I dont have a wideband (yet) and it seems like now that I advance my timing the exhaust smells richer. Maybe it's just me but does changing the timing effect your AFR?

 

Yes it will effect it a lot.

From what I understand, if you are too far ahead or behind you wont get a full burn and will end up running rich. If your plugs fire after the exhaust port starts opening the unburnt fuel starts to escape before being ignited... but at that point you're losing power as well, and probably backfiring a bit on decel.

...Kinda like the Misfiring systems on rally cars that retard the timing when the throttle plate is closed so that the ignition dosent spark until the exhaust port is open causing the backfire to keep the turbo spooled up... NEATO!

I wouldnt worry about the smell, but if you start getting black smoke when you floor it, somethings not right, you're WAY too rich. LOL! Try turning back the mixture screw on your carb 1/4 turn and see if that helps.

I COULD be wrong, correct me if I am.

 

Thanks... makes sense...

I'm keeping my eye on some widebands on ebay so that I dont have to play guessing games.

 

dude widebands are great, but if you just want to go simple- and alot cheaper but still pretty accurate, just get an A/F ratio gauge- $50ish. a generic 02 sensor- $20ish, and wire it up! hardest part is getting a bung in your exhaust, but if you know someone who can weld decently a bung is like $1.50 at the hardware store, just ma two cents...

 

AFR's are not effected by timing. AFR stands for Air Fuel Ratio. No where in there does spark come into the equation. The only thing that you'll do by changing your timing is more ore less raw fuel out the exhaust.

 

Well I lost the bidding on a FAST wideband even though I sniped...

So whitey85mtu, if you measure AFR through a sensor in your exhaust wouldn't sending more raw fuel through your exhaust make the sensor read a richer AFR?

Not cracking wise... just trying to understand....

I have 24L & 16T marked on my pulley but I was just going a few degrees after that to see if that would make a performance difference... and the exhaust started smelling more like raw fuel.

 

how much timing are you running? typically you have to go way beyond the optimal range to start smelling rich exhaust with no other changes. I would suggest bringing it back a few ticks to get it in a better range. Timing is a delicate balance. Keep it on the aggressive side of the factory settings and you will be making good power and have a happy motor.

Typically, the idea for more timing is to allow for more fuel to be added. The sooner you spark the more time that you have for the flame to develop and apply pressure durring the expansion stroke. If you've advanced your timing to the point it smells rich then that is an indicator that you've gone too far. you should NEVER have to remove fuel due to advancing your timing on a setup like yours.

pull a few degrees and your smell will go away.

Ray

 

you won't have different AFR's because you have the same amount of fuel going through the engine, regardless of your timing. your spark plugs are completely independent from your carb, so your timing is completely independent of your AFR's. the only thing that will change is if you retard your timing too much, you'll be still burning fuel in your exhaust, which causes a loss of power.