running on 3?

[steveq]

gidday guys, i hope you can help as this problem is the only thing left to do.took my 77 gs 550 for a quick spin around the block- definate lack of power on returning home, i noticed that numbers 1,2, and 4 header pipes were hot to the touch, but no. 3 was only warm, also, on removing spark plugs, all had colour except for number 3, the plugs were wet just no colour on number 3. ive cleaned and adjusted the carbys correctly and the bike starts second kick from cold. just seems to be only running on 3. could i have a faulty coil? also, i havent checked the timing yet -could this be part of the problem? thanks regards,steve.

[tom203]

gidday guys, i hope you can help as this problem is the only thing left to do.took my 77 gs 550 for a quick spin around the block- definate lack of power on returning home, i noticed that numbers 1,2, and 4 header pipes were hot to the touch, but no. 3 was only warm, also, on removing spark plugs, all had colour except for number 3, the plugs were wet just no colour on number 3. ive cleaned and adjusted the carbys correctly and the bike starts second kick from cold. just seems to be only running on 3. could i have a faulty coil? also, i havent checked the timing yet -could this be part of the problem? thanks regards,steve.

Just so we all agree- #1 carb is on left, under clutch hand? Does this bike have a vacuum operated petcock? If so, where is the vacuum hose connected?
A faulty coil would likely show up on two cylinders- timing problem is unlikely, but you could also have misadjusted valves.

[Big T]

On your 77, the VM carb vacuum line goes from #3 to the petcock. Is that line attached? Does it have gas in it? Is your crankcase oil level overfilled?

All of the above are signs of a faulty petcock, which can affect cylinder #3


The coil itself is not bad, as it is firing #2, which is on the same coil. The #3 coil wire could be bad. Have you checked for spark on #3? Swap the plugs around and see what happens.

Timing being off shouldn't affect #3, as #2 fires off the same point. However, your timing should always be spot on if you want the motor to last. You do have points?

[steveq]

gidday, just went out and lifted the tank to check the vaccum line,although it hasnt been started since last nite, should there not be at least a small amount of petrol residue in the line itself?when i removed the line from the tank and inverted the hose, it was empty-no fuel does this mean fuel tap problems conected to number 3 cylinder?regards, steve

[tom203]

gidday, just went out and lifted the tank to check the vaccum line,although it hasnt been started since last nite, should there not be at least a small amount of petrol residue in the line itself?when i removed the line from the tank and inverted the hose, it was empty-no fuel does this mean fuel tap problems conected to number 3 cylinder?regards, steve

Nope,not a good test, cuz it could all drain to #3 carb as it sat.This is a vacuum line- it should have no fuel in it. Plug the fitting at the carb end and at petcock and take a spin ( dry off #3 plug). But first, remove oil cap and take a whiff- does it smell like petrol? Is oil level higher than usual?

[Big T]

gidday, just went out and lifted the tank to check the vaccum line,although it hasnt been started since last nite, should there not be at least a small amount of petrol residue in the line itself?when i removed the line from the tank and inverted the hose, it was empty-no fuel does this mean fuel tap problems conected to number 3 cylinder?regards, steve

Sorry,mate, but you've got to answer all the questions!

Not just one!

Shouldn't take you more than 15 minutes to check all that

[steveq]

thanks,i just got home so i started her up and done a plug test -taking the plug cap off numbers 1,2 and 4 the motor wanted to die, when i did the same to no.3 no difference, so started her up and removed cap to no.3, put in a good plug and there is real good spark- so that eliminates that, so i took your advice and checked the oil, only slightly higher,but it definately has a fuel smell im guessing that all this points to a faulty petcock vaccum? i'll remove the tank and test the vaccum by doing the suck/blow test on the vaccum line-is this the correct proceedure? what i dont understand is - why a faulty vaccum only affects number 3 carby and not the rest? kind regards, steve

[Billy Ricks]

The reason the carb/cylinder with the vacuum line is affected is because there is a diaphragm in the petcock that leaks and the fuel ends up in the vacuum line.