Some good mechanic will know the answer to this....

[chuckycheese]

Several weeks ago, my bike was popping and sputtering badly. I noticed that even after running for several minutes, pipe #4 wasn't even warm. I also noticed that if I pulled the plug wire from #4 while it was idling, it had no effect on the way it ran.

So.....I cleaned carb #4 really well and put everything back together. The problem seems to be solved and it runs fine....but: Now that it runs fine, I notice that if I pull the plug wire from #4 while it is idling, it will die immediatly.

That leaves me completely stumped and I'm suspecting that maybe the problem had nothing to do with the carb itself but, rather, something else. So my question is: Why would the engine not die when I pulled the plug wire from a non-functioning carb...but will die when I pull it from the carb, now that it's working?

There's got to be a simple answer but I can't imagine what it is. I'm hoping someone can help me out because I feel like I really may need to know. Thanks, all!:-D

 

[nert]

You probably have the Sync screw too enabled for that carb and it has become the bassis for your current idle speed.

 

[49er]

When you cleaned #4 carb I presume you cleaned the others as well. When reassembled, did you re-tune and re-sync them? You may have changed the air/mixture screw settings and the sync from the settings that you had when the fault was diagnosed. If so, #1-#3 may be sharing less load and causing the engine to stall when the #4 plug lead is removed.
Another thing to check is your valve clearances. If #4 carb was faulty but the clearances were right, it may cause the engine to die if the others are too tight when the plug lead is removed. Do a compression check when the engine is hot and with the throttle wide open. Readings should be in the range of 125-175psi. If they vary more than 20psi, check your valve clearances.

 

[chuckycheese]

Thanks

Thanks

Thanks for the replies; I will try to respond to each of them.
The idle has not been adjusted. The bike will not run with #4 (or any of the other 3) pulled...at any RPM.

I can almost completely disassemble #4 on my bike without removing the rack. This isn't ideal but, considering how recently and how thoroughly they were last cleaned, it seemed like a good idea just to work on the one that wasn't working.

No valves were adjusted, nothing was re-synched and no air screws were tampered with since I assembled everything. The only two things that I've noticed are: It now runs on all 4 carbs..and the bike won't run with plug wire #4 removed (whereas it did before).

Thanks, again, for your suggestions!

 

[Road_Clam]

Several weeks ago, my bike was popping and sputtering badly. I noticed that even after running for several minutes, pipe #4 wasn't even warm. I also noticed that if I pulled the plug wire from #4 while it was idling, it had no effect on the way it ran.

So.....I cleaned carb #4 really well and put everything back together. The problem seems to be solved and it runs fine....but: Now that it runs fine, I notice that if I pull the plug wire from #4 while it is idling, it will die immediatly.

That leaves me completely stumped and I'm suspecting that maybe the problem had nothing to do with the carb itself but, rather, something else. So my question is: Why would the engine not die when I pulled the plug wire from a non-functioning carb...but will die when I pull it from the carb, now that it's working?

There's got to be a simple answer but I can't imagine what it is. I'm hoping someone can help me out because I feel like I really may need to know. Thanks, all!:-D

So how does the engine behave when you try to pull the other 3 plug wires? An in-line 4 engine should not completely stall from pulling only one sparkplug wire, unless you have another cylinder(s) not firing either.

 

[chuckycheese]

So how does the engine behave when you try to pull the other 3 plug wires? An in-line 4 engine should not completely stall from pulling only one sparkplug wire, unless you have another cylinder(s) not firing either.

Yeah, I thought about that, too. When I checked (which was after #4 started working), it woudn't run with any single one unplugged...but before I worked on it, it would run pretty well with #4 unplugged. It really puzzles me!8-[

 

[Dink]

Have you considered NOT doing that!!!:shock: :-D

Dink

 

[Boondocks]

My first advice would be to quit worrying about it, leave it alone, and go for a ride.

If you must have a theory of what could have changed:

a. It wasn't running on one cylinder but could idle on the other three.
b. When the carb was cleaned and the cylinder returned to action, the idle speed should have increased substantially.
c. Did you reduce the idle speed to the normal range after all four cylinders were operational?
d. If so, that's the answer. No normally tuned bike should idle on three cylinders unless the idle adjustment had been increased enough to overcome the resistance of a non-firing cylinder.

 

[flyingace]

My first question would be did the idle speed go up once you got the #4 cylinder to fire? It should have gone up 20-25% once the additional cylinder started running. Additonally, are you saying a fully warm bike idling at 1000-1100 RPM just dies when you pull one plug cap? That would be unusual and indicate a possible electrical problem.

 

[chuckycheese]

My first question would be did the idle speed go up once you got the #4 cylinder to fire? It should have gone up 20-25% once the additional cylinder started running. Additonally, are you saying a fully warm bike idling at 1000-1100 RPM just dies when you pull one plug cap? That would be unusual and indicate a possible electrical problem.

Yes, and that's part of what has me wondering if the carb was ever the problem.

 

[chuckycheese]

My first advice would be to quit worrying about it, leave it alone, and go for a ride.

If you must have a theory of what could have changed:

a. It wasn't running on one cylinder but could idle on the other three.
b. When the carb was cleaned and the cylinder returned to action, the idle speed should have increased substantially.
c. Did you reduce the idle speed to the normal range after all four cylinders were operational?
d. If so, that's the answer. No normally tuned bike should idle on three cylinders unless the idle adjustment had been increased enough to overcome the resistance of a non-firing cylinder.

I'm not losing any sleep over it and I did take it for a nice ride yesterday but, as I said in my previous post, if the carb wasn't the problem, I think it would be very prudent to figure out what is was. (And no, I didn't notice any appreciable change in the idle speed.)8-[

 

[Dink]

Test voltage to the coils. You probably had more than one problem to start with.

Dink

 

[chuckycheese]

Coils

Coils

Thanks, Mate...in the beginning, I did switch the wires on #1 and #4 (and the problem remained with #4) so I figured it must be something else...is that right?

 

[Dink]

Thanks, Mate...in the beginning, I did switch the wires on #1 and #4 (and the problem remained with #4) so I figured it must be something else...is that right?

Yep this would normally exclude that coil; note only that coil, as being "the Problem". It only takes a small voltage drop;i.e. 11.8V to have an effect. Please check the voltage, as if it is OK you then should look at the idle circuit of the carbs, all four.

Dink

 

[chuckycheese]

Thanks

Thanks

Thanks, again, Dink. I'm unable to do that today but should be able to in a day or two (I'm one place and my bike is in another). I've rebuilt carbs a number of times but don't know what you mean by the "idle circuit".

 

[KEITH KRAUSE]

Several weeks ago, my bike was popping and sputtering badly. I noticed that even after running for several minutes, pipe #4 wasn't even warm. I also noticed that if I pulled the plug wire from #4 while it was idling, it had no effect on the way it ran.

So.....I cleaned carb #4 really well and put everything back together. The problem seems to be solved and it runs fine....but: Now that it runs fine, I notice that if I pull the plug wire from #4 while it is idling, it will die immediatly.

That leaves me completely stumped and I'm suspecting that maybe the problem had nothing to do with the carb itself but, rather, something else. So my question is: Why would the engine not die when I pulled the plug wire from a non-functioning carb...but will die when I pull it from the carb, now that it's working?

There's got to be a simple answer but I can't imagine what it is. I'm hoping someone can help me out because I feel like I really may need to know. Thanks, all!:-D

If #4 carb was running rich due to a loose jet or blocked air passages, then that rich mixture would foul the plug. You'd have no spark to begin with so pulling the plug cap off would make no difference.
Now that the cleaned carb is allowing a correct mixture and therefore a good spark, pulling the cap off forces it to run on three cylinders. Many bikes will run on three or even two cylinders if you keep throttling them, though not well of course. Many other bikes won't run at all on three cylinders because they're not in the best of tune to begin with or are still warming up.

 

[chuckycheese]

Thanks

Thanks

Thank you, Keith. That seems to make a great deal of sense!!:-D

 

[tateG]

Have you taken the plugs out and cleaned them since this all happened? I have noticed plugs in bikes can make a much more substantial difference in the way the motor runs than a car engine.

For example, a friend bought a super nice low mileage Honda CB350, could not get the thing to start. Checked the carbs, gas flow, and even checked the spark; all seemed good. Called my motorcycle mechanic friend and he told me to get two new plugs and it would fire up, and sure enough he was right. The old plugs looked ok and had spark, but I guess it was weak and wouldn't fire the bike. New plugs and it fired off immediately, no other changes.

ANyway, new plugs are worth a shot. I know my bike can idle on three cylinders, but that problem was due to a plug boot that was loose where it connected to the wire.