Mark Maras

Have you looked for a totally rusted out but reasonably complete 510 and join the two?

Thanks for the trip in the Way Back Machine. 1970, BST concert, in the Seattle Center. We got front row seats right in front of the horns, the stage was about 4' high and about twenty feet away.

4.3 p.s.i. won't supply any more gas to the carbs than 3.2. The carbs only take as much fuel as the engine can use. The needle valve in the float chamber shuts off the fuel when the fuel reaches the preset float height and only dribbles a tiny amount into the float chamber to keep the fuel at the preset float height while you're driving. Stumbling, popping and sputtering is NORMAL behavior in a cold engine with little to no choke, even in Panama. These symptoms could actually be a very good sign that your engine isn't running too rich. And if you're going to tell me that you didn't have to use the choke before, forget it. It ran like crap before. Two questions for you. Does the engine run and drive reasonably well when it's cold with the choke on? How does the engine performance feel when the engine is warm and the choke is off.

Don't adjust the idle. Use the choke when the engine is cold, That's what it's for.. Your description of a problem, ISN"T a problem. Does it run OK cold with the choke on?

Jalex, I'm curious about something. Who convinced you, or how did you convince yourself, that 3.2 p.s.i. isn't enough fuel pressure? We used to run an econo-rail dragster with a 327 c.i. V-8 Chevy and a Holley carb. with 3 p.s.i. Roughly twice the cubic inches as a Z and the 327 was always run at full throttle. There was never a fuel starvation problem.

IMHO, Absolutely perfect. Stance, height, offset, finish, you nailed them all. Can you give us more info about the wheels, tires, springs and shocks?

Step 1, Read post, # 31. Step 2, Put the calipers down. Step 3 , Floats installed, Remove the domes and pistons. Step 4, Using a flashlight, visually determine the fuel level in the nozzles. Step 5, Adjust the float tangs up or down until the fuel levels in the nozzles are 1/16" below the nozzle tops. Nozzles are 2 1/2 turns down during this procedure. Also, after each adjustment, move the floats up and down to ensure smooth operation, remove a little fuel from the bowls, reinstall the floats, crank the engine over or start it up for a few seconds to fill the float bowls to the new level. Recheck the fuel level in the nozzles.

No need to run the car for two minutes. In reality you just need to fill the float bowls to the new setting. if you're lowering the float setting be sure to remove some fuel from the bowls so they can refill to the new level. If you haven't readjusted the floats just pull the lids and measure with a caliper and readjust. I've not used the 10 turns down previously but here's my understanding of the 10 turns vs the 2 1/2 turns. 10 turns down should be an accurate method of setting the fuel height. My assumption is when the floats are reinstalled they displace the fuel raising the level to 2 1/2 turns down. Now for the big IF. If all floats displace the same amount of fuel, the fuel level will rise to 2 1/2 turns down in all float chambers. I doubt if all floats are equal, especially 45+ year old floats. The final goal, after using whatever method one chooses, is to visually check the fuel heights in the nozzles at 2 1/2 turns down.

Thank you David F. @jalexquijano This what I've been trying to explain. It works.

Someone correct me if I'm wrong. I'm assuming the 10 turn down method is viewed with the float cover removed and the 2 1/2 turn down method is with the floats installed. More assumption now, that would mean the installing the lids (floats) would raise the fuel level in the bowls about 7 1/2 turns. is this a correct assumption or am I missing something?

Bruce beat me to it. Thanks Bruce. Let's try this. It may be an easy way to support the floats while checking the height. Remove the gasket from the float cover. You'll be using the lid surface for your float measurement reference point. Cut two strips of something flat (plastic, card stock, shim stock, etc,into strips about 3" long. One strip will be 9/16" wide, and the other 5/8" wide. With the float lid inverted, insert the 9/16" strip under the unsupported end of the float, resting on the lid gasket surface and blow thru the fuel inlet fitting. The 9/16" strip, then the 5/8" strip. Adjust the float tangs until there is air flow past the needle and seat using the 5/8" strip but no air flow using the 9/16" strip. Hopefully the 5/8" and the 9/16" strips will act like a go, no go feeler gauge. This method should work for getting them close. We'll check the fuel level in the nozzles, when you get it reassembled, to be sure they're correct.

@DaveR, was the 10 turns down setting with the floats removed? What was the "original location" that you mentioned?

Progress is good. Keep us posted.

Unfortunately, I can't. There seems to be different opinions about the fuel height in the bowls on three screw carbs. My suggestion is set the float heights by visually verifying the fuel level is 1/16" below the tops of the nozzles at 2 1/2 turns down. That way you're sure they're 100% right. I would suggest measuring the fuel height in the bowls using the tubes AFTER the floats are set. That info could be valuable to others.

I'm not surprised. That would explain the lean condition that you told us about previously. We'll proceed with the adjusting the floats until the fuel level is 1/16" below the tops of the nozzles. It will be interesting to see where the final fuel level ends up.

Good job. A little hard to see but it appears the fuel is at the nozzle tops. That would be OK if we didn't have to lower (richen) the mixture screws later. If we have to lower the mixture screws later, the fuel will be puddling on the nozzle tops. Not a good thing. Next thing to do is readjust the floats and get the fuel level 1 1/6" below the nozzle tops. You'll be lowering the fuel level in the float bowls to accomplish that. That will allow for fine tune adjustment later. Go thru the readjustment, start it up run for a minute, shut down and look at the new float levels and report back please.

Sounds good. Pics will help but I also want your impression on the fuel height too. I'll be gone until early evening.

#1 A minute or two should be enough to reset the fuel level in the bowls. #2 No need to drive the car or warm it up. #3 Yes #4 When you're done screwing around with the clear tubes and the 23mm, (which may or may not be correct for both 3 screw carbs) tell us the fuel height in comparison to the tops of the nozzles. The only way you're going to know if the levels are 100% correct is to compare the fuel levels with the nozzle tops.

If the needle and seat are leaking the float bowl will fill to over flowing with fuel and flood the area above the nozzles with fuel. One could possibly see fuel spilling out of the intake side of the carbs too. 4.2 psi shouldn't have ruined the needle and seats and since they're relatively new, I doubt they'll be a problem. Where is the fuel height in the nozzles?

It backfires and hesitates because the fuel mixture is too lean, which is what we're trying to fix. We're working on the PRIMARY MIXTURE ADJUSTMENT which is the float (fuel) level. Ignore how it runs for now, it'll get better as we go. What is the fuel level in the nozzles? Yesterday I said to adjust the fuel level anywhere from the top of the nozzles to 1/16" down. I'm going to change that. I think you should set the fuel level as close to 1/16" down as possible. Doesn't have to be exact, just eyeball it. The 1/16"drop below the top of the nozzle should allow for some mixture screw adjustment if we need to richen it up. All we need to know, at this point in time, is where the fuel level is in relation to the top of the nozzles.

Jalex, what is the fuel height in the nozzles? Backfiring from the intake is caused by a lean mixture. It's possible the floats are too low. Also possible it's not getting enough choke because of mis-adjusted choke cables. Ignore the fuel pressure (you've been down that road in the past and the problem still exists) and report back on the fuel heights in the nozzles.

Sure, you can use the tube method and it will get you there or close to it. Probably "good enough". The method that I'm suggesting is the 100% sure way to know that the fuel is at the proper height. Keep in mind that the float adjustment is THE PRIMARY MIXTURE SETTING. Get that right and everything else gets a lot easier. Not over the nozzle. The fuel level should be even with or just below the top of the small hole in the center of the nozzle. This is the hole that the needle slides into. The fuel level can be below the nozzle top as much as 1/16" but should never be over the top of the nozzle. Fuel over the nozzle top will result in fuel puddling above the nozzle. No need to measure the 1/16". Just eyeball the fuel level so it's as close to the nozzle top as you can get it without going over. Luck.

Any noticeable difference in the oil pressure cold or hot?

Sounds good. Give it a crude (grey area) 9/16" adjustment and reassemble the carbs. Start it up, run it for a minute, shut it down and check the fuel height in the nozzles. Readjust the float tangs to get the fuel level to within 1/16" of the nozzle tops which are still 2 1/2 turns down. This may take a few tries (along with float gaskets) to get them right. Keep us posted on your progress.

You can run both pumps. By 74 (maybe earlier) Nissan used both pumps to try to resolve a fuel percolation, vapor lock, problem with limited success.