Swapped plugs. No change. Measuring ~13V at coil on new battery.Swap your new plugs just in case, measure the resistance in the lead between the plugs, or measure the voltage at each coil with the ignition on.
I tried the WD-40 trick to check for a vacuum leak on the intake manifold. Couldn't detect anything. Regarding the cylinder, I suppose it could be something mechanical here. I did the compression check which looked good and I can see the intake and exhaust valves opening as expected. How else can one diagnosis a bad valve seal, piston seal, or cylinder head seal? The exhaust is the crossover type.If the misfire is proving to be immovable, then maybe it is in an immovable part of the engine,
Inlet tract, —leaks or blockage
cylinder, -valve leaks, ring leaks, cylinder head gasket
exhaust - blockage if not a crossover type.
Champion N3C. I've tried a new set and swapping the old set side to side. So 4 different plugs have been in the non-firing cylinder to no avail.What brand / number spark plugs are you using?
That was an interesting test! Immediately when I connected the white lead to the battery negative it frontfired, scaring the crap outta me! I was able to get the bike fired up, and it ran, albeit on one cylinder, for about 5 seconds then the fuse blew. Not sure if that was supposed to have happened, but it did not get the other cylinder to fire.Could you try connecting the white Boyer box lead direct to the battery? I am assuming your machine is positive earth, so connect direct to battery negative.
This is what led me down the path of not believing it was the carbs. I swapped them side to side. The only component I did not swap was the cable/slide. The body and the needle were swapped. After swapping the fault did not switch sides.Did you swap the carbs, complete with slides, over, or just some half effort with one carb?
How sure are you that the pilot jet is clear? How do you know?
A shot of carb cleaner into the carb when running on the opposite cylinder does get the non working cylinder to fire. I agree Peg that everything points to fuel delivery, but I just can't wrap my head around why swapping carbs did not transfer the fault. Nevertheless I am willing to do a carb rebuild because it is relatively painless compared to tearing down the top end of the engine.I think it might be worth:
a) checking the fuel height in the float bowl.
b) checking that the sealing between the float bowl is not compromised, especially where the fuel transfer port is located.
Sounds like your carb has gummed up passages. 2 products that will work extremely well for cleaning out varnish from old gas are; "Berryman B12 that you can pour into the tank. If you have the carb off the bike, their spray carb cleaner will melt the gunk in the carb very fast. The 2nd option is to put some Marvel Mystery oil in the gas tank. As long as the bad carb is pulling some fuel through, it too will melt that varnish.Hi all,
Finally a warm enough day here for me to fire up the 77 bonnie for the first time in a few months and try out some of the repairs and tweaks I've done. After a few kicks, bike fired up, ran very rough, then died. I did a few quick tests and determined the left cylinder is not firing. I don't think it is electrical (good spark, swapped cables) or valve train (clearances correct), so that leaves me with fuel/carb. I tried flushing out the float bowls and putting in fresh fuel to no avail. The only thing that seems to get the left cylinder intermittently firing is if I give the bike lots of gas, or I hold down the tickler to flood the carb.
Two things I did recently that I think are relevant: change the throttle cable and remove the choke slides from both carbs. I noticed that the throttle cable has excessive slack in it: so much so that it jumps off the mounting point on the grip. So I may need to shorten the cable. I did check that both carbs were in synch by the twist grip when I installed it. Interestingly, the previous throttle cable was not in synch with the slides on each carb: there was about 1/8 inch difference between the left and right slide, so I'm wondering if that is relevant -- as in, did the previous owner compensate for a known issue. Or could this be because I removed the chokes (I have never once used them), which I know lots of people have done, in which case, do the carbs need to be adjusted?
Any suggestions as to how I should go about narrowing this down, so I don't end up chasing a red herring?
If the battery does not hold a charge at 12.2 volts, the battery is dead or dying and can't be revived. New battery.Hmm, I did a quick battery test on my way out this morning. Ignition and headlight on for ~1min dropped the voltage by ¼ - ½ V, so it was reading 12V after this brief test. I'm inclined to replace the battery cause I'm running out of ideas pretty quickly.
Rusty1: Interesting to hear that you also had a one cylinder misfiring issue and turned out to be the battery. Fingers crossed this is the same issue I'm having.
Sounds like your carb has gummed up passages. 2 products that will work extremely well for cleaning out varnish from old gas are; "Berryman B12 that you can pour into the tank. If you have the carb off the bike, their spray carb cleaner will melt the gunk in the carb very fast. The 2nd option is to put some Marvel Mystery oil in the gas tank. As long as the bad carb is pulling some fuel through, it too will melt that varnish.
Have used both products for over 30 years on bikes, cars, lawn mowers and snow blowers. cheap stuff for fast cure.
Tried this -- got a brand new battery, no difference.If the battery does not hold a charge at 12.2 volts, the battery is dead or dying and can't be revived. New battery.
Yup, it is the left, although bike is parked with a brick under the kickstand so it is more or less level. Nevertheless, will proceed with stripping and rebuilding the carb. If that one carb was gummed up, though, it should have transferred the fault to the right cylinder when I swapped carbs, which it did not. So either the tolerance of the right cylinder for a really lean mixture was higher, or it is not the carb and something mechanical in the left cylinder.is it the LEFT carb/cylinder that is the problem? My suggestion would be more likely if it is. When the bike is on a side stand the fuel in the left carb tends to sit longer than in the right carb. That would cause the gunk buildup in the passages.
Hi -- this is next on my to-do list. I'm thinking of just replacing the floats with the Amal stay-up float which seems to be more resistant to ethanol-based fuels. As long as I'm stripping and cleaning the carb, might as well replace some parts in there that will give long life.have you checked floats on bench making sure they aren't sticking up or down flooding or starving
This would be wise, given modern fuel.thinking of just replacing the floats with the Amal stay-up float