Carb Jetting....

[67resto-coupe]

I'm thinking my 625 Road Demon is still running a bit rich. The ignition bugs should be ok by now and I've down jetted 1x already.
The factory jets were 71-primary, 78-secondary....super rich. But then I dropped to 67/72 and it still seems a bit boggy and plenty of
black sooty goodness on the rear body panel/bumper. -4 step on the primary and -6 on secondary. Any recommendations on add'l
downjetting that can be done? 65/71? My plugs are still a little black....not moist as they were before, but not brownish/white either.
Thanks for the tips.

5.0 roller motor
e-303 cam
gt40p heads, 1.7 rockers
air gap rpm intake

 

[Sluggo]

What power valves?

 

[tarafied1]

reading the plugs is how I do it. You need to really drive the car for a bit, not just down the street. Once it gets good and warm at running temp you need a road where you can run it hard, shut it off and coast to a stop, then be able to pull the plugs without letting it idle. Otherwise you are not really reading the jets impact.
The jets or air/fuel mixture ratio shows up on the base. This is the last thread ring, it has the strap welded to it. You want a light soot color on the base ring. If the base ring has a a light soot color, but there are "spots" of heavy build-up of "dry soot" on top of the color, then jetting is too rich. With this build-up, REGARDLESS, if the porcelain is "BONE-WHITE", jetting is still TOO RICH.
You also need a good light with a magnifying glass to read the plugs. Unleaded gas adds oxygen and makes it hard to see the color with the naked eye. It takes a while to get the color on new plugs. It may be really hard to tell any changes on used plugs.

 

[67resto-coupe]

power valves? ....good question. whatever shipped with the unit. i haven't the slightest on that one. but according to the barry grant webpage, the power valve is the 6.5 size.

as for checking the plugs....without even pulling the plugs, if i walk past the exhaust pipes, i get a blackish spittle of condensation from both pipes. i've got black sooty stuff all over the rear chrome bumper and tail panel. would that be a sign of too rich? i just had the car out for a lot of highway driving this afternoon, so the plugs should read the current condition at this point.

thanks.

 

[AzPete]

Once you slow down from the highway speeds and drive thru town, you do not get a true reading from the plugs. They most likely will read rich from the slower driving and idling.

Black soot from the pipes can indicate a rich condition but if running rich for a while, they are not a good indicator of tuning changes as they take a while to run clean again. The soot collects fast and cleans out slow. Also, modern gas seems to leave a black pipe, not like the grey pipes of leaded gas.

 

[tarafied1]

Once you slow down from the highway speeds and drive thru town, you do not get a true reading from the plugs. They most likely will read rich from the slower driving and idling.

Black soot from the pipes can indicate a rich condition but if running rich for a while, they are not a good indicator of tuning changes as they take a while to run clean again. The soot collects fast and cleans out slow. Also, modern gas seems to leave a black pipe, not like the grey pipes of leaded gas.

agreed!