Need help! At my wits end.

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RAMCTD2003

340dart
Joined
Oct 5, 2007
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Location
Grand Junction, Colorado
I have been building a 74 dart sport that I put a magnum 360 in and I am running into a problem. I don't know if it is fuel or ignition. Let me give you the specs.

1995 magnum 360 block
LA Edelbrock heads w/ stage 2 porting from Mike at MRL
1.6 hughes shaft mount roller rockers.
Roller cam exh 227 @ .050 int. 231 exh.
110 LSA Center Line 106
.530 lift int. .535 lift exh. w/1.5 rockers but I have 1.6 ratio.
Open seat pressure 320 closed seat pressure 140
springs installed height 1.81
Smith brothers push rods
Turbo action 3500 stall converter
8.75 rear with 3.91 gears
MSD 8388 ready to run distributor.
Walbro in tank fuel pump regulated down to 6 psi
AED 750 HPHO carb.
18 degrees initial timing 18 degrees mechanical for a total of 36 degrees
using the blue springs which brings the mechanical all in by 2500 rpm.

The car starts and idles just fine. I can rev it up and it will be clean up through the rpm range. I took the car to the track last week and it ran just fine. Now all of the sudden when I put it in gear and drive down the road it starts to break up above 3000 rpm.

I live at about 4700' here in Colorado so I jetted the new carb down 2 sizes per the recommendation of the AED tech.

Everything on this is brand new. There are maybe 50 miles on this combo.
I pulled my MSD plug wires and measured the resistance on all of them and they checked out according to the spec of 50ohms per foot.

I am running vacuum advance. When I rev it up the advance goes up to 50 degrees.

I have checked everything I can think of and am at my wits end.

Hopefully somebody has some suggestions.

Thanks
 
so your distributor advances 50 degrees? I think thats your problem right there. most cars with that kind of Bild don't even use the vacuum advance system. mechanical time it all in has 36 and see where it idles at before the centrifical kicks in.
 
The above is not necessarily true

Are you running "full vacuum"? What is the advance (mechanical + initial) at high RPM WITHOUT the vacuum hooked up.
 
This MAY not be your problem. I went thru the same with my car. Thinking it was electrical went thru and checked everything and then changed everything when I didn't find anything.Did the same with the fuel system that was new from the new tank to the carb. Same problem. Thinking that it was too lean started jetting the carb fatter.Same thing.For the heck of it went leaner than the starting point. Problem solved.I'm not as high as you only at 2500'. Again this is what worked for me.Just a thought.
 
My combo is very similar.

My timing maxs out at about 34*@2800 power and up to 22* more from the V-can for PT cruising. That would total up to 56*@ around 2800. Then my dash-mounted, dial-back,timing device can plus/minus 7 more. So theres up to 63* cruise timing available,
However I dont cruise at 2800. I cruise at 2300. Here the cruise timing is closer to 55 * max available.
Anyway, I digress

I think you cooked the plugs. Check the color. I bet they indicate lean.
Change your plugs and rejet .RN12YC is what I run. They have over 100,000 miles on em.I run the Accel Super coil. The big square one. Its probably of similar age.
I could be wrong. The plugs could just as easily be sooted up.
Point is unscrew em and look.

Theres a small chance that the coil is going away.
 
AJ/FormS said:
My combo is very similar.

My timing maxs out at about 34*@2800 power and up to 22* more from the V-can for PT cruising. That would total up to 56*@ around 2800. Then my dash-mounted, dial-back,timing device can plus/minus 7 more. So theres up to 63* cruise timing available,
However I dont cruise at 2800. I cruise at 2300. Here the cruise timing is closer to 55 * max available.
Anyway, I digress

I think you cooked the plugs. Check the color. I bet they indicate lean.
Change your plugs and rejet .
I could be wrong. The plugs could just as easily be sooted up.
Point is unscrew em and look.

Theres a small chance that the coil is going away.
Click to expand...
My plugs are all sooted up (very black). They are new plugs and I don't have maybe 5 miles on them.
 
Darter6 said:
This MAY not be your problem. I went thru the same with my car. Thinking it was electrical went thru and checked everything and then changed everything when I didn't find anything.Did the same with the fuel system that was new from the new tank to the carb. Same problem. Thinking that it was too lean started jetting the carb fatter.Same thing.For the heck of it went leaner than the starting point. Problem solved.I'm not as high as you only at 2500'. Again this is what worked for me.Just a thought.
Click to expand...
Thanks for your input I will check it out.
 
j par said:
so your distributor advances 50 degrees? I think thats your problem right there. most cars with that kind of Bild don't even use the vacuum advance system. mechanical time it all in has 36 and see where it idles at before the centrifical kicks in.
Click to expand...
It advances to 50 degrees with the vacuum hooked up. Without it is 18 initial and 18 mechanical for 36 degrees total.
 
I also reset the preload on the lifters at .030 again just to make sure it was good.
I started it up before I did this a little earlier and when I revved it up and got into the secondaries it back fires through the carb.
 
Thats typical of sooted plugs.

If youre reving it up in neutral, It should be very difficult to get the secondaries to open.Thats not a very good test.

Change the plugs.Figure out whats causing the soot.Disable and Block the secondaries closed.Sync the transfer ports.Adjust the mixture screws.Make sure your PCV is working, and that the hose is not collapsing.

Now heres how you are gonna adjust the mixture screws;
With engine warmed up, tranny in park, V-can hooked to the spark-port.If you have a 4-corner idle system and its adjustable, set them to the minimum recommended setting.Adjust the secondaries as far closed as possible, but not sticking.
Now,block the primaries open at 2400 to 2600rpm or so. Screw the mixture screws in until the engine rpm falls. Turn em back out 1/4 turn.If the mixture screws end up outside their working range,something is wrong.
-If you cant get enough fuel from them,crank the secondary idle mixture screws richer 1/4 turn, and try again.
-If you cant seem to take enough fuel out, check the boosters for signs of PV drippage.Replace it as may be required.
-Repeat as often as necessary,to get the primary mixture screws close to the center of their working range. Keep an eye on the temp gauge during this procedure. Return the primaries to idle.

Mine idles at 700 no sweat (stick car).Put yours in gear. If your TC drags the idle down too far, adjust the speed as may be required.If the neutral idle gets past 850, or the sparkport reads over 4inches, Crank 2 degrees more initial into it and start all over from the beginning,starting at"now".
-If the initial gets up to 24*, and still has not achieved these goals,shut the engine off and immediately restart it. If it starts normally,you can add 2 more initial into it.But I dont think you will need to go far from where you are.
-Finally, you will have to limit the power timing.And possibly delay the all-in point a little higher,say 2800 to 3400, staying below the TC flash-stall.

My Eddy headed 360 seems to make the same power at 30/32, as it does at 36*. I have a tight quench of .034, so that seems to require a bit less timing.I run about 32.
-Next, go out and cruise at around 2200 for a half hour on those new plugs. Stay on the low-speed circuit as much as possible. Pull over, let er cool, pull a couple of plugs.What do you see?

OK, I need to go to sleep now.
 
RAMCTD2003 said:
I'm running ported vacuum. The mechanical + initial is 36 degrees without vacuum hooked up.
Click to expand...

Then "for now" you should be fine. In fact you can leave the vacuum unhooked for peace of mind until you get this sorted, it "should" really not matter
 
You didn't change anything since it ran fine at the track, and started to crap out? I say ignition coil. Does the "mis-fire" change with engine load? When it does it's thing at 3000 rpm, is that wide open throttle only, or any load?
 
norcal-fjo said:
You didn't change anything since it ran fine at the track, and started to crap out? I say ignition coil. Does the "mis-fire" change with engine load? When it does it's thing at 3000 rpm, is that wide open throttle only, or any load?
Click to expand...
I changed nothing! It's at wide open throttle only. It has a surge when you are cruising but no backfiring.
The coil is brand new but that may not mean anything. It's an MSD blaster 2.
 
AJ/FormS said:
Thats typical of sooted plugs.

If youre reving it up in neutral, It should be very difficult to get the secondaries to open.Thats not a very good test.

Change the plugs.Figure out whats causing it.Block the secondaries closed.Sync the transfer ports.Adjust the mixture screws.Make sure your PCV is working, and that the hose is not collapsing.

Now heres how you are gonna adjust the mixture screws;
With engine warmed up, tranny in park, V-can hooked to the spark-port.If you have a 4-corner idle system and its adjustable, set them to the minimum recommended setting.Adjust the secondaries as far closed as possible, but not sticking.
Now,block the primaries open at 2200rpm or so. Screw the mixture screws in until the engine rpm falls. Turn em back out 1/4 turn.If the mixture screws end up outside their working range,something is wrong.If you cant get enough fuel from them,crank the secondary idle mixture screws richer 1/4 turn, and try again.Repeat as often as necessary,to get the primary mixture screws close to the center of their working range. Keep an eye on the temp gauge during this procedure. Return the primaries to idle.
Mine idles at 700 no sweat (stick car).Put it in gear. If your TC drags the idle down too far, adjust the speed as may be required.If the neutral idle gets past 850, or the sparkport reads over 4inches, Crank 2 degrees more initial into it and start all over from the beginning,starting at"now"
Click to expand...
Thanks for the info. I will see where this gets me. The carb is brand new, I just got it yesterday from AED. I know that means nothing, but I thought you would like to know.
 
What ignition system are you running, as I didn't see that info anywhere.
Running good then all the sudden black plugs could be a weak ignition as well.
 
And before somebody says anything, I was running a 750 vacuum secondary Quick Fuel carb when I ran it at the track and it started the backfiring with that carb and now I have an AED 750 mechanical secondary carb. Same problem with both carbs.
 
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