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.