WOT too Lean

[fastd]

I actually had a different carb on there that kind of did the same thing; i.e. lean into the secondaries...that was an older one that did not have adjustable air bleeds and restrictors...

[fastd]

Update:
Increased PVCR from 70 to 73
Reduced the PV from 7.5 back to 4.5
Reduced the primary main to 83 from 86
Reduced secondary main from 94 to 88

Results:
WOT is much better; comes down to low 13s at WOT
BUT still spikes to mid 15s for like the first 2 seconds of WOT

Next step:
I am thinking that I could use the 50 cc accelerator pump; I have a 42 squirter in the rear now so I am thinking the 50 cc will give me a longer shot of 42

Note: Before I did the above in increase the PVCR to 73 from 70 and changed the 7.5 PV to a "High Flow" 7.5 PV; I could barely keep it running it was so rich at idle. The engine was cold so I had to feather the throttle warm it up; but the feathering caused the vacuum to drop below 7.5 so I got a rich mess. Then I took out the 73 PVCR and went back to 70s but kept the high flow PV in and still the same thing; pig rich. My point is: that high flow PV really works; it has 4 windows instead of 2 so I am guessing it was like adding an additional 6-8 jet sizes. Was surprised how much it effected me at idle though; of course I the 7.5 was too high but still...

[lippy]

If your idle is rich you may also want to look at your idle restrictions. They should be sized so you have the right idle mixture with the 4-corner screws roughly. 1.5-2 turns out. If you need to turn your idle screws all the way in to get the right mixture then your idle restrictions are too big.

If your idle settings are off, it will impact all other settings.

[fastd]

Idle is OK; right around 13 +/-

[fastd]

wondering about the accelerator pump though; move to 50 cc with a 42 squirter...is that gonna fix my 2 second a/f spike? It doesn't bog...it just goes lean...i don't feel the leanness until i get to like 3500 rpms from say 2500; after 2 or 3 seconds the a/f comes down to mid-to-low 13s.

Trying to get it to the 12s at WOT; gonna fine tune for that after I fix this spike.

[lippy]

Idle at 13 is too rich. You want idle to be near stoic, which, if you are at 10% Ethanol, is low 14's. WOT should probably be in the 12.8-13.0 range.

[Gaz64]

Does the engine flat spot when this spike occurs?

If the engine responds well I wouldn't worry about an A/F gauge spiking like that.

Have you got hollow squirter screws?

The Holley 850 XP/HP is known to be lean out of the box, I would think about a better carb, like Pro systems or one from Troy Patterson (TMP Carbs).

[fastd]

Lippy,

Will try to lean the idle up a bit.

Gaz64,

It doesn't flat spot; it just gets lean. I do have the hollow squirter screw for my 42 in the back.

I've heard that the 850 xp is lean out of the box also.

I rehooked up my vacuum gauge and paid a lot more attention to it.

It's interesting how it moves when the engine is warming up as compared to when it is warm. To warm it up, it's easy to get the vacuum down to 6.5-5.5; that caused problems with my 7.5 - and when I used the high flow 7.5 it just drowned itself.

Anyway, I think the spike has more to do with WOT leaness than accelerator pump.

Gonna try a high flow PV but get like a 4.5 and 3.5 (instead of the 7.5). If the high flow is too much, might bring the PVCR down from 73 to 70, 67, or so.

[Gaz64]

Originally Posted by fastd

Lippy,

Will try to lean the idle up a bit.

Gaz64,

It doesn't flat spot; it just gets lean. I do have the hollow squirter screw for my 42 in the back.

I've heard that the 850 xp is lean out of the box also.

I rehooked up my vacuum gauge and paid a lot more attention to it.

It's interesting how it moves when the engine is warming up as compared to when it is warm. To warm it up, it's easy to get the vacuum down to 6.5-5.5; that caused problems with my 7.5 - and when I used the high flow 7.5 it just drowned itself.

Anyway, I think the spike has more to do with WOT leaness than accelerator pump.

Gonna try a high flow PV but get like a 4.5 and 3.5 (instead of the 7.5). If the high flow is too much, might bring the PVCR down from 73 to 70, 67, or so.

If you have WOT lean condition, I can't see why you want to reduce the size of your PVCRs.

Even a standard Holley picturewindow PV outflows PVCRs of about .090.

I think a lot of your troubles stem from the factory calibration of the 850 XP.

I'd love to know what engine Holley had it on when they did the calibration.

Gary

[fastd]

Gaz64
I am not necessarily going to reduce my pvcr. I am going to try a high flow pv and it seems like tuning that high flow pv will require changing the pvcr either higher or lower. When I used the 7.5 high flow pv I was surprised how rich it got.

Put another way, if a high flow pv doubles the fuel through the pv then I might have to decrease the pvcr to tune the pv.

[lippy]

I don't think a four window PV will make a difference. The PCVR controls how much fuel you get with the PV open. The PV is just a door that opens at a specific vacuum. As Gaz said, the standard PV is adequate for any PVCR, so it's not a limiting factor.

Btw I bought a Braswell carb awhile ago. Worth every penny. The best part is that you can get tuning advice from Dave Braswell, who is one of the best carb guys on the planet.

[G_Edmonds]

If you have a 37 or larger squirter you need a 50 cc accelerater pump.
After all the changes you have plenty of fuel flow-ability. I think your booster signal is not strong enough. When the throttle blades are suddenly opened at a relatively low rpm, the air flow gets lazy. That's what the pump shot is supposed to cover up. There are high gain boosters available.

[fastd]

Lippy,

I think I disagree about the four window PV...here's why: at one point I made just one change: replaced the 2 window 7.5 PV with a 4 wind 7.5 PV - no other changes. Tried to start it but ran so rich that I could just barely just keep it running. Vacuum gauge showed why: as I was trying to warm up the car the vacuum kept dropping to just under 7.5"; all that extra flow through the high flow PV richened it up too much. I put the 2 window 7.5 back in; although it was still in warm up mode, it ran OK (well enough to warm it up so that it could just idle at 11.5").

G Edmonds,

I'm gonna try to add the 50 cc pump and bring the squirter down from 42 to 37-40...

Also, I also changed the HSAB and PVCR in the 2ndaries but didn't change the Primaries...gonna make those same changes in the Primaries also to help WOT.

Thanks.

[lippy]

If you have a PV that is opening to early, you should run rich whether or to a 2 or 4 window. Make sure your PV Isn't blown also. To do this you can visually inspect it, or hold the body and try to rotate the thin end. If you can, it's blown.

[Gaz64]

A few things to look at while changing power valves.

They should be NO fuel moisture AT ALL on the vacuum side of the power valve.

The fuel bowl is sealed from engine vacuum in two ways, one is the diaphragm, one is the valve gasket.

I test every power valve I have prior to fitting for leakage.

There is a tool for this from Moroso, and others maybe.

A quick test as Lippy has said is if the stem can be turned easily the valve is blown. I've seen this with new valves. I don't even attempt to use them if I can turn the stem.

And another thing that has me beat is if a power valve is open at idle it only allows the PVCR fuel area to be added to the MAIN JET area TO THE MAIN WELL.

It should have nothing to do with the how the engine idles, whether you have 60 mains or 98 mains, it makes no difference.

Make sure all fuel jets are snug in the metering blocks, and Power valves are torqued to 100 in/lbs.

Gary

[fastd]

I agree with you guys about the pv at idle but the fact remains that the 6.5 4 window pv (previously I said it was a 7.5 4 window) did make it idle very richer. When warming up, feathering the throttle the vacuum did drop pretty easily below 6.5. It ran ok with the 2 window because the vacuum drop was momentary and the 2 window didnt drown it like the 4 window.

Anyway, I added a 50 cc acc pump on the back: didn't notice much of a difference except that throttle response is a bit better.

Also decreased the front Hsab from 34 to 28. Helped a bit at the margin I think.

Move idle a/f from around 13 to around 14.

Everything is very close but still have lean condition on WOT but getting closer.

Gonna next try a 3.5 or 2.5 4 window pv in the secondaries. I think that should be low enough not to upset my warm up idle and good enough to catch the vacuum at WOT. I have read on other forums that the pv may not be the restricting factor until pvcrs get bigger than .080 but my experience so far suggests otherwise. Gonna keep for now the 2 window 4.5 pv in the front.

[RockBit]

I'm wondering if somehow air is getting to your O2 sensor at high rpm, maybe through an exhaust leak. Any chance of that?

[fastd]

another update:

After several iterations and multiple mail orders, including blocking off the rear PV, I finally got my WOT to richen up to the low 13s mainly by increasing the PVCR from the factory size of 70 to 76 in the front and 78 in the rear. Decreasing the HSAB from 34 to 26 & 28 (gonna move the 28s to 26s) helped but not significantly. I am targeting 12.5-13 WOT a/f ratio so I am going to increase the 76s to 78s and maybe the 78s to 80s if I need to.

Based on my experience and comments (Holley tech told me it was a drag carb - of course they didn't mention that when I called initially for a suggestion of what would fit), I do think that the Holley 850 XP is a lean carb so beware. I like the carb though because of its extra large fuel bowls with clear fuel level sights, adjustable air bleeds/and emulsion jets, idle bypass value...

I am still lean at 2/3-3/4 throttle when I am into the secondaries but not into the PVs. I can't really increase the PV from my 4.5 in front and 3.5 in back because it's pretty easy to be a 5.5" when I am warming the car up on initial start and sometimes on part throttle acceleration and all the time when the a/c is running. I don't even want to tell the size of the secondary main jet I installed cause I'll get lambasted for it so I will put it this way: increasing is 2ndary jet size are not richening this part of the curve; typically I think that would mean that I would need to decrease the HSAB size but I can't go lower than 26 and I this HSABs 1: don't really move the "needle" to much and 2: I this HSAB impact WOT more than cruise/acceleration when the 2ndaries kick in. If I can get the WOT perfect, then won't spend too much time at 3/4 throttle.

Thanks for your previous comments and suggestions.

Regards.

[Gaz64]

I would be interested in what size and how many emulsion bleeds are in the metering blocks.

Here is a thread on the 850:

new holley 850 ultra hp WAY out of wack - Yellow Bullet Forums

Gary

[fastd]

Gaz64,

Will check the size and #; I hadn't really focused on these bleeds but I guess it's time to start.

So if I am trying to richen my 2ndary circuit, but before the PV kicks in, I assume I need to decrease the size of the emulsion air bleeds. Which ones? What about the anti-siphon bleed? Any suggestions...I haven't found much good info about tuning these emulsion bleeds.

Regards,

Phil