Engine Bogging And Losing Power...

[csx4590]

Got my car back about 2 weeks ago and have a few questions regarding the engine losing power. It's a basic 440 (non HP) motor with a Mopar aluminum intake and a 750 Edelbrock carb. I am not a numbers guru and not much of a mechanic. I change oil, plugs, water pumps, basic stuff but have no idea what cam degrees are and timing degrees etc. The car starts fine and runs great for about 30-40 minutes then it starts to lose power. It feels like it's either a flooding problem or an ignition problem. It has all new fuel stuff (tank, lines, sending unit etc). Fuel filter has fuel in it. The first trip in the car it had a stock fuel pump and we got the power loss after about 30 minutes of driving. We changed that to a larger Holley pump and it seemed to run fine after that. Second trip it ran great all day. 3rd trip, back to the 30 minute power loss. It has the orange box electronic ignition distributor kit and stock coil. Any ideas as where to start eliminating the problem? Is the intake/carb set up too much for a stock engine? Could the coil be the problem (getting too hot/losing spark)? Any help would be greatly appreciated as usual...

Tired of sitting on the side of the road as everybody goes by waving or shouting "nice car"...

Al

[303 Mopar]

The carb is not too big for a 440.  It sounds like you potentially have a fuel boiling problem.  Do you have a return fuel line?  Have your wrapped your fuel line in the engine bay?  Are you running a carb spacer?

[Back N Black]

Did you check fuel pressure? when you changed the pump did you check the fuel pump push rod for wear?

[csx4590]

Did you check fuel pressure? when you changed the pump did you check the fuel pump push rod for wear?

Both the stock style pump and the Holley pump we switched to were brand new. I think the shop said the stock one was at 4psi but we did not check the Holley...

[csx4590]

The carb is not too big for a 440.  It sounds like you potentially have a fuel boiling problem.  Do you have a return fuel line?  Have your wrapped your fuel line in the engine bay?  Are you running a carb spacer?

Like I said before, I only know some mechanic basics. Where would/does the return line run to/from? No, we did not wrap the line. It looks like there is about an 1/8 inch carb spacer. Can't do too much taller as the air cleaner barely clears the hood now...

[csx4590]

There is a lot of pressure at the gas cap when I open it after driving it for awhile. Does anyone have a photo of the routing of the original style pump to carb line??? 

[303 Mopar]

Like I said before, I only know some mechanic basics. Where would/does the return line run to/from? No, we did not wrap the line. It looks like there is about an 1/8 inch carb spacer. Can't do too much taller as the air cleaner barely clears the hood now...

I added a 3 line filter before the pump (1 inlet and 1 outlet on the tank side, and 1 to the carb), or you can get the stock vapor return which mounts near the fuel pump.

[BSB67]

There is a lot of pressure at the gas cap when I open it after driving it for awhile. Does anyone have a photo of the routing of the original style pump to carb line??? 

Are you sure that it is pressure, and not suction?, and you did not answer the earlier question about the fuel pump push rod.

[birdsandbees]

Pressure or more likely vacuum, sounds like your tank vent line(s) are plugged. Mud dabber wasps love openings like that.

[csx4590]

Now the engines starts but bogs down right from the start when cold. So it's not a heat/boiling gas related issue. Now it starts and runs really rough/has no power and I haven't changed anything yet...

[Dino]

Have you checked for a blocked fuel tank vent line?  Pop the fuel cap while it's idling and see if something changes.

[csx4590]

Have you checked for a blocked fuel tank vent line?  Pop the fuel cap while it's idling and see if something changes.

When this all started to happen a few weeks ago, I did pop the cap to let the pressure out. I closed it back up thinking that the pressure wouldn't build up that fast. I popped it today after I read your post and it did idle better. Took it for a 15 minute trip and it seemed to run ok. I guess I'll give it a longer drive tomorrow to see if that is what the problem was. Hopefully that's it. I am not familiar with this vent line other than it runs along the gas filler tube from the cap to the tank. Is it supposed to have rubber hose at both ends? At the top by the cap, where does the vent actually vent to? I guess I'll take it off tomorrow and see if it is clogged or plugged up. Hopefully that is it and I don't have to throw any more money at this thing...

Thanks again...

Al

[Dino]

The vent line does not run back to the tank, rather it dumps into the frame rail.  The whole idea behind it is to have air behind fuel, without the air you're not getting the fuel you need. Same principle as air behind water in the drains in your house.  With a blocked vent pipe it's going to take longer for water to drain.  Opening the fuel cap bypasses the vent and air rushes in from the top.

Run the tank near empty and remove the entire filler neck.  Then put compressed air on the vent tube to get open it back up.  Reinstall and you're all set.  Doesn't hurt to run air through the frame rail either.  Simple job so let's hope that's all it is.   

Sweet ride by the way.   

[PlainfieldCharger]

The vent line does not run back to the tank, rather it dumps into the frame rail.  The whole idea behind it is to have air behind fuel, without the air you're not getting the fuel you need. Same principle as air behind water in the drains in your house.  With a blocked vent pipe it's going to take longer for water to drain.  Opening the fuel cap bypasses the vent and air rushes in from the top.

Run the tank near empty and remove the entire filler neck.  Then put compressed air on the vent tube to get open it back up.  Reinstall and you're all set.  Doesn't hurt to run air through the frame rail either.  Simple job so let's hope that's all it is.   

Sweet ride by the way.   

Vent tube was clogged on mine. Had a ton a vaccum when you opened the gas cap. Had to use a solid wire and compressed air... running great now...

[csx4590]

I am a little confused about this vent line. We are talking about the small line that runs along the pipe that runs from the cap down to the top of the tank correct? At the cap end, what does it hook to and what does it do at that end exactly? Sorry for all the questions...

Al

[Dino]

Yep it's the small line running alongside the fuel filler neck. 

It is attached to the filler neck, close to the cap.  It's not attached to the cap itself.  The vent then runs down through the trunk floor and ends inside the driver side frame rail.  This is just to keep even pressure inside the tank so the fuel is free flowing.  When that vent line is clogged, the pump is unable to get sufficient fuel into the carb.  Popping the cap restores the pressure equilibrium and the car runs fine again.  All that line does is provide air, that's it.  It just opens into the frame rail and is not hooked up to anything.  Get some compressed air through that vent line to clear it out, just don't get anycrap in the tank!.  You can also add a piece of rubber hose to the end of the line once it's cleared so you can have it stick out of one of the rail holes if there's a lot of crud in the rail.

Keep us posted!

[1974dodgecharger]

mine just breaks off.....

[csx4590]

A few posts back, I posted that my car was running rough after about 20 minutes. Several theories were posted about either hot fuel/vapor lock or a blocked/plugged/improperly installed vent line. Now it runs rough right from the start so hot fuel can be ruled out. I took the tube off today and I can blow through it fairly easy. But I noticed this where the vent line comes into the gas filler tube. Looking down into the filler tube is a small screw/bolt that is where the vent tube comes in. Is that supposed to be there? I have the gas cap open, and the vent tube removed and it still runs rough. Any other ideas that I might be able to try to correct myself without being overzealous with my limited mechanical skills???

Feeling very frustrated...

Al

[csx4590]

A few posts back, I posted that my car was running rough after about 20 minutes. Several theories were posted about either hot fuel/vapor lock or a blocked/plugged/improperly installed vent line. Now it runs rough right from the start so hot fuel can be ruled out. I took the tube off today and I can blow through it fairly easy. But I noticed this where the vent line comes into the gas filler tube. Looking down into the filler tube is a small screw/bolt that is where the vent tube comes in. Is that supposed to be there? I have the gas cap open, and the vent tube removed and it still runs rough. Any other ideas that I might be able to try to correct myself without being overzealous with my limited mechanical skills???

Feeling very frustrated...

Al

I can't figure out how to delete the above message. It seems as though the shop I last had the car at, sent the vent line back into the tank. It had a little gas in it so I guess that was causing it not to vent as it was blocked by gas. I cut the hose, blocked off the end from the tank temporarily and then hooked the other end up to the vent line and so far, it seems to have worked. When I get a chance to get the car up on a lift, I can fix the temp repair with a more permanent one. Gonna take her out for a spin this evening to see what happens. I hope that is all it was...

Thanks for the great replies and ideas on this site. You guys are a big help...

Al

[Dino]

It has to be the vent, all sign point toward it.  I think it'll run just fine now.   

[csx4590]

We missed the first car show we went to by 2 football field lengths. It shut off and wouldn't start again. 

Second show was a little more successful. We made it there and back. Hope this fixes the problem so I can break in the motor and start enjoying this great Maryland weather...

[c00nhunterjoe]

What part of maryland?

[csx4590]

What part of maryland?

Laurel, Md

[csx4590]

Well I took it out for a drive and had to be towed home. So what I changed didn't help. Back to the drawing board...

[c00nhunterjoe]

Thats quite a hike for me. Did you verify if it was a fuel or ignition problem when it died?