Firing on one cylinder

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MikeM

MikeM

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Got the bike out today and after 6 months it started on one kick. Its running on only the left side and intermitently on the right. It kicks in occasionally. Seems to have fuel as it smells pretty bad,
Not sure where to start. 71, 750 recently rebuilt with no issues for the last 2 years.
Wiggiling wires seems to have no effect. I am electrically challenged for sure.
All wires seem to be plugged in.
Where to go first?
Thanks MikeM
 
Did you drain old gas and put fresh in? Replace spark plug? Check easiest items first. Was it running good when out away? Any possible rodent damage or nest in the exhaust? Fully charged battery?
 
michael levato said:
Did you drain old gas and put fresh in? Replace spark plug? Check easiest items first. Was it running good when out away? Any possible rodent damage or nest in the exhaust? Fully charged battery?
Click to expand...

All of the above were checked an OK. Running fine when put away, no apparent rodents.
 
MikeM said:
L.A.B. said:
MikeM said:
Where to go first?
Click to expand...

Check for a blocked pilot jet?
http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html
Click to expand...

Would a blocked pilot jet still cause the problem off idle? I had it up around 2500RPM an still one cylinder.
Click to expand...

Yes, it could, because although significant RPM, nil LOAD, so still on the tiny end of carburetion. Test... ride it, see if mid range kicks in. Or, at standstil snap it open with at least 1/2 throttle (you only have a second or two to listen for firing till RPMS get higher than safe no load speed.
Test... connect the spark lead from the side not firing to a spare plug, lay it on the head, start the engine and observe spark... or not.

Didgoo use fuel stabilizer properly run in before storage? :?:
 
MikeM said:
[

Would a blocked pilot jet still cause the problem off idle? I had it up around 2500RPM an still one cylinder.
Click to expand...
Yes, absolutely, especially if that RPM is at a no load, in neutral condition as in on the center stand in your driveway.
 
Biscuit said:
MikeM said:
[

Would a blocked pilot jet still cause the problem off idle? I had it up around 2500RPM an still one cylinder.
Click to expand...
Yes, absolutely, especially if that RPM is at a no load, in neutral condition as in on the center stand in your driveway.
Click to expand...

So the pilot jet is located just to the left of the float bowl screw in this photo? Remove the screw and use a wire to fish out the offensive debris?

Firing on one cylinder
 
MikeM said:
Biscuit said:
MikeM said:
[

Would a blocked pilot jet still cause the problem off idle? I had it up around 2500RPM an still one cylinder.
Click to expand...
Yes, absolutely, especially if that RPM is at a no load, in neutral condition as in on the center stand in your driveway.
Click to expand...

So the pilot jet is located just to the left of the float bowl screw in this photo? Remove the screw and use a wire to fish out the offensive debris?

Firing on one cylinder
Click to expand...

yes. The jet is waaaay down in the hole. I followed the knowledge learned here, got the #78 drill bit and mounted it in a brass holder. Shop tool.
 
Huh? A blocked pilot circuit wouldn't cause missing at mid throttle (Needle and slide cutaway are working at that throttle setting).
But a stuck float needle will. Does fuel dribble out of carb when you depress the tickler? Are you using the choke? Are you sure both slides are lifting? Try swapping plugs. Maybe you have a bad coil. Does this bike have points or electronic ignition?
 
mschmitz57 said:
Huh? A blocked pilot circuit wouldn't cause missing at mid throttle (Needle and slide cutaway are working at that throttle setting).
But a stuck float needle will. Does fuel dribble out of carb when you depress the tickler? Are you using the choke? Are you sure both slides are lifting? Try swapping plugs. Maybe you have a bad coil. Does this bike have points or electronic ignition?
Click to expand...

"mid throttle" was never mentioned. I believe MikeM is talking about NO LOAD/2500 RPM. This is easily achieved with very little throttle opening and almost entirely dependent on the pilot air system. Needle and cutaway have little to no influence here.

If a # 78 bit is not easy to find, single strand from a wire brush will work. The exact size is .016" which is the exact diameter of the "B" string from a set of "light' guitar strings. (By the way you can get a single "B" string from your local guitar shop for about $3 and have enough material for about 25 little "pilot pokers".) Actually, though, before you stick anything in there to mechanically clear the jet, you may try just a good shot of carb cleaner with the little wand. Could be something very soft and easily dislodged in there.
 
Hi,
May be the jet needle lost the clip.
So the jet needle fell down blocking the main jet so preventing the passage of petrol.
It happened to me.
Ciao
Piero
 
Biscuit said:
mschmitz57 said:
Huh? A blocked pilot circuit wouldn't cause missing at mid throttle (Needle and slide cutaway are working at that throttle setting).
But a stuck float needle will. Does fuel dribble out of carb when you depress the tickler? Are you using the choke? Are you sure both slides are lifting? Try swapping plugs. Maybe you have a bad coil. Does this bike have points or electronic ignition?
Click to expand...

"mid throttle" was never mentioned. I believe MikeM is talking about NO LOAD/2500 RPM. This is easily achieved with very little throttle opening and almost entirely dependent on the pilot air system. Needle and cutaway have little to no influence here.
Click to expand...

OK, then what magic is making the engine rpm increase to 2500 rpm if the slide and needle have no influence?

When I got my first Commando years ago my pilot jets plugged constantly. I could still ride the thing as long as a blipped the throttle at stop lights or if I nudged the choke lever a tad to keep the engine spinning. But as long as the slides were lifted off the stops the bike would run just fine. Plugged pilot jets only affect idle.

I'm not saying his pilot jets aren't plugged, but there's something else going on here. Mike needs to check the basics first, like fouled plugs, old fuel, stuck float needle, a dead coil. We need more information here. Is the spark plug wet? Will the cylinder fire if you increase the throttle to say 4000 rpm? Does the choke have any affect?
 
mschmitz57 said:
[


OK, then what magic is making the engine rpm increase to 2500 rpm if the slide and needle have no influence?


. Plugged pilot jets only affect idle.

I'm not saying his pilot jets aren't plugged, but there's something else going on here. Mike needs to check the basics first,

?
Click to expand...

It's not magic, of course the needles have some effect. The engine would not run at all with no needles and I did not say the SLIDE did not have influence, it IS the throttle. I said the slide CUTAWAY had little to no influence. Slide cut mostly influences the operation of an accelerating engine under load. Try this experiment...With your bike idling, turn the throttle (slide) screws in a turn. This will raise your slides around 1mm and I'm guessing your RPM will easily approach if not exceed 2500. Cutaway does not matter at this small opening. The increased air under the slide is mixing with air/fuel mix from the pilot circuit increasing RPM. If the pilot circuit is clogged, lifting the slide this small amount will only add more air and still no fuel. You won't get any fire until you have lifted the slide enough to draw fuel from the bowls up through the main and needle jet. (exactly what was happening when blipping the throttle was keeping your bike running).

As far as "basics" are concerned, I should think assuring the pilot jet is clear would be as basic as it gets, before taking carbs apart and messing with coils.
 
MikeM said:
Got the bike out today and after 6 months it started on one kick. Its running on only the left side and intermitently on the right. It kicks in occasionally. Seems to have fuel as it smells pretty bad,
Not sure where to start. 71, 750 recently rebuilt with no issues for the last 2 years.
Wiggiling wires seems to have no effect. I am electrically challenged for sure.
All wires seem to be plugged in.
Where to go first?
Thanks MikeM
Click to expand...

What ignition are you running? If it's a Boyer your problem is a fractured wire from one of the pickup coils.
 
Tried cleaning the pilot jet this AM. Still running on left side. Went for a ride and put it under a load it backfired a couple of times and Im assuming this is the cylinder cutting in and out. Scratching my head. Whats the best, easiest way to switch coils to see if one is bad? This is a points ignition system.
Thanks
 
Easy way is to switch your plug wires to the opposite plug while leaving other end attached to same coil and see if other jug acts like the troubled side
Craig
 
Craig said:
Easy way is to switch your plug wires to the opposite plug while leaving other end attached to same coil and see if other jug acts like the troubled side
Click to expand...

It's "points ignition" so swapping plug wires over won't work.
 
Maybe check throttle cable at the junction block or carb tops. Pull the air cleaner, put your fingers to feel both slide together and turn the throttle to check that they are equal and in sync.

This may seem a little simplistic, but worth a check.

Maybe swap coils. As LAB said, you cant just swap the plug wires. You will need to literally swap the coils out.
 
pete.v said:
Maybe check throttle cable at the junction block or carb tops. Pull the air cleaner, put your fingers to feel both slide together and turn the throttle to check that they are equal and in sync.

This may seem a little simplistic, but worth a check.

Maybe swap coils. As LAB said, you cant just swap the plug wires. You will need to literally swap the coils out.
Click to expand...


I have done that as well. I also put new plugs in before I started it this spring. I switch back to one of the old plugs just to be sure its not that. What it is doing is that when I turn off the fuel taps as it begins to run out of fuel it seems like the cylinder starts to come back just before it dies from lack of fuel. Seems that it is carb related? If the float is stuck wouldnt it leak fuel and run rich but still fire the plug? The pipe is cold to the touch, that is how I know its not firing. The tickler is working. Carbs are the OE Amals. I pulled the slides yesterday and all seems to be fine in there. I also checked the points and ran a file through them. Back to doing some research. Thanks for all the ideas. Keep them coming if you got them. Just wish I knew more about the electrical system.
 
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