SF2 main jet PHF 36

I am not English.
Neither are the Americans.
Oddly the US has imperial but drives on the right.
Australia has metric but drives on the left.
UK has metric AND imperial and drives on the left.
Wonder if we'll get rid of metric when we win our independence from Europistan.  :D :D :D
 
zorba75482 said:
Checked TDC with a Dial indicator down plug hole PM spot on both cylinders
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Then your timing is obviously way off... why don't you set that right before continuing?  Anything else is simply pointless and a waste of time, and is potentially endangering your engine.

piet
 
thousandths of an inch is a metric division of an imperial unit,
so why does the barrel on the micrometer (analogue) have to turn twice to get 100 of them?
CLEM
 
sfcpiet said:
Then your timing is obviously way off... why don't you set that right before continuing?  Anything else is simply pointless and a waste of time, and is potentially endangering your engine.

piet
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Timing spot on with a strobe.for both cylinders and advances to A mark at 3000rpm on both cylinders
 
Grant said:
Could still be fuel flow restriction. If the taps or the carbs can't flow enough fuel the bowls will be starved and lack power at higher speed.
Regarding cam timing, when did this problem appear and at which point was it running ok.
If the bike has stood a while unused but ran ok when parked then I would think fuel restriction is more likely.
Can you tell us more about this?
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Been like this since restoration. Gas seems to flow freely. Anyone any data on volume per minute to check flow rate? I have checked breather in filler and opened it at high speed I see if I had n airlock , but no improvement.
Carbs cleaned and rebuilt twice.

Nobody mentioned coils. Am running out of things to check

Scott doubts the motor would run anywhere near half decent with a tooth out and it is kinda running half decent.
 
It can run very sort of decently a tooth out. I had an SF3 come in for a service, it idled pox, had lousy power etc and things just seemed amiss. One tooth out. The owner had ridden it for years like that! A compression test will probably show it up as valve overlap is way out. Your double from expected fuel consumption is a strong sympton that could well point at valve timing too. I would eliminate this possibility. You have confirmed ignition timing. Your carbs are checked and rechecked (chokes shutting off?) and you have run without air filters?
It is not in any way a typical coil related problem.
You are sure it isn?t some non tuning related thing, a restriction in the drivetrain like dragging brakes, everything is loose and turns freely, including the motor with the plugs out? 
 
Tippie said:
It can run very sort of decently a tooth out. I had an SF3 come in for a service, it idled pox, had lousy power etc and things just seemed amiss. One tooth out. The owner had ridden it for years like that! A compression test will probably show it up as valve overlap is way out. Your double from expected fuel consumption is a strong sympton that could well point at valve timing too. I would eliminate this possibility. You have confirmed ignition timing. Your carbs are checked and rechecked (chokes shutting off?) and you have run without air filters?
It is not in any way a typical coil related problem.
You are sure it isn?t some non tuning related thing, a restriction in the drivetrain like dragging brakes, everything is loose and turns freely, including the motor with the plugs out?
Click to expand...

Compression test shows 150psi both cylinders. Dry. Cold engine  throttle wide open. Does that eliminate cam
timing?
Am about to run without airfilters after resetting the timing by static method.

Everything turns freely.

Read an old post from a guy having exactly the same symptoms and cured by repairing the number 15 wire between coils. Doubt that is my issues I put a new loom on from Wolfgang but will check.
 
I am staring to think that you must have a broken valve spring, and since these are double type, on twins, the unbroken one and the remains of the broken one, will probably still give you normal compression pressures at cranking speed, because the valve they work on will still get closed, but after maybe 3,000 RPM ????? I doubt it.
CLEM
 
Well, some progress was made today.  Went for a run and had same bogging at 4500 in 4th and 5th, so stopped and pulled the airbox rubbers off.
No stumbles at 4000. Pulls to  an indicated  95 mph and still more to go but saw the local constabulary eyeing me and don't want to run too hard with no rubbers so came home.

 
Removed the dense foam filter ND made a temporary one from skotchbrite. Still better than with the foam. Runs to about 95mph but stutters at 4500 in 4th and 5th still. Seems to Rev through compete range in the lower my ears. Maybe a minor hesitation at 4500.
 
You don?t need to use top gear to check power. If you can find a decent hill use a gear that takes time to wind out, third or higher probably. If it winds through the redline under those conditions it?ll do so in higher gears too. From full throttle, under load at high revs, if you snap back a few degrees on your twistgrip you get a fair indication of your jetting in the first second or so. If it just slows a bit you are close to the mark. If it actually picks up, it is happier with a bit less air, meaning you are a bit lean. If it stutters it wasn?t happy with a bit less air meaning a bit rich. This is "seat of the pants" so as someone mentioned earlier a dyno session with diagnosticsis would pay off. I set the mains on my racebike like this and the dyno confirmed it was spot on.
You should get have no difference either with or without air filters, of you need another type of filter.
 
Tippie said:
You don?t need to use top gear to check power. If you can find a decent hill use a gear that takes time to wind out, third or higher probably. If it winds through the redline under those conditions it?ll do so in higher gears too. From full throttle, under load at high revs, if you snap back a few degrees on your twistgrip you get a fair indication of your jetting in the first second or so. If it just slows a bit you are close to the mark. If it actually picks up, it is happier with a bit less air, meaning you are a bit lean. If it stutters it wasn?t happy with a bit less air meaning a bit rich. This is "seat of the pants" so as someone mentioned earlier a dyno session with diagnosticsis would pay off. I set the mains on my racebike like this and the dyno confirmed it was spot on.
You should get have no difference either with or without air filters, of you need another type of filter.
Click to expand...

Thanks . I tried lessening the throttle a tad and it made no difference, still stutters. I'm in small town east TX and dynos are a ways off, let alone finding someone I could trust, but I will make some inquiries. Am trying to thinking a decent hill in this flatland😣
 
zorba75482 said:
Unfortunately not. Seems to be working OK and can feel spring pressure when twisting by hand. Wouldn't a faulty advance mechanism show up in all gears at same revs?
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You're probably right but vibration induced problems can be very strange and vibrations aren't the same in every gear.
Check that the condensers are earthing properly against the points back plate. The rivets work loose with time and give a vibration induced misfire.

Paul
 
Paul Marx said:
You're probably right but vibration induced problems can be very strange and vibrations aren't the same in every gear.
Check that the condensers are earthing properly against the points back plate. The rivets work loose with time and give a vibration induced misfire.

Paul
Click to expand...

Thanks Paul , i will check tonight
 
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