Fuel restriction question

[Doug&Deb]

I thought I had my fuel problem sorted but it acted up again yesterday. I finally got the correct pump and was running it with a rubber line between the pump and carb to make sure the pump was working properly. Once I made a new hard line that seemed to trigger the problem again. I’m pretty sure I know the answer but I’ll ask anyway. Because of the heater box and my inability to make a tight 90 degree bend at the carb end I installed a 90 degree fitting into the carb. Did I create the restriction? The car is a 52 Coronet by the way.

[Ivan_B]

I doubt that a 90-degree fitting will create a restriction of any kind, unless you did something very special. And I assure you - you are probably not that special 😁

Can you please remind us what seems to the the problem, though? Is the fuel not getting into the carb? How do you know? Did you remove the top and confirm that the bowl is not filling-up while the pump is working? How about if you manually push/blow some gas/air into your custom line from the pump's side, is it going through?

[Doug&Deb]

I was running a rubber line to the carb after I changed the fuel pump. I had been using the wrong pump. The problem never occurred until I made a new hard line. The problem is very random only happening when pulling a hill and even then it’s random. I know most fuel problems are ignition but what is causing it is beyond frustrating. I just checked the tuning with my analyzer and everything is in spec. 

[Ivan_B]

Well, the carb usually has a reserve of fuel in the bowl, which is kept-up by the pump. The pump is generally pumping more fuel than you need, that's why we have the shuf-off float and the needle in there. I would not suspect that whatever you did to your lines is causing the carb to starve on fuel. Thus, I would look for another explanation of the observed performance problem. Maybe even not a carb-related explanation.

If everything else fails, have you tried putting your rubber line back on to see if it changes anything?

[soth122003]

Random thought hit me. How steep is the hill? This question is in relation to the carb attitude. (and no I don't me it's mental state, tho that mite apply) It has to do with the float level and the angle of the carb on the hill. If the float is set lower than normal and the angle lets the gas in the bowl settle to the back, the float won't come down until the gas in the bowl is reduced at the back to lower the float. That amount might be an almost empty bowl that borders on empty and the refill of the bowl might cause an air pocket that cause the stumble.

 

Since you say this random does it happen on the same hill or different ones? Crud I just fell in the rabbit hole. What is your gas tank level on these hills close to empty or more than a 1/4 of a tank? I think I'll stop here before I get really weird. Uh Oh Might be timing set just a touch to far on advance and only visible on harder loads like hills.

 

Joe Lee

 

 

[Doug&Deb]

Full tank but you may be onto something with the timing. I don’t think the hill is too steep but yes it usually happens on the same one. More investigation is needed. No I haven’t put the rubber line back on. I’m still confused why the electric pump clears up the problem. I should add that I ran only the electric pump for a few months and never had a problem. I just don’t trust that to be the only fuel source.

[Ivan_B]

So, if you use your new fancy metal line + electric pump there is no problem? Have you checked your mechanical pump output and pressure to make sure it is within specs?

I am only using a mechanical pump, by the way, and did not notice any issues with the fuel delivery 😏

[Sniper]

A sharp 90 is a restriction to flow, but the question here seems to be, is it the issue?  Seems so in your case based on what you are saying.  Bend up a hard line with a smoother. more gentle 90 and see if that does it.  A coat hanger can be hand bent as a template.

[Doug&Deb]

Sniper that’s the next step. I don’t have a tool to make a 90 short enough to fit between the carb and heater box but a coworker has something that might work. I should add that the newer carb kits use a different needle and seat that is a 1/8-27 pipe size which requires an adapter for the inverted flare line. That is a restriction by itself let alone adding a 90 . Why Stromberg carbs have the inlet on the right instead of the front is a mystery to me.

[Harley PHD]

How close is the metal line to the exhaust?  I could be vapor locking

[Doug&Deb]

I’m sure that’s part of it. The 90 degree fitting keeps the line closer than it should be.

[Ivan_B]

I am not really into hydrodynamics, much, but here is the most general rule regarding bends and flow restriction I was able to find in a smart article: Designers usually apply the general rule that a 90◦ elbow bend has a pressure drop equivalent of 30 to 50 pipe diameter lengths of straight pipe (page 40).

[Doug&Deb]

Ivan I’ve heard that also. That’s why I think eliminating the 90 degree fitting will help.

[desoto1939]

doug: are you using the NICad tubing? Suggestion is when you are at the point of making a bend install some large grass triming cutting string usually plastic where the bend will be located and leave enough so you can pull the line out when done. This will keep the line from getting pinched and help make a smoother bend.

 

Rich Hartung

Desoto1939@aol.com

[Ivan_B]

2 hours ago, Doug&Deb said:

That’s why I think eliminating the 90 degree fitting will help.

I would not expect a slight pressure loss causing any noticeable difference for the carb. I doubt that the engine will use that much gas that the bowl gets empty and the pump is struggling to fill it due to, essentially, an equivalent of a slightly longer line.

Just try putting your soft hose back on, without changing anything else, and see how it works 🙂

 

[DJK]

On 4/3/2025 at 7:08 PM, Doug&Deb said:

Full tank but you may be onto something with the timing. I don’t think the hill is too steep but yes it usually happens on the same one. More investigation is needed. No I haven’t put the rubber line back on. I’m still confused why the electric pump clears up the problem. I should add that I ran only the electric pump for a few months and never had a problem. I just don’t trust that to be the only fuel source.

MY Carter P4259 has been on for 6 yrs., about 18,000 miles, no issues.

[Doug&Deb]

I replaced the 90 degree fitting with a new line but no improvement. I’m really getting frustrated with this. I’m going back to the rubber line and seeing how it works. If that doesn’t work then I have to look into ignition problems. I’m probably due for a tune up anyway but I’d rather not just throw parts at it hoping something works. 

[Ivan_B]

Let us know what you find out 🫠

[Sam Buchanan]

On 4/3/2025 at 6:08 PM, Doug&Deb said:

Full tank but you may be onto something with the timing. I don’t think the hill is too steep but yes it usually happens on the same one. More investigation is needed. No I haven’t put the rubber line back on. I’m still confused why the electric pump clears up the problem. I should add that I ran only the electric pump for a few months and never had a problem. I just don’t trust that to be the only fuel source.

Sounds like you have a defective mechanical pump.

[Doug&Deb]

Sam, I’m not ruling that out. Today I went back to the rubber line. It worked for a while then the car just died and wouldn’t restart. Eventually it started but wouldn’t idle. Because I have extra parts I tried another dizzy. No joy. Then I tried a different carb. No change. I was able to take it for a drive but I had to leave the electric pump on. I need to get underneath and look at the mechanical pump. That will be another day. With my back problems I strained it enough for today. Because I was using the wrong pump for the last year I’m wondering if I damaged the cam lobe. 

[Dave72dt]

I doubt the wrong pump damaged the cam lobe.  The pump arm is contacting the lobe in the same place on either pump and in the same place it has for years so it's not likely the wrong pump wore the lobe down in a year of limited miles.  I would look at the filter you have before the electric pump, if you have one or how readily gas will flow through the electric with it turned off.

[Doug&Deb]

Dave the pump contacts the cam differently. My engine is a 58 truck engine and the cam is a different part number. I’m not disagreeing with you. I’m just out of ideas here. The electric pump has a pre-filter that is crimped on. I also use an inline filter before that. I don’t think it’s restricted but it’s possible.

[LazyK]

Possible there is a sintered bronze filter inside the tank.

[Doug&Deb]

New tank.

[LazyK]

Proper vented gas cap?

Edited 13 hours ago by LazyK