• When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.

Too Lean???

MarPar

MarPar

If it weighs, it pays
FBBO Gold Member
Local time
5:39 PM
Joined
Nov 21, 2008
Messages
18,509
Reaction score
42,495
Location
In GTXtacy Illinois
I've had an off-idle stumble with my GTX since i got her, and have had a lot of "advice" on what to do to get rid of it. It would stumble and die at stop lights and stop signs if i sat there too long and i would die going up my driveway in reverse (longish, prob 4* upslope from garage to house). it ran great cruisin' and foolin' around on the streets, but damn thing wouldn't stay running @ the lights!!

So i did some research on my own, and with help from a friend who didn't reply with "you should get rid of that Dodge and just get a chebby, (like the rest of us)":mad_6: IT'S A PLYMOUTH DAMN IT!!! Sorry dodge guys :tongueflap:

Anyway, i digress...so we started with the IMS (idle mixture screws) on the carb (800 eddy thunder) and did a little fiddlin'. Holy crap!!! it's like a brand new car!!! :th_krazy:

Now, i know there are A LOT of variables that come into play with my question, and i will try to answer them as much as i can. I have a limited knowledge of carbs and timing, but my buddy explained it to me, and it made sense, so we went for it!!

We re-set the IMS by screwin' them all the way in, and at the end, we were about 4 1/2 to 4 3/4 turns out, with the idle speed @ 850rpm (no load), and 650rpm (w/load). I think she may need a bump up 100 rpm or so (no load), which i will have to reset the IMS again anyways??? either way, my actual question is do y'all think 4+ turns is too lean or will hurt the motor??

I know, there's a lot up in the air here, but i would much obliged, if anybody could offer sum help!!! :grin:
 
I am at 8500 ft. and I have nothing more than 2.5 turns and a bit less than that for perfection If than helps.
I run only Carter or Edlebrock afb or avs
 
Not sure...but i think i'm pretty close to sea-level....Chicagoland area :edgy:
 
The problem you describe can have alot to do with float levels and manifold heat. Make sure you have a good thick insulator type base gasket. Make sure your float levels are set per factory spec and that the floats are not toed down and sitting level at seated position. If you are running fuel that may have ethanol in it as most do nowadays you might wanna freshen up the needle and seat sets too. Excessive fuel pressure may also be an issue. You may have a float taking on fuel. Take them loose and shake them and see if it feels like they are getting fuel inside or weigh them seperately and compare.
 
This is my own P.O but I think four turns out is a bit much on a stock setup, not exactly knowing what you have. The norm is three to three and a half.
Turning up your idle stop screw to another 100 rpms won't dictate adjusting your air and fuel mixture.
I, from years of tune ups on carb type engines have found that you go for the highest rpm you can get starting with the fuel mixture first then the air screw last with a starting point of about two and a half turns out. This is providing that the timing is set correctly first and there is no vacume leaks, gaskets ect.
You might have to go back and forth between the two once or twice to get your best rpm. Use a rpm meter, I used to be able to do it by "ear". Then once you obtain your best rpm give your fuel adjustment about a quarter turn out so your not too lean. More than likely your "idle stop" screw will have to be decreased to a lower rpm when done.
Now if you are turning your fuel or air mixture screws and there is not much of a change in rpm, then you could be having a problem inside of your carb. with a number of things. Dirt in the bottom of the float bowl, water in the same place, (water is heavier than gas) dried out accelerator pump (thats what pumps the gas thru to your "squirters"), loose screws, top of your carb, base plate, ect.
I hope this is some help, I haven't had to put what I know about tuning carbs into words before. It is something that you are shown to by someone else or you learn on your own. Also, with all of the newer cars out there with throttle bodies and multi-port fuel injection tuning carbs is becoming a lost art. (hope I wasn't too long winded)
 
khryslerkid said:
This is my own P.O but I think four turns out is a bit much on a stock setup, not exactly knowing what you have. The norm is three to three and a half.
Turning up your idle stop screw to another 100 rpms won't dictate adjusting your air and fuel mixture.
I, from years of tune ups on carb type engines have found that you go for the highest rpm you can get starting with the fuel mixture first then the air screw last with a starting point of about two and a half turns out. This is providing that the timing is set correctly first and there is no vacume leaks, gaskets ect.
You might have to go back and forth between the two once or twice to get your best rpm. Use a rpm meter, I used to be able to do it by "ear". Then once you obtain your best rpm give your fuel adjustment about a quarter turn out so your not too lean. More than likely your "idle stop" screw will have to be decreased to a lower rpm when done.
Now if you are turning your fuel or air mixture screws and there is not much of a change in rpm, then you could be having a problem inside of your carb. with a number of things. Dirt in the bottom of the float bowl, water in the same place, (water is heavier than gas) dried out accelerator pump (thats what pumps the gas thru to your "squirters"), loose screws, top of your carb, base plate, ect.
I hope this is some help, I haven't had to put what I know about tuning carbs into words before. It is something that you are shown to by someone else or you learn on your own. Also, with all of the newer cars out there with throttle bodies and multi-port fuel injection tuning carbs is becoming a lost art. (hope I wasn't too long winded)
Click to expand...


Thanks Kid! i'm going to try sometime this week to put a new felpro valley pan in (the one that blocks the manifold cross-over) and take a gander @ da carb while it's out...i'll look at what you suggested and report back!!! :grin:
 
khryslerkid said:
What are you working with? Stock 440/ afb carb?
Click to expand...


Yeah, pretty much stock...800 cfm eddy carb, 440 w MP purple cam..228/241 IIRC, 906 heads, i think they are zero-deck pistons too, i'll have to check that out...port and polished. The guy i bought the car from gave a list of all the thing the previous owner did to it. I'll confirm it when i get home..:grin:
 
You should not have 4 turns out on the idle mixture screws. Set dwell (if you have points) then timing. Another thing to make sure of is the primary throttle blade position in the carb relative to the the transfer slot and the ported vacuum port. Typical adjustment will be 1.5 - 2 turns on the idle stop screw from the blades lightly seated. If you have the throttle screw cranked open to keep the engine running this could be a sign of retarded timing. Also, where is your vacuum advance hooked up to? Do you have vacuum advance?
 
Yeah, he did, and 4 turns out is unusual in my experience.

Mar, idle mixture screws don't necessarily make the mixture lean or rich by them selves. What they do is add more or less of an already corrected fuel/air mixture to the engine at idle. You still get the rich and lean effect but that's because you are not progressively opening the throttle valve while adjusting the mixture to allow more air. The fuel enters the idle circuit through the idle feed restriction, or a pilot jet, and that fuel is mixed with air from the idle air bleeds. The fuel/air mixture is already pre set before it ever hits the screws. If the engine was too lean it would have a lean misfire. Simple as that. Why your screws are 4 turns out who knows at this point, but I suppose it can be a restriction in a passage somewhere or general tuning issues.
 
It will die at a stop due to:
Idle speed and mixture being incorrectly adjusted.

To set the idle mixture screws:
1.Get the engine up to temp.
2.Shut the engine off.
3.Install a vacuum gauge to a full manifold vacuum port.
4.Turn the screws all the way in until lightly seated.
5.Next, back them out 1 full turn and restart the engine making sure the choke is completely off.
6.While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved.
Be sure you keep all 2 or 4 screws even. You can also do this adjustment without a vacuum gauge, the adjustment are the same except you will adjust to highest engine RPM at idle.
 
74sundance said:
It will die at a stop due to:
Idle speed and mixture being incorrectly adjusted.

To set the idle mixture screws:
1.Get the engine up to temp.
2.Shut the engine off.
3.Install a vacuum gauge to a full manifold vacuum port.
4.Turn the screws all the way in until lightly seated.
5.Next, back them out 1 full turn and restart the engine making sure the choke is completely off.
6.While at idle, back them out 1/8 turn at a time, alternating between the 2 or 4, until highest vacuum is achieved.
Be sure you keep all 2 or 4 screws even. You can also do this adjustment without a vacuum gauge, the adjustment are the same except you will adjust to highest engine RPM at idle.
Click to expand...

Thanks Sundance!!! that procedure is pretty much how we did it, well xcept for the # of turns lol...but me suspects that the timing is a bit off, if i get home early enough from work today, i'm going to take the intake off to change out the valley pan and give the carb a good cleaning.

Thanks for that explanation Meep, it cleared up a few things i was wondering and now i know i should pop the carb off and give 'er a good cleanin', and get a good baseline. BTW i think do have vacuum advance and i have the MP orange box ECU. I'm not much of an engine guy, but i'm trying to learn!!! where would the vacuum advance be hooked up from/to??

So then do the timing first (about 36 total? i know my initial is set @ 5), then the IMS (which turned out to be 23Hg highest this past time), then the idle speed (900 (no load) / 750 (on load)), that sound about right?? Any thing to look for when cleaning up the carb??? any parts to specifically clean?? (DUH i just re-read your post Kid :p )

Thanks gents for all your responses, my trepidation on fiddling with the carb has been alleviated with all your help!!!! :tiphat:
 
Last edited:
Damn I didn't think we did all of that! But if you meen thanks for all the imfo. so you can "F" around with your carb., your welcome! :)
 
The vacuum advance should be hooked to the ported port on the carb. This is the port that does not have vacuum at idle but has vacuum as the throttle is opened.

Yeah, 36 total (with vac advance disconnected and plugged) is about right but might have to bump the initial to 10-12 to get some response and drivability. Make sure the total doesn't go over 36 - 38 though. I don't think I have ever run a BB MoPar at 5 deg. With vac advance hooked up you should see about 45 deg as you start to open the throttle - i.e. pull vacuum on the advance can.
 
So here are the stats...finally!

-stock mopar intake (and a K&N for WIW)
-edelbrock 800cfm thumper
-stock converter


2nd owners description (in his own words)

-Balanced, blueprinted
-block was decked
-steel crankshaft/indexed
-double roller timing chain+steel gears (confirmed by me)
-new fuel and water pump (stock)
-Hi-volume oil pump (i think i gotta cal B.S. on this one. it's @40 psi at idle w/load, and gets up to 60 psi when you romp on it; should be higher, i think!)
-crank was drilled for oil holes/balanced
-906 hi-perf head pocket, ported and polished
-new cam+lifters and bearings (which bearings??)
-windage tray (new, saw it)

and this cam...
http://www.summitracing.com/parts/DCC-4452783/

Meep, it has a hose going from the front of the carb (middle port) to the top of the valve cover (PCV??). I don't know if that port has vacuum or not..not yet anyways...BTW, aren't 440's ('67) RB blocks? or were you talking about B-Bodies (BB)?

Thanks guys!! :)
-Mar
 
Mar, that cam is basically a stock Road Runner cam. Nothing wrong with that.

BB was my abbreviation for big block. Yeah, 440 is RB and 383 is B.

The hose you speak of is 3/8" diameter and is the crankcase ventilation (PCV) hose. You should have a breather on the opposite valve cover with a 5/8" hose fitting that goes to the air cleaner. Or just open to air but NEVER sealed tight.

Dist vac is a small hose that goes from one of the tiny ports on the front of the carb. I'm not familiar with the 800 Thumper carb but if it's anything like a 625 or 750 AFB then it's the throttle side port.
 
Ah!! ok, thanks for da clarification, Meep! :grin:

Well, when we fiddled the other day, we used the carb port that goes to the PCV to measure our vaccum and adjust the carb.

There are two other ports on the front, one on throttle linkage side (capped not goin' to anything), and on the other side is another port with a hose that goes to the distributor.

Next time i adjust the IMS Should i use one of the side ports to measure it instead?
 
You must log in or register to reply here.

Similar threads

Triplegreen500
Plumbers - building code question, sprinkler pipes
2
Replies
26
Views
1K
BB BELLA
BB BELLA
mikedonz
Need Help Moving, any ideas?
Replies
14
Views
609
mikedonz
mikedonz
Krooser
I'm holding my breath....did my grandson figure out my Coronet has LH lug nuts.
Replies
5
Views
371
Krooser
Krooser
Aron Gleason
Carburetor stumble update
Replies
0
Views
463
Aron Gleason
Aron Gleason
Tom Petty Lives
Transporter looking for return load
Replies
0
Views
424
Tom Petty Lives
Tom Petty Lives
Auto Transport Service
Back
Top