Tuning my new engine

[travis]

What in it for a PV?

Should be whatever it came with from the factory, so a 6.5 I assume

[Firedome8]

Find a local chassis dyno, the operator will likely be more experienced in getting your tune up sorted out..

[My427stang]

Have you gone through this carb?

If not, I would make sure the metering surfaces on the throttle body are flat, put a fresh kit in it, set float levels, make sure it has the correct gasket TB to base plate, and set throttle position to stay out of the transition slot. Add idle with the secondaries if it's too low, and make sure the accel pump circuit is right and adjusted correctly

If it is fresh and you trust it. I would check for vacuum at the metering block port (primaries in front of choke) and see if it's alive at hot idle. If it is, then the primaries are too far open. Same drill, close primaries open secondaries to get idle. I'd also make sure your shot starts immediately, adjust the arm correctly, and never know you may have a sticky accelerator ball or umbrella depending on design. Check float level too

That engine shouldn't need any more shooter, some do, but often guys bathe it

Last thing is 40 total is a lot for a tight quench engine, if it's a decent chamber you may make max power with way lower. If it is a crappy chamber, you are in the ballpark but watch for detonation when hot.

[travis]

Have you gone through this carb?

If not, I would make sure the metering surfaces on the throttle body are flat, put a fresh kit in it, set float levels, make sure it has the correct gasket TB to base plate, and set throttle position to stay out of the transition slot. Add idle with the secondaries if it's too low, and make sure the accel pump circuit is right and adjusted correctly

If it is fresh and you trust it. I would check for vacuum at the metering block port (primaries in front of choke) and see if it's alive at hot idle. If it is, then the primaries are too far open. Same drill, close primaries open secondaries to get idle. I'd also make sure your shot starts immediately, adjust the arm correctly, and never know you may have a sticky accelerator ball or umbrella depending on design. Check float level too

That engine shouldn't need any more shooter, some do, but often guys bathe it

Last thing is 40 total is a lot for a tight quench engine, if it's a decent chamber you may make max power with way lower. If it is a crappy chamber, you are in the ballpark but watch for detonation when hot.

The 40* setting was more of me trying to get the low speed and idle manners right...it was definitely too much timing. 36 total is better, but still feels like a bit too much. But...it’s really cantankerous at idle especially when cold with 12 or less initial. So much for the “performance” advance curve in this distributor

I do not trust this carb at all. I don’t think anything internally was messed with by the previous owners mechanic, but the externals was a mess.

It’s getting better, but it isn’t there yet

[Geoff2]

Travis,
Use a dist with an adjustable vac adv connected to MANIFOLD vacuum [ MVA ]. This will add timing at idle to improve idle & off idle throttle response. You can use any combination of Initial+ MVA to get the desired amount of timing for good idle.

More info on MVA benefits, scroll down to post #6.

www.hotrodders.com/forum/vacuum-advance ... 47495.html

[Belgian1979]

I have 175 psi cranking compression on an engine, so your cranking pressure is about similar. I run 18° initial with 36 total at 3000 rpm. Engine seems happy with that.
SBC though.
Cold intake air is important.

If worried about detonation etc. set the carb on the rich side and use a little colder thermostat.

[travis]

I think I found the problem...

When I pulled a plug to check cranking compression, I kind of blew off the fact that the plug had some weird grey sooty deposits on it, just assuming that it was from assembly lube or something. I worked on it some more today after going through the carb...and noticed a significant amount of trans fluid dribbling out of one of the vacuum hoses. It would appear that the trans vacuum modulator is blown...and guess what no parts store within an hour in any direction carries?

[PRH]

How about a trans shop?

[travis]

How about a trans shop?

I ordered one...it will be here tomorrow. The trans shops around here don’t carry anything on the shelf for stuff this old

[travis]

Fixed the trans modulator, and fixed a tiny leak around the carb base. 16.5-17” idle vacuum at 750 rpms and will idle down to 500 rpms if you want it to.

Still have a nasty stumble at light throttle from a dead stop or at any speed rolling down the road under about 2200-2400 rpms...above that it is fine. The only way to get past the light throttle stumble is stab the gas and get past that hole.

At a 1500 rpm roll, just rolling lightly into the throttle it will fall on its face and die, if you don’t stab it to get past the hole.

Once above 2500 rpms, it is very responsive to light or heavy throttle.

The squirters shoot a nice shot of fuel as soon as the throttle is touched.

Would jetting have anything to do with the poor low rpm response?

[travis]

Something is definitely wrong with this 670 Holley. I farted around with it all day and still couldn’t get rid of the stumble no matter what jets, pv’s, or squirters I put in it. Out of sheer frustration, I dug out my grungy worn out 20 year old Edelbrock 1407, still calibrated lean for a much milder engine it was on for years. All I did was take it partially apart to blow all the crud and spiders and junk out of it...it was literally like bolting on 50+ Hp.

[Tuner]

Fixed the trans modulator, and fixed a tiny leak around the carb base. 16.5-17” idle vacuum at 750 rpms and will idle down to 500 rpms if you want it to.

Still have a nasty stumble at light throttle from a dead stop or at any speed rolling down the road under about 2200-2400 rpms...above that it is fine. The only way to get past the light throttle stumble is stab the gas and get past that hole.

At a 1500 rpm roll, just rolling lightly into the throttle it will fall on its face and die, if you don’t stab it to get past the hole.

Once above 2500 rpms, it is very responsive to light or heavy throttle.

The squirters shoot a nice shot of fuel as soon as the throttle is touched.

Would jetting have anything to do with the poor low rpm response?

I've had two of those act just as you describe, one on a SBC and the other on a SBF. The fix was to close the secondary completely, but with just an absolute minimum of a crack open so the blades won't stick in the bore. I tried a grip of combinations of primary metering, several different combinations of idle jet and idle air bleed, main jets big and small, float level up and down, different blocks and E-bleed setups, with and without emulsion tubes, pump cams, squirters, etc, etc, and could not eliminate the stumble, just move it around a bit. Finally, tried opening the secondary a bit more and that made it much worse ... Ah Hah ....... close the secondary and flat spot gone. The second time around was easier.

The 670 Holley is probably weak because your engine wants a bigger MJ in the secondary than the #68 they come with. Try a #74. The R2818 used on the '64 350 HP 327 is same size carb, but flow rated as 585 CFM, came with #76 SMJ

[Tuner]

On the probability that your heads are the fast-burn variety, you might try less spark advance than has been suggested in this thread. For pump gas, a lot less, such as in the mid 20s, 24 to 28 range. The vacuum advance should advance it from there up into the mid 40s for level road.

[travis]

On the probability that your heads are the fast-burn variety, you might try less spark advance than has been suggested in this thread. For pump gas, a lot less, such as in the mid 20s, 24 to 28 range. The vacuum advance should advance it from there up into the mid 40s for level road.

That’s where I was going next. My thinking was to temporarily limit the mechanical advance to about half what it is now. It starts best hot or cold around 14* initial.

Doing some reading on the interwebs last night, it seems that these carb problems are VERY common for this particular carb.

[PRH]

I’m sure there are probably people who have had satisfactory performance from an ootb Holley street avenger........ but every time I had one in the dyno they were “not good”.
All around poor performance. Too lean, poor power, poor response. I am def not a fan.

Some friends have a chassis dyno in town, and for a while they saw a run of cars come in with those carbs on them.
All underperforming...... with driveability issues.
Sniffer in the exhaust showed way lean.

The 670’s seem to be the worst offenders.

My first hands on experience with one(670) was on the dyno, on a very mild Pontiac 455.
Low-300’s for HP........ ootb a/f ratio in the 15’s-16’s.

My dyno mule 850DP had the a/f ratio in the 12’s and 13’s........ and picked up about 20hp.