How to get 260Z to daily driver status?

[porkbun]

Changed the fuel filter and driving it has gotten a little better, but I think the problem is the fuel pump and its getting worse. Any recommendations besides this universal pump: ( http://www.autozone.com/autozone/parts/Spectra-Premium-Fuel-Pump/1974-Nissan-Datsun-260Z/_/N-iopilZ8vcz2?itemIdentifier=191528_173884_4967_ ) f

[Captain Obvious]

I don't have any input into which fuel pump is the best, but you might be able to tell if your having a fuel delivery problem by checking your float bowl levels.

Is the problem at idle, or somewhere else?

[porkbun]

When I start the car, it idles just fine, but after driving it for a bit, it will die if im not nursing it on the gas. When it dies, im cranking the starter for up to 10 seconds and pumping the gas pedal before any action happens. Its going to a garage that I sort of interned at over the summer which sees a ton of vintage cars (always a different Citroen SM there). Ill have them check everything else while its there.

[Captain Obvious]

Heh. Sounds like a typical "old car sat for a long period of time and now it just doesn't run right sometimes". Still could be just about anything.

Taking it to the shop that has some familiarity with vintage stuff sounds like a plan. Let us know what they find?

[porkbun]

The shop says my carbs are dumping fuel into the engine, so it wasnt that there wasnt enough gas, but that the car was flooding. Theyre going to give me a price for rebuilding the flat tops, but Ive got my eye on a pair of round 240 carbs and im doing the research to find out how much itll cost and what other work needs to be done. Just realizing now that I was only getting 13mpg the past 2000 miles.

Edited October 22, 2012 by porkbun

[Captain Obvious]

Yup. From what little I've heard from others, that's the typical failure MO with the flat tops. They fail rich more often than failing lean. There are lots of things that can cause them to run rich, but not all of them will be addressed by rebuilding the carbs. Depends on what's wrong. If the problem is with your float levels or your power valve, then you stand a chance that it will be better when they're done. If the problem is with the needle or the nozzle, then you're scrod.

You can (and should have already) checked the bowl levels yourself. I assume they're OK. My theory would be that you lodged a goober in one of your power valves when you were doing full throttle donuts. Now the goober is making it stick partially open all the time and dumping fuel into the engine.

You might see if the garage would rebuild the power valves first before they took the carbs completely off the car. You can get the power valves off the sides of the carbs while the carbs are still on the manifolds. You have to get a bunch of plumbing out of the way to get access, but it's the same plumbing that would have to come off anyway if they were to pull the carbs completely.

They could also use a flat plate of metal to completely eliminate the power valves if they wanted to try that. You would lose some full pedal performance, but it might narrow down the problem area.

I'm sure the garage wouldn't be interested in either suggestion, but it's just a thought. :bulb:

[porkbun]

I got the car back, took the power valve off the front carb and the diaphragm was intact, and nothing looked like it was in need of replacing or repairing. I didnt get a chance to check the rear carb (closer to the cabin) behind the air cleaner, but what should I be looking for when I take it apart?

[Captain Obvious]

Been a while since I looked at one of these so please forgive... I'm going from memory here.

There is a tiny slotted head screw with a nut on it. I believe the screw passes through the diaphragm. Under the head of that slotted screw is a small (maybe 1/2 inch diameter?) rubber washer. That washer is the seal that prevents fuel from flowing through the power valve when it's not supposed to. In other words, when the valve is closed, that rubber washer provides the closing seal. I've found that those washers either turn to dust or turn to goo. Probably because of the ethanol added to today's fuel.

Basic function of the power valve:

Vacuum behind the large diaphragm provides the closing force.

The spring behind the diaphragm provides the opening force.

The washer under the little slotted screw head does the sealing.

In order to test the system without the power valve, you can cut a new round gasket without any of the "functional" holes in it and install it between the power valve and the carb body. Cut yourself a round disk out of gasket material and only put in three holes for the three mounting screws. Let the gasket disk block off the small fuel and vacuum holes. (Does that make sense?)

For a more permanent modification, you can make a flat block-off plate. Here's what I did:

You might not want to leave it on forever, but it helps narrow down rich running issues. If you completely block off the power valve, then there the only way fuel can get to the engine is through the main jet (or the choke nozzle, but I'm assuming that's not your problem).

[porkbun]

While checking the power valve on the font carb, I put too much pressure on this hose (in the middle of the picture) and coolant started streaming out. I loosened the radiator cap, the streaming stopped and I readjusted the hose and tightened the clamp. Now im noticing that my car likes to blow out white smoke when pushing it through low rpm in 1st and 2nd gear (up until about 3). I did notice some coolant in the airfilter which im hoping is from when it was spraying when I loosed that hose, but if its not, its from the valve cover breather hose which means theres coolant in my oil. No overheating problems that day I drove it, but right now its parked. Going to try and get a ride to autozone to get a coolant pressure checker and hope its not my headgasket.

[Captain Obvious]

I'm not sure what hose you're talking about. If you're talking about the inch or so diameter hose in my picture here:

then I don't have a good explanation for that... There should be nothing in that hose except air. If you've got coolant streaming out of that hose, then you got real issues.

There are other hoses in that area that are supposed to have coolant in them, but I removed them from the car with that block off plate. The stock setup has coolant running into the carbs to heat them up, and I disabled that feature as well. Are you sure you're looking at the same hose shown in that pic?

[porkbun]

Sorry I forgot to attach the picture:

My power valve is the bottom right corner. Im pretty sure the hose goes back into the top of the radiator. I plan on replacing that hose since it doesnt seem like the most reliable fit right now, but its no longer leaking and the smoking is whats worrying me (diagnosing a car problem online is like trying to diagnose an illness online). Im pretty sure its the droplets in the air cleaner, but ill have to check that tomorrow before I put it into the garage before the storm.

Im looking at buying some 240Z carbs, but they have the individual air cleaners. What happens to all those things connected to the air cleaner if I go the dual air filter route?

[Captain Obvious]

That hose in your pic makes a whole lot more sense. That hose is the coolant input to the front carb. From there, the coolant passes through the front carb - comes out of the front and goes into the rear - passes through the rear carb - comes out of the rear carb and connects back to the hard lines at the brake booster corner of the engine.

If you decide to go the 240 carb route, search around this site and the other Z sites. There is lots of good conversion info available. Will probably answer most of your questions. Not all, but most?