Rich wot but reducing secondary jets isn’t helping?

[Sonny]

I believe all carbs will come with a medium spring installed, then if required the lighter or heavier spring can be used.
Stock settings will work with most applications, the light spring would be more for radical cams with poor vacuum.

The fact that changing jets is not doing anything made me think of what could cause a lack of air, but i am not sure if this is the right thinking.

I added the heavier spring because I’ve got I have a car with a really highway type gear and I was trying to delay the power coming in. But the fact that changing the secondary jet changes didn’t make any differences I think you’re a spot on that the secondaries are not opening at all.
I am optimistic you got this one right!

 

[Wietse]

I am hoping i was right...means i started to learn something about carbs.

You could check the Holley website and read up on the manual for your carb, they explain there how to install a paperclip or so on the secondary linkage.
Not sure what carb you have, but i have a Street avenger 770 with vac secondary's.
Then after a test drive, making sure the car should have used the secondary's you can check the position of the paperclip, if it moved across the linkage it means they moved and if it is still in the same position it means they never opened.

 

[Sonny]

I am hoping i was right...means i started to learn something about carbs.

You could check the Holley website and read up on the manual for your carb, they explain there how to install a paperclip or so on the secondary linkage.
Not sure what carb you have, but i have a Street avenger 770 with vac secondary's.
Then after a test drive, making sure the car should have used the secondary's you can check the position of the paperclip, if it moved across the linkage it means they moved and if it is still in the same position it means they never opened.

I did not have a paperclip, but are used a really small fine zip tie and tied it very loosely just enough to stay put. I gave it a couple of hard runs and it’s not moving at all. My secondaries are not opening. That would explain why the jet changes had no effect. I added the quickchange vacuum secondary kit to the carb. I wonder if I am missing a gasket or a ball valve somewhere?

 

[RJRENTON]

Wietse,
The carb's secondary opening signal comes innitially ftom the primary venturi pressure drop. The diaphragm determines the degree of sensitivity to the building pressure signal. Too much spring will result in very slow opening of the secondaries (if at all). And conversely, too light a spring will result in too fast an opening rate and a lean mixture and lower engine performance. After the secondary's start to open, their venturi pressure drop signal combines with the primary venturi drop signal to open the secondary butterfly valves subject to the secondary's diaphragm spring AND the check ball in this vacuum passsge, which petmits the vacuum signal to slowly increase opening the secondary butterfly valves (regardless of the diaphragm spting). Without this check ball, the secondaries will open too fast causing a severe lean condition until the secondary booster venturi begin adding fuel. Double pumpers have an accelerator pump to overcome the fuel flow lag....aka a "bog". Remember, carbs operate on air flow; and, fuel flow follows air flow subject to the fuel metering components....jets.
Bob Renton

 

[Sonny]

Wietse,
The carb's secondary opening signal comes innitially ftom the primary venturi pressure drop. The diaphragm determines the degree of sensitivity to the building pressure signal. Too much spring will result in very slow opening of the secondaries (if at all). And conversely, too light a spring will result in too fast an opening rate and a lean mixture and lower engine performance. After the secondary's start to open, their venturi pressure drop signal combines with the primary venturi drop signal to open the secondary butterfly valves subject to the secondary's diaphragm spring AND the check ball in this vacuum passsge, which petmits the vacuum signal to slowly increase opening the secondary butterfly valves (regardless of the diaphragm spting). Without this check ball, the secondaries will open too fast causing a severe lean condition until the secondary booster venturi begin adding fuel. Double pumpers have an accelerator pump to overcome the fuel flow lag....aka a "bog". Remember, carbs operate on air flow; and, fuel flow follows air flow subject to the fuel metering components....jets.
Bob Renton

I did not have a paperclip, but are used a really small fine zip tie and tied it very loosely just enough to stay put. I gave it a couple of hard runs and it’s not moving at all. My secondaries are not opening. That would explain why the jet changes had no effect. I added the quickchange vacuum secondary kit to the carb. I wonder if I am missing a gasket or a ball valve somewhere?

 

[Sonny]

I took the secondary quick change spring kit back of the carburetor and checked the round cork gasket, and the rubber diaphragm, and they were all fine. I did a test drive and nothing seems to have changed. The zip tie didn’t move and air fuel ratio still in the 10.5 - 11 range wot. I’m out of ideas.

 

[beanhead]

You stated in the first post it runs good..don't get too caught up in the gauge readings. Get a plug magnifier, or cut the threaded portion off a plug after doing the shut-down procedure hemi-itis described. It's the only way to get a true reading especially with today's gas. Depending on the total combo, your best performance at WOT may not be at the same number as someone else's, and you want it on the rich side at WOT. That said, 11 may be a bit much...so look at it from another angle- if you want it leaner, but reducing fuel hurts performance, then get more air in the mix..

 

[Wietse]

RJRENTON: Thx for explaining that part.

The secondary's are not opening at all...
Sonny, did you install the medium spring this time?
What carb are we talking about? How i understand you added the quick change type vacuum assembly?
Maybe this combo does not work with your carb?
As RJRENTON explained, it needs those venturi signals to work.
When you do any work on the carb, make sure to reinstall the jets with the ones you had in there.
If you do get the vacuum secondary to work it will jump in an insane lean condition probably at WOT, which is something you don't want.

 

[Sonny]

RJRENTON: Thx for explaining that part.

The secondary's are not opening at all...
Sonny, did you install the medium spring this time?
What carb are we talking about? How i understand you added the quick change type vacuum assembly?
Maybe this combo does not work with your carb?
As RJRENTON explained, it needs those venturi signals to work.
When you do any work on the carb, make sure to reinstall the jets with the ones you had in there.
If you do get the vacuum secondary to work it will jump in an insane lean condition probably at WOT, which is something you don't want.

I used the orange spring, which is the second lightest just to verify that it’s opening. This is the carb I have and I added the kit to convert to a 4150. I spoke to Holley tech support and those kits do work on that carb. When I spoke to them, I didn’t realize the vac secondary wasn’t opening. Guess I’ll call them back tomorrow.

 

[Sonny]

On Friday I replaced the 68 primary jets with 71s because the plugs were so white I was worried it was too lean on cruise. Here are the plugs this morning...much nicer shade of tan. My afr with these jets at light throttle cruise is 12.5-13.4. What do you think of that timing strap mark? Note when the plugs were white, that heat mark on the strap was in the middle of the curve.

I live in a big city and long country roads are not close by so I can’t do long wot runs with immediate shut downs to check plug color unfortunately.

 

[Sonny]

These are the plugs I’m using.

 

[Wietse]

Normally that location of timing strap mark is the idle mark, the WOT timing strap mark supposed to be at the middle of the curve.
But as you mentioned it is hard to test WOT in your area.
At light cruise people say going in to 15's AFR is also ok, just makes a clean/lean burn and low consumption on long stretches of road.
I think your primary is set where it should be, just need to get the secondary's to work and see what readings you get.
Then adjustments can be done to get the afr readings good at high load and WOT.

 

[beanhead]

Calling @Sonny.....
Ever get your rich WOT resolved?

 

[Sonny]

Calling @Sonny.....
Ever get your rich WOT resolved?

Thanks. Not yet. I still think most of my problem is the 276 gears and heavy car. I did make some headway. Put both heavy springs on my MSD dizzy and helped stop the pinging and was a little quicker. I swapped the 650 Avs2 for a 800 avs2 to get more air into the primaries (power mode) then jetted down the secondary jets and that helped too. realized this week that I put an open square bore 1/2” wood spacer on my dual plane intake and therefore negated what the dual plane does! Removed the spacer and used correct divided gasket and it’s never idled so well. Off the line response is also improved. And now my tuning is a little off but not much. My next mission is to slow down the opening of the secondary air valves And use a smaller squirter. I am making progress! Also changed plugs and the color is better.

 

[beanhead]

Ok thanks for the follow-up!

 

[RJRENTON]

Out of curiosity, the plug you show in your pixes APPEARS to be, in the first set of pixs, to be a platinum/irridium extended tip plug and the last pix shows a conventional (non ) platinum/irridium electrode design. In NGKs heat range chart, heat range 5 is a relatively hot plug, which would show a white(r) coloration. Should you consider a slightest colder range of 6 or possibly 7?? The ground electrode (aka "strap") does show the correct coloration, but the shell shows a rich condition. USUALLY, the premium plugs have an improved ground electrode construction allowing better heat dissipation characteristics and as a result, color differently. Also NGKs offer a "V" shaped ground electrode claimed to provide a better flame kernel development and better fuel charge ignitability...better for lean mixture operation.
BOB RENTON

 

[Sonny]

I think I’ve finally solved the issue. I installed a Carter m4862 (9psi) fuel pump and Holley fuel regulator back in may thinking I could help the fuel boiling issue by recirculating the extra fuel. This pump is for 6 packs and double carburetors. I have a 1/4” return line but the regulator requires at least a 5/16 which I ignored. While in park if I rev the engine over 3,000 rpm the fuel gauge reads over 8 psi as the regulator can’t relieve the pressure through the small line fast enough. I’ve tried 3 different carburetors all with the exact condition (Air fuel ratio in the 9s wot).

I ordered the stock Edelbrock 6.5 psi carb and will report back. Anyone needs a carter hp fuel pump with 1000 miles on it hit me up. Paid $167 for it new at summit.

 

[Sonny]

View attachment 852903 View attachment 852904 I think I’ve finally solved the issue. I installed a Carter m4862 (9psi) fuel pump and Holley fuel regulator back in may thinking I could help the fuel boiling issue by recirculating the extra fuel. This pump is for 6 packs and double carburetors. I have a 1/4” return line but the regulator requires at least a 5/16 which I ignored. While in park if I rev the engine over 3,000 rpm the fuel gauge reads over 8 psi as the regulator can’t relieve the pressure through the small line fast enough. I’ve tried 3 different carburetors all with the exact condition (Air fuel ratio in the 9s wot).

I ordered the stock Edelbrock 6.5 psi carb and will report back. Anyone needs a carter hp fuel pump with 1000 miles on it hit me up. Paid $167 for it new at summit.

well so much for that theory. Installed the new pump and it’s dead on 6psi; however I still have the wot bog. I’ve tried a 650 eddy, 750 Holley, and now a 800 eddy and all 3 have the same issues: 1/2 throttle it’s awesome. Wot it chokes and surges and falls on its face and stays there. Air fuel gauge drops into the 9s (could be wrong but who knows). I went from super lean .092 secondary jets to .104. No change. Played with step up springs. Nothing. I can control idle and cruise fuel mixtures but nothing helps wot. Timing is with a MSD ready to run dizzy 18 initial 36 total with light blue and light springs. Vac advance hooked up. What am I missing? 1978 440, stock heads, raised pistons, comp cam specs attached. Newly rebuilt.

 

[beanhead]

I don't remember, have you ever tried a different ignition? A/F readings are one thing but "chokes/surges/falls on it's face" can be ignition related. (Seen it!)

 

[RJRENTON]

I don't remember, have you ever tried a different ignition? A/F readings are one thing but "chokes/surges/falls on it's face" can be ignition related. (Seen it!)

Certainly sounds like a Chevy problem.....they seem to have similar difficulties. Now is the time for the MSD or Pertronix proponents to proclaim the benefits of their equipment. Seriously, another check for uniform fuel distribution/cylinder combustion efficiency, is Exhaust Gas Temperature, measured at the cylinder head outlet with individual thermocouples, one per cylinder. This will show which cylinder is richer or leaner, based on exiting gas temps, perhaps in the 1200° - 1400° F range. Down stream oxygen readings or air / fuel ratios are helpful but are an average of the engine's combustion process. Individual EGT will pinpoint which cylinder is not performing uniformly with regard to the others. The other possibility is a bad/loose connection or a bad ground....but not likely. Just my opinion of course.
BOB RENTON