Wideband O2 lean spikes
#1
Where To
VIP Member
Thread Starter
Join Date: Nov 2001
Location: Alexandria Bay, NY 1000 Islands
Posts: 2,517
Likes: 0
Received 3 Likes
on
3 Posts
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
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
__________________
Air, Sea, and Land...Exploring the planet in 3-D!
Air, Sea, and Land...Exploring the planet in 3-D!
#4
Where To
VIP Member
Thread Starter
Join Date: Nov 2001
Location: Alexandria Bay, NY 1000 Islands
Posts: 2,517
Likes: 0
Received 3 Likes
on
3 Posts
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
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
__________________
Air, Sea, and Land...Exploring the planet in 3-D!
Air, Sea, and Land...Exploring the planet in 3-D!
#7
Where To
VIP Member
Thread Starter
Join Date: Nov 2001
Location: Alexandria Bay, NY 1000 Islands
Posts: 2,517
Likes: 0
Received 3 Likes
on
3 Posts
Dave
__________________
Air, Sea, and Land...Exploring the planet in 3-D!
Air, Sea, and Land...Exploring the planet in 3-D!
#9
Where To
VIP Member
Thread Starter
Join Date: Nov 2001
Location: Alexandria Bay, NY 1000 Islands
Posts: 2,517
Likes: 0
Received 3 Likes
on
3 Posts
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
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
__________________
Air, Sea, and Land...Exploring the planet in 3-D!
Air, Sea, and Land...Exploring the planet in 3-D!
#10
Platinum Member
Platinum Member
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.