78 cb550k 605cc bore misfire...

[photoputz83]

so i had a little issue with a strong misfire that would lead to stalling out after. it seemed like it would only happen when the engine was hot or when i hit high revs while riding and then let off. there were a few occasions where i would try to start it again and then the battery would almost be completely drained. i ended up going all out replacing the coils, the ignition (dyna s), and eventuallly the entire engine as i wanted to have more spare parts on hand or to rebuild so when one engine messes up or needs a rebuild i would have one to drop in. well after all of this was done it seems like the misfire hasnt got any better. i pretty much chainged everything but the carbs which have been cleaned, the wire harness, and the rectifier. would the rectifier cause a misfire for any reason. im looking for any ideas as to what may cause this to happen. the riding season is almost at its end so any help would be halful at this point.

[crazypj]

Fuel tank cap vent

[photoputz83]

actually on the 78 there is a door that covers the cap. it isnt out in the open like the 550s from the previous years. there is a hole in the tank under that door next to the gas cap and it is clear at this point.

[Geeto67]

quote:Originally posted by photoputz83

actually on the 78 there is a door that covers the cap. it isnt out in the open like the 550s from the previous years. there is a hole in the tank under that door next to the gas cap and it is clear at this point.

yeah? really? you are confusing the fuel door drain for the tank cap vent?

1) the fuel door doesn't seal airtight over the cap. Least it shouldn't

2) your cap should still have a vent in it otherwise it is a sealed container.

3) learn the parts of fuel tank and how it works.

[jaguar]

when you say miss fire what do you mean?

[photoputz83]

the drained battery and misfire would not be an issue with the fuel or supply. i am getting enough fuel to the engine as i am running a little rich at idle and almost perfect at 3/4 to full...

quote:Originally posted by Geeto67

quote:Originally posted by photoputz83

actually on the 78 there is a door that covers the cap. it isnt out in the open like the 550s from the previous years. there is a hole in the tank under that door next to the gas cap and it is clear at this point.

yeah? really? you are confusing the fuel door drain for the tank cap vent?

1) the fuel door doesn't seal airtight over the cap. Least it shouldn't

2) your cap should still have a vent in it otherwise it is a sealed container.

3) learn the parts of fuel tank and how it works.

[photoputz83]

the engine runs fine in normal conditions or atleast it did. the misfire from what i am feeling is a shudder and then refusal to spark / ignite the gas. the it seems to start happening when i push the bike pretty hard, and after i let off is when things all start to go downhill. i know it isnt the coils, or the ignition as it is timed correctly, and both are new. i do however suspect something electrical which is why i was wondering about the rectifier.

quote:Originally posted by jaguar

when you say miss fire what do you mean?

[photoputz83]

oh and i ran it with the gas cap off and it did the same thing.

quote:Originally posted by Geeto67

quote:Originally posted by photoputz83

actually on the 78 there is a door that covers the cap. it isnt out in the open like the 550s from the previous years. there is a hole in the tank under that door next to the gas cap and it is clear at this point.

yeah? really? you are confusing the fuel door drain for the tank cap vent?

1) the fuel door doesn't seal airtight over the cap. Least it shouldn't

2) your cap should still have a vent in it otherwise it is a sealed container.

3) learn the parts of fuel tank and how it works.

[mlinder]

Connect multimeter to battery terminals.
Tape multimeter to middle of handlebars.
Go ride, check voltage when misfire happens.

[Geeto67]

Not saying your misfire has to do with the vent, just saying you identified and checked the wrong parts.

The cap has a vent so your petcock can feed fuel without creating a pressure problem. The gas door is there to prevent the bike from dousing you in gasoline in case of a front end accident. The hole near the gas cap is just in case you spill fuel filling the bike up or you ride through a rain storm and need a place for the water that collects under the door to drain.

Misfires are caused by two things fuel or spark. Running it with no gas cap eliminates it being a vent problem.

Have you checked your spark advance mechanism? Might be hanging up.