Tii rich cruise lean acceleration

[Mike G]

I’ve been tuning my tii engine with an afr gauge and it runs great now but it’s around 12.5 at cruise and leans out to 14.8ish with light acceleration. Idle is 12.8 and can’t go leaner without raising the idle rpm simultaneously. Full throttle is 12.5-12.8. 

 

I’m trying to lean out just my cruising ratio and hopefully richen the light acceleration, I think I need to go leaner on the V screw and richer on the D cam simultaneously. I have a little wiggle room on the top end, I’d be comfortable up to 13.5 and it would clean up my idle as well but I don’t know if the D cam adjustment would fix the acceleration lean spot or just offset the v screw adjustment. I’m only able to test one change per day because of my work schedule so I hope to avoid chasing my tail on this for too long. 

 

Ive already moved the v screw so don’t worry about changing it from factory setting, it’s too late. 

 

Thanks for any suggestions!

[Einspritz]

Make SURE that your timing is exact because it affects the rest, provided your advance curve is correct. Too much advance will cause detonation.

 

11 hours ago, Mike G said:

Full throttle is 12.5-12.8. 

 

That's about right, perhaps just a bit rich, depending on what gas composition you are using.

 

When you change the pump screw it shifts ALL of the P curves up/rich or down/lean.

 

When you reach about 85% of the throttle opening, that is about all the air you are going to get vis a vis enrichment on the pump.

 

Any transitory opening of the throttle will show a lean condition immediately shown on your AFR gauge but should stabilize "back" to your true settings. This is where you have the most opportunity for knock, before you get toward full throttle enrichment.

 

Try moving your "D" cam CCW just a hair to enrichen the cruising ratio to ~13.30/ 3% to 13.20 / 3.5% and see how that goes.

 

The idle is the last to set and you shouldn't worry about the AFR so much as smooth running at 800 RPM or whatever idle speed you choose.

 

11 hours ago, Mike G said:

Ive already moved the v screw so don’t worry about changing it from factory setting, it’s too late.

 

You're lucky here, but still need to take a penalty lap around the car.......

[Mike G]

My cruise is already at 12.5. I’m trying to lean it out more without leaning out light acceleration more than it already is. Under light acceleration I see 14.8 and it stays there for as long as I’m accelerating. So what I’m asking is how to lean just the cruise setting, do I move just the D cam clockwise, lean the V screw, or lean the v screw and richen the D cam. Currently the D cam covers half the hole. 

[mvliotta]

On 8/23/2019 at 11:53 PM, Mike G said:

 

I’ve been tuning my tii engine with an afr gauge and it runs great now but it’s around 12.5 at cruise and leans out to 14.8ish with light acceleration. Idle is 12.8 and can’t go leaner without raising the idle rpm simultaneously. Full throttle is 12.5-12.8.

 

 

You are pretty close to the best you are going to get, IMO. Any change you make to richen up your light throttle (with D cam or V-screw) will affect the whole range. 

 

After reading lots of posts and spending a fair amount of time tuning my own ‘72 tii, I’ve come to the conclusion that stock tii’s will run a bit lean on light throttle. A bit rich on idle is typical too. 

 

Have not seen anyone with a stock setup maintain around 13.0 afr throughout the throttle response, but would be happy to be surprised if anyone has cracked this nut..... anyone?

 

Your numbers look pretty good to me. 

 

Mine is at

Idle: 11.5-12.5 (Seems to depend on outside temp)

Cruise: 12.5-13.0

Light acceleration: Swings to 14.5-15.0

WOT: 13.0

 

I’m pretty happy with how it runs with those numbers. I would just go out there and tear it up. 

 

Vince

[Einspritz]

29 minutes ago, mvliotta said:

Have not seen anyone with a stock setup maintain around 13.0 afr throughout the throttle response

 

it is not the same across the RPM range, depending on where you are on each of the P curves, RPM vs. throttle;  WOT is richer than cruise, acceleration, and the idle ends up where it ends up without fouling the plugs.......

 

31 minutes ago, mvliotta said:

but would be happy to be surprised if anyone has cracked this nut..... anyone?

 

yes, but certain conditions apply.

[Mike G]

1 hour ago, mvliotta said:

 

You are pretty close to the best you are going to get, IMO. Any change you make to richen up your light throttle (with D cam or V-screw) will affect the whole range.  

 

Mine is at

Idle: 11.5-12.5 (Seems to depend on outside temp)

Cruise: 12.5-13.0

Light acceleration: Swings to 14.5-15.0

WOT: 13.0

 

I’m pretty happy with how it runs with those numbers. I would just go out there and tear it up. 

 

Vince

 

Thats what I figured but thought I’d check. I’m happy with how mine runs as well, probably should just unplug the afr gauge at this point and enjoy.