360 magnum troubles

[JelloB1afra]

I rebuilt a 360 magnum and threw it in my Dart, but I can't get the damn thing running right. This is my first engine build and after a ton of problems, I finally got it to idle. The new problem arises when I apply any throttle. I can get it to start up and idle; but when i give it any throttle, it sputters, dies, and coughs out of the carb. Anybody had similar issues and have some sage like wisdom to share?

here are my specs:
Junkyard 360m bored .030 with stock bottom end
Keith black pistons
Custom ground cam on old core
Engine quest heads
Edelbrock RPM air gap
Holley 750 double pumper (recently gone through, maybe i'll do it again just to be sure)
Doug thorley headers

 

[xLURKxDOGx]

Whats the timing set at?

Jake

 

[MOPAROFFICIAL]

That above, probably too advanced and the pump shot is or could definitely be too lite. and just a side note...what's been done to the heads?

 

[JelloB1afra]

That above, probably too advanced and the pump shot is or could definitely be too lite. and just a side note...what's been done to the heads?

I havent done anything to the heads besides put on the stock rockers. They did have the 2.02 and 1.8 valves though. by pump shot being too light, do you mean its running lean or might need a bigger accelerator pump?

Whats the timing set at?

Jake

20* initial. i couldnt get it to run right with any less.

 

[67Dart273]

That above, probably too advanced and the pump shot is or could definitely be too lite. and just a side note...what's been done to the heads?

Doubt it's too much but for sure check pump shot AND IDLE TRANSITION SLOTS

With the idle set up "best" remove the carb or look down with a bright penlight and see if the throttle blades are "in" the transition slot area

Here

holley transition slots

Also how did you set idle mixture?

 

[xLURKxDOGx]

Is it a new balancer? How did you confirm timing, get it at TDC and it was correct on balancer?

Jake

I havent done anything to the heads besides put on the stock rockers. They did have the 2.02 and 1.8 valves though. by pump shot being too light, do you mean its running lean or might need a bigger accelerator pump?



20* initial. i couldnt get it to run right with any less.

 

[273]

Sorry
Got no input
But love the name

We came
We peed
We conquered
You bleed

 

[JelloB1afra]

Doubt it's too much but for sure check pump shot AND IDLE TRANSITION SLOTS

With the idle set up "best" remove the carb or look down with a bright penlight and see if the throttle blades are "in" the transition slot area

Here

holley transition slots

Also how did you set idle mixture?

ill check the pump shot in the sun tomorrow. i wouldnt think its too light, but maybe it is. the squirters are pretty big (forgot the number). maybe i need to step up to a 50cc pump assy or change the pump cam? it drops a hefty amount of fuel when i move the throttle linkage. the idle seems pretty spot on. this is actually the first time of heard of transition slots.

Is it a new balancer? How did you confirm timing, get it at TDC and it was correct on balancer?

Jake

yeah i used this one (or one pretty similar. i ordered it a while back).
https://www.summitracing.com/parts/pfs-80012
i put it to tdc and it matched up on the balancer. checked it a bunch of times too because i was kinda suspicious of it. i am also using the LA timing chain cover if thats worth mentioning.

Sorry
Got no input
But love the name

We came
We peed
We conquered
You bleed

Thanks man!

 

[nm9stheham]

Can you give us the piston model and the cam specs? It is not clear on how you set the cam timing. What is the cranking compression?

While the carb setup is suspect, it could also be ignition related.
Spark plug gap?
Ignition system type?

Does it die if you open the throttle very gradually? The pump shot sounds quite adequate for just coming off of idle; does the shot start the instant you move the throttle?

 

[JelloB1afra]

Can you give us the piston model and the cam specs? It is not clear on how you set the cam timing. What is the cranking compression?

While the carb setup is suspect, it could also be ignition related.
Spark plug gap?
Ignition system type?

Does it die if you open the throttle very gradually? The pump shot sounds quite adequate for just coming off of idle; does the shot start the instant you move the throttle?

i used these
https://www.summitracing.com/parts/uem-kb107-030/overview/make/dodge
the cam is .282/.282 duration and around .525 lift. i didnt degree it though, and when i put it together i didnt even know what cam timing was. just stabbed it in there. I do know the cam and crank gears are oriented correctly though. (had to do it twice)

i went by the book with .040
my distributor is one of the skip white ebay "hei style" ones

yeah. ill only get maybe 1/4-1/2" push on the linkage and itll die. the shot start Almost immediately

 

[MOPAROFFICIAL]

Doubt it's too much but for sure check pump shot AND IDLE TRANSITION SLOTS

With the idle set up "best" remove the carb or look down with a bright penlight and see if the throttle blades are "in" the transition slot area
Here

holley transition slots

Also how did you set idle mixture?

I said It's too lite, or little, or lean...but not too much.

 

[MOPAROFFICIAL]

ill check the pump shot in the sun tomorrow. i wouldnt think its too light, but maybe it is. the squirters are pretty big (forgot the number). maybe i need to step up to a 50cc pump assy or change the pump cam? it drops a hefty amount of fuel when i move the throttle linkage. the idle seems pretty spot on.

Highly doubt you need a 50cc pump.

What number is stamped on the shooter/squirter ?

 

[rumblefish360]

You might need to degree that cam.
Is it possible that you have a multiple key way sprocket and it has the cam 4*'s advanced or retarded?

A new balancer is good. The true TDC may not line up with the TDC marks on the balancer.

 

[nm9stheham]

I'll agree that from the symptoms when the throttle is opening gradually, it sounds like it is just going too lean overall. The suggestions on the transition circuits is where I would focus.

Also, having a stock PCV valve with this cam is going to cause problems; the vacuum signal from this cam is going to be low, and a stock PCV will be at the wide open setting all the time, and will dump a bunch of extra air into the intake.

And, I suspect the carb does not have a choke plate on the top of the primaries which is making things worse.

OK on the spark plug gap and ignition. Just to be sure it is good, take one spark plug wire, and place the metal end 1/4"-3/8" from metal and crank a few cycles. You should get a bright, blue spark. If so, then move on to the carb and intake.

Since this is a used carb, look at the butterfly plates and see if there are any small open holes drilled in them. And look at the airbleeds in the top to see if anyone has drilled them out. A used carb is a VERY big unknown here.....regardless of having been gone through. Do you know any history of the carb? Do you have another that is known good?

Some troubleshooting suggestions:
1. Block the PCV and see if that helps. If so, then it is time for another PCV.
2. Spray some combustible liquid around the intake flanges and carb mountand see if it speeds up to see if you have a vacuum leak. (This will not say if you have a vacuum leak on the underside of the intake-to-head flanges.)
3. Get a vacuum gauge and take intake vacuum readings at idle.
4. Cover the carb primaries most of the way with a gloved hand and see if that helps it to run as you open the throttle a bit and gradually; if so, then it is the transition adjustments.

If you are not aware of what the transition slots are, there are some small slots in the carb throats just above the throttle plates when closed. These feed full into the carb when the carb operation is 'transitioning' from idle to the main circuits. The secondary has a a stop that sets how far the secondary butterflies are open when at idle; this setting determines how much air is fed into the intake from the secondary side, and that stop is adjustable. Then there is the adjustment of the primary transition.....

BTW, have you been able to get the revs up to break in the cam? If not, then you ought to stop any extended cranking or idling.

 

[pishta]

Im wondering if he has a huge vacuum leak and has adjusted the carb to idle with it? buddy installed an OOTB Edelbrock without the rear plug installed (why do they even ship it like that?) and it was like that, would idle after turning every screw but no rev. normally on a out of the box holley, the throttle blades uncover the transition slots about as far as they are wide, to make a perfect square. then you sort of work the carb settings around that constant. But used could have all sorts of mods to it.Are all your vacuum ports plugged in that carb? the accelerator pump arm should just touch (wiggle the link arm and tighten screw until you feel it contact) and then back off about 1/8 turn. .031 shooters are pretty common on a 750. Does it have a good power valve? what color is the plastic accelerator pump cam on the throttle shaft? Used Holleys are dangerous like that: they are so modular that you can get one that has 12 things altered from OOTB settings. What port do you have your HEI tied into? Is it in fact getting manifold vacuum off that port? dont run ported vacuum (would have the spud over the throttle blades). suck the vacuum hose of the distributor and watch the advance plate, does it in fact move, and does it hold when you plug the line? A good way to get to know your car.....and go get yourself $3.44 vacuum gauge. loads of info from that little tool. Mini Dial Air vacuum Pressure Gauge Scale Black HP | eBay

 

[67Dart273]

You might need to degree that cam.
Is it possible that you have a multiple key way sprocket and it has the cam 4*'s advanced or retarded?

A new balancer is good. The true TDC may not line up with the TDC marks on the balancer.

I was thinking THIS

I would recheck EVERYTHING

You can "somewhat" degree the cam.......enough to tell it's in the ballpark........right off a junk pushrod. Pull the no1 rockers off and "rig" an old pushrod so you can see what's happening, and with an indicator

Also use a piston stop and verify your balancer mark is right. This is the ONLY way to do this on an assembled engine

Also have you milled the heads, had valve work done? Maybe the pushrods are trying to hold the valves open, IE they have become "too long" due to head work.

The easiest way to "fight the carb" is to borrow a known good one off a similar "build" engine from a friend

You want lots of timing.....perhaps 15 BTDC at idle, and make sure it's advancing. Do you know what the setup in the mechanical advance is? Have you checked that it actually is advancing and not stuck?

Also monitor voltage TO the ignition system. If I understand what you have there should be 12V right to the coil and right to the ignition. If this is low or you have a wiring problem, it might not be providing decent spark

 

[AJ/FormS]

I rebuilt a 360 magnum and threw it in my Dart, but I can't get the damn thing running right. This is my first engine build and after a ton of problems, I finally got it to idle. The new problem arises when I apply any throttle. I can get it to start up and idle; but when i give it any throttle, it sputters, dies, and coughs out of the carb. Anybody had similar issues and have some sage like wisdom to share?

here are my specs:
Junkyard 360m bored .030 with stock bottom end
Keith black pistons
Custom ground cam on old core
Engine quest heads
Edelbrock RPM air gap
Holley 750 double pumper (recently gone through, maybe i'll do it again just to be sure)
Doug thorley headers

I had an engine like this with a 292/292/108/.508 cam and it liked a lot of idle bypass air, so the PCV worked well. It also wanted some thru-holes in the throttles valves. I moved that cam around from 100* to 112* installed and it didn't change the idle tune much at all. It was ok with 12 to 16 degrees of idle timing.My plug gaps have always been .045 to .055, and I use the sq-top Accell SuperCoil electronically triggered.
I think your T-port sync is just too far off,
and the pump-shot(as mentioned) may be; late,lazy, or insufficient.
and possibly the PV is late to the party
Or you have a massive vacuum leak,
Or some combination, of the above.

As mentioned, your T-port exposure under the plates should be a little taller than wide.And the mixture screws should be in the middle of their travel. On Holley types this will be about 1 turn out, while most others will be about 1.5 to 2 turns out. Then you leave those alone for a long while. To set the idle speed you will use idle-timing and idle-air bypass. To speed it up you add timing,and to slow it down, you subtract timing. When the speed is in the ballpark, you adjust the idle quality with the bypass, that you will have to engineer.
This is a recap of all that has been mentioned.
BTW, at this point I don't even use a timing lite. The T-port sync will command a timing that you just push or pull the dizzy around to get the right idle speed.

After you get this far,, and the engine is responding,then we can revisit the T-port sync,as may be necessary.
Don't be discouraged, this is an easy to-tune-combo, it just might take time.
The biggest monkey wrench is when the intake sucks air from the valley side, but this too is an easy find.

And as mentioned, if you have a flat tappet cam, you need to break that beast in before any of this gets done. I assume that since you are at this point, that, the cam has been broken in. If not, then the cam may already be junk.

 

[Lelo Dart]

It can be hard to get a tune right with a big cam. Esp with a tight convertor. Didn't catch if you were running a auto or not.

 

[skizzo]

Vacuum leak. Did you use the cork/end seals or RTV on the intake?