Mastering Carb Tuning: Secrets for Perfect AFR | 1970 Plymouth Cuda
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- čas přidán 28. 08. 2024
- I swapped out my Edelbrock 1407 carb for a Quick Fuel Q750 a few years ago. The change was dramatic and although I knew that it was running very rich, I had never bothered using the AEM Wideband to tune it.
Recently I drove to both Mopar Nationals and Moparty. On the way to the Nats, I knocked out an astounding 12.2 mpg. After a gear change I got up to 14.2 on the trip to Moparty.
Something needed to be done. - Auta a dopravní prostředky
Hiya Chuck - yeah, the old Holley vs. Carter/Edel debate rages on to this day.
Truth be known, either can be made to work fine on a typical street engine and I've had both
on some of my junk over the years.
The killer to either is the accumulation of tuning junk you acquire for whatever one you're running
at the time, really - bluntly put, I ain't a carb part collector, not my bag, not why I'm in the hobby.
I'd rather take all that money and throw it at a needed part elsewhere on the car.
That said, beginning with the right size carb is all the difference and makes tuning so much easier
and the correct starting point for these engines is fairly well known settled science, too.
Nonetheless, I enjoyed watching you bebop through the process we've all done countless times. 🙂
(BTW, I'll be trying out the AVS2 800cfm Edelbrock on Fred's mildly built 440 over the winter).
See you next one, Ed on the Ridge
You'll be happy with that Carb, it's the same that was on Louise. With that being said, I probably should have put a 650 on the motor too.
Another great video Chuck. Thanks for sharing your tuning and that sharp E body.
BA
Thanks Bryan
My 340 is similar to yours. To maintain. 040 T slot you can adjust secondary idle screw. I found that leaning secondary mixture screws half turn in compared to primary alllows me to richen primary a little more to cover lean transition. I've owned my 70 cuda convertible for 30yrs. Always satisfying when you can drive your mopar like old man or 18yr old. Keep at it. Will only get better.
Thanks Paul, I just did a screen shot and of your recommendation. The car is asleep for the winter but when I get her back out I’ll be doing some more “playing” for sure.
Idle air fuel is adjusted by the idle mixture screws only. The idle air bleeds, set how many turns the idle screws will need to be turned out. Like you did here. Cruise a/f gets it's fuel from the transfer slots, even at 50-70 mph. If your rich or lean at cruise, change the idle restriction jets in the metering block. Changing the main jets will not have any effect on the cruise a/f ratio's. Fuel is coming from the transfer slots. They get their fuel from the idle jet restrictors. If you want to get more precise with the cruise a/f, then you can tune the emulsion jets in the metering block. The top ones are for low rpm, and the lower ones are for the higher rpm's. Hope that all makes sense and helps.
I'm going to have to screen shot this reply as well and cipher on it for a bit.
After I leaned it out at idle I went for a short ride and was seeing mid 12 AFRs. With the main jet swap from 74 to 71 I was seeing high 13 to mid 14 AFRs at 55-60 mph.
Are you saying that the main jet swap had nothing to do with that? If so, when does the main jet come into play?
I actually only have 2 emulsion jets in the metering block, on both sides, even though there are 4 holes, I was wondering about that.
Thanks
I believe you mentioned your car has a 4 speed manual. If so, then your cruise rpm's may be on the high side. So you might be into the main jets some. Usually, yes, the carb is only on the transfer slots at lower power cruise speeds. The main jets would be in use as you accelerate up through the gears, as long as you don't drop the vacuum below the power valve size. Once the power valve opens, then you will get a richer reading, as should be. If your a/f ratio goes too rich when the power valve opens, you need to reduce the power valve channel restrictors to get the a/f ratio you desire. The Power valve channel restrictors are what you change, not the main jets. The main jets are what you run on, when the power valve is closed. So you need to watch vacuum as well as afr. I'll let you chew on that one for a while.@@Chuck_House_of_Mopar
@@Dynodon64 I had actually heard that you cruise on the T slot in the past. I need to suss out everything a bit more.
I have a 2.76 gear and at 70mph I'm seeing 2400 rpm and, if I remember correctly, around 13.4-13.8 AFR. You may have heard me mention that. When I give a little gas to go up a slight grade, the AFR drops into the mid 12s. I think that the 8.5 PV is about what I need.
I know that to really get the AFRs to near perfect, ha ha, I should have the vacuum gauge in the car with me. That will be next summer.
At any rate, she's a whole lot better now and I'll get after it next year.
Thx Don
Yes I followed your numbers you mentioned. As for the 8.5 power valve , I would hold off on that until you see what your vacuum is at cruise when you tip into the throttle going up a small grade. It sounds like you need to lower the PV size. The number on the PV is how much vacuum it takes to hold it closed. Sounds like it opens too soon as causes it to go rich, when it doesn't need to. I think your on the right track. Good luck in the spring. @@Chuck_House_of_Mopar
Adjustments make you go crazy. My 440 4 spd with a Brawler on it was pig rich at idle, would kill you in the garage. Hooked up AF guage ,13 to 14 runs good. Go back to basics . Timing, float level, idle mix screws, read the plugs after a good cruise. Good luck. Enjoy your channel.
Thanks Kevin. As you could tell, I just wanted a ball park AFR and didn't bother with plugs or timing. Looking at the plugs should be next for sure.
Great video again Chuck. I'm putting my 64 Polara to bed for the winter this month here in Quebec Canada. Curious about your winter storage ritual? Perhaps that could be a future video? Always looking for new tips about winter storage. Especially if little critters can get in your garage.
I pretty much just fill the tank and cover it with a cover. I usually run some Stabil in the tank but I forgot to this year. Not too many mice, thankfully, where I keep it but I always put the sun visors down so that they won't get up there and chew into the headliner.
I wash it up because it's always nice to have a clean car when you pull it back out.
Thanks
great video found your channel short time ago David Vizard has youtube channel and is doing a project with Uncle Tonys Garage with a 318 pretty interesting. he pronounces his name Vi-Zard
I'm going to look him up with Uncle Tony. David has a lot of good stuff out there and thanks for the pronunciation.
That is one good looking cuda, and yes black is horrific to keep clean.
Thanks Jeff, yep it's a bunch of fun at times.
Love your work Chuck ….now body work 😩
Thanks Sir. Body work, yeah I can't wait it's going to be awesome.
That was a great video. I've been curious about all of the idle bleed restrictions and stuff on those fancy carburetors. Thanks for the ride along and explanations.
One question...I was under the impression that at idle or cruise, leaner AFR in the 14s or even 15 would be OK, and that it wouldn't be a problem unless the engine is under more load, and at that point, the power valve covers it plus getting into the secondaries. Did I understand that wrong? Thanks.
Well I think that is getting a bit lean for cruise. I had always believed the same as you but it seems that 13.6-13.8 is a better spot.
I could be wrong.
Another thing is the timing. if it not just right it's harder to get the carburetor right.
Yeah, she's pretty happy with what I have. This was a quickie and I may look at that the next time I work on the AFR.
Thx
First thing I'd do is put an air cleaner on it while tuning, unless you plan on running without one🤷 One thing i noticed, the floats should be adjusted to the marks on the middle of windows, not the lower third. Another thing that helped me is to set the transfer slot, install carb and leave it alone, adjust idle with secondary screw. Also im pretty sure the mains start flowing at 2000 and above at a steady throttle(not into power valve), some cars cruise on the slots, some on the mains, depends on your cruise rpm. Ive also found these carbs need a transfer slit restrictor installed to get rid of the super rich transition. Is that carb optimal? Not on paper, but that little formula you find on the net isnt the end all be all,.. thats a nice carb, annular boosters right?
Good information, I'm going to work on this some more when it warms back up. It does have annualar boosters.
@@Chuck_House_of_Mopar nice, that's a really nice carb. One other thing, what most say to do is set the primary slot to a square and keep the front and back throttle blades equal, install carb and if it doesn't idle high enough, drill holes in the throttle blades. I try to prevent that scenario unless there just isn't any other way. Start with 1/16 holes, install carb. Keep doing that till it idles correct. I try the "adjust the secondary blades to set idle" method first, but there's really a small window of adjustment there before you get the primary and secondary blades uneven. And for reference, the smaller transfer slot showing is leanest, the more slot you leave showing, the richer it will be on transfer. Anyways, I hope that will help somewhat. Oh and dam, your car is SWEET!
I know it's old school, but what are your spark plugs telling you?
I didn't pull them, this was just a quickie to get the AFR into the ballpark from being so pig-rich.
Thx
Hi chuck,great tuning info ! I have a 750 DP on my 360 , simple carb but i wish i had one with air bleeds . my 360 has low compression so i run manifold vacuum at idle and it cleans up the idle abunch but it still runs rich at idle 12.2-12.9. I know i need to get adj. air bleeds. It cruise"s at 13.0-13.4 at 3000 RPM and vacuum adv. at about 40 -45 degrees . no detonation because of low [9.0] compression . Any idea of the duration and lobe seperation on that sweet cam ? how are those manual disc brakes ?
I would use manifold vacuum for advance at idle as well, I used to do that on my Satellite. The industry did the same until 1968 when emissions came into play.
I'm sure that you must have played with your idle mixture screws at idle.
It's a Comp solid cam CRS 2948-10
.525 total intake and exhaust
.356 @ .050
110 lobe separation
My son has the same hydraulic grind in his Duster.
how good are the manual brakes ? are they disc or drum?@@Chuck_House_of_Mopar
@@doughelmle6575 Manual disc brakes from the factory and they work really well. Thing is, you need a small 15/16" master cylinder to make them work without a lot of extra foot pressure.
Personaly I would take that 750 off and put a 650 on it, unless you have 100% volumetric efficiency and your spinning 8000 rpm there's no way anyone needs a 750 on that small cube of an engine, better fuel milage, better throttle response, less fumes etc.
Agreed on all. These carbs are around $1000 shipped these days.
It's what it is.
Thx
Very nice bad mofo mopar.
Thanks, you can't beat a black car for sure. It's keeping it clean is where the fun begins.
You never mentioned your timing. So many carb problems can be traced to engine timing . Just saying.
Yeah, actually I did. Around 18 and 38, I mentioned it around the time that I spoke about the chassis dyno session from a few years ago.
This was just a quick deal to get the AFR under control a bit, not a true nuts and bolts throwdown what's the best that we can pull off.
I didn't recheck timing, look at the plugs or really get serious about the vacuum.
More of that next spring when she comes out of hibernation.
Thanks Gary