1985 454 quadrajet will only idle when choked

[legomybago]

Hi all, been awhile since I've posted. Got a mystery vacuum leak I can't seem to locate?? The motor home was pulling a long grade when all of a sudden it started acting like it was running out of gas (bogging down), then it started popping out both exhaust pipes, the motor home barely made it to a rest area when I received a phone call to come and try to fix it (I wasn't the one driving it). So when I began trouble shooting the issue, I verified it was getting plenty of fuel to the carb, I can only keep it running when the carb is basically fully choked, or if open choke I can cup the airhorn pretty tight with my hand and it will idle, but when I do this, fuel splashes up on to my hand probably due to low vacuum drawing the fuel down inside the carb?? It has 14* of vacuum at idle, needle on the gauge bounces 1* at idle,  I've plugged all vacuum ports at the quadrajet still no change, I've emptied two cans of eyther

[legomybago]

My computer froze up on that last post. Engine has 60k miles, runs like a sewing machine as long as its choked. I can't seem to locate any large vacuum leak on the exterior of the 454. Could his be a quadrajet issue?? It's all original. I have it on the bench now, but I didn't want to tear into it just quit yet. I know it's not an ignition issue due to me being able to manipulate the way it runs controlling the air flow on top of the carb.

[CapnDirk]

Have you checked a cylinder or two for compression?  Almost sounds like you might have jumped a tooth on the timing chain under the load.

[legomybago]

If it was a timing issue, I would think it would miss at some point?? It run real good under choke? I can't get it to pop/backfire at all

[Rickf1985]

Sounds like timing to me also. Throw a timing light on it and see where it is at. I will bet it is substantially retarded. If it is then get a helper underneath with a socket on the crank bolt and turn it one way until the rotor moves, then start turning back the other way and see how far it turns before the rotor moves again. Should be almost instantly. If not then the chain is pretty loose and probably jumped. The did use the plastic timing gear on these.

[legomybago]

Ok, I will put a timing light on it the next time I go over to the inlaws place. I hope it's not the chain....

[legomybago]

Ok, I put a timing light on it. 8*Before. The air cleaner says factory is 4*, but we removed the smog equipment long ago, I advanced the timing back then and it always ran cool and strong. She was running a bit ruff today, I had to rig the choke semi (80%) closed so it would idle while I checked timing. If I had a jumped timing chain, I'm going to guess these numbers wouldn't be anywhere near where they were. I used the number 5 wire and the timing tab drivers side underneath.

[Rickf1985]

No, It would be off by quite a bit. You are going to have to open up the carb and see if something got sucked in and is clogging up the works. You said you went through a couple cans of ether so I am assuming you were checking for vacuum leaks? I prefer carb cleaner since it does not blow away or evaporate as fast as ether so the engine has more time to react. Does this engine have EGR? It should and if the EGR valve stuck wide open that could give you this issue, you can try tapping all around it and see if it drops back down. Sometimes the only way to check it is to remove it and look and test on the bench. Be sure you can get a gasket or gasket material first.

[legomybago]

Yes it has an EGR valve. If I put vacuum to the egr when idling it kills the engine, I can also here the valve moving up and down when the engine is off if I put vacuum to it. Not sure if that means it's sealing internally though?? I used both eyther and carb cleaner searching for a vacuum leak, I've had luck using one or the other in the past tracing down leaks on other motors, so I had both products on hand for this one.

[Rickf1985]

This is going to be a tough one, we know it is not the timing. We know the egr valve is working but we do not know if it is closing all the way, could have a piece of carbon stuck in the seat. We do not know if if something got sucked into the carb and is blocking a jet. we are pretty sure there are no vacuum leaks. I am guessing you tried the tapping on the valve so lets concentrate on the carb. Are the secondary throttle plates closed ale the way? I have seen where a wire or vacuum line has gotten in there and jammed the linkage open. There is a BIG vacuum leak internally that you would not find. Quadrajets had problems with the bodies warping if they were tightened to much, If that were put together with the extra heat from a long hard pull it is possible the body warped and you have an internal leak in the carb that will not respond to carb cleaner or ether because it could be affecting a liquid passage.
The only way to find that is to completely disassemble the carb and wet sand the body parts on a piece of glass. I do that with all of my rebuilds and you would be amazed at how many are warped. All brands, not just Quadrajets.

[legomybago]

I think I will be pulling the EGR out due to getting a small amount of reaction with the starting fluid, its possible like you said Rick that it may not be closing or sealing shut all the way. It didn't seam like a large leak, but I did get a small reaction of a vacuum leak in that general area a couple times, and the carb base gasket has scene better days too. When the rig was broke down at the rest area, I found a vacuum leak at the front base of the carb, I pulled the carb and saw the base gasket was allowing some dirt in, not a lot but some. When I reinstalled the carb, the float needle was stuck open and fuel began to pour out the top of the carb. I pulled the carb again and played with fuel inlet blowing air (with my mouth) while opening and closing the needle by gravity, reinstalled carb and now the needle seals fine. I also noticed small rusty garbage that came from??? somewhere and was laying down inside the carb on top of the secondary throttle plates, probably came out of the secondary fuel nozzles or something...so I have some pretty good clues to this carb being tired. AND while playing with it keeping it running so I could check timing, the motor was acting different at different times, so that is leading me towards the Quadrajet also....

[M & J]

When our 87 454 started acting like that, a float was stuck in the carb. But it was flooding out and only running above idle and terrible back firing. We had it towed to the house to keep the exhaust from being blown off.

[legomybago]

Found the issue.....Took the Quadrajet apart, and it was full of little black pebbley crap, I mean full!!...I believe it was remnant's from deteriorated old rubber fuel lines. The carb fuel filter was clean as a whistle too? I replaced all the rubber fuel lines back at the tank about 4-5 years ago, so I think we have been running around with crap in the original Quadrajet for a while....surprised it didn't have any issues before. I just used carb cleaner and an air compressor and gave the carb bodies a ruff clean, a new rebuild kit, didn't soak anything. But it worked out good.

[Rickf1985]

That was happening a lot when they first went to alcohol in the gas.

[legomybago]

A little new info to this....The father in law put about 20 miles on the motorhome, and it starting crapping out and would only idle, then I think it wouldn't idle. He was taking the rig out of storage and was driving it to a mechanic to have the brakes looked at when this happened. I knew nothing of this until he called me and said he took the rv to a mechanic shop and the shop said they found a leaky brake line and they also said the rv needs a new carburetor?? I thought....ok Hm? I think this was a little over a week ago. Yesterday morning I woke up with an epiphany? (not sure if that's the right word?)....anyway I was thinking about the mystery black crap we found in the quadrajet originally, and we found nothing on the fuel system (filters) side of the carb?  I now think the mystery black garbage is from the charcoal canister. sucked in from the vacuum side of the carburetor. I think the carb just needs to be cleaned out along with the large vacuum line to the canister, and replace the charcoal canister or remove it from the system. Now the motorhome is at some mechanics shop in town right now as I write this, probably with a new 600?? dollar carburetor just waiting to suck a bunch a crap into it. I let my father in law know this yesterday, so hopefully they will approach their repairs differently before sending him on his way with a fat bill. I'll update this when I know for sure...Im only speculating on this right now because I don't have the rv in my possession to confirm. The reason he didn't bring/or call me on this recent break down is because the in-laws are going through a divorce and things have been weird lately...

[Rickf1985]

The charcoal canister is just that, charcoal so it will not turn to goo and come up the line. It is just vapor going up there, there is no real massive airflow. Also, That does not go into the fuel system, it is vented into the air inlet side of the carb. So don't blame the canister. There is no real reason to take that system off and if you do then you will have the vapors coming from the tank to deal with. That black stuff could very well have been parts of the fuel pump diaphragm though. It does not need a carb, just a carb rebuild. The problem is that nobody knows how to do that anymore. I would say that it needs fuel lines and a fuel pump probably.

[legomybago]

We haven't found any contaminants in the fuel filters? Clean as a whistle. So we know nothing has been entering the carb on the fuel side.....You can google search and find info on people dealing with charcoal inside there carburetors...some people actually put inline fuel filters between the charcoal can and the carb. Idk, like I said, I haven't seen the motorhome or talked to the father in law about it yet. I'll update when I know more. If the carb was full of crap again, but nothing was found in the fuel inlet filter, then we'll have to look deeper.