Hi guys, hope everyone is doing alright over seas.
Here in Belgium things are finally getting better and as the lockdown rules are lowering, I can finally get the car out again.
Now in this period of lockdown I did few things to the car, inlcuding making a custom 2.5" exhaust and installing an O2 sensor in there.
Just some specs of the car in case this is needed:
351W 1969
stock ported heads and matched edelbrock intake
unknown solid flat tappet cam
FMX trans with unknown/perhaps stock converter
hooker comp. longtubes with full dual 2.5" exhaust with H-pipe
Mallory unilite distributor with vacuum advance, initial timing at 11°, total mech. timing 35°, total timing with vac. 50°
Holley 4160 600cfm manual choke, vacuum secondaries
Fuel: 98 octane, 5% ethanol pump gas
Anyway, my question is about my air fuel ratio’s, after installing the sensor, I noticed it was way lean on acceleration and cruising.
So I’ve upped the main jets (size #70), and these are my afr’s:
Idle around 14:1
Cruising 13:1
Part throttle acceleration: 13:1
Full throttle acceleration: 12:1 and climbing to 11:1
So I do believe it’s a bit fat up top, I pulled the plugs after a pull and they are indead black.
I’ve tried lowering a jet size again, but then the part throttle and cruise are on the lean side again, so I’m guessing those are kinda where they have to be?
Overall, the car really pulls well, so maybe it doesn’t need more fine tuning, but I was just wondering what you guys think?
I could change vacuum sec. springs perhaps, or accelerator pump cam, or … ?
Or just leave it as is is also a possibility
See if the float levels are set - at warm idle, carefully unscrew the sight plugs on the passenger side of the bowls. You should get only the slightest trickle of fuel.
That seems really rich (71s) for a 600 CFM Holley, especially for non-ethanol fuel as here in the U.S. I have 67s or 68s up front for northeastern U.S. oxygenated fuel. Factory on the 600s is 66 these days. I have the usual conservative 6.5 inches Hg power valve. I am surprised your plugs are black, though.
Drop 4 sizes on the primaries. I run 67/71 on my similar carburetor. Also check the float levels as above. My A/F numbers, if I recall, are 12.3 to 12.7 at wide open throttle, 13s cruise, 14.5 or so at warm idle.
I checked again in my jet box, #70 is in there now, originally came with a #65
Here in belgium there is a 5% minimum of ethanol in the fuel, 98 octane pumpgas.
With #67 which were in there before I installed the o2 sensor, it showed 16:1 afr under acceleration and above 14:1 on cruise.
Can’t adjust the float lvl think, i have part number 0-1850C
Which says Holley 4160 Non-Adjustable Float Carburetors (When I bought it a few years ago, since then they made them adjustable it seems).
Summit and amazon still show the one I have
Holley does offer some dry float setting info here - that is, bowls off. I surmise for your carburetor you’d gently bend the float tabs as with Autolites.
If it’ll take another couple of degrees of timing advance without pre-ignition, I’d try that and see if it doesn’t lean things out a bit at full throttle.
Also, do you know what size power valve is in it? Changing to one that opens later might help.
Stock power valve is in there, so 6,5" i believe?
Could try adding more timing, that has crossed my mind. I guess this can only be tested on the road to see if it doesn’t ping right?
I wouldnt change timing. Your cruise sounds like it could stand to be slightly leaner. Acceloration is lean. But, it depends the level of acceloration. Do you mean light acceloration, normal acceloration like in regular traffic or hard/fast acceloration? Monitor your a/f at those three levels. Are you running a vacuum gauge to see if your lean condition occcurs above the opening point of the power valve? Perhaps if you add a little bit more throttle, does the reading richen to show your power valve is opening? If it richens a sufficient amount, you can get a power valve that opens at a higher vacuum to accomodate. If it doesn’t richen enough you will need a wire drill kit to open the passage in the metering block.
It’s been a while since I’ve tuned a Holley, but I would set the primary jets for optimal cruise. Secondaries are several steps richer. The carb you be pictured doesnt have rear jets, just a metering plate. For adjustment, do you have to replace the plate? Set the jets for the “lean best” cruise. Then focus on the power valve opening level and volume for enrichment.
Correct. Optimum ignition timing depends on many factors; the weight of the car, gearing, altitude, transmission type, fuel octane and others. It’s a trial and error process to get right.
A previous poster mentioned the rear metering plate, and if the rich condition is primarily or exclusively at wide throttle openings where the secondaries are in play, then a different rear metering plate may be the solution, or at least a significant part of it.
Cruising 13:1 is a tad on the rich side and should i aim for 14:1 then?
Now it’s 13:1 normal acceleration within traffic
Hard/fast acceleration is now 12:1 and climbing to 11:1
You think this is lean or do i misread?
I am running a vacuum guage, since I have to keep my eyes on the road aswell, maybe i’ll take my gopro with me and aim it at the O2 guage and vacuum gauge at the same time, because the 2 are not near each other
I don’t have a rear metering plate, this is a very basic holley, without any fancy options
Could start with 1 or 2 extra degrees and see how she responds.
Yes, you do have a metering plate in the rear. You don’t have a metering block (in Holley definitions). Metering plates come with a number of Holleys to hold costs down. Metering plates capture the function of both jets and metering block passages; you can convert, if bored, to metering blocks with Holley kit 34-6 (and don’t forget to buy some jets).
I think, for what my opinion’s worth, that under 12.0:1 at wide open throttle is indeed a bit fat.
Thx for the input guys, i’ll see if I can’t improve a bit, maybe a main jet leaner and maybe some timing. I’ll let you guys know how it goes when I have some time.
Rule of thumb for all Holley cabs was no more than two jet sizes up or two down from stock jetting. You have went way to far up on your main jets. Ignore AFR readings and go with plug readings and overall performance. Our old carbs never were that efficient over the entire RPM range. They would give good plug readings on long trips at normal throttle opening for driving. They were ok at idle and horrible on choke. And you need a long sustained drive of a couple hours at 60 MPH plus to get them to clean up and turn light to medium brown. Around town diving equals black plugs, but that is not necessarily bad.
Given that all ignition components and timing is correct, look for basic drivability. If it has flat spots off idle it can be acceleration pump tuning and squirter sizes either up or down. Depending on weight of car and gear ratio. Do not treat this car as a modern fuel injected car with a computer. You will go crazy chasing your tail with AFR readings. Gosh for us old guys what are AFR readings!! Yup, we know, but do not care!!
I think that you would be better served with a Holley carb with more adjustability with both a primary and secondary metering block and externally adjustable floats. I personally think that a 600 cfm carb is a bit small for your application. I would opt for a 670 Holley Street Avenger for your application with an auto tranny. They are close to spot on out of the box and infinitely adjustable. Heck, bring that bad boy over to me shop and we will tune together. Might be a long ferry ride from Belgium!!
Do not overthink this and go for drivability. Remember, “There is more to life than gas mileage”!! You want performance above all!
Been learning alot about tuning the engine, still not there yet though.
The reason my main jets were that high was because my idlespeed was set too high, therefore the blades were opened more than they should and pulling from the mains i think?
What i’ve done so far:
Gone down 1 jet size to #69
Lowerd idlespeed to 800 in gear, which results in 1000 in park. (was 950 in gear and 1200 in park before)
Although this resulted in a lower than normal vacuum, only about 10" and not stable, if I increase rpm to around 1300 it ends up very stable at 18"
No idea why this is, cam has an unknown grind on it so maybe that could have something to do with that?
Had to richen the idle circuit to compensate for lower idlespeed and lower main jet
Increased initial timing to 13° (was 11° before)
All these things gave me a bit smoother ride as far as I can tell, except for the idle
No noticable gain (or drop) in power.
Also after adjusting all that, my afr numbers are still the same across the board
Will play around a bit more, probably go a jet lower again, maybe a tiny bit more timing.
I’ve looked at my notes from when I was restoring the car, it then had 20° of initial timing, but the vac advance was capped off.
Must note that the car did not run well then, but it had other issues as well so not sure if the high timing had something to do with it.
The car has the same distributor in it, but I am running it with vac advance now though.
Will update as I go
Been a while again, hope everyone is still well over the big pond.
Since I like to drive a while after each adjustment, it takes time to post some progress
And I have made quite a bit of that actually.
I’ve dropped the jets to a size #68 now (came stock with #65).
The big difference however lies in the timing. (I know, timing is everything).
I’ve gone to 20° initial timing and the engine now makes 44° mech. timing at 3000rpm
I cannot believe I’ve driven all these years with 12° initial.
The idle has smoothed out (not smooth like a stock cam though).
The vacuum (set at 800rpm) at idle is very erratic around 9" of vacuum and only smooths out at around 1300rpm to 18"
Normal driving has not changed that much, but up top, oh boy!
It’s like this engine likes the added timing in a big way, pulls much much harder than before.
Too bad no drag strips in Belgium, so can’t post any 1/4mile times but feels really fast.
I can only conclude from this that my unknown cam is degreed?
It had 20° initial when i bought the car, but since it ran like crap lowered it. Should not have done that.
Seems the guy who installed/degreed the cam also set the timing accordingly
Pretty happy with the results, will drive a while to make sure I don’t run into pinging.
If I don’t encounter any pinging, should I try to go even higher? Have not heard any pinging so far, car starts easily cold and hot on the first try.
of initial timing, but the vac advance was capped off.