Jump to content

MY1PATH

SU carbs will not sustain Heavy load

Recommended Posts

2 minutes ago, 240260280 said:

LOL 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 by MY1PATH

Share this post


Link to post
Share on other sites

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!

1530141869081932606834.jpg

Edited by MY1PATH

Share this post


Link to post
Share on other sites

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?

Share this post


Link to post
Share on other sites
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.

Share this post


Link to post
Share on other sites

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.  LOL

Share this post


Link to post
Share on other sites

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 by MY1PATH
added web links

Share this post


Link to post
Share on other sites

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.

Share this post


Link to post
Share on other sites

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.





Sent from my iPhone using Classic Zcar Club mobile

Share this post


Link to post
Share on other sites

I've used Holley Red and Blue pumps and I found them both ferociously loud and rather unreliable (correctly positioned at the level of the bottom of the tank). I wouldn't recommend them.
I'm currently using an old quiet Bosch 4 bar diesel pump out of my BMW. I've got an Aeromotive FPR that regulates it down to 2.5 psi and I'm very happy with it.

I haven't read the whole thread but I read the first post and I'd say if it's going lean almost immediately at 3k in 3rd when you apply load, I don't think it's the fuel supply, it would take a few seconds to use up the float chambers. I think your needles are too lean. Are they the ones that came with the carbs?
Apologies if you've been over this.

Share this post


Link to post
Share on other sites

 Here's a remote possibility that I experienced long ago. Similar symptoms, different vehicle. After much testing and frustration, I found the culprit to be an old rubber fuel line that had delaminated inside and had essentially made a flapper valve that closed when the fuel demand was high. I had to cut the hose lengthwise to discover how it worked. I could blow through the line in both directions and it seemed to be clear but the fuel would force its way behind the delaminated piece, push it into the mainstream and block the flow.  

Share this post


Link to post
Share on other sites
4 minutes ago, jonbill said:

I've used Holley Red and Blue pumps and I found them both ferociously loud and rather unreliable (correctly positioned at the level of the bottom of the tank). I wouldn't recommend them.
I'm currently using an old quiet Bosch 4 bar diesel pump out of my BMW. I've got an Aeromotive FPR that regulates it down to 2.5 psi and I'm very happy with it.

I haven't read the whole thread but I read the first post and I'd say if it's going lean almost immediately at 3k in 3rd when you apply load, I don't think it's the fuel supply, it would take a few seconds to use up the float chambers. I think your needles are too lean. Are they the ones that came with the carbs?
Apologies if you've been over this.

 It might be time to pull a needle to identify them and cross them off the list of possibilities.

Share this post


Link to post
Share on other sites
37 minutes ago, jonbill said:

I've used Holley Red and Blue pumps and I found them both ferociously loud and rather unreliable (correctly positioned at the level of the bottom of the tank). I wouldn't recommend them.
I'm currently using an old quiet Bosch 4 bar diesel pump out of my BMW. I've got an Aeromotive FPR that regulates it down to 2.5 psi and I'm very happy with it.

I haven't read the whole thread but I read the first post and I'd say if it's going lean almost immediately at 3k in 3rd when you apply load, I don't think it's the fuel supply, it would take a few seconds to use up the float chambers. I think your needles are too lean. Are they the ones that came with the carbs?
Apologies if you've been over this.

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.

32 minutes ago, Mark Maras said:

 It might be time to pull a needle to identify them and cross them off the list of possibilities.

 

34 minutes ago, Mark Maras said:

 Here's a remote possibility that I experienced long ago. Similar symptoms, different vehicle. After much testing and frustration, I found the culprit to be an old rubber fuel line that had delaminated inside and had essentially made a flapper valve that closed when the fuel demand was high. I had to cut the hose lengthwise to discover how it worked. I could blow through the line in both directions and it seemed to be clear but the fuel would force its way behind the delaminated piece, push it into the mainstream and block the flow.  

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.

Edited by MY1PATH

Share this post


Link to post
Share on other sites
21 hours ago, MY1PATH said:

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)

 

21 hours ago, MY1PATH said:

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...

Your free-flow test seems to show that the pump flows fine.  25 versus 30.  25gph is a lot of fuel.  I don't think anyone here has an engine that could burn that much.

If you do decide to get a new pump, I'm with jonbill on the brands.  Get an OEM brand, without the hypey name.  Most of the old brand names like Holley have been sold and the quality level minimized for profits.  You're buying an expensive name on a cheap product.  "Sniper"?  What does that have to do with cars and fuel?  Hype.

I didn't read the whole thing either but where is the pump mounted?  Was the flow test with it mounted in its normal spot?  Position can affect performance.

Share this post


Link to post
Share on other sites

 Many Z owners have found the pumps from the 1st gen. Mazda RX7s (1980ish) are nearly silent and put out the proper pressure for carbs. Less than $50.00 at RockAuto.

Share this post


Link to post
Share on other sites
1 hour ago, Mark Maras said:

 found the culprit to be an old rubber fuel line that had delaminated inside and had essentially made a flapper valve that closed when the fuel demand was high. I had to cut the hose lengthwise to discover how it worked.

I had this same type of problem on a lawnmower.  I think the hose delaminated because I had been using starter fluid to start the mower and overspray got on the hose, swelling it.  Still, same effect.  It would start but lean out and die after a few minutes.  Not obvious by eye.

Don't forget that the inlet side of the pump is under suction.  

  • Like 1

Share this post


Link to post
Share on other sites
8 hours ago, Captain Obvious said:

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.

I started out with a holley red but it was just way too loud.  I switched to the Carter and it is a little better but not much.  I have never had any issue with fuel delivery affecting performance with either pump

I like the carter design. It is hermetically sealed so the motor is cooled by the fuel.  That may be what also makes it a tiny bit quieter.  Do be prepared to hear them though.

Share this post


Link to post
Share on other sites
On 12/3/2018 at 11:02 AM, Zed Head said:

Your free-flow test seems to show that the pump flows fine.  25 versus 30.  25gph is a lot of fuel.  I don't think anyone here has an engine that could burn that much.

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....

Share this post


Link to post
Share on other sites
8 hours ago, MY1PATH said:

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...

Could be.  Back pressure can make a difference, for sure.  If a new pump doesn't fix it, at least you'll have a spare pump.  Always good to have spares.

I asked about pump position because sometimes people put the pumps in the engine bay.  That creates a long path to suck on for the pump.  The electric rotary pumps like to have the inlets supplied by gravity.  They don't like to suck.  I just saw that yours is back by the tank, so that's good.  The pre-filter can cause problems also if it's too fine.  Too hard to pull.

The mechanical cam eccentric actuated pumps have been used for years.  That pump alone should supply what the carbs need.  Are you getting side-tracked, maybe?  You might go all the way back to 1971, remove the pre-filters, use only the head-mounted pump, and a high-flow filter, or just the banjo-fitting screens.  Sometimes we're overprotective.  Probably fine for a test and might tell you something.  Back to basics.

Share this post


Link to post
Share on other sites

If you really want a Holley Red, I have one out in my garage.  I ran it for about 200 miles then went for the Carter.  I don't link the Carter was that much quieter, at least not worth the effort of changing it out.  If you are interested we can work out the details.

BTW what are you using for a restriction/regulator?  I had CO modify a Holley non BP regulator to make it a bypass.  I'm not sure that it is always working...  That is on my short list of to do's when warmer weather gets back.

Share this post


Link to post
Share on other sites
Could be.  Back pressure can make a difference, for sure.  If a new pump doesn't fix it, at least you'll have a spare pump.  Always good to have spares.
I asked about pump position because sometimes people put the pumps in the engine bay.  That creates a long path to suck on for the pump.  The electric rotary pumps like to have the inlets supplied by gravity.  They don't like to suck.  I just saw that yours is back by the tank, so that's good.  The pre-filter can cause problems also if it's too fine.  Too hard to pull.
The mechanical cam eccentric actuated pumps have been used for years.  That pump alone should supply what the carbs need.  Are you getting side-tracked, maybe?  You might go all the way back to 1971, remove the pre-filters, use only the head-mounted pump, and a high-flow filter, or just the banjo-fitting screens.  Sometimes we're overprotective.  Probably fine for a test and might tell you something.  Back to basics.
I'd agree. Definitely get a decent pump, get a decent regulator and see if you've still got a problem or not. If there's still a problem, at least you'll be sure where the problem isn't.

Share this post


Link to post
Share on other sites
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. 

Share this post


Link to post
Share on other sites

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

DSC01678.JPG.5fa757d486867d471003d8bbc500448e.jpeg

 

 

  • Like 1

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use. We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.