Technical Engine runs extremely RICH?

OK, here’s the pooda.

347 Ford; Brawler double pumper carb; Cam; headers; aluminum heads; MSD.

New engine from a reputable builder…it runs good & the car is much quicker. BUT the plugs are nasty black and mileage is terrible. Recently the plugs were so fouled that it wouldn’t start. I cleaned them a bit and it fired right up. In an attempt to get it straightened out I have: gone down two sizes on the main and secondary jets (now running 68 primary/72 secondary. The fuel pressure is dead on at 6.5 psi, which is what Holley recommends. I put new plugs in it after making those changes, drove it almost 200 miles today and pulled the plugs. The attached photo shows how the new plugs look. What am I missing here?

 

I forgot to say that I’m running 90 octane non ethanol fuel. The fuel level in the float bowls is half way up the sight gl***.

 

1. Engine vacuum to low and opening up the power valve.
2. Not enough ignition timing

 

Wrong power valve? On my BBC with Comp Cam roller the vacuum at idle was less than the power valve rating allowing extra gas to flow. Did the same thing as yours. Changed power valves now it's good. Just something to consider. I'm ***uming the Brawler does have a power valve.

Edit: AHotRod beat me to it.

 

It has 36 degrees of timing.

 

I'm referring to Initial-timing .... you have not provided the camshaft specifications, or id the ignition system is full mechanical, or vacuum ***isted.

I stand by what I said before, the power valve is most likely the issue.

Have you put a vacuum gauge on the engine while it warm and in gear (if automatic)?

 

Have you played around with the mixture screws? With a four corner idle an 1/8 of a turn on all four can make a big difference.

 

I don't have the cam specs at the moment, I'll dig them up in the morning and post. Ignition is MSD plug and play distributor, full mechanical and was set up by the engine builder...tested on dyno.

 

The mixture screws are set to factory recommendation...I'll see if leaning them a bit makes a difference, but they just affect mixture at idle, right? When going down the road under higher rpm they wouldn't have much impact on the mixture? At least that's what I have been told.

 

No vacuum advance will cause it to run rich (not enough ignition advance) when cruising at light throttle.

 

What's vacuum reading at idle? As two previous posters mentioned your power valve may be causing it to run rich if vacuum is low due to a bigger cam and power valve has a higher rating. Could also be a blown power valve. All it takes is one backfire to take it out. Have you checked the float level and verified the needle and seat and float aren't leaking?
The amount of deposits on the plugs suggests a carb problem but you might take a close look at ignition as well, considering it wouldn't fire the plugs until you cleaned them. Good wires, cap, rotor, etc? Full 12 volts to MSD - not connected to OE resistor wire from ignition.
Sounds like you had this running in the car before the rebuild and all was OK. Anything changed other than the rebuild?

 

I'll put a vacuum gauge on it tomorrow. This is a completely new engine with less than 1,000 miles. The ignition system checks out in terms of voltage and installation.

 

You may be on to something. I wondered why the engine builder used a non vacuum distributor, but since he came so highly recommended I didn't question him. I figured he would put the right springs in the distributor to make it work correctly. I need to get back to him and ask.

 

Fuel level sounds too high.

Was the fuel curve set on the engine dyno w/sniffer? Too cold of a plug? CR? Manifold vacuum reading and hot idle RPM?

Which MSD SYSTEM are you running?

A mechanical distributor and a double pumper can be a bear on the street.

SETUP DIRECTIONS - https://m.roadkillcustoms.com/holley-brawler-double-pumper-carburetor-installation-and-basic-tuning/

 

Check float level or sticking float valves

 

For a race car it's fine, but for a street car you absolutely need a vacuum can for mileage, idle, cooling and drivability.

Your total timing of 36 doesn't cut it, unless you plan to run WOT most of the time. Anything under 52 degrees (mechanical and vacuum full in) produces less than optimum fuel economy and response at cruise speed. Depending on fuel, compression, cam and a few other factors, it may even take up to 58 degrees.

And no - you can't make up with springs and weights. Mechanical and vacuum are two systems that work hand in hand and correct each other, based on RPM and load . If you loose the vacuum, you loose the load hand.

Here is some reading for you, that explains it pretty good: https://www.crankshaftcoalition.com/wiki/images/e/e4/Vacuum_Advance_Specs.pdf

Also - looking at your plug, it seems way too cool for what you got. But I would first fix your vacuum situation and deal with stuff the other guys mentioned (power valve/fuel levels etc.) before you try other plugs.

Side note: IMHO fuel level is way overrated and to some degree a myth - but that's a whole other can of worms.

Frank

 

Your timing must be set first to were the engine is happy, you have to find the sweet spot. Then you can tune the carb. I agree with Glenn, check vacuum and install the correct PV. Tuning is a process. A air /fuel ratio gauge can be your friend here, getting you on the right track during the tuning process. Take your time and make one change at a time.

 

Like others posted ,
800-1000 rpms Idle , ( Some engines like more)
The engine will let you know what it likes .

""Initial timing"" more likely be 15-20 average, some engines like more.
The engine will let you know what it likes .
Vac gauge for adjusting mixture , & point to witch pv needed ,

You have to start Tunning @ idle
( idle rpms , initial timing , mixture screws )then work from there ,

Plug heat range will be another tunning procedure,

 

Also a good Quality O2 gauge will help Cruise to wot carb tunning , reading plugs with modern blends of fuel off pump is miss leading, Look @ modern OT tail pipes ,
(Black & Study) Here in N Va there is only a few suppliers selling non-ethanol fuel, (some Wawas & Farm Royal some Sheetz) it seems to not be consistent, it looks contaminated to have a white ish tint like water present, or lube.

 

With the electronic ignition, plug gap can be opened up to.040 or .045" to reduce fouling.

 

Is this the same carb the builder used to tune it on the dyno?

 

Is this a racecar? Is it truly a double pumper (mechanical secondaries)? If so, just for grins, disconnect secondary accelerator pump and take it for a spin. Or is it a Holley with vacuum secondaries.

 

Pretty sure the Brawler Holley carb is mechanical secondary.

 

Maybe 10%..
Mileage Depends more on load/ throttle opening , does the vehicle weigh 2000 lbs or 6000 lbs , do you drive up & down hills , stop start traffic , steady cruise rpm ?

 

... hmm ... flip ... flip ... flip ...

Well, I guess they changed that since the seventies ...

 

Actually in some cases , they have . Plus , these are m*** manufactured , which means there's room for error .

 

With center hung floats the best way is when you have the bowls off, flip them upside down and set the float so it is hanging level and you are good to go.

 

Yes

 

Lots of ideas to investigate here. I’ll be busy for a while.

To answer some of the other questions, car is a Deuce roadster with manual transmission; it weighs 2470# without driver and half a tank of gas. It’s not a race car…I was hoping for a faster street car.

When I put the new plugs in about a week ago, I started it and let it just idle for about 5 minutes…pulled a couple of plugs and they already had a fine coat of soot developing. Once I drove it at speed it only got worse. Maybe I just need to switch to a vacuum distributor? I should hasten to add that while I’ve been messing with cars for most of my adult life there’s a WHOLE lot that I’m still learning. Appreciate all the answers and help here.