can a weak MSD ign.effect AFR.

Yep.....

No it does not.

Lbs of air and lbs of fuel (the Air to fuel ratio) does not change because of a lack of or presence of a ignition source. Now if you are reading with a O2 sensor the lack of combustion will change the reading but the A/f has not changed at all.
Climbing down off of my soapbox.

Joe

REPHRASE:can a weak MSD ign. effect AFR READINGS.I think thump knew what I ment.

I knew what you meant and I stand by what I said.....no different than a bad spark plug/wire cap/rotor etc. Weak spark = rich mixture seen it many times..................

I would guess you mean a plug fires but the spark is weak and barely enough to fire the plug ? Or do you mean weak enough that it causes a missfire ? Cause a missfire will cause the 02 to go very high since when the plug dont ignite the mixture you still have around 14% air to 1% fuel so a missfire will see a big difference of a very high reading on an 02 sensor. If the plug fires but is a weak sprark and does not cause a good flame then I would think the plugs may read rich if all the fuel is not burned. Ron

this car was running perfect then all of a sudden it just started running real rich at cruise.it went from 13.8- 14.5 to 10.00 to 11.00 on the afr meter.ive checked everthing possible.the only thing I havnt changed out is the msd and the dist.

What makes you think it's an ignition problem? Could be a fuel issue - carb related.

Its the ONLY thing left that hasnt been replaced or thuroughly vetted.

Its the ONLY thing left that hasn't been replaced or thoroughly vetted.

if the ingnition was weak, or misfiring,. you would have incomplete combustion and the O2 would read lean (there's more oxygen left). There is only 2 ways for the O2 to read rich, you have added more fuel or you have less air. In each of these cases you must have combustion to burn all remainding oxygen.

just a note, with a weak ignition the O2 will read lean, plugs will be rich.

Have you checked your IAB's? they may have gotten pluged.


Joe

I checked the carb out several times and even sent it back to BIGS. it came back with a clean bill of health.

Fuel pressure or carburetor power circuit.

R.

been there ,done that,up down back and forth.

If all that's left is the box and dist., go with the box first. All the wiring up to snuff? Alternator putting out at least 14 volts? Battery load test good?

brand new alt and batt.

Weak coil? How old and what type of coil?

good place to start!

brand new blaster 2,now I have a spare.

OK, I changed the 6al to a 7al-3 and put my old msd dist back in.no change.

Have you checked each plug wire and changed the plugs yet?

Is it rich, or does your meter just "say" that it's rich?

new plug wires and im on my 3rd set of plugs.wires aint brand new maby 6 mo old.MSD 8.5

plugs are black and sooty.it idles pretty fair but loads up real bad at cruise.if I let it idle awhile it will cruise ok for a few mi;les then load up again.

FIX THE CARB.................

Sounds like you have carb issues. My old style 9375 dominator would foul out plugs going down the highway at 60 mph, but would idle clean all day. WOT was good too.

im tryin to find someone around here with another carb or would be willing to try mine.ive had this carb apart numerous times and replaced every soft part.like I said I even sent it back to Bigs and he said it was perfect,he even X-rayed the dang thing.if I cant figer this DELEMA!! out pretty soon I may have to let that Thumper guy take a look at it

Does the carb hold the float level while running? Sight plugs removed and fuel level set at the bottom of the sight plugs?

yes it does