Ωmega

iTrader: (28)

Hi all, I'm having some issues getting my carbed ls1 started up. I was working with a choke-less carb before and couldn't get it to catch and start, so I switched out to a 750 street demon.

Yesterday I was able to get it started, as seen in the video. It backfired twice through the exhaust, then through the intake and died. I'm able to almost get it started, but it doesn't quite catch. This is what it's been doing since before this new carb, and now after. Every now and then when cranking, it'll spit up through the carb when I stop.

I'm not sure what the issue can be. I have a Black box 6010 grounded both to the battery and to the engine block, and the timing tables are below. Everyone keeps telling me it's a timing issue. I set my tables based on what I've seen here.

Any ideas what the problem can be? Could the box be bad?

I'm running stock block LS1, EPS 236/248 .617/.617 110lsa cam, and about stock compression.

LLLosingit

iTrader: (4)

Is this a first startup after adding a new cam? It does seem like a timing issue but there can be other causes, Wrong pushrods, Bad crank sensor.

Ωmega

iTrader: (28)

It's the first startup after a full swap. Bought a good running block, new heads, cam, intake, carb, etc.

LLLosingit

iTrader: (4)

Did you check pushrod length? If they are the wrong length they can keep the valve from closing causing hard starting and backfiring through the intake and or exhaust.

LLLosingit

iTrader: (4)

Did you check for piston to valve clearance?
I don't know what you have for tools but you could try a compression test to see if you have valves hanging open. A backfire through the carb can be caused by a valve open when the plug fires, This can be caused by a bent valve, Misalignment at timing chain or the plug firing at the wrong time. Since you just put in the cam it could be any of the above.

monte383sbc

iTrader: (15)

Are all your coil plugged in correctly to the correct firing order , make sure the wire harness isn't crossing coils to the wrong cylinders,

Doug G

Seems this issue has popped up a few times here....
Make sure your battery is fully charged
While cranking, have laptop hooked up to see if its reading RPMs during cranking.
You might also try taking 1st dot to 0 rpm and 2nd dot to 1000 rpm and see IF that helps any also ?

1973 STEP A SIDE

iTrader: (4)

Like said above Check coil pack wiring !!

Ωmega

iTrader: (28)

Thanks for the replies, everyone. Pushrod length is okay, as is PTV clearance and the coil wiring. I'll do a leak test to see if that could be it.

In the mean time, any other ideas are appreciated.

LLLosingit

iTrader: (4)

Do you have a good ground for the 6010? I was doing some searching at it seems the 6010 is sensitive to how it's grounded. Another post where someone had a similar problem it was the cam sensor. Do you happen to have extra sensors you could swap in to see if it's possibly the cam or cranks sensor? I know you can't just throw parts at it but if you have extras or could borrow them it would be easy to see if it makes a difference.

Ωmega

iTrader: (28)

Thanks for the suggestions. Yep the cam sensor is good. The ground was my first thought, so I split the ground and ran it to both the battery and engine block and there was no change.

LS1-450

iTrader: (33)

Was the cam degreed w/ an adjustable timing set? If not was dot to dot alignment confirmed? Once cam install is confirmed to be correct...

I'd first confirm spark from every coi while cranking. If spark is there, try to start it w/ only starting fluid, no fuel pump & drain carb bowls. If it runs on starting fluid, either the primary squirters are too big &/or the accelerator pump may be too large. May also be too much fuel pressure over filling the bowls & adding pressure to accelerator pump when fuel is sent to the carb. Check pressure before trying starting fluid. Are there sight windows on the bowls to confirm proper level of fuel?