Timing question 318 with LD4B

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Davis911s

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Bought a 1987 B350 van to make for a camper for my boys. It has 318 engine that was originally propane powered, but was converted to gas by previous owner. It has LD4B intake and Edelbbrock 1406 600 CFM carb. I am getting hard cold starts and backfiring through carb. Plugs were new, new fuel filter and carb was cleaned. So I am thinking timing. I do not think anything was done to the internals of the engine, just intake and carb swap. What should timing be on this set up? TIA
 
Every engine is different, I would say if your trying to time it based on the base line stock setting of like 10 degrees its going to most likely want more.
 
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Typically 10-16 deg. intial 32-36 total, each build is different. 65'
 
Timing can be anywhere from 5 to 25 and by itself will NOT cause backfires thru the carb during a cold start or idling.

A backfire implies that there is fire in the intake manifold.
More often than not, this happens because of an incorrect firing order, cross-firing inside the cap, induction firing along the wires, a wet coil top, or just plain old lean mixtures, due possibly to a non-functional choke, but could be a huge intake leak like a blown PCV hose or bad brake-booster. And don't forget stale gas and/or water in the gas.
These are your first go-tos; the simple stuff.
But this can also happen when one or more intake valves are not closing. This is usually because the Cam is out of time, or valves are hanging up, or are burned.
Therefore
after checking the simple stuff, it is time for a timing-chain stretch test, then a check to see where the rotor is in relation to where it is supposed to be, then a compression test, and finally, possible a check of the cam timing, or at least to see where split overlap is.

If you have log manifolds, and a restrictive single exhaust or a plugged muffler/cat, I suppose a pressure build up could backfeed into a cylinder with an open exhaust, on the overlap cycle, but that's a stretch.
 
Thanks everyone
UPDATE: I put a Mr Gasket fuel gauge at the carb inlet form the filter, and it is only showing 2PSI?? Once engine is started it will idle and even rev up nice, but then it will die if you just quickly let off the fuel. But I am surprised it would run with this low fuel pressure. Is it possible the gauge isn't working , or more probable that the fuel pump the previous owner put in is this low of pressure? Could that low of pressure cause the backfiring when letting off fuel?
 
Davis911s said:
Thanks everyone
UPDATE: I put a Mr Gasket fuel gauge at the carb inlet form the filter, and it is only showing 2PSI?? Once engine is started it will idle and even rev up nice, but then it will die if you just quickly let off the fuel. But I am surprised it would run with this low fuel pressure. Is it possible the gauge isn't working , or more probable that the fuel pump the previous owner put in is this low of pressure? Could that low of pressure cause the backfiring when letting off fuel?
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Your carb does not care about fuel-pressure.
Your carb cares only about one thing, that the fuel level is always correct.
Fuel pressure is used to push the fuel to the carb against the closed or nearly closed float valve. Two psi when stopped and idling will be just fine. You can gravity feed that carb at zero psi when stopped and idling, and it will idle all day.

If it stalls when you close the throttle, have you considered that it is idling too slow? Turn the speed screw in (faster)about 2 or 3 full turns, reset the mixture screws to 2.5 turns and try it again. If the idle is too high, retard the timing. Your target is 600 to 700 with a stock to near stock cam. If you still have stalling or backfiring, you will have to hunt for a vacuum leak.
If you have a timing light try 10 degrees at idle. adjust the idle speed up or down as may be necessary.
 
AJ/FormS said:
Your carb does not care about fuel-pressure.
Your carb cares only about one thing, that the fuel level is always correct.
Fuel pressure is used to push the fuel to the carb against the closed or nearly closed float valve. Two psi when stopped and idling will be just fine. You can gravity feed that carb at zero psi when stopped and idling, and it will idle all day.

If it stalls when you close the throttle, have you considered that it is idling too slow? Turn the speed screw in (faster)about 2 or 3 full turns, reset the mixture screws to 2.5 turns and try it again. If the idle is too high, retard the timing. Your target is 600 to 700 with a stock to near stock cam. If you still have stalling or backfiring, you will have to hunt for a vacuum leak.
If you have a timing light try 10 degrees at idle. adjust the idle speed up or down as may be necessary.
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It is idling closer to 1000RPM which I knows is too high. And it still stalls as soon as you let up on the gas. I will check and set the timing better this week. And I will check for vacuum leaks. Thanks
 
I'm wondering if the timing chain has slipped a tooth? Check for vacuum leaks/ cracked/ disconnected hoses
 
67Dart273 said:
I'm wondering if the timing chain has slipped a tooth?
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I'm fearful after watching one video on timing chain that it is stretched. So much work to get at the timing chain. I fell like I basically have to pull the engine and take the whole front end off the engine to check
 
If it backfires starting when cold.....but starts ok when hot, then it is NOT ign timing.
Could just be the choke is adjusted too lean. Stalling: have you tried adjusting the idle mixture screws for best idle quality/rpm. You should check the float levels, should be 7/16". Can be done on the car; no gaskets reqd if you are careful.
 
You can check the timing-chain slack from underneath the vehicle no problem; I have done it several times.
My brother brought me his van of about that vintage, but there was no way to check the timing. So what I did was drill a large hole in the BH, about in line with the ring-gear, and with a piston stop, I determined true TDC of #1 piston and marked the torque convertor thru the hole. Then I could use my dial back timing light on that mark.

In the video, it can be seen that the choke is partially/ mostly closed, and the carb seemed to be on the fast idle cam. If that is true, she may be flooding.
You said;
Davis911s said:
Once engine is started it will idle and even rev up nice,
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In this case I really doubt the chain has jumped.
I tried to listen for a vacuum leak, but that engine seems to be making a lotta top-end noise, which made it impossible to hear any vacuum leak, for me at least. But I also could not see a vacuum-advance hose.
If that van left the factory with a lean-burn system, then is it possible that it still has the ELB distributor in it? If so, it will have to be swapped out, because it has no provision of any kind for providing timing-advance.
If it just quits as the rpm comes down, then I would suspect, in order of probability; stale gas, a huge vacuum leak, a non-functioning slow-speed circuit in the carb, extremely retarded ignition timing, metering rods bent and stuck in the lifted position, or a missing checkvalve in the accelerator pump discharge circuit.
 
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I saw 1.5 psi fuel pressure at 3K RPM. If you think that's enough, well.....I don't know what to say. What do you think will happen to that 1.5 psi under a LOAD going uphill, or trying to pass a car? Or get on an interstate ramp. The carburetor certainly DOES care about fuel pressure. If it sucks the float bowl dry before it can refill, then there's a problem. A lot of times though when one shuts off like that when you let off the gas suddenly, it's because the idle air screws are out of adjustment. You might put a vacuum gauge on it and adjust those. But that's going to do nothing for that fuel pressure. IMO you need to track that down.
 
Here's what Edelbrock says about fuel pressure for that particular carburetor.

"Fuel Pumps and Pressure Avoid extremes in fuel pressure. At IDLE, there should not be any more than 6.0 psi; if the vehicle has an adjustable fuel-pressure regulator, set it to 5.5 psi. With most fuel pumps the minimum fuel pressure is encountered at high rpm and WOT. Fuel pressure should not drop below 2.0 psi. If it does, a fuel pump with more capacity may be required. Note that some later model vehicles (the 5.0L Ford is one example) have mechanical pumps that will give more than 6.0 psi at idle. The vehicle will perform well, but may be prone to stalls on quick turns and stops with the clutch disengaged. If this problem occurs, check the fuel pressure. If it is more than 6.0 psi at IDLE, it should be reduced through the use of a regulator, such as Edelbrock #8190, or by creating a restricted by-pass bleed to the fuel return line. Edelbrock Street Fuel Pumps are highly recommended for all Edelbrock Performer Series carburetor installations. Always use a filter, such as Edelbrock #8873 between the pump and carburetor. Note that a good filter is large in area, so it may be able to transmit a significant amount of heat to the fuel. It is a good practice to keep the filter away from heat and not allow it to come in contact with any part of the engine."
 
RustyRatRod said:
The carburetor certainly DOES care about fuel pressure.
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The question was;
Davis911s said:
Is it possible the gauge isn't working , or more probable that the fuel pump the previous owner put in is this low of pressure? Could that low of pressure cause the backfiring when letting off fuel?
Click to expand...
I wrote;
AJ/FormS said:
Your carb does not care about fuel-pressure.
Your carb cares only about one thing, that the fuel level is always correct.
Fuel pressure is used to push the fuel to the carb against the closed or nearly closed float valve. Two psi when stopped and idling will be just fine. You can gravity feed that carb at zero psi when stopped and idling, and it will idle all day.
Click to expand...
OP added
Davis911s said:
It is idling closer to 1000RPM which I knows is too high. And it still stalls as soon as you let up on the gas. I will check and set the timing better this week. And I will check for vacuum leaks. Thanks
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Notice it ran fine at 3000rpm on two psi. What I said is exactly correct.
 
AJ/FormS said:
The question was;

I wrote;

OP added

Notice it ran fine at 3000rpm on two psi. What I said is exactly correct.
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Yes, it sounded good at 3K while not under a load. I'm not arguing with your majesty, I simply posted what the carburetor manufacturer recommends.
 
Is the gauge oil filled? If so they fluctuate horribly with heat. I had one that at idle it would go from zero to 10 lbs and back. Idled for 20 mins at zero. Drained the oil out of the gauge, rock steady 5 lbs in all conditions.
 
You want enough fuel pressure to keep the bowl full while at the highest fuel demand. I had to go with the bigger needles and seats with my AVS. I had issues at 3lbs. To much fuel pressure and you can create foam in the bowl.
 
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