What A:F ratio does engine start to run rough?

[ChasBean1]

Greetings all,

I hear gas engines run rough when burning rich and run smooth but stall when burning lean. I was curious whether there is common knowledge on what gas engine A:F ratio (rich end) will rough engine running first become apparent... If you have an answer, are there any sources I should look at? I realize "rough" is not well defined. What would be the most common cause of rich burning forklift operation?

Any advice you could give is appreciated. Thanks, -CB

 

[evelrod]

Depends on the engine and setup. A guess would be something like 10:1 on the low side and 15:1 on the high side. Just a guess though as I have seen engines run perfectly well at those settings.

Rod

 

[ivymike]

gas engine

Which gas are you refering to?

 

[comnean]

Hy,
I have some experence with LPG systems fitted on gasoline engine. Is very important to know that aprox. 1,3-1,4 l of liquid gas are equivalent with 1 normal fuel litre. (according caloric power of each). One other very important factor is temperature of gas in expansion time via the vaporisator unit, the temperature of intake air and the shape of TB mixer and intake air duct. From my experience (with adjustable and eleqtronically busted LPG sistem) I agree one normal (engine hot) AFR around 11:1.

 

[Andy330hp]

Yeah, defintely depends on engine setup, but in general it's the reverse of what you mentioned, most engines will run smoother (especially at idle) slightly rich. It also depends on timing, since if you advance timing to compensate for the leaner mixture (talking light load here!!) you can get an engine to run smoothly over a range of A/F ratios. Our MGB will barely idle at 14.7 unless you give it a ton of timing, and even then it's not pretty. But, at 13.8 to 14.0 it will idle nicely (as much so as you could expect an MG to idle). Under cruise conditions, an engine can run lean, I don't know if it's "smoother" but it's more fuel efficient. I've heard A/F's of 15.4 under these conditions can be most economical.

 

[LadaTrouble]

If your MGB is still using SUs,it will certanly be running rich on an analizer - the SU has no idle circuit,fuel still comes from the needle at idle,this gives poor atomisation,so will always show high HC.But you are right,rich is always better,we have no emission tests,so set our cars rich(if it's possible,not often these days)the customer is always happy.

 

[Andy330hp]

Our MG is fuel injected, so we actually played with idle mixture. It's partly because the design is ancient, but those things despise lean, and even 14.7 makes the driver hate life.