Wideband O2 lean spikes
 

Was out tuning this weekend and felt some surging just before the secondaries opened up. N/A 509's, Demon 850's, Dart 6200 intakes, Crane 741, AFR 315 heads, 10:1 compression.

Things I've already checked:
Fuel pressure holding steady across all RPM's at 7.5 psi
Timing is 16 idle and 36 at WOT ( all in at 2500)
Carbs are fresh and clean

Running the wideband, I am seeing lean spikes in the even bank of the port motor when the surging occurs. Not so much below 3500, but above.

AFR port motor:
3000 - 12.8
3500 - 13.2
4000 - 13.4 (right before secondaries)
4500 - 11.8
WOT - 12.0


Thinking that I have a vacuum leak or an intake that is not sealed on the even bank.

Going to take some propane up o the boat this weekend and try to find a vacuum leak, but am looking for other suggestions?

Thanks,
Dave

Powervalves?

aren,t those numbers a little on the lean side?

Thinking they are 4.5 in primary only, plugged in secondary

Just on the port side, that's why I posted them. Remember, naturally aspirated. I'm good with a low 13 at cruise and a 12-12.5 WOT.

This isn't my first time, I've been at this for a while, but never seen a spike like this. Thinking the little lean may also be part of the issue. I jetted up to get here. 90 on the primary (from 88) 97 secondary (from 94).

Dave

fixx
 

secondary accelator pump timing,,check to make sure its gstting enough squirt just b4 the secondary's open..may just need a slightly bigger squirter..

There is alot of oxygen in water. may be getting some in that exhaust manifold.

I'm not so worried about the transisition primary to secondary, more concerned with the spikes. Secondaries open or not, it still does it.

Really? Get a clue....


Dave

Maybe try a 6.5 PV? Whats your vacuum at cruise?

Or maybe go up again with the primary jet, and pull some out the rear.

Are you using a high flow PV?

Maybe I didn't explain the spikes. The meter will just jump to 18-20 and I can feel the surge from the loss of power.

I feel that if I can resolve the spikes, I may be jetting back instead of up. Just looking for ideas, and I do appreciate the comments. I know this setup works, I've had it for a couple of years with little changes.

This year I put my old intakes back on and now trying to figure it out. Was hoping someone else has seen this.

Thanks,
Dave

Here is my 2 cents. I think you are over jetting (slightly rich in mid-range and slightly lean at WOT). I suggest you try (2) 4.5 PV (richer at 4500+ RPM) and try square jetting with 87 X 87 (or 86-88) as a starting point. We run a steady 13.6-13.8 until the PV's open. The AFR at WOT is 12.4.