NCross

iTrader: (18)

1980 GS all stock minus charcoal canister and exhaust related emissions.

My problem started on a ten mile drive after installing MSD blaster coils. Stock ignition otherwise. The car started bogging and when i came to a stop it stalled. I restarted it with some work flooring the gas pedal and drove a bit more. Stalls at the next stop. I restart it and get home. I immediately check the coils and all seems to be wired correctly and i am getting spark on all plugs. compression test indicates 95 PSI. On all facings.

I run the engine again with the carb filter off and i notice fuel dumping out of the secondary venturi squirter and an uneven arithmic dribble from the primary on the rear side of the carb. I shut the car off and notice a boiling sound coming from the gas tank and a hissing sound coming from the vacuum line that goes from the gas tank to the pcv valve. I unplug that line and vapors shoot out like you unscrew the gas cap. Pssshhh!

So by my understanding is that the PCV failed and was over pressurizing the fuel system. This caused something inside the nikki to fail and cause overflow from the rear bowl. Im typing this at work so i haven't had a chance to tear into thebcarb yet. what should I look for? Torn gaskets? Stuck needles? Bent float? Should i check the return line? Fbvs?

t_g_farrell

iTrader: (1)

I doubt you have to do anything to the carb. Get the PCV valve fixed and see how it works.

Whats your vent/PCV valve/vacuum hosing routing look like?

j9fd3s

iTrader: (3)

how did you remove the charcoal canister? if you plugged the vent from the tank, the symptoms you describe are what will happen

NCross

iTrader: (18)

The tank vent was routed to the PCV valve. PCV valve failed I guess not allowing the vapor pressure to escape (to the Racing Beat filter) basically the same way as stock via a large vacuum line going to the rubber grommet they come with. I guess the valve jammed in a closed position and built up pressure which caused the bowls to over flow (creating too much fuel pressure).

To update though, I seem to have the problem fixed. I unplugged the fuel vent line from the tank to vent to the atmosphere. I also drilled two tiny (one mm give or take) holes on the fuel filler cap. I think the main problem was that the return line seemed to be clogged up with fuel which require some forceful blowing by me to free it up. Vapor lock from pressure build up? After all this the car runs just fine again. Only difference now is the carburetor seems to make more of a whining whirring sound under light throttle.

j9fd3s

iTrader: (3)

yep! if you have a sealed tank, it'll actually have a vacuum when its running, and low pressure in the tank > fuel pump.

there is even one year (83?) where there is a bulletin about plugged charcoal canisters causing a collapsed fuel tanks

NCross

iTrader: (18)

NCross

iTrader: (18)

That is how its plumbed right now. Incorrect mostly, I know, but it seems to be working just fine. The hard line that the nipple from the intermediate iron and the FBVS goes to is just unused/disconnected. The FBVS is free venting. The tank vent line is free venting. The intermediate iron nipple is going straight to the air filter. The oil filler neck is going to the PCV vave which is now stuck open for the crank vent circuit and going to the vacuum hard line right behind it. e vacuum caps are on the PCV valve just in case. I could probably just delete the PCV and run a line from the filler neck straight to vacuum in that case unless the internals of the valve meter vacuum.


On a side note... the coils are wired correctly, right? One BW wire going to the LEADING + and two BW wires going to the TRAILING +. I think it was the other way around before I swapped coils around, but I dont see how it makes a difference seeing as how it ties into each other anyway. The wire on the TRAILING - is for the tach right? What do the two - wires on the LEADING coil do? Relay trigger?