Mark Maras

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.

I'm sure he had a good reason at the time, although I can't explain why. But, if I had to hazard a guess, he may have been trying to compensate for a float setting that left the fuel too low in the nozzle. Let's proceed. Your goal now is to get the fuel level within 1/16" of the top of the hole in the center of the nozzle. (Leave the nozzles at 2 1/2 turns) To achieve the 1 1/6" fuel level, you'll be adjusting (re-bending) the float tangs either up or down. At this point you don't care about the 9/16" float measurement. Ignore it. Don't even go there. After each adjustment, reassemble the carbs, fire it up, run it for a minute, shut it down and pull the domes and pistons. Look again to see the new fuel level. Readjust the floats until the fuel levels are correct. Then we'll go into fine tuning with the mixture screws. Piece of cake.

Clean the pistons and get back to the floats. You'll find out later if the staining was caused by poor tuning. So he's telling you that unless he unscrews the mix. screws to somewhere down near 4 turns (on one carb only) it runs too rich? Someone has something backward. The farther the mix. screws are unscrewed (dropped), the richer it will run. Based on the info from your mechanic, you already know more about your carbs than your mechanic and have the desire to tune the floats yourself. The only thing that's stopping you, is you. Go for it. WE CAN DO IT.

It sounds like you're taking it back to original design. I believe that you're shooting for 23 mm in the front bowl and 21 mm in the rear. Someone, anyone, correct me if I'm wrong. Opinions vary on these measurements. Most seem to like the 21 mm in the rear and if the difference in pivot point height is 2 mm, 23 mm in the front would be a good starting point. BUT you'll never truly know if the floats are correct until you pull the domes, pistons and look at the fuel level in the nozzles, 2 1/2 turns down. Then and only then will you know for sure if they're right.

The second method is one way to double check the accuracy of the 9/16" setting which, as you've discovered, is a very grey area. The other two common ways to double check the float setting (9/16" grey area) are the sight glass and the clear tube. Both screw into the drain plug hole. Now that you've gotten the floats in that grey area they call 9/16", install the newly adjusted floats, start it up, run it for a minute or two, shut it down and pull the domes and pistons. This is the 100% method mentioned above. With the mixture screws 2 1/2 turns down, the fuel in the nozzles should be within 1/16" of the nozzle tops. If the fuel level is either too high or too low, a minor float tang adjustment will be needed. If you find the fuel levels are within the 1/16" of the nozzle tops and you GOT IT on the first try, a celebration is called for and maybe a lottery ticket while your luck is still holding. It wasn't until yesterday that I realized you were working on a spare set of floats. I'm assuming they have the different length pivot ears, are your needles and seats different lengths too?

@siteunseen Cliff, When you shimmed? the needle and seat in one of your carbs, did you have equal length needles and seats in unequal pivot ears? I'm kinda in uncharted territory. My experience is with 4 screw SU's where all things are equal. It seems to me that it would be best to get the different length needles and seats and go back to the stock pivot point. Opinions are needed.

Jalex, I can see that both nozzles are equal distance down. I can't see how far down the fuel is in relation to the top of the nozzle. Is the fuel within 1/16" of the nozzle tops? In the "open another can of worms" paragraph above, he's describing the same thing we're doing here. The setting he didn't know was the 2 1/2 turns down on a 3 and 4 screw.

Stanley, You spoiled the ending of the SU float drama. I was just trying to get Jalex to the 2 1/2 turn intermission before the fine tuning grand finale. Jalex, don't let this scare you. Setting SU floats is like eating an elephant. You can't look at the whole meal. Just take it one bite at a time. You can do it. Even with our help.

A clarification is in order. If the fuel level at the top of the nozzles is too high or too low, a readjustment of the float tang is the next step. The goal is to see the fuel level 1/16" or less below the nozzle tops, mixture screws 2 1/2 turns down. One is actually adjusting the fuel level to the 2 1/2 turn down nozzle height. When that's correct one fine tunes the mixture screws to obtain the proper spark plug color.. (Old school) Jalex, You should take a good look at both needles when you remove the pistons. They should be the same. Hopefully they're visibly ID marked at the base. Compare the lengths too. Frequently, different needles have different lengths. Also. are your new needles and seats the same size or is one longer than the other. Another also, Do you know if the needles and seats that are in the carbs now are different sizes? One more thing, after installing the domes, do the drop test to insure the needles aren't sticking in the nozzles. Got to go back and re-read this thread to see where we're at.

Pink-n-Pull, St Louis, Mo. has an 81 280. parts pricing says that it's under $100.00.

@jalexquijano Don't obsess about getting them perfect. As you're discovering, measuring floats is not easy. Get them as close as you can without driving yourself crazy. Reassemble the carbs, start it up, shut it down, pull the suction chambers, pistons (not the float chamber tops) and see where the fuel level is in relation to the nozzle tops at 2 1/2 turns. Then you'll know IF the floats need to be readjusted or if you got it right them first time. Rest assured that you're experiencing the same frustration that everyone has had at one time or another setting floats. Keep up the good work.

Probably a dumb question but did the old pump have the spacer under it? If it did, I'd have to chalk it up to metal fatigue.

Caig DeOxit is a liquid that one can use on suspect electrical connections to clean oxidation and improve continuity. Great stuff.

I've used Copper Coat Gasket Compound over the years. CRC and Permatex are two brands that I've used. Good stuff, especially on old imperfect surfaces.

Put it back together, start it up to be sure the float chamber has been filled to the new float setting and to see if the float level is now correct see post #54 and #56. Mixture screws 2 1/2 turns down the fuel level in the nozzle should be within 1/16" of the top of the nozzle.

Lower fender bolts, I had to bend the bent flange down to get to mine. Used a Crescent wrench, (adjustable spanner) to get the leverage to bend it down. Cowl screws, copious amounts of penetrating oil, heat, cut a straight slot in the head with a Dremel Tool. Headlight buckets can be removed with the fender. Side trim, heat. I'd try a hair dryer first. If you use a heat gun, take care, the sheet metal is very thin.

Jalex, while you have the pistons out take a close look at the needle bases to be sure the shoulder of the needle is flush with the piston base, NOT flush with the bottom of the recessed section. You should be able to see the fat base of the needle sticking out of the piston.