The Stovebolt Site Forums The Shop Area Engine Shop 390 Holley on 261

Just an FYI for any of you who have been cussing and discussing your 4 bbl on your 235/261. Have finally got the carburation adjusted on my 261 bored .60/shaved .20/Clifford 6=8 intake/Fentons. The 390 is mounted backwards to keep original gas pedal and linkage, .60 primary jets, .65 drilled secondaries, purple secondary spring, vacuum reading 18. Running like a scalded cat.

Good info I will file. My 235 +0.030, Clifford In/EX is running but not drivable yet. My 390 was dead on for idle mixture. I've got a wide band O2 sensor in the headers to tune mine. How did you tune? Dyno, seat of the pants, or gas analyzer?

Paul R. Wisner

Have a friend who is an old race car mechanic. Accomplished settings by trial and error using his expertise. Had the truck out last night and experienced just a slight warbling at heavy acceleration in both 1st & 2nd. Will do some fine tuning again next week and report.

Previously had a 600 cfm Holley on my old 235 & current 261. 235 had limited vacuum; 261 has plenty. Of course, on either engine--way overcarbed, but had both running strong with #70 jets and aggressive accelerator cam. Mpg was pretty pathetic at about 9 mpg. Son's 454 does better.

56picup,I ran a 600 Holley on a 261, overcarbureted some but #62's in the primary worked fine. Your carb was jetted rich, got a heated manifold? The aluminum intake runs too cool, needs rich part throttle jetting to avoid bogs.Your jetting on the 390 seems rich also, stock jets are #50's, Holley stock jets are about 5% percent rich for most applications.But I guess you have to jet it to your situation.

I was running 54 jets in the primaries of the 390 on my 235. I always had the prob of my plugs running white, but the pipes were coal black. Whats with that?

Probably rich secondaries and lean primaries, chip.

Don't wanna hijack the thread but...

I had to use a stiff spring, like the brown or black to keep the secondaries from opening too soon. I could feel the car slow down if I put my foot into it below 2300 rpm. Too lean on primary or secondary?

Also, I just pulled my 235 apart after 125 miles. Piston crowns were already really sooty. What am I doing wrong? Should I convert to a 4150 secondary block so I can change secondary jets?

Still can't figgure if Im too lean or rich.

thanks

chip

Chip, I have noticed the plugs in my vehicles won't color properly anymore, something about the gas.Check new vehicles, black pipe, pull a plug ,pretty white in color.I jet the primaries by leaning down until the engine stumbles slightly when accelerating easy at perhaps 40 mph in high gear when the engine is fully warmed up. Then go up one jet size.This also depends on the accelerator pump being adjusted properly.Secondaries are more difficult to jet, but again Holley carbs are usually jetted close right out of the box.Your bogging does seem like secondary the opening rate is too quick.Holly claims if you have to rejet 8-10 sizes from the standard jet size, you have the wrong carb or fuel delivery problems.Holley has a nice catalog/tuning book you can get from their website

I appreciate all the info. As usual, you guys are always a big help. Back to fine tuning this week before we go to Goodguys in Des Moines over the 4th.