bears416

5.3 lm7 in a 91 s10. Stock cam. Just a Vic Jr and 1 5/8 headers. When I try starting it its spits and back fires and catches the fuel in the Carb on fire. Then after a while of trying to start it it'll finally start and die randomly and if I blip the throttle real quick it'll shoot flames and almost die but I can ease in to it and it won't miss much. What cud this be? All my searches brought up dizzy probs on sbc's. Carb is a 4160 750 Holley dual feed vac. Secondarys. Fuel pressure is 6psi

Thanks


Ethan

ZONES89RS

iTrader: (25)

Well, if it was running fine before, a cam or crank sensor could be at fault.

bears416

Iv never heard it run b4 but they said it ran fine

dogsballs

leaky needle and seat?

squirters too big??

too much fuel pressure??


is the fuel half way up the sides of the bowl?

Blowerman

If it's doing this when cold that's normal. Welcome to the carb world. If your carb still has the choke plate in it. Hook it up to a cable and problem solved.
Back in the older days we kept a glove box full of power valves because when we'd get a sneeze it usually blew the diaphragm out. Now they have a check ball to prevent that.

Luke_Siebert

If you have a GOOD carburetor, this is not true.

bears416, what is your timing curve like?

Pop N Wood

iTrader: (1)

Carbs can be hard to start when cold but shouldn't be backfiring. You might have multiple issues. Backfires are usually timing related but too lean can make it worse. Not wanting to idle could be the tune is off or choke out of adjustment.

Could be a vac leak. Double check all connections and cap all unnecessary vac lines (like the brake booster/PCV) until you get it started.

Start with the idle mixture screws out about a turn and half. Check float levels good, no bad gaskets in the carb. Can't hurt to pull the plugs and give them the once over.

What timing curve do you have in the MSD box? if you don't have a MAP sensor make sure and zero out the vac advance.

The car will run without a cam sensor but you have a 50-50 chance of it starting up right. the other half of the time it will be 180 out causing back fires. Still, half the time it should be OK.

You might try a little starting fluid to see if it will catch. Since it is backfiring squirt some in the carb, step back and then try to start it. Otherwise you might trim your eyebrows.

bears416

The Carb is seeing 6 psi fuel pressure. The fuel was almost to the top of the glass. I backed it down some.

bears416

For now its the stock number 1 pill that comes with the 6010 box with the map sensor hooked up. I think I cud benefit with the higher cranking timing of the number 6 pill.

Luke_Siebert

I highly suggest a custom tune with a laptop.

bears416

You think its really gonna make much of a difference just for Getting it running?

Blowerman

Really dude? A good carb is more likely to be lean on a coldstart than a problem carb with fuel leakdown. Hence is why I suggested hooking up the choke. And a custom tune on an ignition box?
OP,
While the engine is idling, hold a rag over the carb bores and see if the rpm rises and engine smooths out. That would indicate a vacuum leak or overly lean condition. This is easy to check. Let us know.

bears416

OK it'll be a while b4 I can do that I have no cooling system at the moment

ZONES89RS

iTrader: (25)

A tune that you do yourself is night and day difference.

Luke_Siebert

Not meaning to ruffle any feathers Blowerman. I am just saying, a nice four corner idle carburetor that is setup right doesn't need a choke....even in 30* air. I have done it......a lot. The laptop tune might not fix the starting issue, but like ZONES said, night and day. Again, just trying to HELP!

Cunning69

Here is my 2 cents, the only way you can get flames firing up thru the carb is if a spark plug fires at the same time an intake valve is open on a cylinder. This is usually an ignition timing thing but since you have a MSD I am not sure how that could happen. If you had a distributor I would say your wires are crossed. (!) Maybe you have the left bank and the right bank wiring mixed up?

speedtigger

iTrader: (16)

Backfiring through the carburetor can be caused by:

• Lean condition
• timing too far retarded
• ignition firing at the wrong time

Now, you must find out which one is at play. Start by trying to determine which is the most likely and work toward the least likely.

I would say most likely is an improperly calibrated or adjusted carburetor. I would start by checking the float levels, jetting and accelerator pump operation and adjustment. Adjust the float levels. Start with factory recommended jetting. Then check the accelerator pump for proper operation and adjustment.

Also, you will likely find that you need at least .037" accelerator pump discharge nozzles. This is common on LS engines.

If you are running an Edelbrock Performer RPM, make sure the ignition module mounting holes are plugged.

The timing being too far retarded is not likely as even the factory settings create this condition, but it needs to be and is easily checked.

There have been multiple complaints of failed cam sensors. That will need to be investigated if the other potential problems do not pan out. I have also seen 1 or 2 complaints about some wiring issues.

One more thing is make sure you have good voltage. I have seen some threads complaining that the MSD 6010 and 6012 models will develop problems when the voltage drops too low.

kevleetee

I had an issue with my MSD 6010 box that caused a similar problem, it was a ground wire pulled loose out of the msd harness. The msd box would fire all 8 sparkplugs as soon as I turned the key and supplied power to the msd box. It would backfire out of the carburetor and exhaust manifolds at the same time! WTF was my first thought then I tracked down the loose ground and fixed it and it stopped shooting flames out of the carb and exhaust. Goodluck with your setup, I know working the gremlins out of my stuff seems to be on going.

bears416

Problem fixed pulled up my 6010 diagram on my phone both cylinder banks had coil plugs ran to wrong cylinders. Soon as I fixed it fired rite up in less then a second and held an idle all in 35 degree weather

speedtigger

iTrader: (16)

Well, that'll cause some problems. LOL