Rich 3000 rpm cruise

[PRNDL]

"It runs great but my plugs are black and I burn through fuel a lot."

I don't know what would be different about that carb to require a #77 primary jet. On a 750 I usually end up with about #69 primary jet along with about 68 to 70 TSR.

Yeah man. It’s weird. This model carb comes factory with 77 p-jet and 4 .036 MAB. I thought it was weird but figured it was due to such big MAB and figured Holley knew what they were doing. Carb ran good except the 12.5 rich cruise, wot stumble, and lean WOT. Changing it to the old version of this carb specs, 75 p-jet and .025 p-solved any lean or stumble issue, but I wa cruising at 13. Naturally I jetted down to where it stumbled and went back up and I ended up at 73 jets.

I do wonder if this metering block is bad.

[ClassicComp]

Close rear idle mix screws and open primary mix screws to compensate.
Take another ride.

[PRNDL]

Just FYI on some testing I did in the past. I have a ME Wagner PCV. I opened the idle valve to let more air in as a test. Another time I tried opening the secondary idle I little more to lean things out. All it did was screw up my transition cruise. Gave me lean stumbles at cruise. Car felt weak. Not on acceleration but steady under 50 mph cruise. This would cause me to have to richen the idle mix.


Then on testing, same 3000 rpm rich spot. I think it’s pulling from the idle ports at high vacuum.

[PRNDL]

Ok will do

[PRNDL]

I’ll report back this weekend.

[PRNDL]

Could I be using the wrong metering block gaskets? I use the red reusable Interface brand gaskets

[Tuner]

Not familiar with those but I wouldn't use anything but Holley® blue gaskets

[PRNDL]

I been working and haven’t gotten to test what we spoke of.

I have a question though. I have an old very clean metering block laying around. It’s a two emulsion (.026) unit with pressed in .033 IFR’s on the bottom. It has the numbers 10569 on top. I was thinking I could try this unit as a test. I think the .033 IFR’s will be too big especially when I’m having a rich condition with my factory blocks having four .029 IFR’s.

I would like to tap these and run 6-32 .028 IFR’s Z I read through Tuner’s threads on how to do it, but I’m confused about two things:

1. When I order the 6-32 spiral flutted bottoming tap, do I just order a 6-32? Some have different letters behind the 6-32. I’m guessing different threads? Any other numbers or letters I should be aware of when ordering?


2. What size drill bit do I use first?

I’m going to order BLP 6-32 hex IFR’s

[PRNDL]

This is my block I’m thinking as using as a test

[skinny z]

Reading this with interest in that I've experimented quite a bit with my Barry Grant VS 750.
I've tuned for a lean cruise. 16:1 at 2500 RPM (Locked in OD).
While you've obviously worked with the PV seeing as it's a 10.5, could there be some weirdness going on with the valve at the 3000 RPM cruise and load? Weird as in something defective?
One thing I've come to enjoy with an 8.5 PV (.059 PVCR) is the massive enrichment when I load the engine enough to employ the valve. Such as moderate passing. Very normal but again, if there's something not right with yours, could that be a contributor?
Just throwing my 2 cents onto the pile.

[arlancam509]

1. When I order the 6-32 spiral flutted bottoming tap, do I just order a 6-32? Some have different letters behind the 6-32. I’m guessing different threads? Any other numbers or letters I should be aware of when ordering?


2. What size drill bit do I use first?

The letters behind the numbers are just indicators of thread class. The '32' shows how many threads per inch. A #6-32 tap is all you need - as long as it is a bottoming tap, of course. Although, If it was me, I would buy 2 taps - one 'hand' tap (or a spiral point) and one 'bottoming' tap. The hand tap will be much easier for starting the threads and then you can finish them with the bottoming tap.

My handy-dandy tap drill chart hanging on my desk says you need a #36 drill bit. That has a diameter of .1065 inches.

[PRNDL]

Well, I did what tuner said. Cleaned up the secondary valve edges and closed them tight. Closed off the secondary idle mixture screws and ran off the front ones. The engine did not like it. Gave me a stumble at secondary opening onset. Ran very weird.

For giggles, I did the usual. I opened them the same and balanced all four and it ran ok.

I put it back how I had it at 3/4 primary curb idle, 1/8 secondary curb idle, and 3/4 all four idle mixture screws and back to square one. Idle, transition cruise, and WOT are flawless. High speed cruise to high vacuum at 3000 rpm, I don’t have overdrive, very rich.


Based on everything I did above, nothing seemed to affected the 3000 rpm area.

I really think it’s the metering block.

I’m going to test out the other metering block I mentioned.

I tried two 10.5 pv’s and an 8.5. Same issue.

[PRNDL]

Thank you for the info on the tap!

[steve cowan]

Well, I did what tuner said. Cleaned up the secondary valve edges and closed them tight. Closed off the secondary idle mixture screws and ran off the front ones. The engine did not like it. Gave me a stumble at secondary opening onset. Ran very weird.

For giggles, I did the usual. I opened them the same and balanced all four and it ran ok.

I put it back how I had it at 3/4 primary curb idle, 1/8 secondary curb idle, and 3/4 all four idle mixture screws and back to square one. Idle, transition cruise, and WOT are flawless. High speed cruise to high vacuum at 3000 rpm, I don’t have overdrive, very rich.


Based on everything I did above, nothing seemed to affected the 3000 rpm area.

I really think it’s the metering block.

I’m going to test out the other metering block I mentioned.

I tried two 10.5 pv’s and an 8.5. Same issue.

As a test I would fit rear powervalve and PVRC jets if they are blocked off,square jet as a starting point.
I think the vacuum secondary is opening at that rpm/ throttle position making it go rich.
Vac spring tuning might be on the cards at a later date.
If you have dirty spark plugs,buy a few new ones and replace one on each side of engine that's easy to remove and road test.
If possible have some one with you with pen and paper writing down AFR,rpm ,speed,throttle position etc.
Sometimes it hard to remember everything at least for myself anyway.

[PRNDL]

Shit man. I never thought of that. My secondary servo pod has a lid with a screw that controls the opening rate. Due to the purple spring, I have it at the stock 1.5 turns setting, but I can close it all the way and disable the secondaries. I will try that next.