SU carbs will not sustain Heavy load

[240260280]

FYI  I am rebuilding round top SU's with Hitachi needle valves stamped 2.0.   I guess they are not original size but the carbs did seem untouched. 

[MY1PATH]

25 minutes ago, 240260280 said:

FYI  I am rebuilding round top SU's with Hitachi needle valves stamped 2.0.   I guess they are not original size but the carbs did seem untouched. 

According to your earlier post 2.0 IS original. 

[240260280]

I thought it was 1.7mm  .... getting too old.

[MY1PATH]

2 minutes ago, 240260280 said:

I thought it was 1.7mm  .... getting too old.

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")

 

Edited June 21, 2018 by MY1PATH

[MY1PATH]

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!

Edited June 28, 2018 by MY1PATH

[Captain Obvious]

Well that's some progress, huh? I still think you've got a fuel delivery issue upstream, and I wonder if the pump just isn't up to the task.

If you're thinking you've got a blockage issue at the tank itself, you could test that theory by running from a fuel can in the hatch area feeding the input to the pump. In other words, same pump but different (temporary) tank.

If the problem goes away, you drop the tank. But if not, try different pump?

[MY1PATH]

2 hours ago, Captain Obvious said:

Well that's some progress, huh? I still think you've got a fuel delivery issue upstream, and I wonder if the pump just isn't up to the task.

If you're thinking you've got a blockage issue at the tank itself, you could test that theory by running from a fuel can in the hatch area feeding the input to the pump. In other words, same pump but different (temporary) tank.

If the problem goes away, you drop the tank. But if not, try different pump?

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.

[Captain Obvious]

Two weak pumps is unlikely, but certainly possible. For me, it's more about doing anything else I can think of before I would go through the PITA of dropping the tank.

Maybe it's just dealing with the rock hard petrified filler tube and vent hoses, but I would do a lot of other things before I would finally concede to go through that again. 

[240260280]

Try blowing >100psi compressed air through all hard lines and into the tank  connections (open filler when doing).  It worked for me ?

[MY1PATH]

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...

 

 

Edited December 2, 2018 by MY1PATH
added web links

[Captain Obvious]

Cool. Glad to hear you are narrowing in on the root problem. So if you measured 25 GPH with the only restrictions in the line being a filter and a couple feet of hose, then I can certainly believe that number will go down even further when you have all the piping in place. And then there's the fact that some (most?) fuel just get's routed back to the tank.

@GGRIII has gone through two different electric pumps in his car. Don't remember which ones they were, but I'm thinking one of them was the Holley red?  I do know that he pulled the first pump and replaced with a second, but I don't remember if it was a delivery issue, or simply because the first pump was so durn loud.

Hopefully he'll see the tag and chime in here to provide some input.

[heyitsrama]

Interesting, I was having a similar issue with my l26, and was able to tune ( adjusted floats) the issue out of 3rd gear, but it became more prominent in 4th.

I’m currently running a carter-4070 fuel pump which says it’s rated 50gph.

I was informed that my gear ratio can also “amplify” the felt effects of loosing torque. That I sort of understood, running a 3.36 on a close ratio 5spd. But I don’t have anything to compare it to.





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