Tuning a big roller cammed motor - how to do it?

[IQ52]

I don't know the bleed sizes but will check tomorrow. I think you and I are on the same page. I initially set the initial at 24 because that is where the motor seemed to want to be. As I added initial it kept speeding up until I hit 26 and then didn't anymore so I backed it back to 24 and set the distributor to throw 10. I downsized the 65 to a 25 as I had a few backfires through the carb so I wasn't sure the 65 was still good. Once I get everything sorted out I am sure my idle vacuum will be near 10" so I will go back to the 65.
I don't recall what I have for jets on the secondary side but I believe they are either 93's or 94's. So where do you think my problem is?

My problem is a misunderstanding. Your opening post says the carburetor is square jetted with 84's and a 2.5 power valve. To me square jetted means all four corners are using #84 jets.

 

[Brewzer67]

My problem is a misunderstanding. Your opening post says the carburetor is square jetted with 84's and a 2.5 power valve. To me square jetted means all four corners are using #84 jets.

No misunderstanding on your part. It was square jetted when i wrote the post but I put it back last night to the out of the box settings and am going to restart from there.

 

[Brewzer67]

If this were a true statement my 511 would run pig rich at idle with the 6.5. It does not its very clean at idle. Again the pv system is part of the main circuit. You dont use the main circuit at idle. I've been spending a lot of time playing with different things on my rr since I bought an A/F meter. I can tell you when my vacuum drops to 5" the carb does not richen up from the pv opening, it actually goes the other way do to the fact there is not as much pull on the idle circuit. Not going to continue to argue this, believe what you like.

Though If someone can explain to me how the pv system enrichins the idle circuit and bypasses the IFR I will surely listen. I'll even include a picture of a metering block so someone can explain it. By the way this is the metering block that's currently in the rr's center carb. Anyone spot what i've changed since it's out of the box configuration?

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This is new info to me as well. Your explanation makes sense but definitely contradicts what I was always taught (but apparently should have questioned). I put the carb back to a 65 last night anyways so I could start back from square one. I'll try again tonight hopefully.

 

[Bigal75]

I run a 9.5 PV with 4.5 inches of vacuum at idle. Works great. When cruising I have 13inches of vacuum. Anyway...that little flutter could be because you're to lean. Have you looked at the plugs?

 

[Bigal75]

If this were a true statement my 511 would run pig rich at idle with the 6.5. It does not its very clean at idle. Again the pv system is part of the main circuit. You dont use the main circuit at idle. I've been spending a lot of time playing with different things on my rr since I bought an A/F meter. I can tell you when my vacuum drops to 5" the carb does not richen up from the pv opening, it actually goes the other way do to the fact there is not as much pull on the idle circuit. Not going to continue to argue this, believe what you like.

Though If someone can explain to me how the pv system enrichins the idle circuit and bypasses the IFR I will surely listen. I'll even include a picture of a metering block so someone can explain it. By the way this is the metering block that's currently in the rr's center carb. Anyone spot what i've changed since it's out of the box configuration?

View attachment 496734

Ya...you moved the idle port to the bottom and added a restrictor.

 

[Bigal75]

Spark is good on 1 and 2 (all that I spot checked) as checked with one of those variable gap spark testers. Both tested good to over .100 gap so I didn't check the rest. I only run .040 so I should be good.

Reduce your gap as well. Try 0.035

 

[Brewzer67]

So I spent the night finishing getting things back to a starting baseline. New plugs have been put in without clipped electrodes and gapped at .040 again as I am fairly certain the ignition system is not adding to the issue because I tested all plugs and they are good to over .100 gap with a fat blue spark. I did find that both the primary and secondary side had more transfer slot exposed than should have been. I reset those to my normal starting point (see pictures) and will not change them more than 1/4 turn as I am tuning. I also tore down the distributor again and cleaned up everything so nothing is sticking at all. I had to change the limiter bushing as it seemed to be stickier than I liked at letting the weights return to their 0 advance position. It also looks like there may have been a small vacuum leak at the carb gasket at the base of the pcv nipple so I put a new gasket on. I'll finish putting it back together tomorrow and then warm it up and readjust the valves. Wish me luck.

 

[dvw]

Operation is pretty simple. It is correct if the main circuit isn't flowing, the power valve being open will have no effect on idle quality as it discharges fuel from the main circuit. Therefore at idle when the thottie plates are in the correct posistion, with correct fuel pressure, and correct float level the power valve is a non issue. A ruptured power valve will feed fuel through the vacuum signal port at all times. The power valve is worth roughly 8 jet sizes when it is open only when the main circuit is flowing fuel. The vacuum rating on the power valve controls the timing at which this flow will begin. That's it, no Voodoo.
Doug

 

[Budnicks]

You don't have to pay any attention to me if I'm all screwed up. I would run a dead minimum of 20 degrees and 24 seems better to me.

Thanks IQ52

Yep I agree, mine likes 20* - 22*'s btdc initial & 34* - 36* total
depending on air quality we're at altitude & the fuel quality usually,
straight pump gas lower side of total 20*'s
I'm still using a Mopar Perf. CEI dist. with adj. vacuum advance too,
32*'s with the crappier 91 oct. Calif. std.,
93 oct. if you can find it, I can run "almost" like a race combo
or really crappy ethanol mix stuff, but initial is up &
with good or much better blended or race gas 105-110 octane
I can easily run 24* initial & still 34*-36* total...

with these engine they don't like the ol' OE std.
8* btdc - 12*'s at idle {1200-1500rpm}
they need/like far more initial advance, +6* - +10* more initial
sometimes even more than that, especially for a lower compression combo...

That has worked well for me on both street & race combos...

 

[Brewzer67]

Been kind of busy but here is where I am at...
I reset everything back to baseline and put a power valve plug in. I put new springs and a new limit bushing in the distributor. I also used the old school trick of putting a piece of rubber fuel line on the distributor shaft to reduce timing bounce (like the Hughes collar does). With the fresh plugs and everything reset, it now idles much steadier. It holds 9" of vacuum and only bounces a degree or two on the timing. That's still more than I like so I'll keep working on that. I haven't had a chance to look at the plugs as it is at the trans shop right now and I won't get it back until Monday. Once I see where I am at I will reintroduce the power valve. On a related note I have a question regarding mileage. I only got 6.8 to the gallon with most of that being freeway. How far off the mark is that for this level of build? I'm not looking for killer mileage but my previous heads and cam (.616 lift hydraulic [email protected]) got me 13.8 under the same conditions.

 

[IQ52]

This is confusing. Carburetor back to baseline? #85 primary and #93 secondary jets? But you plugged the primary power valve? If so, did you square jet to #93 to compensate for the loss of the power valve fuel?

 

[Brewzer67]

This is confusing. Carburetor back to baseline? #85 primary and #93 secondary jets? But you plugged the primary power valve? If so, did you square jet to #93 to compensate for the loss of the power valve fuel?

Yes. I went back to a square slot for the transfer slot on both Primary and Secondary sides, 85 primary jets, 93 secondary jets and no power valve. This removes the power valve from any contribution when trying to get the at idle settings squared away. It removes a bad power valve as a contributor to a rich idle condition. Now that I am OK from the idle settings perspective (clean idle, stays running in gear, and not eye burning rich) I will add the power valve back into the mix and see how the carb behaves off idle and at cruise. If I add it the power valve back and the idle goes to crap again, I have found a source of the problem.

When I test and tune at the track I always make a baseline run, I change one thing, I make another run and see what the net change is. To validate the change, I return to the previous setting and re-test to see if it returns to pre-change status. When it does, I re implement the change if desired and re-validate that I get the same results as the first time I made the change. When it validates correctly, it becomes a new baseline and the next change goes from there. This method has always worked pretty well in the past and I just need to get back in the habit of doing things that way. I have been away from tuning and racing way too long so I am rusty.

 

[66Satellite47]

I run a 9.5 PV with 4.5 inches of vacuum at idle. Works great. When cruising I have 13inches of vacuum. Anyway...that little flutter could be because you're to lean. Have you looked at the plugs?

Wow that is great. Can't imagine how it works, but if it does it does.

 

[Bigal75]

Why? So what if the valve is open at idle. All it does is allow more fuel into the main well. Once I start moving the vacuum goes up so the valve closes (still running on the idle circuit). Runs great.

 

[actionange1]

My 2 cents
Wait until you get the new converter installed, buy another intake and a Dominator. No power valves to mess with. I ran this on my street /strip Belvedere with a .685 lift, 285 degree solid roller. Good street manners and low 10s.
OBTW- I'm old school and tune with a screwdriver...

 

[66Satellite47]

My opinion only, the right converter makes the performance of the car. BTW my experience on carbs was with 3.5 or 4.5 power valve with big cams & the 850 DP. Then I to used the power valve plug and re-jet accordingly on my 650 DP tunnel ram setup, used plugged power valves & nearly stock jetting. Worked well, seldom changed jets for weather conditions.

 

[66Satellite47]

BTW, valve lash settings will go either way from the cam card. Try a few thousands and see if anything happens. Tighter gives a little more cam.