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Coughs Out After a few miles

  • Thread starter Thread starter Randomize
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Randomize

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Okay guys, here's yet another "won't run right" thread.

Symptoms:
Starts and idles fine. Runs fine for a few miles. Starts to cough out, mostly at high speed/accelleration, running on 3 cylinders intermittently. Pulled the plugs and most look fine although number 3 looks pretty white.

Things I've done:
Valves have been shimmed.
Carbs have been stripped and dipped with new o rings. Mixture screws set at 2.5 turns out. Vacuum synched.
Fuel and vacuum hoses replaced.
All new boots and carb boot o rings.
Sealed the air box and replaced air filter (although I noticed it's dripping oil so maybe I over oiled it?)
Plugs gapped.
Gas cap cleaned out.

Things I haven't checked or replaced yet but will do shortly:
Petcock behaves normally but maybe a clogged filter would do this?
Coils
Timing

Is there anything else to take a look at? As you might imagine, it's been pretty disheartening to do all that work and still have it run poorly :\
 
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Make sure your petcock is behaving "normally" by testing -at least pull fuel line off , turn to prime and watch flow. The petcock filter might be gunked up restricting delivery especially at low tank level. Also try running on "PR" spot and try leaving gas cap loose in case your cap vent cleaning didn't work.
Squeeze excess oil out of air filter .
 
I didnt see anything in the original post about vacuum syncing them..has that been done? If the sync isnt done you may also have the number 3 butterfly closed a tad too much in relationship to the others. This would acct for the "intermittent" firing of that cylinder. You can loosen the adjuster nut and turn the adjuster screw a little with the bike running to see if the #3 fires off better.

And it sounds like the classic fuel starvation symptoms of a malfunctioning petcock on the dying after a few miles. I would inspect it to see if its working right. In the ON position, take a length of vac hose and put on the small nipple of the petcock while holding a catcher under the fuel line nipple. Suck on the vac line to see if fuel flows..should be a good solid stream and not just a trickling. If it just trickles, that would lead me to see what the petcock internal filter looks like..which was already mentioned above.
 
Okay so now it seems to only want to run on 3 cylinders even at startup so the petcock can probably be ruled out (let it sit at prime for a few seconds before starting to fill the floats). Number 4 is the troublemaker. It is getting spark although my coils are only getting about 10.5 volts.
 
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I would get that 10.5 improved. For the moment swap 1 and 4 ht leads and see if the problem moves to No. 1 cylinder.
 
I got back over a Volt to the coils without doing the relay thing but it was a lot of work. Kill switch, ignition switch, fusebox and the wiring plugs at the coils all had to be torn down and sorted. I rode bikes of this era new back then and never had electrical problems. I can only surmise that old age is finally catching up with these machines. I'm fairly confident I have it sorted but have the distinct impression that glass fuses aren't being made to the standards they once were and see a blade box in the future.
 
Mission Accomplished. Got the relay mod done and am now at 12+ volts. It's never ran better! Thanks, guys!
 
Just to follow-up on this thread, I noticed that the voltage at the battery was a little low (13.5v at 4K rpms) so I went to do the stator test procedure only to discover that 2 of the 3 bullet connectors on wiring between the stator and the R/R had corroded and melted into each other. Oops! Replacing those got me a full volt back.
 
you may as well go and do the charging system health mod. what that involves is basically removing the headlamp leg and wire the stator straight to the r/r. and you could go and upgrade that r/r to the sh-775 series r/r. doing this eliminates the potential for electrical contact/wire corrosion and having said connections and wires go way past well done due to the increased resistance.
 
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