idle issues with new A500 behind a fresh 318

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str12-340

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So I've been getting a new Dart on the road and have run into what seems to be a transmission issue. The engine is a newly built mildly modified 318 and the trans is an A500 4 speed automatic (based on the 904). I havent even hooked up the electrically triggered overdrive or lock-up converter yet. Just driving it around like a three speed 904. The engine will idle smoothly at 800 rpm. But if I leave it there it dies whenever I put it in Drive or Reverse. If I crank up the idle to 1200 rpm, when you put it in gear it pulls the rpms down to 600. That keeps it from crapping out when you put it in gear or coming up to a stop. On my other Dart with a 318 and a 904, it idles at 900 and when you put it in gear it drops to 700 - no drama involved.

I know this might be an engine tune issue and I keep working on that, but I'm starting to think it is the trans pulling the motor down too much. Any ideas???
 
timing ?
check balancer for slip
advance the dizzy until it bucks starter back it off abit see if that works
vacuum reading?
 
^^Above^^ Likely needs more timing or vacuum leak or idle too lean
 
As mentioned, it could be timing... Or a vacuum leak/lean at idle... Or it's possible the T/C lockup solenoid is leaking internally allowing the convertor clutch to drag..... If your thinking it's related to the trans get the power & ground hooked up, get an accurate tach on it & take it for a drive.. Lock the convertor & watch the tach looking for an rpm change...
 
600 rpm is a huge drop going into gear, no matter what the idle timing is. I would suspect an issue with the trans.
 
600 rpm is a huge drop going into gear, no matter what the idle timing is. I would suspect an issue with the trans.
Not necessarily, If he's running an MP electronic ignition it's pretty common.... The mechanical advance springs are so light it brings in advance at idle... So when you drop it in gear it's not the load that causes the engine to die, the load causes a slight drop in rpms that slowing of the engine is enough that some timing falls out, as the timing falls out the rpms drop further causing more timing to fall out... Next thing that happens is the engine stalls...
 
Yep It's an MP distributor and because I've had problems with the MP curve, I sent it to Halifaxhops and he rebuilt and recurved the unit, but even then, what you describe is exactly correct as the vacuum and mechanical advance are both moving the timing significantly between 1200 and 600 rpms. If the trans pulls the engine down and it loses 5 degrees of advance and that means the idle drops even more...

Like I said I've done the usual due diligence with idle screw setting and searching for vacuum leaks. I think I'll even try another carb on it to see if it is internal to the carb.

Thanks to everyone for a speedy response - you've given me a lot to try. I'll let you know what happens.
 
To tune the Idle;
Set the T-slot exposure underneath the throttle plates to between square and slightly taller than wide, them leave it alone.
set the idle-mixture screws to in the middle of their adjustment range
Make sure the Power-valve system is not flowing
Make sure the PCV system is working
Make sure that whatever air the engine is getting, it is coming thru the Primary venturies, or if the Secondaries need to be cracked, that there is at least some fuel in that air. If your carb does Not have a 4-corner idle, then close the secondaries up tight but not sticking.
Set the idle speed by timing, as low as it will idle in gear to between 550 and 700, depending on the Convertor stall.
Make sure that the Vacuum advance is not affecting the timing below ~1200rpm
The idle-speed goals are;
1) To not have it bang on the Neutral to in-gear shift, and
2) To not have a stumble when tipping the throttle in, and
3) To not have a stinky idle.

A/B) At idle, the more timing you give it, up to around 25/30 degrees, the more power she will make. If it the trans bangs when going into gear, she is either;1) making too much power, (rpm is too high); just take timing away; or 2) either the low band or the hi-drum, is coming on too fast, or the Convertor has issues. If the rpm gets to be too slow with reduced timing, she wants some Idle-air bypass. If she simultaneously has a tip in sag, then she wants a tiny bit more transfer fuel first.
Remember, at this time, the Power-valve system must be shut off, and the timing has to be stable.
If your idle mixture screws wander more than 1/2 turn from the center point, then the Transfer-fuel needs adjusting. Your idle mixture can be any combination of Transfer fuel plus mixture fuel, that it takes to eliminate the tip-in sag. But, if the mixture screws are too rich or too lean, then the entire slow-speed system, coming off-idle, will be wrong, which is why I recommend to set them in the center of their range.
C) if the exhaust is burn your eyes stinky, either; your valve lash is too tight (if solids)/ or the engine coolant is too hot or too cold/or the AFR is wrong/ or the timing is too much.
If you have to add bypass air, the idle speed will go up, same as if you had adjusted the curb-idle screw; but with one difference; whereas the idle screw will open the Transfers, adding fuel; the bypass air will not unless you are cracking the secondaries of a 4-corner idle. If your cam is smaller than [email protected] you should not need any bypass-air. If your cam is bigger then 240* then it will for sure need bypass. Between 220 and 240 degrees it gets tricky, with varying amounts of air.
D) if you just can't get it, get the back wheels off the ground; maybe you convertor is too tight. Put it in gear, then drag the brakes until the wheels stop spinning. If the engine stalls or nearly does, either; the TC is going out, or the engine lacks low-rpm power and needs more tuning time.

Just so you know, my 230*@.050 cam will idle down to 500/550 in First-gear (manual-trans) and has enough power at 5* advance to pull itself (10.97) roadgear, on a flat/level/hard surface. At one time, I had a 292/292/108 cam (249*@.050) that would do the same but at 8* idle-timing. The point is that mega idle timing is NOT required. However, once in gear and the throttle tipping in, the more you have the snappier it will feel. and that is where the combination of Vacuum advance and a fast timing curve, and/or hi cylinder pressure will really shine.
Happy HotRodding
 
Yep It's an MP distributor and because I've had problems with the MP curve, I sent it to Halifaxhops and he rebuilt and recurved the unit, but even then, what you describe is exactly correct as the vacuum and mechanical advance are both moving the timing significantly between 1200 and 600 rpms. If the trans pulls the engine down and it loses 5 degrees of advance and that means the idle drops even more...

Like I said I've done the usual due diligence with idle screw setting and searching for vacuum leaks. I think I'll even try another carb on it to see if it is internal to the carb.

Thanks to everyone for a speedy response - you've given me a lot to try. I'll let you know what happens.
Just a FYI, I am running an A500 as well and have been for years.
The power not being connected makes zero difference, as the trans will work like a 904 normally does as you suspect.
Converter is a factory 1,800 stall.
I do have to run a richer idle to keep it from stalling when put in gear. (Around 11:1)
My idle timing is 18 degrees.
Mechanical comes in around 2,000 and adds 16 degrees.
Grand total timing at 2,500 cruise is around 50 degrees with vacuum advance all in.

Try richening the idle a bit and see how it acts.
 
OK so here's the deal - THE PROBLEM IS FIXED!!!!!! After spending a bunch of time looking for vacuum leaks and finding none, I was talking to a knowledgeable friend who said, "Hey don't you have an Edelbrock AFB clone on your 318 Swinger? It works great - put it on the GT and see what happens." I swapped it over, turned the key and it was like a different engine - idled fine at 800 rpm, dropped to 5-600 in gear and didn't run rough or crap out. Since it ran great at WOT with the bad carb, I think that it has a fault that was dumping gas at idle. Now it runs great at WOT and it idles!!!

Now to get Edelbrock to take the AVS2 back and send me a new one...
 
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Guy on the phone from Edelbrock seemed pretty straightforward about replacing the carb this morning, but I haven't seen the promised return authorization in the e-mail yet. I'll let you know if Eddy stands behind their stuff. I have 3 Eddy Performers (AFB) and another AVS2 on other cars and they have run great right out of the box, some of them for close to 20 years...
 
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