carbs backfiring

I started out at 3 turns out, then I went to about 3 1/4, I was told on this site that 3 to 3 1/2 turns out is factory for these carbs. I will check the number on the frame. According to the tag on the frame the bike was manufactured in 11/79.

The carbs have chrome tops, brass slides and black rubber/plastic floats and are set at 22MM.
 
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Your bike is a 1980 model. Bikes are like cars - the current model year begins production in the Fall of the previous year. BS34 carbs are correct for your model however the 1980 versions had brass floats. The plastic floats can be swapped in, which may be what's happened to yours, or a whole later carb set could have been mounted. No matter really, the float type is the only major difference between the 1980 and later BS34 carb sets. All the other jetting specs are the same. At 22mm, you have the plastic floats set correctly.

You're only a few sizes over stock on your mains so changing a size shouldn't effect starting. What might is the pilot jet size. That is for your low speed circuit. The 47.5 may be too big. Personally, I'd start out with 45 pilots and 137.5 or 140 mains. With your mods, the bike should run with those sizes. They should be close to what you need.

You say the spark plug caps look good but they are 30+ years old. They can and do go bad. Their resistance starts increasing and eventually that starts to choke off the spark. I would replace them. Most of us use NGK 5K ohm resistor caps.
 
Well, im stumped! I put in the 45 pilots, 137.5 mains, the floats are set at 22MM, checked for spark, got spark, battery is fully charged, got good plugs, I even swapped out the wires and caps with ones I had laying around, still wont fire, took the plus out, they do smell like gas, I even tried some starter fluid, not a sign of firing, it turns over good but won't fire. Could it be the valves I set them at .002" intake and .004" exhaust. Could I have blown something electrical, the fuses are fine.

What is strange is Its been starting great when I pull the choke all the way out, now with the choke all the way out, it just cranks no fire!!!! Im at my wits end!!!!:banghead:
 
When i was putting my carbs on i was using pop bottle. It was causing vacuum in the bottle as it was sucking the fuel out because i didn't have a vent on the bottle. This caused back firing through the carbs. Long story short, is your gas tank vented properly?
 
I dont know, if I leave the cap open and try to start it would that make a difference. also, is it possible when I rode it yesterday could the valves, if not tightened down enough go out of setting, it started fine yesterday, ran ok, then stalled, no start since.
 
If you mean the lock nuts on the valves were not tightened enough then absolutely they could go out of what you set them at.
 
xs650dude63 said:
I dont know, if I leave the cap open and try to start it would that make a difference. also, is it possible when I rode it yesterday could the valves, if not tightened down enough go out of setting, it started fine yesterday, ran ok, then stalled, no start since.
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Started yesterday and no start to-day...................that is classic loss of power to the ignition. Does your bike still have the original 4 position fuse panel with glass fuses?
You can't tell if they are good just by looking at them. They can appear to be OK but the spring clips can have high resistance and the resulting voltage drop. Its best to replace them with automotive blade type fuse holders.

You could test this by using temporary jumper wires bypassing the main fuse and the ignition fuse.
 
It does have the original fuse panel. I can try that, but I don't know how, is there somewhere on this site that has a diagram?
 
I always thought that if you have spark and you have fuel the motor should start, the bike has electronic ignition, no points, I don't mean to sound dumb, but what else could it be? Thanks!
 
xs650dude63 said:
I always thought that if you have spark and you have fuel the motor should start, the bike has electronic ignition, no points, I don't mean to sound dumb, but what else could it be? Thanks!
Click to expand...

Its not that simple. I think you have intermittant spark. Here one minute and gone the next. Those kind of faults can drive you crazy! You have to replace or check one item at a time to eliminate the actual fault.

Many lads with electrical problems, always say their original 4 position fuse panel looks good to them. Yes, that is the trap.................they look good visually, but they are intermittant electrically. Don't even think about this, just replace that old fuse panel with new automotive blade type fuse holders.

OK once the fuse panel has been replaced, you must look at other items. The ignition switch itself can be faulty; it can be taken apart and checked/cleaned. Also the kill switch may be worn out and falling apart inside.

If all the above has been checked, then the TCI black box (ignition) could be worn out after all these years. The ignition coil itself may be failing.

Sometimes the small magnet on the rotor becomes weak, which means the TCI does not get proper trigger pulses. You can test by unplugging the the rec/reg unit to see if the engine starts and runs better. Charge the battery fully and unplug the headlight for this test.
 
Good information, thank you, once I get the new fuse panel, I will probably have to splice new wires to the ones leading to the panel, what gauge wire should I use?
 
xs650dude63 said:
Good information, thank you, once I get the new fuse panel, I will probably have to splice new wires to the ones leading to the panel, what gauge wire should I use?
Click to expand...

You can use 14 gauge for the main 20 amp fuse, and 16 gauge for the other three 10 amp fuses. Solder the connections and use heat shrink insulation.
 
I got it started, I replaced the spark plugs and put in a new ignition fuse, I put in 47.5 pilots and 137.5 mains, mixture screws 3 turns out, its idleing at about 1400 rpm's drops down to about 1000 when put in gear, I am getting a little bit of popping out of the exhaust.
 
xs650dude63 said:
I got it started, I replaced the spark plugs and put in a new ignition fuse, I put in 47.5 pilots and 137.5 mains, mixture screws 3 turns out, its idleing at about 1400 rpm's drops down to about 1000 when put in gear, I am getting a little bit of popping out of the exhaust.
Click to expand...

Good to hear! Be sure to replace that old fuse panel.
 
xs650dude63 said:
I got it started, I replaced the spark plugs and put in a new ignition fuse, I put in 47.5 pilots and 137.5 mains, mixture screws 3 turns out, its idleing at about 1400 rpm's drops down to about 1000 when put in gear, I am getting a little bit of popping out of the exhaust.
Click to expand...

Try turning the mix screw out 1/4-1/2 turn...see if that helps with popping.
 

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