SU carbs will not sustain Heavy load

[240dkw]

On 12/2/2018 at 12:59 PM, MY1PATH said:

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 was just reading a TSB for the 1973 carb mods and the fuel free flow test with both the elec and mech pumps is 3 pints/min or 22.5 us gal/hr at 1000 rpm's so I do not think your pump is weak. If you do not find a "smoking gun" with a fuel problem, you should try changing out the capacitor on the dizzy. As they get old they can start to fail at higher voltage and create a problem where the rpm's go flat at WOT looking like a fuel starvation issue. 

[Mark Maras]

 Post #64 he says he pulled the bowl covers after it "starved" and found the fuel levels "significantly lower."

[siteunseen]

I haven't read all the post but I found my low float level after running up a very long and steep mountain.  About half way up it started running on the back carb, half power.  I cut the wheel and rolled it perpendicular with the road, cranked on it a few times and it cleared right up.  Went about another mile, same thing.  I went back down and it ran great the rest of the way home.

After a week I had the floats set right and it runs fantastic now all the way to 6,000-6,5000 rpm.

Sorry if already told this but it's the best thing I've done to my SUs.

Cliff

 

 

[Mark Maras]

 Thanks, Cliff. That low fuel level made me wonder if it is float level related. 

[MY1PATH]

On 12/8/2018 at 12:00 PM, 240dkw said:

I was just reading a TSB for the 1973 carb mods and the fuel free flow test with both the elec and mech pumps is 3 pints/min or 22.5 us gal/hr at 1000 rpm's so I do not think your pump is weak. If you do not find a "smoking gun" with a fuel problem, you should try changing out the capacitor on the dizzy. As they get old they can start to fail at higher voltage and create a problem where the rpm's go flat at WOT looking like a fuel starvation issue. 

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.
 

 

23 hours ago, siteunseen said:

I haven't read all the post but I found my low float level after running up a very long and steep mountain.  About half way up it started running on the back carb, half power.  I cut the wheel and rolled it perpendicular with the road, cranked on it a few times and it cleared right up.  Went about another mile, same thing.  I went back down and it ran great the rest of the way home.

After a week I had the floats set right and it runs fantastic now all the way to 6,000-6,5000 rpm.

Sorry if already told this but it's the best thing I've done to my SUs.

Cliff

 

 

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.

 

Edited December 9, 2018 by MY1PATH

[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...)