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Let's talk fuel starvation!

vwbusman66

vwbusman66

Stößelstange über alles
Joined
Oct 12, 2016
Location
SE MI
So, I've been trying to drive the 142, but keep having severe lean popping.

At first, I thought it was mixture. I tweaked and tweaked and tweaked.
Then, I replaced my metal fuel line that had a suspect kink in it.
Then, I replaced my fuel filter to make sure it wasn't clogged.

I am running a clear fuel filter, and when the car is running, it doesn't stay full EVER, regardless of RPM.

It seems to me, furthermore, it is only running on the front carb, as any attempt to richen/lean out or even lift the dashpot/needle shows no change in RPM.

The car has an original Pierburg stamped mechanical pump. Could it be piss-poor fuel pressure?

Help.
 
Probably a good idea to replace it. Id say chuck in an electric pump as a test/permanent replacement. A clickety clack can't cost much at a parts store.

Does it run better momentarily after coasting to fill the bowls?
 
Cwazywazy said:
Probably a good idea to replace it. Id say chuck in an electric pump as a test/permanent replacement. A clickety clack can't cost much at a parts store.

Does it run better momentarily after coasting to fill the bowls?
Click to expand...

Parts store low pressure (carb) electric pump is like $40 :wtf:
I doubt I can get a mechanical in time before I leave, so I'll rig up the electrical and order a mechanical to my apartment in Morgantown.

Funny you say that. If I stick my hand over the usable carb, I can watch it suck more fuel through the filter and it momentarily runs better.

It also backfires gratuitously, due to the ****ty mixture to compensate for zero fuel pressure.
 
Might be also worth checking the often-forgotten filter in the fuel tank.

This little blighter.
pg51c.jpg
 
It might be wiser to check the fuel pressure with a gauge before throwing a pump at it.

Having an air pocket inside a clear filter is not unusual in my experience with carbed B20s.
Looks weird, but it always runs with no starvation issues.
 
Why not check before replacing parts?

>Measure fuel pressure:

Enough> Investigate carb
Low> Check in tank filter:

Dirty> Clean and measure again
Clean> Check pump:

Defect> Replace
Propper functioning > Check lines and hoses

It's such a shame to spend money and replace random **** while praying it works. It wouldn't surprise me if the problem sits in the carbs them selves. We've seen plenty enough issues with current fuel when sitting, even a short while.
 
Carbs are apart again.
Re-checking float level after watching some John Twist videos and reading Thomas Bryant’s article. I think I may have put the front float cover on backwards :oops:

Also, the front carb’s jet bushing retainer nut was backed all the way out!
 
What kind of carbs? And generally speaking, the float bowls should be vented to outside air, so putting your hand over the carb inlet while it's running shouldn't have any effect on the fuel supply, although it will make the carb run really rich, rich enough to kill it.

Are bubbles entering the fuel filter? It doesn't take much of a hole in the line between the tank and pump to make the pump not work well - it's not good at pumping air, and it needs to pull a partial vac along that line to pull fuel up to the engine.

Generally speaking, a fuel supply issue will be most noticeable at speed, where the car is using the max amount of gas. Idling barely uses any gas, so if you have a weak pump or something, it can usually at least supply enough to idle. But if it runs like crap at idle, and runs like crap while driving, it's probably something else. But idling fine, and falls on its face when you have the pedal down for more than a few seconds (while the bowls slowly empty out and aren't refilled properly), - def good chance it's a fuel supply issue.
 
JohnMc said:
What kind of carbs? And generally speaking, the float bowls should be vented to outside air, so putting your hand over the carb inlet while it's running shouldn't have any effect on the fuel supply, although it will make the carb run really rich, rich enough to kill it.

Are bubbles entering the fuel filter? It doesn't take much of a hole in the line between the tank and pump to make the pump not work well - it's not good at pumping air, and it needs to pull a partial vac along that line to pull fuel up to the engine.

Generally speaking, a fuel supply issue will be most noticeable at speed, where the car is using the max amount of gas. Idling barely uses any gas, so if you have a weak pump or something, it can usually at least supply enough to idle. But if it runs like crap at idle, and runs like crap while driving, it's probably something else. But idling fine, and falls on its face when you have the pedal down for more than a few seconds (while the bowls slowly empty out and aren't refilled properly), - def good chance it's a fuel supply issue.
Click to expand...

46think the gas phase stuff in the filter is fuel vapor, not air, at least whit has been used for a while.
 
This 15mm nut in the center came loose:
SBy6jYxl.jpg


Turns out, both carbs' jet bushing retainer were loose. The rear carb's needle had dropped into the jet and was out of the dashpot/dampner.
Took both apart, properly set the float levels (1mm gap from the CENTER of the float to the bottom surface), cleaned them, tightened the bushing nuts, and viola! I took the car for a quick drive, and it is now running well on both carbs and actually has power. Plugs are a nice burnt-tan and the fuel filter stays full. I still have a small weep from the fuel line union, but that is easily addressed.
 
Glad that worked out. When you start playing with the fuel pumps and want to change to an electric. You can open a can of worms. As I recall you are using the HIF6. SU carbs use low fuel pressure. Typically 1.5-2.5psi. The pierburg pump works perfectly. If you replace the pierburg with an aftermarket mechanical pump. They are usually set for 3-4psi and can overflow the bowls on SU especially the older ones. Or it'll make it run rich all the time. Adding an electric pump means adding a pressure regulator since they too are set to high for SU carbs.

Strombergs are a little more tolerant but they also run at the lower pressure.

Make sure the heat shields are under the carbs. That can cause fuel vapor lock issues. You have to have something on there.
 
dl242gt said:
Glad that worked out. When you start playing with the fuel pumps and want to change to an electric. You can open a can of worms. As I recall you are using the HIF6. SU carbs use low fuel pressure. Typically 1.5-2.5psi. The pierburg pump works perfectly. If you replace the pierburg with an aftermarket mechanical pump. They are usually set for 3-4psi and can overflow the bowls on SU especially the older ones. Or it'll make it run rich all the time. Adding an electric pump means adding a pressure regulator since they too are set to high for SU carbs.

Strombergs are a little more tolerant but they also run at the lower pressure.

Make sure the heat shields are under the carbs. That can cause fuel vapor lock issues. You have to have something on there.
Click to expand...

I'm planning on keeping the pierburg mech pump. I'm running dual HIF 6's.

Heat shields and phenolic spacers are present. The one piece mani is there too.
 
I have no idea if my tank has ever been removed and/or coated. This car had a lot of ?restoration? type work done to it before MikeSr had it I believe. So who knows what?s in there :e-shrug:
 
AndrewNance said:
I have no idea if my tank has ever been removed and/or coated. This car had a lot of ?restoration? type work done to it before MikeSr had it I believe. So who knows what?s in there :e-shrug:
Click to expand...

It was common back in the day to remove it and put one of those cheepie plastic fantastic fire hazard dealies up by the front of the valve cover.
 
Be careful when pulling the plug for the filter. It's made of soft brass and the square drive is an odd size. I ground down a piece of 7/16" square stock until it fit snugly in the plug.

D-JetIFilterPlug.jpg


Redwood Chair said:
It was common back in the day to remove it and put one of those cheepie plastic fantastic fire hazard dealies up by the front of the valve cover.
Click to expand...

It's important to have the in tank filter on fuel injected cars to protect the fuel pump.
 
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