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73-87 Chevy _ GMC Trucks => Engine/Drivetrain => Topic started by: team39763 on December 29, 2008, 05:39:18 pm
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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.
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I would re-adjust your valves and verify cam timing. Also double check your firing order, distributor cap and ignition timing.
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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?
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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.
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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?
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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.
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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
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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.
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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
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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.
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Have you replaced the regulator?
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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.
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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.
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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.
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If the carb doesn't flood the engine when the fuel pump is off it's probably the regulator.
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Team, It sounds to me that you have several problems. When the carb/carbs flood the engine...do they all pour the gas out the vents? Is this DP pouring gas out both the front & back vent? If so, I would question the accuracy of the pressure gauge or the "pepper" stuff in the carb you mentioned about the other day. I question what it is & where it's comming from. This might explain why your friend's carb worked at first, then when it got some of this "pepper" in it & then started sticking the needle? Are you still finding this stuff in the bowls? I agree with the others about the misting/coughing fuel out the carb as it stalls, sounds like a timing problem. Lorne
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Sometimes the gas comes out through the boosters, and sometimes it shoots out through the vents or both. The pressure gauge is one of those summit liquid filled ones(the small one)placed 8" from the regulator, but I was told to drain the liquid, so I did. I'm going to check out the regulator in the morning. How big of dirt does it take to affect the needle? I'm going to figure out the pepper source in the morning...I'm taking the entire fuel system apart for cleaning.
Maybe the misting was due to all the raw fuel left in the intake? Is it possible that the trails of raw fuel were slightly ignited?
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Why would my pressure gauge not read right? It's setup like this - regulator, then to a inline filter, then pressure gauge, then to fuel log/carb. I'll try like vile said and put the gauge as close as possible to the regulator. Should I refill the gauge with liquid?
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why did you drain the gauge? I have a summit liquid filled gauge on my regulator too. What do you have for a fuel pump? You can also install a vacuum pressure gauge to verify it's accuracy.
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A few guys on a different message board said to drain it so it would be more accurate...it didn't make sense to me, but I was really "new" at that time so I believed them. I have a mallory 110 electric pump and mallory 4309 regulator. I'll try the vacuum gauge on there and see what it says.
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I still haven't had much time to mess with the truck. But I tried removing the carb from the motor but leaving it hooked up to the fuel lines so I can test it without losing a whole'nother gallon of gas in the motor. I removed the set screw from the regulator like the directions mentioned for testing. It said pressure should be no more than 3psi like that, and mine came out to 2. I adjusted the floats dry and set them to be as low as possible, but the float level was still a little high...especially considering that there was such little pressure. I'm thinking once I set the pressure to 6, it'll fill the bowls again., but the only gas leaks I had this time were from the set screws above the needles. I already ordered new needles/seats, gaskets, and screws. I have a hard time believing that the gauge is wrong, but I'll check it. The source of the pepper seems to be from the threads of all my fittings after the filter. I'm going out there right now to try the vacuum gauge on there.
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I tried the vacuum gauge and it read 1psi higher than the gauge, but theres a filter before my FP gauge so maybe that dropped the pressre a little. Anyway, I set the floats at both extremes and both times it did almost the same thing. With them all the way in, the float level was too high and fuel sprayed out the adjustment nut. Then with them adjusted out a good bit, the fuel level went past the sight holes and started coming out throught the vents and the adjustment nut. The fuel pressure was at 3 or less the whole time. I tried adjusting the needle all the way in(lowest float seting), and I removed the sight glass...so I could do it like the holley book says. All it did was make a nice steady stream of fuel pour out the hole.
I'm stumped and not really sure what to do with the truck at this point. I was going to just part it out, but wife says to just crush the whole thing. We already found another truck for me that already runs. But I'd like to figure this out before we give up for good. Anymore suggestions?
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Just slap on a new carb! Don't give up!
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Well, I went out there again...determined to get it right and it worked. I don't know what exactly fixed it, but it should run fine when my new gaskets get here. I'll see if I can sell my carbs and buy one new one.
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Just an update. I got it running again. It's running a bit rough, probably from all the excess gas still in there along with the fouled plugs. I'm planning to pick up some new plugs and more oil this week. Thanks for all the help and suggestions. I hope this time it'll run good enough that we can take some video of it.
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New carb?
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Na, LOL...not yet. I just can't get myself to spend the money on a new carb just yet. I'm convinced that I'd still be in the same boat even with a new carb. I think I'm gonna continue to make my rookie mistakes on this carb and this motor, that way I don't mess up some really nice/expensive parts later.
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So you're still not sure what fixed it huh? Maybe it was that swift kick you gave the tire. I know my truck really shapes up after a good beating.
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I followed up on most of the suggestions posted. I just need to get the compression test done aswell as order the right timing chain. I was just about to go out there and install the new needles/seats, but I don't think I should be running it with the plugs fouled like this and the oil contaminated with so much gas....or does it not make a difference? I'm tired of changing plugs and oil. That's 21 times that it's fouled the plugs and this will be the 8th oil change which is rediculous for a truck that's been driven less than 50 miles. Hopefully this next set will be the last one.
LOL...I've been holding back from inflicting damage on my truck out of frustration. Maybe it was my 2yo daughter...she said a little healing chant in spanish for my truck....something about "heal heal little tail of the frog"...I don't know the rest because she speaks more spanish than me.