Dyno shows Air Fuel Ratio rich

[Blu427]

Hi,

Looks way to rich right across the range . Some spikes on the AFR . What do you think it could be the issue ?

351c 2V
268 CAM
Holley 4160 600 cfm
Offy 360 inlet

Have run on a dyno and results show

RPM AFR RWHP Torque

2500 10 145 308
2750 10.5 150 318 Peak
3000 10 178 310
3500 10.25 200 300
4000 10.5 220 298
4500 10.75 245 290
5000 11.25 250 265
5250 11.25 260 260

Cheers

[elmariachi]

Install smaller jets by two #s at a time and see what happens on subsequent pulls. So if it has 68s, go to 70s and make a pass and then to 72s and so on. Once you make the first jet change, you'll be able to do the math on what it will take to get to where you need to be. Do the pipes and plugs look sooty?

[jhv48]

Wouldnt that be making it richer rather than leaner?

[Gaz64]

Way too rich, smaller mains will make it leaner, pull the bowls and see what jets are in there first.

I'd drop by 5 to start.

Is the Offy 360 a single plane manifold?

4160 600, old school, there are way better carbs out there.

[Blu427]

elmariachi,

I think smaller jets in the main as jhv48 says so I need to be going down in size from present 66 mains not larger so might try 62's .

Gaz64, I am not sure if the Offenhauser 360 Degree is a dual plane .Engine was built in 1994 by Racing heads .

Cheers

[Blu427]

Hi,

Done some checks today ,

Checked both float levels whiche were found to be low no fuel dribble out of bowl screws and so adjusted . I dont think this will cause a rich issue. Checked power valve and found this to be on at no throttle so adjusted .
Fitted in -line fuel pressure gauage and found pressure at 2lbs so not over pressure .
Few more checks tomorrow.

Cheers

[elmariachi]

Originally Posted by Blu427

elmariachi,

I think smaller jets in the main as jhv48 says so I need to be going down in size from present 66 mains not larger so might try 62's .Cheers

Correct, it was a typo. Smaller jets make it leaner, larger make it richer.

EDIT....One item thing worth mentioning, in the absence of a chassis dyno, Innovate Motorsports makes a nice O2 sensor setup you can connect to a laptop that's let's you log A/F readings. Made a huge difference for me dialing in my carbs.

[Jerry Clayton]

How did you adjust power valve??????

[Blu427]

Sorry Jerry ,

It was the Accelerator pump adjustment . Been having a few problems follwing adjustment seems since I adjusted it it would not tick over even screwing in the accelorator RPM adjuster . I did find a split in the cap off vacuum pipe hose on the side of the carb when I fitted a vacuum gauge to measure the vacuum and adjsut idle mixure . Revs sat at 1500 rpm . Have a look tomorrow after battery charged up.