Dave E

Ok guys... got my 86 magnum swap done... she is now officially a Magnum 5.9 carburetor motor truck. I was trying to start it for the first time today and It spins over well but spits back through the carburetor. I mean bad enough that it was spraying raw fuel on the windshield. So my question is what would cause this?

Engine is a low milage short block with new cam, heads, intake and carburetor.

moe7404

sounds like a valve is open when it should closed. valve stuck open, cam out of timing, distributor out of timing, dist cap / rotor bad. my dad had a saying "all ways check the easiest and the cheapest things first". dont for get the carb doesnt care what direction the air is going through it. it will kick fuel out no matter if the air is going in or out.

Dave E

Yeah my fear is the valve timing... I am guessing the only way to check is figure out compression stroke and check to see it builds?

moe7404

OH sorry i didnt think of doing a compression test. but check the cheapest things first.

RacerHog

Keep us posted on what you find...

pro-tech

Could be 180* out on the distributor..Does it backfire? How did you find #1 on the firing order? Bill

Dave E

It was given back to me with the instructions that it was tdc on number one and to put in distributor with button pointing to #1. Guy that did the motor had the same thought. He recommended going 180° on the distributor. When I get home off work I am going to give it a shot. It doesn't backfire just spits... If that makes any sense.

440roadrunner

EASY to figure out. What did we do? before Al Gore invented the internet?????

You don't have to "guess" either

Quick check.........Pull the coil wire!!!!!! If it still spits raw fuel out, it's not IGNITION timing!!!!!

(Might still be cam timing, but probably a valve hung open as above)

If it seems to be ignition, there is NO REASON to fiddle with all this "180 out" nonsense. You, as a mechanic, SHOULD be able to time one of these to GO and KNOW that it will FIRE

So how? EASY TWO ways to do so.

1... IF you have either valve cover off...........This requires "no" beer and paying attention. Bump the "marks" to TDC. LOOK at both valves for no1 and no6 cylinders. One set will be "both closed" the other will be "both open." This might be hard to see on a "stock cam". On the cylinder that is "both open" move the engine slightly with a wrench. Both valves will move, one closing, the other opening. On the cylinder with both valves closed, they will not immediately move.

ON THE cylinder which has both valves closed, this is the cylinder "ready to fire." If both no6 are closed, you can either plug the distributor in with rotor pointing to no 6, or rotate the engine one revolution and plug it rotor to no 1.

Before you do, back the engine up some, then come back CW NOT to TDC but rather to WHERE you want timing, say, 10* BTC on a "stocker" and 15-20 BTC on a hotter cam
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If the valve covers on both on, the easy way is to pull the no1 plug, stick your finger in the hole, and bump the engine. Stop when you start to feel compression. You may have to "go round" a couple of times when you first do this. When you start to feel compression, look for the marks which should be "coming up." Again, set the marks NOT at TDC, but rather where you want timing

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Now, with vacuum advance "in the middle" of it's rotation, clear from obstacles, plug the dist in with rotor point towards no1. You can ACTUALLY allow the rotor to point "anywhere." It can point to China as someone on another forum said.

Now look at the cap, remove/ replace until you "get" which tower the rotor is just coming to. This will be no1.

Rotate the distributor "way retarded" CW for a SB and CCW for a B/ RB.

Slowly ADVANCE the dist until either the points just open (use a test lamp) or look at the reluctor / pickup, and center the reluctor tip in the pickup core.

Now just plug the no1 wire into what tower the rotor points to and START IT UP
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Dave E

The distributor was out 180°. Thanks for all the help guys. IT'S ALIVE!

RacerHog

Wooooo Hooooooo...... Glad you got it going...... We love trucks...

moe7404

" before Al Gore invented the internet?????" and i was getting ready to hear that he invented the light bulb, to. but what ARE we going to do with him now?

440roadrunner

The real question is, "do you know" how to do it right the first time now?

HINT: If you are firing a new engine with a new flat tappet cam, you can't be cranking it endlessly for six hours with your buddies leaning on the fenders, because in a short time, you might not have a camshaft left

Besides, "all those" fireballs coming out ' o ' the carb are hard on power valves, eyebrows, and the underhood paint.

Dave E

No I'm not the type to crank and crank and crank. Also this happens to be hydraulic roller :-) I still have a long way to go... it will run but doesn't idle well and occasionally backfires through exhaust. I'm concerned that my lack of exhaust will make it difficult to fine tune so that is my next step.

CMJ

I had the same problem. the distributor was way off. have someone crank the engine while you turn the dist. slowly. you need to turn it in the advance direction.