Camshaft Guru; Tell me where to start with jets

[Lynn]

Agree. Eric sent me an email. What a great resource.

[x33rs]

I set them up here for various applications. What you have shouldn't be difficult to start with. You can subtract at least 10 degrees duration from the solid cam right off the bat so that camshaft really isn't all that big. The tighter LSA might make it choppy compared to 115 on a DZ cam, but it will shorten up and bring in the torque curve a bit sooner and feel stronger.

I run a similar flat tappet solid in our DZ, with 112 LSA, with other specs close to the 30/30, but with more lift and tight lash. Basically a cheater cam. I also run Hooker Super Comps. Everything else about ours is stock OEM issue with a true 11:1 compression.

I find the stock DZ intakes like a stagger jetting in the carb. Mine made a pinch more HP. The way the runners are designed prefers more jet on the driver side. Before I'd worry about that I'd concentrate on a basic setup and make sure everything is okay.

72/76 jetting is perfectly fine and should perform well enough to get things going. As far as power valves, a common misconception on them is that they have to be lower than the vacuum reading at idle or they'll flood the engine. Doesn't work that way. Fuel is only pulled through the power valve circuit when the throttle blades are exposing the transition slot and pulling fuel through the jets, only then does the power valve circuit become active. They do not work at idle. It's very important to make sure initially that your throttle blades aren't exposing more than about 1/8" of the transition slots both front and rear. Much more than that and you will be pulling fuel through the jets (and power valves if engine vacuum is low enough) and have a very rich condition at idle, and also makes your mixture screws inoperative.

If the car doesn't idle properly like this there could be one of a couple things going on. One may be that you need to create a small vacuum leak by drilling a pair of very small holes in the throttle blades so they can be closed properly. The other issue that I find most common these days, if trying to run this on 10-15% ethanol mixed gas is that the idle circuit may not be rich enough. 10% ethanol stoich is 14:1, not 14.7:1, and will sometimes act a little funky trying to run a very lean mixture with inconsistent idle. Almost every carb I do I have to richen the idle circuit to compensate. On our DZ I had to drill the idle feed restrictors for more idle fuel. I'll have to check but I think I ended up .002 or .003" larger. Every engine is a little different here and I use a wideband to dial things in combined with what the engine is telling me it's happy with and best drivability.

Getting back to the power valves, that cam you're using, if you have a true 11:1 compression, and the cam was installed at a proper ICL, the engine shouldn't have much trouble making at least 12 inches of vacuum at sea level. Mine makes 10" at 5,000 ft elevation and 13 inches at sea level. I'd stick with the 6.5 power valves until you get some driving in. What I find with too low of a power valve in most cases is tip in stumble because the PV circuit is delayed too much, and no amount of squirter tuning will get rid of it. You might be able to bandaid it and cover most of it up, but the PV is the real cure and will also help mid range throttle transitions. My engine still likes 6.5 PV's in it front and rear. Even trying 4.5's creates an off idle stumble.

I found with mine, I stagger jet the driver side up 2 sizes to compensate for the runner design of the DZ intake. I'm at 5,000 ft, and routinely drive the car to sea level so I make a compromise on mine so I don't have to keep fiddling with it. I run 70/72 front and 76/78 rear with the 6.5 PV's. Along with the idle circuit fattened slightly (we run strictly 91 pump gas) Throttle response is crisp and quick. With the wide band up here where we routinely see DA numbers near 8,000 ft in the summer, it cruises around town between 12.5 to 13:1 AFR. Idle is right at 13.8:1 AFR, and WOT hovers around 12.4:1. Wife drives it daily, plugs stay nice and clean, the engine seems to like it, and it knocks down 14 mpg around town and 17 mpg highway with an M-20 and 3.55's. When we drive down to sea level, the AFR's lean out about a full point, and it runs fantastic so I find no need to constantly tinker with it, I just live with it being ever so slightly rich up here on the mountain.
That's with Hooker super comps and a complete Pypes 2 1/2" transverse muffler system. Hope that helps a bit. More questions you can PM me or email if you wish. [email protected]
Larry

[x33rs]

On the distributor, that looks pretty good and close to how I set them up here. On our DZ the only difference is I have my curve coming in a tad quicker at 2400 rpm and it likes 36 degrees total, with 18 initial. I also run a B28 vacuum canister with a simple modification on mine welding the slot to limit 10 degrees at the crank. I found mine likes the additional timing at idle so I run mine off manifold vacuum. I switched back and forth for a while between ported and manifold. Mileage was better around town, and idle was smoother with manifold vacuum so that's where I leave it. I'm still running points in it and Autolite plugs gapped at .035

[Steve Shauger]

X33rs


" What I find with too low of a power valve in most cases is tip in stumble because the PV circuit is delayed too much, and no amount of squirter tuning will get rid of it. You might be able to bandaid it and cover most of it up, but the PV is the real cure and will also help mid range throttle transitions. My engine still likes 6.5 PV's in it front and rear. Even trying 4.5's creates an off idle stumble."


I've had this issue which was caused as you state by too low # power valve. I chased this issue for months, years ago. Very informative post... Thanks Larry!

[Flying Undertaker]

Lynn: My biggest concern is the 2 Quarts fuel dilution of the oil, that's a lot of fuel! Check your fuel pump, they've been known to fail and dump fuel into the oil from the fuel pump mounting area of the block. As for jets, I'd stick with 72 in the primary side until you get the engine to idle correctly, possibly reduce the secondary side to 72 in the future. New Camshaft specs are not too radical for a DZ engine as the original cam specs are .485 lift on both intake & exhaust sides with 254 degrees duration at . 050 lift. with a 114 degree lobe separation to allow better idle for emissions and 50 state usage. The newer cam is 236 degree duration at .050 lift, 18 degrees less. Disassemble the carb and clean with a bucket type carb cleaner, later using spray cleaner through carb metering block passages and air bleed and passages in the main body. Reassemble carb making sure to use correct metering block gaskets (most kits have 2 different style gaskets). Stay with the factory power valve values until you get the carb to idle smooth enough to obtain vacuum readings with a good working vacuum gauge. Adjust power valves to be between 1 to 1 1/2 inches below vacuum reading at idle in neutral. Always use NEW power valves unless you have a tester to insure that the power valve diaphragm wasn't damaged due to backfire as the original carbs did not have a check ball to prevent backfire damage. Ignition timing seems to be fine as is. Always use full intake manifold or carb baseplate vacuum advance hookup to canister on distributor, stay away from ported vacuum. Good luck, keep us updated on the progress. Don.

[x33rs]

Something else you can do Lynn that I check with all Holley carbs here is flatness with the metering blocks.

I noticed you mentioned a large internal fuel leak. If you already checked the obvious (blown PV, transition slots not overly exposed, or dirt in needle and seat) and you're still having a serious flood issue, I find a warped metering block often a cause, especially on these 50 year old carbs. Meter blocks that aren't sealing properly cause all kinds of wonky idle issues and internal fuel leaks.

Holley used to make a tool to bend the meter blocks back into place. Yes sounds crazy but this was a problem even back in the day. I have one of these tools in a box somewhere I haven't found since I've moved but it's just as easy to chuck it in a vice.

What happens over years of cranking on the float bowl screws is that it draws in the corners of the meter blocks. If you run a straight edge across the block you'll find a lot of them bowed in the center. You can carefully chuck it in a vice in such a way to apply pressure and gently bow the meter block in the other direction, and let it rest for a few minutes. It's okay if it now bows slightly the other direction. It will push and seal in the center of the gasket better, and saves some of these hard to find meter blocks.

I also run a straight edge across the face of the carb, and often find the corners of the carb pulled out from the bowl screws. I lightly run a fine file across the face until I see the file contacts the entire surface, then clean and blow out all passages as necessary. I find this is most often the cure for old carbs that most people removed long ago for poor running problems they could never figure out.
Hope that helps.

[Steve Shauger]

Originally Posted by Flying Undertaker

Lynn: My biggest concern is the 2 Quarts fuel dilution of the oil, that's a lot of fuel! Check your fuel pump, they've been known to fail and dump fuel into the oil from the fuel pump mounting area of the block. Don.

I agree, two qts of fuel most likely came from the fuel pump leak into the block. If that much fuel had come from the carb, the cylinders would be washed and the car would be burning oil due to piston ring wear.


Lynn keep an eye on the fuel in the oil issue....