Fuel lean-out problem.

69427

69427

The Artist formerly known as Turbo84
Joined
Mar 30, 2008
Messages
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Clinging to my guns and religion in KCMO.
Had a problem today which shortened my track day. Towards the end of one of the sessions the engine would run like crap coming through the corners. I initially chalked it up to fuel spillage from hard braking (although it never spilled over before) and an overrich condition. However, when I looked at the WBO2 readout it indicated lean (13-22 A/F ratio) depending on the engine speed and throttle position. This sufficiently scared me enough that I backed out of the throttle and decided to pit early. On most of the drive back to the pits (about a mile) the A/F meter read 18-22. At idle in the pits it stayed in that region. My first thought was a plugged jet (but doesn't the idle circuit do most of the fueling at idle?), or possibly a broken plug or plugwire (and a cylinder just belching out uncombusted air), but the idle (exhaust sound) didn't seem to have any obvious sounds of a cylinder dropping out every 8 firings. The idle sound just sounded "anemic", for lack of a better description. The engine barely had enough power to get the car into the trailer.
If the issue was a fuel pump I would assume that the problem would only be at higher loads, and the idle quality and A/F ratio would be normal. But it wasn't, so I'm initially discounting the pump.
If there was a blockage issue in the secondary jets I would expect any WOT leanness to go away at part throttle, but it doesn't, so I believe the secondary fueling is working (although it is normally a bit rich, and that was the reason for running with the WBO2 sensor today to see how much adjustment I need to do to the jetting).
I didn't hear any unusual mechanical noises in the engine, so I don't think (at the moment) that I've broken anything major. So, unless something obvious jumps out at me I'm going to pull the plugs to see if anything looks suspicious (and probably replace them anyway. The electronic ignition gives me great plug life, and these plugs are several years old). and also take the primary side of the carb apart to see if there's any trash in there.

Any ideas or suggestions are welcomed.
 
Couldn't a vacuum leak cause a lean condition? I plan on running an electric vacuum pump for all those vacuum controlled systems like the headlights, wiper door, etc. on the Blue Angle 69 new engine when I get it installed.
 
new weight reduction scheme?

This isn't some new weight reduction scheme is it. Lean mixture is less dense so the weight high forward is reduced?
 
I vote for fuel pump issues...maybe fuel line??, you sure the tank is getting vented??:thumbs:
 
I vote for a clog in the fuel filter. No fuel pressure guage? get one. Take it all apart, brake clean it, replace the filter.

Ya the idle circuit feeds a lot at idle and cruise, but my understanding is that really every fuel passage is always feeding somewhat.
 
enkeivette said:
I vote for a clog in the fuel filter. No fuel pressure guage? get one. Take it all apart, brake clean it, replace the filter.

Ya the idle circuit feeds a lot at idle and cruise, but my understanding is that really every fuel passage is always feeding somewhat.
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it sounds like a clog somewhere.

I'll add this because it's my nemesis right now, 02 sensors can give false readings if they have too much carbon on them (which is why I'm pulling the ez efi off my car and putting a carb back on - the wild cam carbons up the 02 sensor, that's $100 in sensor every 500 miles). In my limited efi experience, it generally won't run at all at anything higher than 16:1...
 
Well, finally getting back to the car (been mowing the grass for the past two effing days). I pulled out a couple of the spark plugs (4&8, as they feed off of alternate sides of the carb, and they're easy to get at). They're both very light tan (and no oil, which surprises me for a BB). I'm not a plug reading expert, but it's my impression that means it was running lean for a while (please correct me if I'm reading them wrong). I looked at the insulators with a magnifying glass but didn't see any aluminum specks, which I'm told is an indication of excessive detonation.

I'm running the stock gas cap, which is vented in 1969. I'm going to blow some air through the vent hole to confirm it didn't plug up.

The inline fuel filter is about three years old, and less than 2000 miles, but I'm going to replace it while I've got other stuff apart.

The fuel pump inlet line (rubber) is new. I replaced it last week when the brand name (Made in USA NAPA) line on the car was all weather cracked on the outside, despite being only about 3 or 4 years old. I would be very surprised (and disappointed!) if that line somehow contributed to the problem. When I've got the fuel filter off I'll do a crude pump volume test to see if anything is reaching the filter area. Anyone know what a decent volume is at cranking speeds (AC brand pump)?

Not aware of any obvious vacuum leaks yet, but I'm checking. Another reason for pulling plug #8 is that the vehicle vacuum system is tied into a fitting in the #8 intake runner. Been like that for decades, but I wanted to make sure that the #8 plug didn't look a lot leaner than the others.

That's all I've figured out so far.
 
Mike, years ago I bought a replacement cap for my '72 and it was NON VENTED....so I finally bought a chrome/aftermarket locking cap....

and noted a silly valve type thing to the left/forward top of the tank, leaking fuel.....witch made the smell, I glued it up with epoxy, and made sure the canister vent was operational....I know the cap is vented,

course I have FI, so my flow out rate is matched by the return rate, minus of course engine demands.....maybe try running it with say 1/2 a tank and no cap????


:twitch::surrender:
 
Well, did a bit of troubleshooting today. I disconnected the fuel line between the inline filter and the chrome line that feeds the two fuel bowls. I then rigged up an "IV system" with a spare lawnmower gas tank that fed the carb, and then also a line from the fuel pump/inline filter into a half liter coke bottle. I started the engine and then had to shut it off in about 4 seconds when the pop bottle started filling up awful damn fast. The engine still ran like crap, and given how fast the bottle filled up I eliminated the fuel pump and filter as the issue. In order to see if I've got a dead cylinder pumping out raw air into the exhaust (the WBO2 sensor was reading about 23:1) I touched the header pipes with my fingers. There was a noticeable difference in temperature among the pipes. Cylinders 1,4,6,and 7 were hot to the (damn quick) touch, while 2,3,5, and 8 were only moderately warm. Looking at the intake manifold runners it looks like the passenger/right side of the carb is not flowing enough fuel. I'm going to take the primary fuel bowl and metering block off tomorrow and see if there's some blockage in the internal passages.
 
Bullshark said:
Damn Mike, they make ir temp guns these days for under 25 bucks. Wtf, u trying to go incognito with the finger prints. :lol::lol:
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Yeah, I hear ya. :amused: I actually do have an IR gun, I was just too damn lazy to go look for it, and it was just quicker doing the test the old fashioned way. To be honest, the pipes are ceramic coated inside and out so they're not that hot at idle, except for cylinder #1 that I had to replace to clear the steering shaft and is now just coated with VHT silver paint. That pipe was damn hot.

IM001100.jpg

I took the primary bowl and metering block off the carb today, but I don't see anything obviously wrong yet. I'll just disassemble everything I can and then spray some carb cleaner and compressed air backwards through the passages to try to clean out any crap that may have gotten in there. I still have to figure out which passage can cut off the fuel at both high and low loads.
 
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Over rich (way over) can give bad af readings. Did you look at the plugs.
 
rtj said:
Over rich (way over) can give bad af readings. Did you look at the plugs.
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Yeah, they looked remarkably tan and clean. Just for safety reasons I might replace the current ten year old plugs with some of a heat range cooler.


Found the problem. The fuel passage that feeds the right side of the manifold had a piece of debris in it.

IM002412_zpse7ae54f6.jpg

I pulled it out with a tweezers and looked at it under a magnifying glass. It looked like a piece of the carb casting, but when I touched it with my finger to roll it over to look at it from another angle it just crumbled into a wet, golden dust. I'm perplexed about what it is/was, or where it came from, but at least it's out of there. I sprayed carb cleaner through all the passages and put the parts back together. Dribbled a bit of fuel onto the throttle plates to re-prime the system and fired it up. The engine ran smooth and the WBO2 numbers looked normal. Back in business.
 
You were holding a gas can over the engine? You need fuel pressure. I need 7-9psi at no boost, not sure about your carb setup. Prob need at least 5-6.

Light tan if I remember correctly is perfect. Lean causes the gap to open?? I dont remember
 
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