Rebuilt w/ Ross pistons. Plugs are Champion N2s. Is the compression too high for N2s? Everything checks out. Plugs fire on compression stroke. Ok and what about squareslide carbs. Mixture is 1 1/2 turns out. What about throttle stop screws. Would they have anything to do w/ not firing? Have no idea where to set throttle stpo screws...
Sf won't fire
- Thread starter Evan
- Start date
The Sock
Hero member
- Location
- London, England
N2s are pretty hard.
What's the ambient temperature where you are?
I had to preheat N2s with a gas torch to start the engine in near freezing temperatures, when I used them years ago. I switched to N2Gs and had no further problems. Sadly they're NLA.
Might be worth trying a softer plug to start it.
What's the ambient temperature where you are?
I had to preheat N2s with a gas torch to start the engine in near freezing temperatures, when I used them years ago. I switched to N2Gs and had no further problems. Sadly they're NLA.
Might be worth trying a softer plug to start it.
Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
Does it cough, pop ?
arancia
Senior member
- Location
- Arizona, USA
As Exmoor Beast asks, it should at least go phut occasionally even if all settings are not ideal if the magic ingredients of compression, fuel, spark and timing are present.
Bear in mind that the standard (w/o electronic ignition system added) is effectively two separate single cylinder systems each with own points, coil, wiring etc and it will run with one cylinder if all those ingredients are present for that cylinder.
I did read your "Plugs fire on compression stroke" but wonder if it's possible that points to coils wiring was switched around or cam alignment set to the wrong piston TDC when you reassembled so that cam and spark (no wasted spark as they're two independent systems at 360 degrees separation) are 360 degrees out of sync? That would mean getting the spark when not full of fuel mixture under compression.
The slides should be only very slightly open at start and idle, try backing the idle screws out till slides bottom and go back in one turn. It may need the enrichment of some choke to start even if not very cold till you get all the idle and mixture settings right. Is there fuel smell or moisture on plugs when you take them out after trying to start.
I run N2s in mine except for racing with no problems except once they did seem to get cooked after a long high speed run and the bike wouldn't restart till a new pair was installed.
Bear in mind that the standard (w/o electronic ignition system added) is effectively two separate single cylinder systems each with own points, coil, wiring etc and it will run with one cylinder if all those ingredients are present for that cylinder.
I did read your "Plugs fire on compression stroke" but wonder if it's possible that points to coils wiring was switched around or cam alignment set to the wrong piston TDC when you reassembled so that cam and spark (no wasted spark as they're two independent systems at 360 degrees separation) are 360 degrees out of sync? That would mean getting the spark when not full of fuel mixture under compression.
The slides should be only very slightly open at start and idle, try backing the idle screws out till slides bottom and go back in one turn. It may need the enrichment of some choke to start even if not very cold till you get all the idle and mixture settings right. Is there fuel smell or moisture on plugs when you take them out after trying to start.
I run N2s in mine except for racing with no problems except once they did seem to get cooked after a long high speed run and the bike wouldn't restart till a new pair was installed.
It will fire intermitantly on the left. Won't idle. Right does not fire. Ambient temp here in Texas was about 70 degress farenheit yesterday & this morning moisture in the air. Shouldn't have anything to do w/ it. It should fire up!
What about plugs???? Throttle stop screws? and mix screws. Dked w/ both...Used a car battery direct to starter. Laverda battery is not going to weaken during turn over....???Should staRT!
What about plugs???? Throttle stop screws? and mix screws. Dked w/ both...Used a car battery direct to starter. Laverda battery is not going to weaken during turn over....???Should staRT!
Exmoor beast
Hero member
- Location
- Minehead,Somerset, ENGLAND OF COURSE
Basics: cam timing, valve clearances, points clean and timed correctly and of course you’ll need fuel- did you clean carbs , have you got a massive air leak at manifolds?
arancia
Senior member
- Location
- Arizona, USA
Really hard to guide without a little more context.
Was it running before dismantle to install pistons? Then what changed?
If a restore of a previously not running bike then any number of possible issues!
If it were me (more than 40 years experience looking after my Breganze 750s), I would start by removing the plugs and dynamo cover so can turn it over by hand with valve adjuster inspection caps off, check points gaps, use a bulb or meter across points slowly turning crank forward to see that spark timing really is at the mark on the compression stroke with both of that cylinder's rockers loose then if all seems good with timing and good fat sparks at each plug in turn, move on to fuel.
Drain float bowls, any fuel in there? Check float levels and that all is clean in the jets and passages and all the rubber seals are in place without damage. Mix screws out about 1.5 turns. Idle screws in about one turn from slide bottomed.
These bikes are very simple, no electronics as such, so a stepwise movement through the necessities of timing, compression, spark and fuel systems should find the problem - if the plugs are new N2s with gaps about right then I'd be looking elsewhere than the spark plugs though it certainly would not hurt to try a new pair.
Was it running before dismantle to install pistons? Then what changed?
If a restore of a previously not running bike then any number of possible issues!
If it were me (more than 40 years experience looking after my Breganze 750s), I would start by removing the plugs and dynamo cover so can turn it over by hand with valve adjuster inspection caps off, check points gaps, use a bulb or meter across points slowly turning crank forward to see that spark timing really is at the mark on the compression stroke with both of that cylinder's rockers loose then if all seems good with timing and good fat sparks at each plug in turn, move on to fuel.
Drain float bowls, any fuel in there? Check float levels and that all is clean in the jets and passages and all the rubber seals are in place without damage. Mix screws out about 1.5 turns. Idle screws in about one turn from slide bottomed.
These bikes are very simple, no electronics as such, so a stepwise movement through the necessities of timing, compression, spark and fuel systems should find the problem - if the plugs are new N2s with gaps about right then I'd be looking elsewhere than the spark plugs though it certainly would not hurt to try a new pair.
Plugs fire on compression. Easy to tell, Turn over w/ 24mm @ starter nut until plug hole pops under thumb. @ that point plug fires. Will check again.
Carbs were rebuilt. Right side puked fuel by throttle stop screw hole @ beginning of turning. Always did that anyway
Plugs were fine before rebuild. Used the same on the same sides. They are sparking orange color. They're supposed to be blue. And What plugs should I buy? N2s, N3s or N3cs or should I try something different? Bosch? N2s & NGK Rs is all I ever used. what does everybody use now?
Gave up this morning. Will check over again tomorrow. Don't want to remove tank yet. No arching. I'm sure it is multiple problems.
Carbs were rebuilt. Right side puked fuel by throttle stop screw hole @ beginning of turning. Always did that anyway
Plugs were fine before rebuild. Used the same on the same sides. They are sparking orange color. They're supposed to be blue. And What plugs should I buy? N2s, N3s or N3cs or should I try something different? Bosch? N2s & NGK Rs is all I ever used. what does everybody use now?
Gave up this morning. Will check over again tomorrow. Don't want to remove tank yet. No arching. I'm sure it is multiple problems.
martymoose
Hero member
- Location
- Sydney, Australia
NGK b9es. Why is carby flooding? Fix that first.
piranha-bro2
Hero member
- Location
- Melbourne
Genuine NGKB9ES as well - never ever once fouled a plug - raced it, commuted on it, raised compression and went to SFC cams, still never a prob. Fuel should not leak from anywhere - sounds like flooding prob (float valve/s not seating. If the head's been off could well be one tooth out on the cam sprocket. Orange spark sounds a bit sus.
Tippie
Hero member
- Location
- Dr?bak, Norway
They fire up and run one tooth out either way. As Marty says don't even bother trying anything before stopping carb flooding. I will start with any of the mentioned plugs, none of them cause your symptoms.
CLEMTOG
Hero member
"Plugs fire on compression. Easy to tell, Turn over w/ 24mm @ starter nut until plug hole pops under thumb. @ that point plug fires. Will check again"
not actually the best way to determine the firing stroke. Remove an inlet valve cover, turn engine (forward rotation) with your spanner/socket and watch the inlet valve open and then close as you rotate, now drop a knitting needle down the plug hole vertically, and continue to turn the motor holding the needle and feeling it rise, when it has reach the top and you can rock the crank back and forth, without piston movement, this is TDC firing stroke, for dead acurate location of TDC you need a piston stop and a degree wheel,, but that is not the point here, with your piston at "near enough" TDC, one of the contact points should be about to open (break) and the alignement mark on the crank should be bob on as well. Make sure it is, and then adjust the points by moving them, not changing the gap, and using a 12v bulb and holder across that set of point, get them to just crack the bulb off,static timing set, but do the set of points on the main back plate first, (which is slotted to move on the pri case) and then the other set (which moves on the backplate) last static timing is then set on both sides.
Another basic check is to position the motor so one set of points is closed, and with both plugs out and earthed to the engine, flick the points open (igniton switch "on" obviously) and the pug will crack a big blue fat spark, do the other one as well, if they dont do this, look for wiring defects, usually badly placed insulators on the points, those little bakelite square washer thingies.
CLEM
not actually the best way to determine the firing stroke. Remove an inlet valve cover, turn engine (forward rotation) with your spanner/socket and watch the inlet valve open and then close as you rotate, now drop a knitting needle down the plug hole vertically, and continue to turn the motor holding the needle and feeling it rise, when it has reach the top and you can rock the crank back and forth, without piston movement, this is TDC firing stroke, for dead acurate location of TDC you need a piston stop and a degree wheel,, but that is not the point here, with your piston at "near enough" TDC, one of the contact points should be about to open (break) and the alignement mark on the crank should be bob on as well. Make sure it is, and then adjust the points by moving them, not changing the gap, and using a 12v bulb and holder across that set of point, get them to just crack the bulb off,static timing set, but do the set of points on the main back plate first, (which is slotted to move on the pri case) and then the other set (which moves on the backplate) last static timing is then set on both sides.
Another basic check is to position the motor so one set of points is closed, and with both plugs out and earthed to the engine, flick the points open (igniton switch "on" obviously) and the pug will crack a big blue fat spark, do the other one as well, if they dont do this, look for wiring defects, usually badly placed insulators on the points, those little bakelite square washer thingies.
CLEM