Got my fuel pump on, but this is getting weird...

[Docmacs'77]

Okay,
my fuel pump went out, like I related in another post. I wasn't getting any fuel in the carb (my bowls were dry and my clear glass inline filter was only about half full). I knew it either had to be a bad pump or a clog in the line somewhere. To help nail it down, I installed a fuel pressure gauge. I primed the carb and cranked it up at which point it would run about 10 seconds or so, but never registered any pressure in the gauge. I swapped in a new pump, cranked it up, and yippeeeeee, 8 lbs. of pressure. Ran great, but about 10 minutes later, I checked the gauge and it was down to 6 lbs. Within the next 5 minutes I watched the pressure gauge drop from 6 to 4. It didn't die or anything, but what the heck is going on? :confused Any ideas? Thanks, Marc.

 

[Vettehead Mikey]

What's wrong with 4 psi? If it's enough to keep the float bowl full, don't worry about it.

 

[SLOVETTE]

Sounds like you may have trash in the fuel line.
Have you tried to blow out the line from the tank to the in line filter?

 

[AKRAY4PLAY]

your intank pickup filter is probably clogged with trash.

 

[Mac]

From what you've indicated, you made the right call by replacing the fuel pump but as a simple insurance precaution, I would replace the fuel filters and blow the lines but I'm pretty old-school when it comes to maintenance. I would rather replace a filter prematurely than save a few cents by extending it's life. For instance, I replace my air filter at every oil change. Yes, it's not filthy dirty but for the couple of bucks it costs to buy a paper filter, I'd rather swap it out.

When it comes to fuel filters, it doesn't take much to plug things up. With these older cars, you can get scaling, rust & other gack in the lines so easily that it's not funny. Pumps (mechanical or otherwise) don't like dirt since they're usually built to fairly close tolerances.

I haven't ever bothered with a fuel pressure gauge on a carburated vehicle. Mechanical fuel pumps generally only deliver 4 to 8 psi so the deviation on the gauge isn't remarkable enough to provide meaningful data. Most electric fuel pumps deliver around 40 psi so if the gauge shows 4 psi, you have a real problem.

Carbs aren't pressure dependent like fuel injectors are. With carbs, as long as the pump is flowing enough to keep the bowls filled regardless of rpm, the psi doesn't matter because the floats are going to meter the amount of gas delivered.

Flow versus psi... think of it like a garden hose. A hose without a nozzle flows at relatively low pressure but the volume of water moved is greater than if you add a restriction (ie: nozzle). If you're filling a barrel, the pressure isn't necessary and, in some cases, may cause problems ie: you'll need to hold the hose or it'll push itself out of the barrel and spray all over the place.

Likewise in fuel delivery systems; more psi isn't necessarily better. In the pursuit of performances, sometimes we cause ourselves more problems than we solve. If you push too much pressure into a carb, you can cause leakage. I don't know about you but I sure don't like the thought of gas dribbling out onto my engine... not to mention the fire hazard.

If your engine is modified enough that a standard mechanical fuel pump won't keep up, that problem won't manifest itself in usual running conditions. It'd only show up in higher rpms when the demand for fuel is highest and chances are you would have prepared for that eventuality.

Sorry to ramble on...

-Mac

 

[Docmacs'77]

Mac, good thoughts on the fuel filter. Right now I have a cheapy glass inline filter and I want to change it out to a higher quality one, which brings me to another question. I have the fuel line coming up from the fuel pump and running into the filter which is the "barb" type connection with a hose clamp. Looking online last night at Summit, I saw alot of inline filters with AN and NPT type connections. Is one better than the other? How difficult is it / how do you make this kind of connection? Does the AN and NPT connectors crimp down onto the rubber fuel line? Probably sounds like a dumb question to you, but I've never fooled with AN/NPT connections.
Thanks for any info you can offer, Marc.

P.S. Good idea on blowing out the lines. I'm planning on doing that as well.

 

[AKRAY4PLAY]

running a metal supply line from the pump to the carb is a really good idea. the glass filter is a fire trap!! several Vettes have met their fate from rubber hoses and glass filters. if you're going to run rubber line from the pump to carb, change it every year and use a metal filter.

 

[IH2LOSE]

AN-are special fittings. I think they came from the air craft industry. They are normally used with steel Braided lines.

NPT is just national pipe threads

I was clue less on this also until recently.

I built a custom 62 vette and had to purchase some performance parts.I found this company http://www.carshopinc.com/ and they help me solve alot of problems.The fellow I dealt with name is Tim and he is very knowledgable. He knew the size of the fittings I needed just by telling him what fuel pump and Carb I had.

I would describe what I needed,Email him a picture. And with in 3 days I would have all of my needed parts. This is customer service at its best. Since I had found this company by axcedent while doing a google search for information on Barry Grant Carburators. He will have my buisness forever

Good Luck

 

[Mac]

The only time I've dealt with AN fittings (I believe that's what it was called) was when I changed my Jeep CJ7 over to fuel injected. I salvaged quite a number of parts from a wrecked YJ, including the fuel lines which were hard steel most of the way but 18" steel braided flexlines with AN fittings at both ends.

The YJ's flexlines were pretty mangled but I took them since the Grand Wagoneer engine which I was using had the same terminations. I had new flexlines made up custom for my application. It wasn't cheap but, given the higher pressure required for the fuel injectors and the existing terminations, it was the easiest and safest method.

For your application, AN fittings would be overkill and likely expensive overkill to boot. A standard stainless hose clamps are all you need since your pressure won't be as great as an electric fuel pump.

I've heard (as AKRAY4PLAY mentioned) of the fire hazard but I have no first hand information to confirm that. I don't care for glass filters but that's just my preference; I just find them cheap looking.

-Mac

 

[pgtr]

For your application, AN fittings would be overkill and likely expensive overkill to boot. A standard stainless hose clamps are all you need since your pressure won't be as great as an electric fuel pump.

I agree. OEMs have produced millions of cars with rubber hose on the supply side and simple 'spring' clamps (I prefer the SS screw clamps) without fire problems. The upper hose in the pic below retains a nominal fuel pressure of ~75psi. It should be noted that the metal tube has an extruded 'nipple' end not visible with the rubber hose installed over it.

 

[JohnZ]

I agree. OEMs have produced millions of cars with rubber hose on the supply side and simple 'spring' clamps (I prefer the SS screw clamps) without fire problems. The upper hose in the pic below retains a nominal fuel pressure of ~75psi. It should be noted that the metal tube has an extruded 'nipple' end not visible with the rubber hose installed over it.

What vehicle/engine application is that on?

 

[bossvette]

without trying to sidetrack this thread there is fuel injection spec rubber type hose and fuel injection spec clamps they are stronger then the run of the mill fuel line and clamps. The TPI units I am familiar with have O-rings in the fittings as well.
Two types come to mind the throttle body type which runs at around 10-12 PSI and the TPI or many EFI systems which run at 45+psi

 

[goertz]

What vehicle/engine application is that on?

I don't know what vehicle that is on, but it's a return line, which is low pressure, and not a high pressure line. but I do agree that rubber lines are not a "fire waiting to happen" nor are glass filters. The problem I've always had with glass filters is that the element the have inside is way too fine, and will plug up all the time.

 

[pgtr]

I don't know what vehicle that is on, but it's a return line, which is low pressure, and not a high pressure line. but I do agree that rubber lines are not a "fire waiting to happen" nor are glass filters. The problem I've always had with glass filters is that the element the have inside is way too fine, and will plug up all the time.

The upper hose is definately the supply side. The lower hose is the return side.

An option: inline filters (glass or otherwise) work great as a secondary filter near the carb w/ the primary filter in the rear with the electric fuel pump.

Here's yet another example of OEM engineering - this is a modern engine with a plastic inline filter and low pressure rubber hose and spring clamps on the suction side. What's interesting (Not pictured due to limited visibility/access) is the SAME hose/clamps on the pressure supply side between the fuel pump and carb. Going from memory we are talking about a couple few PSI in this application. Several nice things here - 1) the rubber hose absorbs vibration between the engine and frame 2) the filter placement protects both the pump and carb 3) filter can be easily viewed for inspection 4) filter is easily serviced with a pair of household pliers and 6) it's all OEM designed and engineered if that's really important to anyone.

 

[JohnZ]

What is the vehicle/engine application for the 2-hose arrangement in post #10 and for the in-line filter arrangement in post #14?

 

[bossvette]

Post #14 looks just like my John Deere riding mower :L

 

[Vettehead Mikey]

Post #14 looks just like my John Deere riding mower :L

It also looks like the rubber hoses were not pushed all the way onto the filter housing and are about to slip off.

 

[gmjunkie]

running a metal supply line from the pump to the carb is a really good idea. the glass filter is a fire trap!! several Vettes have met their fate from rubber hoses and glass filters. if you're going to run rubber line from the pump to carb, change it every year and use a metal filter.

Docmacs'77,I'd Run Rubber!! Metal line in your climate it will probly Vaper Lock on a Hot Humid day!! junk!!

 

[Docmacs'77]

Docmacs'77,I'd Run Rubber!! Metal line in your climate it will probly Vaper Lock on a Hot Humid day!! junk!!

Yeah, Junkie, that's what I'm running and gonna stick with it.