Gas overflow, idle gone bonkers, hesitation/stuttering when accelerating

895 Views 4 Replies 4 Participants Last post by cannonball89, Mar 21, 2011

herbsteiner

Discussion Starter · Mar 20, 2011

Newbie needs help!

Weird things started happening to my Z and before I go to the mechanic, maybe I can get some info from the forum. I'm a newbie, so please be patient with me. I've already done the search thing but it's still not clear to my dense, uneducated brain.

First, the car: A 1973 but with '72 round-tops and the emissions stuff removed and holes plugged. 3-speed automatic. Last visit to the Z mechanic was about 2 months ago. The car is a daily driver.

Now the problem: I recently noticed some intermittent hesitation and stuttering when accelerating, so I thought some kind of fuel delivery problem. Extremely strong smell of gas. Then the idle would vary wildly in neutral from 800 up to 1400, but intermittently. When put in gear it would sometimes run great and other times want to stall in stop-go traffic, cycling down to 500 rpm before stalling. Seems like these symptoms would occur after driving for awhile. Previously... last week... the idle in neutral was around 900rpm and in gear around 700 without stalling.

Today when I opened the hood and pushed on the throttle, gas would spew from the overflow hoses onto the tranny housing. I opened the gas filler spout and back pressure released either gas pressure or actual gas from the spout.

Fuel filter looks okay. So what does the wisdom and knowledge bank of the forum think is the problem these symptoms resemble? I really don't want to drive much with raw fuel draining onto the ground.

Please excuse my ignorance, I didn't get much info I could digest from the search.

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74a2z

· #2 · Mar 21, 2011

sounds like there is a plug somewhere in the fuel tank vent system. if u remove the interior panel on the rear passenger side along with the rear inside taillight cover, you will have access to the vent tank and most of the vent hoses. they are most likely very dry and brittle and possibly plugged. also check where the vent tube goes into the filler neck, as its easy to get plugged if something gets into the filler tube. if the vent hoses from the fuel tank to the vent tank need replacing, DO NOT use heater hose as they are not compatable with fuel. you can often find fuel hoses the correct size from a boat supply repair place.

the return line that is leaking onto the tranny shouldn't be, check for cracks/cuts etc. you should also check the evap canister behind the passenger grill for plugged lines.

and as always, pick up a fsm or a haynes manual, they come in very handy locating where things are and what they do on the car.

g'luck and keep us posted!

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speednick

· #3 · Mar 21, 2011

The FPR needs to vent excess pressure back to the tank soooo, check that line clear OR spew gas overpowering the needle and seat which causes flooding/fouling. The return IN the tank is frequently plugged, too!!
Nick

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herbsteiner

Discussion Starter · #4 · Mar 21, 2011

Gentlemen
Thanks so much for the info. I now can speak to my mechanic with a bit more knowledge under my belt.
hs

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cannonball89

· #5 · Mar 21, 2011

Just so were clear, the FPR on early carburated Z's is the fuel rail itself, most specifically the tiny hole at the end of it on the return side. That tiny hole is easy to clog. Take a needle and make sure you can fit it through there first.

Also, spewing raw fuel is unacceptable under any circumstance. Nissan designed the aircleaner housing to catch the fuel in the event of overflows like what you are experiencing, so please route the lines coming from off of the float bowls to the respective holes on the aircleaner IMMEDIATELY. The WOT vacuum on the intake will also arguably improve the function of the float bowls when they are introduced to it, at least thats how it was designed and seems to work great that way.

Take the top off of the float bowls and ensure that one of your floats is not sticking down, that would definitely cause the overflow you are experiencing. I would give them both a thorough cleaning and inspection. A pinhole in the float itself would prevent it from closing the needle and cause an overflow too. Before reinstalling check the float level per the FSM.

The pressure in the gas tank may be related or it may be a seperate issue. Make sure that the vapor valve under the coil in still intact and the hoses are going to the right places, one to the vent line from the tank, one to the aircleaner, and one to the crancase breather. When you say that emmisions stuff has been removed it usually translates to "essential safety and reliability equipment has been removed" An example of that would be the float overflows venting to the ground.

Good luck, and be careful whenever dealing with gasoline.

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