Hmm...never heard of the unlit propane torch one Ross. Interesting.

I really believe the vacuum gauge is a badly overlooked diagnostic tool. With the proper charts to look at...it can tell you all sorts of things.

 

I just thought of another problem.....Vapor lock on your fuel line!

Also, got a vented gas tank cap?

Are you having fun yet?

Julie

 

The only caveat here is that at idle he doesn't appear to have an issue, so no "data". Lack of fuel under load will mask other symptoms.

 

If using just a rubber fuel line when replacing a hard line, you risk the rubber line squeezing itself under load. There's a reason hard lines are used from the mech. fuel pump up to the carb/filter with little use of rubber. Not sure this is what you did, but you mentioned replacing the fuel line. Another possibility is the manual choke is sliding back closed gradually, or the valve isn't fully opening when the choke cable is pushed all the way in.

 

Gah I hate vapor lock! Only experienced it once but it was enough to make me call the truck many names and threaten to sell before it ran again.

 

I'll take a look with some of the stuff you guys suggested tomorrow, bit worn out today (lol don't you love it when your weekends are more stressful than your work week?)


I really appreciate the help, about all I have gotten else where was to to check the carb. What puzzles me is that everything seems to work flawlessly until the power is needed, then I have no power. Not one thing works wrong under the hood. it's smooth and strong. When driving idle is good. It's just when it needs the power, its no longer there. The engine doesn't die, it just sounds like the volume is turned down. It's been a problem I've had with it since I've bought it, though it has gotten worse over time. The car hasn't seen more than 80 miles since I got it home 2 years ago (I spent almost the first year restoring it, the clutch went out this spring and I haven't been able to get around to it till recently. You don't drive it when there's snow because no one in this town knows how to drive... and snow and Wyoming = most of the year, lol)

So $20 on this being a really stupid problem? lol...

 

I'd recheck the timing and make sure it advances.

 

Had a similar problem with a 1968 fairlane with a 302, It luckly had a see through fuel filter between the carb and pump and it was obvious it was running out of fuel. Replaced the edelbrock pump with a carter and all has been well. Could be alot different things though.

 

I replaced the fuel filter and adjusted the timing. It's still running rather rough. Going to play with the carb some more I suppose.

It just seems so odd that it only happens when the power is needed, so I guess that brings up the question; What's different when it's reving without the need for the power, verse the need for the power?

 

laws of motion, like the gas in the tank sloshing to the rear of the tank, carb float, colder intake air?, etc...

 

It seems to me that revving an engine without load requires very little fuel compared to one working under load. The harder an engine has to work the more fuel it`ll use so if there`s a restriction in the fuel supply it`ll be noticed more under load.

 

Good reasoning, thanks. I'll switch out that fuel pump and see what happens. I know the sending unit needs some attention (gauge is off) as well...

 

One of the most pronounced differences is the drop in intake manifold vacuum at load that doesn't occure when just reving. That difference is substantial and it occures without the instant rpm increase as when in park.

So, there is a higher demand for fuel and less rpm to drive the fuel pump. Although what's in the carb bowl and the accelerator pump should handle this normally, we don't know if it's working normally. It could be the reverse as well: because of the load and no increase in rpm, you could be drawing way too much fuel and flooding the engine. Have you noticed whether it is more pronounced with the engine warmed up?

What goes in must come out. There is quite a bit more influence from possible exhaust system back pressure - in other words with the no load revs, the engine quickly develops enough rpm to push the exhaust past any semi blockage - not true when loaded. (I dated a guy who had the same problem-passing exhaust when loaded). We know this is a 302/4V/4spd, but we haven't yet discussed what kind of car this is. Does it have a catalytic converter? Is the converter plugged up? Are their pollution control devices (the infamous air pump) installed.

How many miles do you have on this engine and have you run a compression check on it? Does it run smoothly when it finally gets up to RPM?

With the timing correct, this still sounds like fuel to me: either too much causing flooding when the accellerator pump dumps, or accelerator pump not working enough. Can you look down the carb throat and see if it is shooting gas?

Just thinking out loud!

J!

 

Thanks for the input!

In a couple of hours I'm switching out the fuel pump, I'll let you know how it goes.

It's in a '67 Mustang.

When it's warmed up things work better, but recently it's been getting worse, my thoughts, or rather my serious hope (because I'm tired of this, ha), is that the spring in the fuel pump has worn out or gets stuck, it's probably the original, and then when it really needs to work it's not rebounding enough to get a good pump. With things being warmer it wouldn't need as much gas. It would also be giving enough gas to idle correctly, but not enough to be used.

Least that's the hopes and dreams of a man tired of this problem who already bought the fuel pump and just needs 5 minutes to swap it out, lol

 

I had an el camino once with an edelbrock carb with a very similar problem. There were some screens in the top of the carb that got trash on them or in them. Cleaned those and it fixed my problem. If I remember correctly all i did was use some carb cleaner and an air blower. I hope this helps. Might save you some checking.