Bad Rings? Head Leak? Causes of erratic Air/Fuel ratio.

Post by **Sluggo** » Sat Apr 21, 2007 12:10 pm

So I got an Edelbrock Air/Fuel ratio meter. Almost wish I hadn't. I'm running very rich (12) most of the time but at idle it bounces back & forth rapidly between 15 (lean) and 12 (rich). If I jet it so that I run stoich while cruising and accelerating then it won't idle and goes way lean.

Most of the stuff I've read says that this is a sign of either improperly seated rings, head leak or low vacuum. I've always suspected that the rings did not seat properly. Being washed in fuel while my carbs were extremely over jetted and never having broken in rings before. I also have oil leaking from the bottom of where the #3 cylinder meets the head. I believe these are related.

Anyway, do you people think this is the cause of my problem. If I jet the carbs to run efficiently I can't idle because of all the blow by and head leak. If I jet them to idle smoothly (somewhat) I'm running very rich.

I plan on replacing the rings and doing a proper break in next week.

vwlover77 · Post by **vwlover77** » Sun Apr 22, 2007 6:57 am

Hmmmmm..... I would be hesitant to accuse the internals just yet.

Have you done a compression test? How about a leakdown test? Those are probably the best way to gauge what's going on in the cylinders.

My carb experience is limited to the simple, single 34PICT3 on upright engines, but can you adjust the idle circuit mixture independently of the main circuit??? Are there separate jets for the idle and main circuits?

vdubyah73 · Post by **vdubyah73** » Sun Apr 22, 2007 8:23 am

If it idles erratically, pull one plug wire at a time while running. Don't worry about shock just keep your fingers clear off the end of the wire. Isolate the cylinder thats misfiring and fiddle with that carb. It took me a lot of years to figure out cause and effect on dual webers. I now tune them to a rock steady idle with nothing but my ear and the plug wire method. One plug at a time if a plug wire makes a big difference that cylinder is banging away happy. both plugs from the same bank make a big differenc and the plugs on the other bank don't make that big a difference the big difference side has the carb ahead of the other side. I gotta get one of those meter's I'm gonna have duals on my new bus engine as well as my buggy engine.

Bill

bottomend · Post by **bottomend** » Sun Apr 22, 2007 12:13 pm

the engine purrs like a well fed sleeping kitten. Do the plug wire check and see if that shows you anything. I doubt it but hey, at this point anything is possible!

Sluggo keeps telling me taht he didn't really break in the rings like he should have. I'm wondering if thats the issues as well but if I rememeber correctly, his compression #'s are good all around. I know the guides are good cause I either did them myself of watched them being put in and fitted for the valves.

RSorak 71Westy · Post by **RSorak 71Westy** » Mon Apr 23, 2007 7:30 am

Is your exhaust system totally leak free? If not this will cause the readings your getting at idle.....Also if the engine burns any oil or has any vacuum leaks the readings will be wacky at idle like your seeing.

Post by **Sluggo** » Mon Apr 23, 2007 10:31 am

bottomend wrote:the engine purrs like a well fed sleeping kitten. Do the plug wire check and see if that shows you anything. I doubt it but hey, at this point anything is possible!

Sluggo keeps telling me taht he didn't really break in the rings like he should have. I'm wondering if thats the issues as well but if I rememeber correctly, his compression #'s are good all around. I know the guides are good cause I either did them myself of watched them being put in and fitted for the valves.

I wouldn't say that. This is from a previous thread and 7 months old.

#1 - 100
#2 - 110
#3 - Just over 80 (same weak cylinder as before the rebuild)
#4 - 105

bottomend · Post by **bottomend** » Tue Apr 24, 2007 12:44 am

hummm.... #3 not good. I was not aware that the figure was THAT low.

Post by **Sluggo** » Fri Apr 27, 2007 11:19 am

Did some tests.

Vac gauge bounces between 8.5 & 10 at idle.

(dry/oil)
#1 100/115
#2 110/125
#3 90/115
#4 95/120

Did the wire pull test too. All have an effect but #3 barely has an effect.

Plugs were gray.

Air/Fuel ratio monitor shows rich on all circuits but at idle blips back & forth form way lean to way rich. But it's mainly way lean.

I don't think I have a vac leak. Can rings also cause low vacuum?

Post by **Sluggo** » Mon Apr 30, 2007 9:54 am

Not getting a response huh? Am I being shunned?

fido · Post by **fido** » Tue May 01, 2007 2:14 am

posted by Twysted1 on shoptalk for a different Q...

If your map values pop all over the place at low RPMs.

(With carbs that will probably happen at idle)

You can stick a new vw fuel filter (plastic, 2 bucks at any parts store) inline with the rubber hose. This helps dampen the oscillations to the map sensor.

Clayton
______________

I'd say running around 12 isnt too bad - better safe than sorry. I wouldnt want to run any leaner than 14 on an aircooler. Its all load dependant and weather dependant anyway with carbs.

Itinerant Air-Cooled

Itinerant Air-Cooled

Bad Rings? Head Leak? Causes of erratic Air/Fuel ratio.

Bad Rings? Head Leak? Causes of erratic Air/Fuel ratio.