MY1PATH

Yeah, its sad, I didn't drive or work on my baby all summer. Work, injuries, other priories and Life in general... But this weekend I ordered an RX7 pump. Its ACDelco branded and externally looks similar to the Airtex pump I was running before. I have some other things to square away before the car can hit the road again but if this RX7 pump solve the problem then I'm probably going to throw in the towel and just live with it until the whole fuel system gets replaced (Future mods...)

The thing is, not all pumps are created equal. Just because the factory pump does X a free flow does not mean it will do the same as another pump under load. Example: say the factory pump does 22.5 free and 10 at 5 psi. and another pump does 30 free but only 3 at 5 psi, it still won't be good enough. Yeah, I toyed with float levels a bit, even made them higher than stock and still no benefit. I like your off vehicle float adjustment.

Yes, but it's just that "Free flow" not under pressure what if I run the same test again right before the fuel rail and with the increased restriction I only get 5 GPH. It only trickles back to the gas can on the return side. Plenty of vehicles can drink over 5 GPH, I think the 4.5 PSI flow rate is too low... Look if you read the whole thread and can still think of a good reason why its not the pump let me know. Correct AFR's are at any RPM just not for sustained periods of heavy load (takes multiple gears to drain the carbs) All hoses are new all hoses , hardlines and rails have been snaked fuel tank is out of the equation and problem still persists Richening the needles brings the problem sooner. (hmm adding more fuel makes me run out of fuel faster) Float valves have been addressed and flow more than stock....

A few seconds? I think all of 1st and 2nd gear make up a few seconds. We're talking about Wide Open Throttle between shifts. All good suggestions but I did a test where I killed the engine when it starved and checked the bowls, they were were drained significantly. That points to there not being enough fuel going to the carbs. I ran a snake down every hose, hardline and fuel rail. I came up with zero restrictions.

Well it only took me 5 months but I spent more time on this today. I ran two fuel lines into a gas can tied down in the back. Then I found a steep hill to see if I could trigger the problem without speeding... Yep pump does not move enough. I also watched it free flow pump. Freeflo (tank>pre-filter>pump> 4ft hose>can) pumping from the tank to a 5 gallon can took about 12 min to fill = about 25 GPH (Airtex E8251 rated @ 30 gph) So I'm going to look at other pumps now. Holley Red 12-801-1 comes to mind first (Flows 97 GPH free flow and 71 GPH at 4 psi) but I'm open to alternatives like the Sniper 80000100 (Holley) with the same specs as the red but half the price...

I'll get there eventually. That is a good test to run. The fact that I had the same issue with the mech pump and again both pumps combined leads me to think it may not be the pump... I won't rule it out completely but two (2) weak pumps? Its possible.

Today I threw on a hose clamp to deadhead the fuel line and drove it like that for the day. The issue persisted but not to the point of cutting out. AFR's only leaned out to 15-16 instead of 18+ In 2nd gear the engine continued to accelerate to 6k under this lean condition but very slowly. Still not priority or space to pull the tank but hopefully next month. Happy 4th everyone!

nope 1.7 is what I got when I ordered aftermarket. Sometimes we can never be quite sure why the aftermarket meddles with things... Mine are now opened up to 2.52 (0.0995")

According to your earlier post 2.0 IS original.

Sorry for the silence, I have opened up the flow buy reaming the needle valve seats to 0.0995" and adding side exit ports. This helped the problem but it did not completely eliminate it. (Power cuts out more softly and recovers quicker) Solving this problem has slipped back down on the priority list a few notches but my next steps will be to try deadheading and then pull the fuel tank... Got a lot on my plate right now and other things to catch up on but I will revisit this thread when I get back to troubleshooting.

I actually don't know what needles I have, there are no visible markings but I suspect they are N54? I read somewhere that those are really Fat idle and lean up top. I think the SU's came of 1972. I have some damaged needles out of a flat top that I have heard are the opposite, I might try to clone those...

At a glance Flat Top valves are nothing close so I stopped right there. Just measured my round top valves at #52 or 0.0635" (1.61mm, side is stamped "1.7" which is only .0025" difference) That's over .0152" (0.39mm) too small. If I was within 0.010" I would not be so concerned but I would rather be bigger than smaller. The more I think about it, this actually MAKES A LOT OF SENSE!!! L28 and carb rebuild happened at the same time... On the L26 I took the carbs right off Ebay, installed them and they ran ok so that was that... When I got ready to install the L28 I took the carbs off and rebuilt them, to include viton O-rings on the shafts (I think I copied someone Obvious) and of course the new Needle Valves. If I can find my old parts I will measure them too I think they were original. The Viton Tip is just under 0.150" (not going quite that big) so if I find my spare set will will see if I can successfully ream and debur them without having them leak afterwards. If I can't find spares new ones are going to be $30+ per carb and I'll have extra viton needles too, just don't lose them this time lol.

Thanks! This is exactly what I need, 2.0mm/0.0787" I totally forgot I had a set of Flat Tops... If the valves are similar I might try them or even try to ream them out without worry of ruining a good set. Better yet I wish I knew where my original valves were as well as the new spares (kits came with one long and one short for each carb) To some extent it may matter... IF The problem is fixed stopped one way but if the root cause worsens does the problem come back? Just for fun: High Flow 0.156" Needle Valve for SU H8 used on 3.4L Jaguar straight 6...

Mine are aftermarket. I can't remember where I got them from but it was a kit with lid gaskets, needle valves and hoses (I used Tygon hose instead). Tomorrow I will take them out and measure them (forgot to today). From looking around I think S30's and other small HS carbs got .070" from Skinner Union but I might try to order some .096" ones...

❓Does anybody know what size the small hole in the float needle valve is supposed to be? Maybe I got the wrong one? Or maybe folks on performance builds are running a larger size? I've seen them go all the way up to 0.125" on other SU's for other engines (race builds) I got it out. Much shimmying in each direction with compressed air helping each direction. Something came out of the vapor line, I just didn't see it but the string was able to slide freely and drag a mop through when I was done. Not an air leak, the problem does not come with RPM, it comes with sustained load and we've already proven the the carbs are running out of fuel when this happens.

So I finally got a string through the chassis vapor hard line. The other lines only took 40 PSI and blew string through quick and easy, they also pulled without too much difficulty. This vapor line took 120 psi and several minutes of air blowing without feeding and then it would take up a few inches and stall again... Granted its smaller and has a few more bends in it than the fuel hardlines but my string does not want to move without a lot of resistance (let alone drag a mop through it to clean it out) Is it possible that the cause of my problem was tank vacuum limiting my pump? I would test this theory by driving without the gas cap but I'm determined to get this string pulled all the way out of my vapor line before put wheel back on and get the car back on the ground...

Sounds good for longevity as long as it doesn't bind. My Z had the factory pump when I got it. It made noise but didn't move fuel so I threw it away and went exclusively mechanical on the L26. Sustained load issues didn't come up until the L28 went in, it was probably right on the edge before the swap.

The electric pump was purchased for a few reasons: -aid in starting after sitting (done) -to hopefully replace the mech pump (done, mech pump has been sitting in my garage ever since I concluded the car can run fine without it) -solve the sustained load leaning out (wishful thinking and nope) I have been driving with this problem running exclusively on a mech pump for years but often other things take priority. The car is still fast enough to get me into trouble before starving out and the top of 1st gear is speeding anywhere on my daily commute (3.55:1 gears). My buddy said he had the same problem once... It was a hole in the in-tank pickup above the fuel level, it would pump fuel but not as optimally as it could due to the loss of suction through the hole... I'm gonna bit the bullet, clean the garage and hopefully have time to drop the tank sometime soon...

Lucky me, I had time to fish out the fuel hardlines. Unlucky me, both were clean. The only thing I found was little waxy gobb which probably came from the very string I was dragging through the hard line. I think I have discovered some blockage in the vapor line, air running through it sounds muffled and my string has not been able to blow all the way through it yet. Once get it sorted I will put all the hoses back on and continue driving it. But now I have motivation to clean my garage (yay) because my next step is to drop the tank... Knowing I was shooting for 3.5-5 psi for an electric pump without needing a regulator; I bought this pump based off recommendations and reviews. Some reviews were from other Z owners, its same-spec sister that comes with a filter was found on another thread but I like the larger off the shelf clear filters for the 260z so I bought the filterless model instead. I find more and more that the info provided by manufacturers (or re-labelers) has become increasingly lacking over the years... This is where I saw "solid state" https://www.amazon.com/Airtex-E8251-Universal-Electric-Applications/dp/B0027I88VQ My mistake on calling it diaphragm however, the principle of an electromagnetic coil moving a pin on a diaphragm or a piston on a solenoid is still the same even if the moving parts themselves are different.

I checked, fuel can flow one way trough the pump when it is off. I only drove the car once the electric pump in line but not powered (was chasing wires) and the was no noticeable decrease in performance. Before that it was exclusively mechanical and after that if it was inline it was powered. I also just remembered that when I added the pump I had to tighten my connection to the chassis hard line right after the pump...it was leaking pretty good with the pump powered.... Maybe another indicator...

I think the little bits I found were too small and crumbly to block the orifice unless there was a large number of them are a larger more solid piece somewhere else. The wire I ran through the orifice was corkscrew twisted so I could feel if there were any larger obstructions. It's just a soldered on cap for the orifice so if need be it could have been removed and reinstalled for more extensive cleaning. Yes I said it looks like it flows "plenty" but I did not take any specific measurement. I doubt any of L6 could drink 1/2 gallon in a minute (refill every 20 minutes at the track?) so even if 30 GPH is probably its freeflow rate its still plenty if its even half that @ 3.5-4.5 psi. PS- this is my understanding... Solid state is commonly misunderstood as "no moving parts" which in many classes is close. What it really means is "no moving electrical parts"... In terms of a diaphragm pump it means that the magnetic coil that moves the diaphragm board controlled electronically pulsed via solid state controller instead of using an analog relay-like mechanism that physically moves electrical contacts to make and break the circuit for the magnetic pulse. In rotary pumps you may instead see the term "brushless motor". But again (more or less) no moving electrical parts, a circuit board dictates which set of coils around the housing are powered to advance the permanent magnets on the shaft and at what speed. (although some still use an analog hall effect sensor to relay the motors position)

Today I pulled all the hoses off the rail, I noticed a tiny crumbly piece what I think was black rubber sticking out of the return orifice. I fished around the orifice area with some wire (turns out there is no check valve) and blew compressed air through all the fittings. Then I drug a cloth mop through the rail from the rear fitting to the inlet, from the front fitting to the inlet and vise versa. I found a few more tiny crumbly bits (not pictured) and some normal white/tan fuel system residue. The mop drug smooth the whole way. Because of the black crumbly bits I imagine that there is some remnants of old rotted hose in the chasis hardline that may be causing a restriction. Maybe Friday I'll run the mop through the 3 chassis hardlines(feed, return & vent) for good measure. If that's not it, I guess the tank is coming out again... I used compressed air to launch my string through the rail to drag my mop I use this trick to clean out aircraft tubing after production.

I don't want to deadhead the rail (permanently) because that increases the fuel temperature. I'm sure my elec pump would peak at 4.5psi if I did but we get 115F days out here in the summer.

No regulator, just the original small orifice restrictor on the rail return i believe it has a spring ball in it to prevent drain back when psi=0. More detail on pumps... Mech: std location (with STD insulator thickness) max 6psi but pulses a lot below 1500rpm (to be expected) Elec: Airtex E8251 solid state diaphragm, rated 30gph for 2.5 to 4.5 psi applications. Located where factory elec pump bracket used to be. Shows about 3.5psi at idle and neutral rev too 6k. Noted driving differences: Mech only: slow starts after sitting for a few days. Mech and elec: faster starts after sitting, low rpm psi pulse doesn't dip as low. Elec only: faster starts after sitting, seems to be enough pump despite the lower peak pressure. Using the electric pump both combined and by itself where my most recent attempts before this thread to combat the leaning issue.

I think running a higher than necessary float level (and re-tuning the engine to suit the higher fuel level) is more of a bandaid than a solution.