Technical Engine runs extremely RICH?

Most Holley style carbs produced after the early 90's have power valve protection circuit built into the baseplate. There should be port with a spring and checkball on top of the baseplate that exits out to the bottom in case of a backfire. Not sure how well they work, but it should be there.

 

Why not drop some more sizes? I just went through this with triple big 97's that were supposed to be jetted close for my combo. I'm down 9 sizes on the primary and 10 on the secondaries.

 

@whateverit takes Thanks for the detailed explanation! As I noted above, my next move will be to go back to the shop that built the engine. This is a new build with less than 500 miles and since it was fouling plugs right from the git go they should have a stake in getting it to run right. If I can't get satisfaction from the engine shop I'll jump back on it myself and the information on this thread will be my guide. Someone pointed out earlier if I do too much to it myself the shop can always decline to make it right on the grounds that it was I who screwed with it and got things out of whack. Thanks again. I'll post the outcome when its done.

 

How do you control the curve without the load sensing of the vacuum can? All you have is mechanical RPM and that alone does pretty much nothing.
For example: at idle (depending on your cam) you want something like 26-34 degr. advanced timing - at cruise speed around 50 - how do you do that just with springs and weights, without totally messing up everything else above cruise speed?

Frank

 

The above is GOSPEL ...

Somewhere along the line the build type was misunderstood ...

Was the desired final result written on the shop ticket or was it just word of mouth?

Confer with the shop before doing anything else.

Is the engine builder and dyno guy one and the same?

 

... hmmpf ...

I once knew a little girl in Baltimore like that ...

There is a tester used with a MITY-VAC that make dialing the correct one in much easier.

 

Engine builder & dyno guy are the same. I called today and they were fine with trying to see what’s going on. ‘Will take it in as soon as I can find a free day to go over there. I think we covered the objectives thoroughly in the beginning. Based on this shop’s reputation I feel like they will fix the problem. We’ll see. I’ll post the outcome when it’s done.

 

Here is a basic tutorial on DIST advance -

https://www.gofastforless.com/ignition/advance.htm

 

So after you set the floats the hard way , what does the site gl*** / bowl opening tell you ?

 

What do you mean by that? Take the plug out, set the float height so that when you shake the car gas trickles out, reinstall the plugs. Simple. Been that way for years. This clear plastic plugs turn cloudy after so long anyway. But hey, you do it your way, and I'll do it mine, right?

 

It depends on the distributor. Most use springs. There are a variety that can slow or speed up the mechanical advance.

 

So how do those springs alone give you 50 degr @ 2500 rpm at cruising speed, and 36 @4500 rpm?
Must be magic springs that become shorter at higher rpm.

Frank

 

I think that the point @FishFry is trying to make is that mechanical (centrifugal) advance can only respond to changes in engine RPM. And that's fine in a high performance application, where the engine spends most or all of its time at a higher RPM under a heavier load.

But a vacuum advance responds to changes in engine load over a wide range of driving conditions. It can advance timing when it senses lower loads (higher manifold vacuum at idle and light throttle cruising conditions). But it can also retard timing when it senses higher loads (lower manifold vacuum when accelerating, pulling up a steeper grade or hauling a load).

Combined with a mechanical advance it's just about the perfect way to make a hopped-up engine more enjoyable to drive on the street, under a much wider range of driving and idling conditions.

 

I agree with both of you but its not the reason his plugs are fouling. I was trying to get his original problem identified and fixed. Vacuum advance on a distributor is not required to tune an engine thats running rich.

 

Again ...

This is how the fuel level is set on this model HOLLEY.

The mixture adj screws are set at the factory for a startup only. The idle screws have to be adjusted to achieve best idle quality (and curb idle RPM adjusted to fit that mixture setting) and this is usually done with a vacuum gauge if you don't have a sniffer.

Idle mixture(s) will vary from one engine to another. There cannot be a one-fits-all preset.

If all else fails, read the HOLLEY INSTRUCTIONS MANUAL.

 

At idle, you usually got a AFR of 16-17:1 - you barely filling the cylinder - the only chance to ignite this at the right time is a vacuum canister that pulls enough advance.
If you don't have one, you need to go way richer - or open your throttle more, so the transition circuit cuts in.

Since the idle circuit works not only at idle, but way into the transition circuit (where you spend most of the time cruising) you are cruising way to rich - hurting mileage and fouling plugs.
Again 16-17:1 AFR or even more would be perfect for a efficient running engine at cruise speed.

Frank

 

I caught up on this thread this morning.
I agree with taking it back to the builder, he can probably accomplish more in an hour than we can guess in a week.
If you're forced to go back to working on it yourself, I agree with putting a known good carburetor on it and see what that does. It should show you which way to go.
While I am fully aware of what primary and secondary mean, everybody I know refers to them as front and back.
Some things I have not seen mentioned:
Sometimes people will plug the power valve in the back, and up the jet size to compensate for it. Did they do that on this one? I have seen the need to crack open the back barrels at idle in order to lower the front down to cover more of the transfer slot. I have also seen fuel dribble out of the shooters at idle making it pig rich.
Just some things to check.
Good Luck!

 

I don't agree with your idle AFR ***umption. You can adjust the idle circuit to an optimal AFR. You can adjust your cruising circuit as well. The vacuum advance is not necessary to make these adjustments. I will repeat that for a street engine a vacuum advance distributor is best but not required.

 

He is doing what's best now, taking back to the builder.

 

(cue old AM radio intro music)

"Ladies and gentlemen, time for the annual vacuum advance discussion, right here on HAMB radio.
KHAM, in Austin Texaa***."

But you said that...

No YOU said I said you said...

Well it thought you said I said you said I said vacuum advance and...

**** kids I didn't have any advance on my last high powered motor. Locked in at 36 and let it eat, started it with 23 deg start retard. Idled clean AND made big power.

When you eat too much you get fat. Kinda like engines, too much fuel in, runs fat.

"And now for a word from our sponsors, MSD and Slim-Fast, right here on...

KHAM, in Austin Texaa***s"

Tune in next week (pun intended) for the new episode ***led "He called me fat just cuz I'm rich." same fat time, same fat channel.

 

I'm waiting for the "Ported vs Manifold" episode.

Frank

 

How do you even run a motor with 50 degrees of timing ?

 

Start with an initial of say 16, then add in some mechanical, to about 36, then add some va***e. Walla?

Chris

 

HAhahah...I rolled out of the rack this morning, checked the HAMB and this popped up. Just what I needed to start the day. Love it!

 

I have the same carb on my 350 SBC build and found the floats were a bit high from the factory. I set them so I just see the fuel level in the sight windows. I also found that even with my aluminum Dart heads, and a big cam, my car was still too rich at idle, and my 4 corner mixture screws were too far open as they came. I have them turned down to maybe 1/4-1/2 turn open when I adjusted them using my vacuum gauge to get highest vacuum at idle. I have a mechanical fuel pump, but I put pressure regulators on everything, regardless. My experience has shown me that the max pressure Holley states of 6.5 psi can be a problem, as often after things warm up I see my pressure gauge reading slightly higher. So I set my fuel pressure around 5-5.5psi at idle, and it's still plenty of pressure to never starve the carb.
After tweaking the carb, and playing with distributor timing my 350 in my 39 Chev gets 17 mpg on the highway with 3.73 gears, and a 700R4 OD trans. And doesn't burn my eyes at idle anymore.

 

Brawler carbs have sight windows, and no reason to remove the bowls to set up float levels. Just look through the sight windows and set them up low so you just see fuel at the lower edge of the windows.

 

Do the Brawler carbs have replaceable idle air bleeds? That might help in making it easier to adjust the idle mixture.

 

Just Carb tunning / metering !!
( this is just a bit of , A hell of alot more to under stand & other components of carb)
Most need to know how a Carb works & know how to tune to engine , lot of work notes & experimenting,
Some carbs work right out of box with simple adjustments, Most think its running correct ,
Then there is Times Others will go extra & required.
Before screw in adjustable , The old Fashion way was drill bits & strain of wire ,ext !

 

I agree with the guys recommending fine tuning of the idle mixture screws. Most recommend using a vacuum gauge, and that is a great tool, but try it also with a tuning tachometer, adjusting each screw to achieve the highest rpm reading, You might find the tach is more sensitive and will show results of finer adjustments than a vacuum gauge will; that's always been my experience. Plus, to get the most crisp throttle response you should do a lean roll on each screw after achieving the highest rpm, i.e. turn the screw In to achieve ~20 rpm drop in idle speed. And, you should reset the idle speed after adjusting each of the mixture screws before moving on to the next and as the final adjustment at the end of the job. Yeah, it's kind of tedious, but you'll get the cleanest smoothest idle, and a nice crisp response when accelerating.