Am I running on my primary jets!
What the heck are you guys doing!??!!
A complete sidetrack.
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Headed right off a cliff too
Let the guy tune his carb.
One change at a time.
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Well, because of this;
74 Duster, full weight cruiser
318/A500(.69 OD)/4.10 gear. 28" tall tire
Quickfuel 750DP.
2400 rpm at 70mph cruise
Question for you all is, am I cruising on my primary jets or the idle circuit? I'm pretty sure it's primary jets but need another opinion.
Cley
and this
I am tuning the cruise by the plugs. Just optimizing. I went from 72 to 69 jets and they are still darker than I think is good. Now for 67s when I get back from the lake. I checked them after a 70 mile cruise at 70mph.
Cley
and this
Yes,, 20 initial, 34 total with the V can on top of that.
Cley
So;
I assumed Cley was tuning for economy.
And as you all know, as for an already-existing engine, tuning for economy begins with tuning the slow-speed circuit, and optimizing the cruise timing.
The mains are for after the slow-speed circuit is all used up, and for before the power valve opens.
You can throw 20 different MJs in there, and until they are really really tiny, and too small, they will have little to no effect on cruise-economy. In fact, on a Holley-style carb,if it were possible to pull them out while cruising, Ops combo would continue to cruise just fine.
And the assessment of throwing all these jets in there could take more than an entire summer!
And so, I was/am, just trying to get this project jump started, by offering a proven method.
But if you all think to to drag him along at your speed, ok fine; I'm tucking tail and scurrying back to my corner.
OP
BTW
cruising at 2400 rpm your engine will want a lot more timing than the factory parts can provide. Think 56 degrees plus or minus a couple.
If you do not provide it, peak cylinder-pressure cannot ever be achieved. and whatever pressure it does make is chasing after a piston that is being yanked to the bottom by the previously fired cylinder. Too much later than that, and the piston has to work to push out it's own exhaust. That's work that could have been used to propel the Duster.
with 20/34 timing, that means 14 in the D. Assuming all in by 3400 and starting at 1000, that makes the advance range to be 2400 rpm. And so a rate of advance to be;
(14/2400)x 100=.58* per 100 rpm
Therefore your timing at 2400 is expected to be (.58 x 14) plus 20= 28*. and so, your Vcan is looking to be 56 less 28=28*. So if you currently have something like 12, then the total is just 40 degrees. And that will cost you gas.
The most I have ever heard of, is a guy named
@TrailBeast , who modded his to 24* . I got mine to 22*. Even if you get yours to 22*, that's a possibility of being 50* and still not enough.
You gotta fix this first.
How to figure your cruise timing;..
just rev it to 2400 and hold it at 2400, then advance the timing. As the rpm goes up, drop it back to 2400 and add more timing. Repeat until the engine rpm no longer increases; then read the timing and subtract three degrees for load compensation. That's all there is to it. It could be 48, it could be 58. Whatever it is, that's what it is.
Later after you get the cruise AFR dialed in, then you can revisit your cruise timing to see if it has changed.
Just do as instructed and you combo will be 90% cruise-tuned in a couple of days. or
just do what the "other guys" say; it will just take longer. The end will be similar, of course I think my way is the best. But only because I used to make a pretty good living doing things my way, when the "other guys" , doing it their way, were making a better living., lol. But I still ended up fixing those other cars when their way took too long.
I could give you some tips to make it even faster, but, I gave you easier .
How to mod your Vcan;
Just cut the stops down.
I can't tell you how far cuz I don't remember; that was 2 decades ago. But you'll figure it out. While the can is on the bench, loosen the set screw that is in the lil hose-nipple. Turn it fully Clockwise, until it meets resistance, and then stop. All you are doing is removing the preload on the spring inside there, to make it easy for engine vacuum to pull in all the advance possible as soon as possible. Later, you might have to slow it down, but maybe not.
