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Motor not firing on cyl 1

  • Thread starter Thread starter yoshisakan
  • Start date Start date
Y

yoshisakan

Guest
Hey all, I have started problem threads all over with this bike, but now that I have it idling and revving, I feel like I have found the problem with the rough starts initially. The motor is not firing on 1 as far as I can tell. I pull the wire and the motor doesn't change idle, if I pull cyl 4, the bike dies every time. I have swapped wires, coils, and spark plugs to no avail - the issue seems to be isolated to cylinder 1. I have verified compression and I am almost positive that the carbs aren't the issue. I have also bench synced the carbs. What could possibly be causing this? Even if the cylinder compression was slightly lower, that would make it hotter than the others because the lack of vacuum to the carb would make it lean. All I can figure out is the other cylinder pipes are hot to touch and cyl 1 is luke warm. Thoughts? Note, this is a bandit 1200 motor with bst36ss carbs.
 
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I guess the first step would be to hook one of your original plugs to the wire and see if it will spark off the frame.
I would make sure to keep it back from your tank while doing this.

I am thinking you will get a nice blue spark as 4 fires and you have replaced the coil and wire for that cylinder.

If you do get a nice spark then It is in that carb body.

Either not getting any fuel at all (can check by opening drain screw at bottom of bowl) or a jet is clogged.
You may also want to check that everything is moving like it should.(re-ganged correctly)

Let us know what you find with your spark check and somebody with more experience will hopefully help you out.
 
Crankthat said:
I guess the first step would be to hook one of your original plugs to the wire and see if it will spark off the frame.
I would make sure to keep it back from your tank while doing this.

I am thinking you will get a nice blue spark as 4 fires and you have replaced the coil and wire for that cylinder.

If you do get a nice spark then It is in that carb body.

Either not getting any fuel at all (can check by opening drain screw at bottom of bowl) or a jet is clogged.
You may also want to check that everything is moving like it should.(re-ganged correctly)

Let us know what you find with your spark check and somebody with more experience will hopefully help you out.
Click to expand...

Thanks for the reply here. I have verified that the plug is sparking. I don't know what else could possibly be wrong within the carb body, I've had these apart so many times. I do feel like it has to be the carb though. I swapped slides from 1 and 4, no difference there. I should note that even when the choke is on, the bike was showing the same symptoms. Although with my current pilot circuit settings, the choke bogs down the engine, so i've got it set a bit rich. On cyl1, adjustment of the pilot screw does nothing. Floats are at 16.5, and there is fuel in the bowls. I bench synced the carbs last night, theyre opening like they should.
 
Maybe ill break them down again and boil the hell out of carb1. I did drill out the pilot air jets to 1.5mm, i guess theres the possibility that theres some brass clogged in there.
 
I'm not ruling out the spark issue either though. When I pull the wire and the bike is running, the motor will shock you if you touch it, I mean is that normal? The engine case is grounded in 2 places with new wiring.

I'm going to get some starting fluid tonight, spray it in through the carb to the engine and see if I can see a difference in idle. If so we can put the electrical problem to rest.
 
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After spraying some starting fluid in through my nitrous fogger, I noticed that while spraying, the revs would increase and it would stumble less. I also noticed if i pull the wire from cyl1 for a bit and touch it back, the revs increase. It is definitely a fuel delivery problem. Going to test compression and go from there.... Also I just realized that when I had the head apart to clean the valves and replace the seals, I don't think I adjusted the valve clearance. I'm hoping after I run the comp check that it comes up low on that cylinder, and that its not the piston ring, but the valve clearance. We shall see.
 
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125, 140, 130, 125 after valve adjustment. Numbers are after 5 cranks.
 
That made no difference. Boiling the carbs for a second time. I'm about ready to part the bike out, in all seriousness.
 
Have you done a sync on the carbs? If the butterfly on #1 is not as open as the others, you won't be drawing the fuel you need. Is the float height set correctly?
 
Floats are 16.5, I did a bench sync only. Put the needle clip as low as it go and it revs really nice now, going to drop it one groove and I think it'll Rev perfect.
 
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Is there a way to use a compression tester gauge to balance the carbs? I have nitrous foggers on the intake that I could hook a hose to. I would only be able to set one at a time though. Trying to avoid spending money on an expensive tester.
 
The best tool for the job is the Morgan Carbtune from the UK. They're expensive but not outlandishly so and one will last you a lifetime. You will be syncing your carbs more than once.

Four ordinary vacuum gauages will probably work okay but then you need to deal with mounting them to something. You will need restrictors on each of the hoses and they will probably have to be calibrated before each use.
 
I hooked up vacuum gauges, they worked perfectly. I reset my dyna 2000 timing to 40deg total and took it for a test drive on 3 cyl. I took it to red line, missed a shift and got off the highway. After coming to a stop I noticed my revs went from 3k to 6k and the bike was firing on all 4. I put 50 miles on the bike today and it's running like a champ. I can't for the life of me figure out what happened to fix that cylinder. The damn thing went from running like a mule to doing power wheelies.
 
For science, can anyone speculate as to what may have been the cause here?
 
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