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

[blykins]

You need to go down in jet size.....a lot.

Also, if your fuel pressure is indeed 2psi, you need to raise that up to about 5-6.

[Blu427]

Cheers blykins,

I thought the fuel pressure was low at 2 psi .

Cheers

[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.

[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.

[Blu427]

Hi,

Back at the rolling road today . Following adjusted fuel levels on both bowls which were low and adjusted fuel pressure to 5psi. I took the choke plate and stem from the horn out as this got struck on when I went on a drive .I think this could have been my problem . New figures show AFR show 13,s . Following timing settings I got 288 bhp up from 267 bhp and torque up to 360 ft pounds .The distributor was well struck . Had to use a co2 fire extinguisher to cool the alum and then it moved with mole grips .I see this as acome problem on the Cleveland blocks .
I think the under exhaust is way to small as its only 1 7/8 pipe from front to back box which is robbing me of more BHP .

What primary headers size and main under pipe size for the exhaust ? Might post this in engines section now