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Left '79 GS550 Carbs in Prime

B

bill_face

Forum Apprentice
Hello all. This is becoming a theme recently of me asking for help with idiot mistakes I've made, so I thank you in advance.

So I recently rebuild my engine and just got it all back together and put the carbs back on and put the petlock PRIME position before starting the engine. As the title suggests I forgot to move it to ON. I took it for a little ride, and got home parked it up, and left it for around 4 hours.

I went back into the garage and found a puddle of petrol under the bike. I observed petrol alternately running out of 1 & 2 carb overflows, with gaps between runs. I then noticed was still on PRIME and turned it to ON. Then I disconnected the tank. As I wasn't sure how the prime featured worked I came and did a search here.

I've found out that in this scenario the fuel can get into the engine, and i was presuming it was just going to run out of the overflow. I was most concerned that my starter motor would be submerged in petrol as I don't have the overflow pipes on. I can't really verify this.

I have emptied the oil which isn't obviously runny, but I have measured around 2.55litres, when the full capacity is 2.4litres. I pulled spark plug 4 and didn't see a lake of petrol in there. Spark plug was also dry.

I have read about removing the spark plugs and turning the engine, then changing the oil. Which I would have no problem doing except one of my spark plugs (no3) is threaded and stuck in. Having just spent ages rebuilding it I was going to leave it in there until I have time to do something about it.

Is there any other workaround for this problem? Can I just turn the engine with 3 spark plus removed, assuming I don't find the other two full of petrol.

Incidentally is there a drain hole in the bottom where the starter motor sits. I seem to remember one, but can't be sure?
 
Pull the 3 plugs and see if anything comes out.
Yes, there is a drain under the starter
Smell the oil to determine if the oil is contaminated
 
You most likely have float valve(s) sticking or out of adjustment as well. Even on prime, properly working float valves should stop the flow of fuel as soon as the bowl reaches its set level.
 
Be sure the bowl gaskets arent rubbing against a float, the float needles rise and fall as you lift the floats, none of the needles "hang up" on the floats as you actuate them. To see if the petcock has gone south heres how i test them. Get two lengths of tubing and put one on the fuel line nipple and one on the vacuum nipple. Put one hose in a dry clear soda bottle and the other into a second bottle. Petcock in ON position and let it set 24 hrs or so..then check each bottle for fuel. If one has fuel in it youll know what section of the petcock has malfunctioned. If alls dry then the petcock is good...just never leave it on PRI once it starts again.
 
Carpetbagger..theres a myth about float needles. They ARENT designed as shut off valves..they are designed as fuel REGULATING valves when the bike is running. Even the very best and newest needles will allow fuel to seep past them over a period of time if the petcock is left on PRI. They simply cant withstand the gravitational weight of the fuel above them.
 
^^ mm, I dunno. I don't think a needle that is "regulating" should let any gas past beyond demand. How can it regulate to a set level if it is letting gas pass in any amount? That is, what is the "acceptable" leakage?
I think float needles and their seats in good condition should stop the flow of a full tank at least well enough to park the bike for the day. In fact I've got several examples of rubber-tipped needles that stop it too well and get stuck (I hate rubber-tipped needles- they save the non-replaceable seats but if you leave the tap on with a full tank they seem to jam themselves tight!)
But metal needles on metal seats do wear....

...that said, machines with gravity feed and simple no-vacuum taps I've had have all had an OFF position on a tap but this doesn't mean I have to shut the tap off everytime I park unless the needles and seat are worn. The tap is there to make tank removal possible as much as it is to stop fuel flow or switch to reserve.
 
I've also had a few machines with on/off/res petcocks, and properly set up and maintained, never leaked gas even though I never switch to off when parked.
 
Thanks for all the input guys.

I've changed the oil and got it going again.

When I saw the carbs overflowing it was only coming from two of them. I was told when it's in prime it might take the fuel from the reserve feed, and so could have picked up a bit of crap that was stopping the needles from shutting off. So I gave the carbs a quick clean.

This petlock doesn't have off. Just On/Pri/Res, and removed from the bike the tank doesn't run on On.
 
bill_face said:
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This petlock doesn't have off. Just On/Pri/Res, and removed from the bike the tank doesn't run on On.
Click to expand...

"On" position is really something like 'Auto Off and On Based on engine vacuum' .
Is Off when no engine vacuum, and is ON when do have engine vacuum (hense why the small tube to number 2 carb).

About not leaving it in PRIme position: I left it on PRIme more than once, then and ever since; I now force myself to not remove my fingers from the lever when put it in PRIme. Yep, I stand there and hold it for a minutes then put back before doing anything else.

.
 
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