I have a Holley 650 Double Pumper...originally has 67/73 jets. The engine is a 355- Home Ported World S/R Heads, 230/236@.050 solid cam (.471/.485 lift), 9.5 Compression, Dart dual plane intake. With the 67s in front I was fouling spark plugs bad while cruising, switched to 65s in front, plugs got a little better but still show running rich(black on base ring), my heated 02 sensor I run(not wide-band) shows I'm STILL running slightly rich at cruise.

What are you guys on relatively mild 350s running for jetting, particulary those with 650 double pumpers? I've read in old posts using the search function that mild 350s shouldn't even run with anything less then a 67 jet in the primarys, but it seems mine wants 63s in front. Does this seem normal to anyone else? What are you guys running?

Car runs 13.5s @102 and I gained 2 tenths and 1MPH going from 67/76 to 65/74, but it seems to want to go even leaner.

 

"Normal" is giving it what it wants.

 

What color should the base ring of the spark plug be(if its in good tune with right mixture) when just cruising around the streets?

 

Every motor's different. Your goal is a good tan colored plug. I too just recently got a new 650DP with the 67/73 jet combo. For my 383 I needed to jet it up to 76/80. Every motor is different just keep trying different jets till you get what you want.

 

another thing to just throw around, i've got a holley book and it says if you use off brand jets actual sizes can vary.

its said machining imperfections can make the sizes from one manufactuer to another not consistant.

so maybe what ur comparing isnt quite apples to apples.


i agree with what others said, go with what ur motor likes as long as ur plugs stay lookin good

good luck!
cya
brad

 

For nice, lean cruise mixtures and good fuel economy I've found that many "universal performance replacement" Holleys want to go 4-8 jet sizes leaner on the primaries than stock. For most typical small block applications they're jetted conservatively fat. Stock primary jet on a 650DP is a 67. Don't be surprised if you end up down around a 62. You may have to richen up the secondary side when you go economy-lean like this on the primaries in order to stay rich enough when you go wide open.

Also, don't depend on your O2 gague for the idle and just off idle mixture readings. You've got too big a cam for the O2 readings to be meaningful at low RPMs/light throttle. Too much cam overlap- too much intake mix flowing straight into the exhaust during the cam's overlap period. Plus your primary jetting changes won't do much until you're at about 10% throttle or above. That's the realm of the idle circuits.

 

i'm havin trouble with my holley too. it runs sweet when idling and under easy acceleration but if i get on it, it starts choking itself out (i think) and performance bites. it's also backfiring if i let off the gas completely when slowing down. Gas milege bites! 100 miles a tank if i'm lucky. i'm guessing waaay too rich. anybody have thoughts? i'm running a 650 holley on a 355

 

I`m running stock jetting 67/76 on my 650dp/ 355 and it seems to be right on.But I had my choke milled off so it might flow a little
more on the primaries.Maybe go down one more jet size on the
primaries but go up one or two on the secondaries to make sure
you don`t lean out when you step-on-it.