to richen as the motor gets hot. One thing that gives a similar symptom is a valve not seating( tight,burnt etc) which may not show up on compression test but would on a leak down test.
Check all the ? new? bits, they are often overlooked as new but can still be faulty. Keep at it and drink tea, Jason
 
It sounds  like a strobe check is called for. In the meantime are the blanking screws for fitting vacuum gauge stubs - on the flat part forward of the choke system - in place and properly sealed. Newer carbs have a tube takeoff fixed in here. Is the crossover tube between the manifolds fully tight or blanked off?
 
Dellortoman said:
That's a weird question Quentin. I assumed the pistons in both cylinders were coupled to the same crankshaft so would both be revving at the same speed. :D
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Making light of the obvious, Cam! A certain degree of inference is required  :-*
 
Dellortoman said:
You've got a better chance of getting there than me.
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I have been stuck at home mostly waiting for work ...... and if I venture too far I may have to isolate for 14 days to meet requirements for certain customers so it really isn't much fun. I fucking hate landscaping. Should be free of the constraints by the end of September.

Jim
 
helicopterjim said:
Say hello from me ..... I've been trying to get there since May.

Jim
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I dropped my SF1 with Wolfgang and Chris yesterday afternoon, the two of them were deep into plumbing repairs in the house so we just unloaded the bike off the back of my truck, discussed a few things to look at and I headed back north to Revelstoke and made it to Golden for the night, a long days driving from Edmonton and got back home this afternoon.

My wife thinks I am nuts to drive 2000Km for a guy to look at a bike, she can't be expected to understand this, but my humble SF1 gets treated to Laverda Royalty! 

I feel very lucky to have Wolfgang to call upon to sort this out once and for all. 

I have not found anyone around these parts with any knowledge of Moto-Morini, Benelli or even 70's Ducati's or Moto Guzzi's to call on. I have relied on owners groups and the internet for the past ten years to rebuild these old beasts and keep them on the road.
 
Good on you. A positive outcome is what you want - and no doubt that's what you'll now get - and can enjoy your beast for decades to come (as long as we're allowed buy fuel for it!).

I did have a thought about the issue - had any top end work been done on the motor? That is, had the cam chain been removed and refitted at any stage? A tooth out could easily cause the probs you've had, and it has been the cause of a similar prob highlighted on this forum a few years back.
 
Piranha Brother 2 said:
Good on you. A positive outcome is what you want - and no doubt that's what you'll now get - and can enjoy your beast for decades to come (as long as we're allowed buy fuel for it!).

I did have a thought about the issue - had any top end work been done on the motor? That is, had the cam chain been removed and refitted at any stage? A tooth out could easily cause the probs you've had, and it has been the cause of a similar prob highlighted on this forum a few years back.
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yes the engine was completely stripped down and the cases vapour blasted. Wolfgang reassembled the bottom end after cleaning the sludge traps and replacing the primary chain and clutch cush drive. I had he top end done locally and then put it together, I did have the cam chain out one tooth after having sunning issues diagnosed on this site. The bike ran terrible back then but it actually runs not too bad now other than the idle issue.

I am looking forward to know what Wolfgang finds!
 
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