I have new 383 in my Duster. The motor is 9.6 to 1, 906 heads, solid 250 @ .50 108 lsa, victor 383, brawler 850, 2” Hedman fenderwell headers, Unilite distributor and MSD digital 6 box. The fuel comes from a pro comp black pump dead headed to a basic Holley regulator. When I got it together in March I took it to Beech Bend at it went 11.36/119 car weighs 3315 with me in it. COVID hit and it sat in the garage until June, then when I took it out it dropped to from 119 to 116-17, 20 degree temp increase so I thought maybe. I pulled the plugs (Autolite 85) and they look just like they did when I put them in (no color on anything-see picture). I started jetting at 76/84 4.5 PV went all the way to 94/94 6.5 PV nothing changed with the plugs. All runs were 6.5lbs fuel pressure and mid glass float level. I tested the PV and they all worked as they should.

From there I tested the fuel pump. I ran it for one minute through the regulator and it delivered almost 2 gallons. I ran a smaller sample from each side of the regulator and got 12 oz on each side in just under 6 seconds. From there, I thought that maybe I was losing voltage to the pump. I have it on a relay tied directly to the battery but my little alternator (40 amp) has trouble keeping up when I run my fan (33 amps). I scored a Power master alternator at a swap meet that puts out 85 amps at idle. I am seeing a significant increase in my voltage now, with everything I have turned on, it is still keeping the battery over 13 volts before when the fan was on it was barely showing 12 volts.

Down track the fuel pressure is staying consistent and my manifold vacuum is nearly zero so the PV should be supplying the extra fuel. Tonight was my first pass with the new alternator, I started back at 76/84 and moved to 82/90 and still nothing on plug color. The car actually slowed down from 116.11 to 115.27. I did try reducing fuel pressure down to 5.5lbs thinking it may actually pick up some volume. The weird part is also I do not feel the car nose over or feel like it quits pulling. I leave at 2500 and shift at 6400.

I am at a loss as to what to do or check now.

This is an interesting problem, and i’m curious as to what’s the problem. Probably not an issue with yours, since you mention you don’t feel it nose over, but did you change the fuel tank or setup? Is the tank system properly vented? I had this problem on my 73 b body, and had to repair the tank venting. But, i felt some nosing over when i hit 2nd gear shift. If you jet up and still no richening of plugs, as you stated, there is fuel system problem. Venting is one area to double check. Good luck.

What size needle and seats are in it?


Joe

Maybe I missed in your post...what fuel???
If unleaded pump fuel,it will not color the plugs very well and bone white is good.
I didn`t see where you posted any E.T. or MPH change with jetting up?
I`m sure you know that if you can`t slow the car by jetting up you are out running fuel supply.
Maybe borrow a carb, to rule out HSB fuel curve variables.

And..... what are you running for a scoop /fresh air arrangement?
I made a Ram-Air set up on my streetcar..... REALLY disturbed the fuel-curve on my wideband......
Oh,and one more thing......2/3 mph from March to summer humidity/barometer/heat is not out of the norm.
Any other cars you know that have been there at both dates you could compare notes with????
I`m never happy going slower.............. but March to July is a BIG variable....

-I have checked the tanking venting. My shop has dirt dobber nests everywhere so I thought one may have found a new home but I was good.
-The Brawler comes with a 120 needle and seat.
-I am running 93 unleaded and last night was my first run with 90 pure gas (no ethanol) and just a touch of Boostane (2oz to 7 gallons)

Last night
1st pass - jetting 76/84 6.5 lbs fuel pressure 1/8 mile 7.378/93.65 1/4 11.596/116.11
2nd pass - jetting 76/84 5.5 lbs fuel pressure 1/8 mile 7.378/93.38 1/4 11.608/115.86
3rd pass - jetting 82/90 5.5 lbs fuel pressure 1/8 mile 7.43/93.12 1/4 11.679/115.27

I was actually thinking about my scoop set up last night and curious if somehow I was restricting air somehow. I have my carb sealed to the scoop using two pie pans. It worked really well with my 451 but I was using a dominator. I made a new pan for the 4150 and maybe I have inadvertently covered or restricted the air bleeds.

Not much change with jet. But nothing unusual. Mine acts the same.
Have you tried jetting down?
I can't see any color on fresh plugs running unleaded no matter how much jet I put in it.
My other car is supercharged 440. Can go 10 jets and plugs do NOT follow.
MPH will vary 4 with the change.
E.T. 3 tenths.
I don't know if you have a problem......weather makes a huge difference when rich.
Lean not so much till it gets cold 60ish here in Ohio.
My car slows in the cold even when I try jetting up.
.

What number air bleeds?

I would take the carb apart and blow thru all the passages. See if one passage isnt plugged up due it sitting for a awhile. I had that happen one time, thats the reason I now use AV gas. It can sit 6 months and never plug anything up anywhere. Just a thought. If it ran ok before it sat still for awhile, then it doesnt run ok, that is where I would look first.

I had a similar issue using the autolite plugs and realized my back accel pump wasn't working changed pump cam and all seems to working now

You got it fat enough to slow it down in the 1/4 mile on the third run, time to try jets between those two set ups

Depending on how much street driving you do, I'd yank that PV out and use a plug, one less variable.

Next I'd install an AF gauge and know straight away what it's doing. Even if it's a temporary setup, you'll know without having to pull plugs.

The carb is new but I’ve had it apart at least 10 times cleaning and checking both excel pumps are squirting and it has 33 high speed and 73 idle bleeds. It looks like I will try jetting it down below the 76/84, I just couldn’t make myself do it before, even though the car was slowing down, because of the plugs. It does make sense as when it went 119 in March it was with 76/84 jetting and mid 60 degree air. I really appreciate 6BBL comments about the unleaded gas and the plugs not following the jetting. I guess in the end this has been my best problem as it only required some education on my part, with a bonus of being free.

Thanks for all the help.

If it worries you and it should about taking jet out.
Make small changes and pay attention to how is reacts.
Based on the plug picture, there's probably room for another degree or 2 of timing.

As far as reading plugs.
If I put fresh ones in after I warmed the engine.....I could take them back for a refund.
They are that clean...

When it comes to plug color, white is right
AKA aside, you don't want them brown or black
look real closely at the center porclyn, look for pepper or silver dots, if their on it NOT good If they are clean with no pepper or silver dots your close
Jet by the spark plugs, all of them, and the time slip
Good luck, test, test and test some more until you disappear at the speed of light

Not true. Burn anything and it will produce carbon. Try jetting up until you get some colour on those plugs or borrow a smaller carb and see if that helps improve the mixture around the plug so you get some colour.

Maybe there's just not a lot vapourized fuel around the plug at the time of ignition.

Combustion patterns

Look at the area around the plug and notice how its clean in some areas and now think about how much combustion is taking place there. Notice how the carbon trail runs from the plug to the exhaust area where the most heat is and look at the colour on the exhaust valve compared to the rest of the chamber.

I would tune it with a wideband.

As for plug color I've done that on 2 strokes but had to cut the threaded section of the plug off to get far enough down on the porcelain to see any color.

I think if you're looking for color on the entire porcelain section of new plugs chopping the engine after the traps you'll end up pretty rich.