Can you guys help me figure out what's going on with my crazy truck?

[team39763]

It's spitting through the carb as if it's running backwards(not backfiring).  I tried 2 different carburetors.  My wife said that the gas came shooting out the carb like somebody was spraying it with a water hose.  My pressure is only set to 6-7psi and I have a return style regulator.  I checked set the float level, but it makes no difference, the carbs just fill with gas and flood the motor.  Why would the motor spit the gas mixture back out?  My timing is very mild and I didn't even get to rev it.  It has done this spitting/run crappy thing since I built it a year ago or whenever and even with 5 or 6 different carbs.  But for some reason when my friend brought me his 850DP it ran pretty good.  Then after a while it was starting to run crappy again.  Is it a stuck valve?  Somebody had mentioned that before and said that would make it spit through the carb.  My wife and I are so frustrated with this truck and we really don't know what to do.  I just changed the spark plugs, but it looks like I may have to change them again since I flooded the motor again and I may need an oil change again.  That's over 20 sets of spark plugs, and 7 oil changes in under 50 miles of driving.  I'd appreciate any help or advice.

[VileZambonie]

I would re-adjust your valves and verify cam timing. Also double check your firing order, distributor cap and ignition timing.

[team39763]

We went out right now and set the pressure to 3psi and used the 670 Avenger instead of the 750DP.  It ran like crap still and still flooded a bit.  But it ran, so we put the 750 back on and made sure the pressure was low.  It immediately flooded and we never got to start it.  There's been so much raw fuel pissed into this motor today.  I was thinking maybe bad needles/seats, but I don't really know.  My floats seem to float, but I might replace them too.

Vile - it's my LS powered truck.  I don't know about readjusting my valves, I'll look into that though.  What is up with this white billow of smoke coming out the carb when it stalls out?  Could that be water in the gas?   

[eventhorizon66]

Well I think the fact that you have tried 5 or 6 different carbs pretty much tells you the problem is not with the carb.  LS motors use non-adjustable rockers, but the cam timing could still be off if someone has messed with it.  Are you using the MSD box to fire it.  Maybe that's where your problem lies.

[VileZambonie]

Yes your LS shouldn't require any special adjustment. I forgot that's what you had. Make sure you have good compression and the cam is good/on time. And what are you using for an ignition control module?

[team39763]

I'm using the MSD ignition controller.  My timing is set to something like 12-15* at idle and locked out to 24*from 1100rpms up.  My wife thinks it's the carburetors - needles/seats and floats, so she's buying me new ones.

[joesgarage71]

Coughing and spitting makes me think either the timing chain is off a tooth or the ignition is causing this. Verify that the #1 piston is at TDC and the timing mark on the balancer is at 0* and both valves (#1) are closed,  If all this is correct then move on to the ignition, process of elimation, check your work and the parts you installed. Do you have good grounds? Is the battery fully charged? Starter wires tight? I'm just throwing stuff at ya get ya to think. It could be something stupid as a burnt plug wire touching the header.
 I can give you the number of my PCM tuner he might help you with this newer Stuff.
 Steve

[team39763]

I'll look into the timing chain thing, I've been wanting to replace it, I just couldn't get my hands on a puller just yet.  My grounds should be good, but I'll add one more.  Battery was charged, starter wires were just tightened.  I'm pretty sure all my plug wires are good, but I may replace them just to check them off the list.  We are still thinking about taking the truck to a dyno tuner, but I really didn't want to.  I really really wanted to figure this out and fix it myself...but I guess it's time to just admit defeat and go learn from a pro.

[joesgarage71]

 I was looking at  MSD #6012 LS controller instructions, do you have a cam sensor? crank sensor? Maybe one of those are weak or giving a bad signal.
 you can test those plug wires with a multimeter, those sensors can be tested.  you can do all this stuff(while learning) yourself, remember process of elimination. Don't pay someone money for stuff you can do yourself!
You have a MSD product before you spend anymore money blindly replacing parts give them a call 915-857-5200
 Steve

[team39763]

Well we know something needs to be replaced on the carb.  The fuel seems to just bypass the carb and just spill into the motor as soon as it turns on.  My wife will watch the fuel pressure gauge next time we try to turn it on to see if the pressure jumps up on startup.  We set the floats with the truck off but with the fuel pump on.  MSD suggested that we check the cam sensor too.  I'll look into that also.  Thanks for the suggestions. 

[TexasRed]

Have you replaced the regulator?

[team39763]

No, I haven't replaced the regulator, but I will try that today.  I have a new one here.  What can I do besides lower the pressure to keep the needle seated?  The only carb that I didn't have this problem with was the 850 which was freshly rebuilt, but after a few months it started doing the same thing.

[VileZambonie]

Install pressure gauge on your regulator. that's how I have mine set up so you can tweak it right there and know what it's set at. I've had mine at about 7 psi with no problems. 5-7 is usually good.

[team39763]

 I didn't get to do much with the truck today.  But I did try turning it on without turning on the fuel pump.  It took a few pumps to get it to run, but it did run on it's own and idle like normal until I let it run out of gas.  We will have the new needle/seat assembly with new hardware and gaskets sometime soon.  I'm also going to take a look at my regulator and determine if my alternate is any better.  I'll move the pressure gauge a little closer to the regulater.  I'm aslo going to order a stronger timing chain.  I'll let you guys know how it goes.

[TexasRed]

If the carb doesn't flood the engine when the fuel pump is off it's probably the regulator.