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A/f Ratio And Flucutations


Zorac

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my a/f ratio fluctuates a fair amount. for example at an idle, it sits at about 13, but bounces to 14 or 14.5 fairly regularly like its getting air into the system. ive tried about everything, new fuel filters, new gas line, no fuel filter, and have felt around all my connections for it sucking air, but nothing is evident. fuel filter never seems to have enough gas in it either, roughly 1/4 full, and no matter how you twist it, or shake it, I can't seem to get it to suck the air through the system.

 

i redid all the gaskets on the carb and reset my float levels as well. thoughts? or is this just normal?

 

the only thing left to replace would be the fuel pump, but i am running a pressure gauge and it is consistent at around 2.5psi.  or maybe a grounding issue on the a/f meter and sensor (not sure how that would behave though and its more consistant when driving)?

 

thanks.

Edited by Zorac
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They all do that it's quite normal I think it's the nature of the beast fuel air mixture & burn are not exact at all times I would not sweat it.

1970 4 speed 2002 (Daily driver/track car ) 
1974  Hybrid powered twin cam engine, Pig Cheeks , ( now a round tail.) Getting ready to Sell 
 

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They all do that it's quite normal I think it's the nature of the beast fuel air mixture & burn are not exact at all times I would not sweat it.

 

good to know!  thanks, i was unsure how much variance was acceptable on a carb.

 

...or work on your distributor- timing will do that sort of thing, too. paradoxically...

 

t

 

wouldnt it go to the rich side, not lean side if it was a distributor/timing issue?  timing has been checked numerous times, so it would have to be rotor/cap or wires, which if there was an issue there, i would think it would miss and push gas straight through on occation.

Edited by Zorac
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If you see wander on the timing ball, it's pretty common to see oxygen variance, too-

the timing affects the quality and completeness of the burn, and thus, oxygen level.

 

Even if you don't, these things aren't very modern, so movement of 1 point at idle,

especially if your idle speed isn't rock- solid, isn't unusual.

 

hth.

 

t

"I learn best through painful, expensive experience, so I feel like I've gotten my money's worth." MattL

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the ball use to wander, but ever since i tightened up the clips for the cap its been solid.  idle doesnt hunt (but does vary day to day a bit depending on temp), but the last 200rpm come off slow when you let go of the gas to back to idle. 

 

idle is set a bit high at 950rpm, but to get any lower it starts to get rough, which i think is more an idication of an agressive cam though.  the cam itself is a mystery, but it appears to be a bmw sport 300 cam (although its missing the appropriate marking on the flang for the sprocket).  800rpm gives a pretty lumpy idle that only runs on its own under ideal conditions, a change in weather is enough to screw it up and it will want to stall.  the engine is still fresh, so it may settle down as the rings seat as well.

 

timing was just done as well.

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