5.7L Mercruiser Rochester Quadrajet flooding with fuel

[tfret]

Just cranking the engine with the throttle in neutral position completely floods the carb with fuel to the point it drips down on the intake manifold. I have no idea what is going on. I bought the carb new about 5 years ago. Never had any trouble with it. Someone suggested that the needle valve on the float may be stuck open, allowing the carb to be over supplied with fuel. I'm pretty good with working on most anything, but I've never really worked on carbs much. I have no idea where to start. I pulled the carb and it's on my work bench. I'm grateful for any and all suggestions.

 

[achris]

Do you have a genuine workshop manual? If not, post your engine serial number and year and I'll point you at the right manual. If you don't have the engine serial number, what is the carb number (should start with "1347-")?

 

[NHGuy]

The oe manual is very good.
But, If you want to know the entire deal on that carb get Rebuilding the Rochester Quadrajet by Cliff Ruggles. It has every bit of detail you could need.
Best money I spent on my Baja.

 

[achris]

The oe manual is very good.
But, If you want to know the entire deal on that carb get Rebuilding the Rochester Quadrajet by Cliff Ruggles. It has every bit of detail you could need.
Best money I spent on my Baja.

Completely agree, but you need the Merc factory manual as well, for engine specific specs.

 

[Oshkosh1]

I had a similar issue on my old boat with the Rochester. Ended up being a tiny eyelash sized piece of stripped threading which kept the float bowl needle from sealing completely. Luckily, Rochester's are pretty easy carbs to figure out. Keep things in order and you should have not issue reassembling it.

 

[tfret]

Thanks for the replys. I'll definately get my numbers and shop for some manuals. I'm sure they will provide in depth details that will help me better understand the entire carb. Do you know if they have a troubleshooting guide that might have my symtoms to look up? I just figured as long as Merc has been using that carb someone has bound to have seen the same thing before. Sounds like Oshkosh1 experienced it too.

 

[skijunk]

Mostly likely it's trash in the needle and seat. This is a common symptom found in any engine with a quadrajet.

 

[achris]

Another reason for the floast not closing the needle could be a 'sunk' float. Some are made of foam and over time absorb fuel and no longer float, some are made of brass and can get a hole in them, and no longer float. All these things will be revealed when you open it up. It might even be just a faulty seat. Also, don't buy any parts until you do have it open.

Chris......

 

[tfret]

Well I do have the service manual, but it is a pdf of a paper manual, and the photos aren't real sharp. Also, my carb appears slightly different than the one in the illustrations. But I followed the disassembly instructions, and watched a couple YouTube videos, and managed to get it disassembled. The needle valve and seat look fine, the float is the black plastic type, and appears fine. I don't see any trash. But I did discover my primary metering rods were stuck in the down (spring compressed) position. I used some sewing machine oil to loosen them up and get them out. The spring inside the brass piston looked like it may of had some light rusting going on. The metering rods had a brown film on them. I cleaned everything well with the sewing machine oil, and reassembled, then worked the spring action several times. It all seems to move freely now, and resides in the up position. Most everything I've read pertains to the float/needle valve/seat system. I don't know how the primary metering system works. Could this have been my problem?

 

[tfret]

I can't seem to locate the serial number on this carb. I've read that the usual locations are on the side of the body where the throtle cable connects. Usually stamped vertical behind the secondary air valve control shaft. I've looked all over I don't see anything but casting numbers. I need to order a kit and need to be sure it's the right one since there are several versions of these things. Any suggestions on how to confirm the right carb #?. The carb is not original to the boat so I don't want to rely on the engine serial #.

 

[tfret]

I found and downloaded a full Qjet service manual that completely explains how everything works. It appears that the primary metering rods being stuck in the full down position would not cause my carb to flood. This is the economy position and is normally in this position during idle and low speed anyway. So I'm back where I started, why is this thing flooding over with fuel while cranking? I did locate the model number info. It is a late model "modified" version. So now I can order gaskets to put it back together. But I still haven't found anything wrong. Was really hoping to find trash in the needle valve but that's not the case. Any suggestions?

 

[hemi rt]

If you have the black float, just replace it as it's probably fuel soaked. They are not expensive and good sense replacing it. You can compare the weight of the old versus new - you see a difference.

 

[tfret]

yeah a bad float or maybe a leaking well plug on the bottom of the carb is what I'm reading on other sites

 

[tfret]

I was mistaken about the carb part number. Each section has a casting number, but mine has no stamped part number anywhere. I believe it may of originally had a stamped tag held in place by one of the front air horn screws, but has since been removed. Any I've decided to just order a kit and renew all the parts, but don't have a good model number to go by. Anyone have any suggestions?

 

[jimmbo]

I found and downloaded a full Qjet service manual that completely explains how everything works. It appears that the primary metering rods being stuck in the full down position would not cause my carb to flood. This is the economy position and is normally in this position during idle and low speed anyway. So I'm back where I started, why is this thing flooding over with fuel while cranking? I did locate the model number info. It is a late model "modified" version. So now I can order gaskets to put it back together. But I still haven't found anything wrong. Was really hoping to find trash in the needle valve but that's not the case. Any suggestions?

Clean the power piston and the bore in slides in very thoroughly with a combustion chamber cleaner. bits of carbon get blown in there when an engine backfires/sneezes and eventually will cause it to stick again. Flooding on a Q-jet is from: 1) heavy float; 2) misadjusted float; 3) loose inlet seat; 4)no gasket under seat; 5) dirty or damaged needle and/seat; 6) improperly positioned needle hanger; 7) incorrect float; 8) excessive fuel pressure

 

[achris]

I was mistaken about the carb part number. Each section has a casting number, but mine has no stamped part number anywhere. I believe it may of originally had a stamped tag held in place by one of the front air horn screws, but has since been removed. Any I've decided to just order a kit and renew all the parts, but don't have a good model number to go by. Anyone have any suggestions?

What year is the engine (or better still, serial number)? From that I can give you an exact carb number.

Chris........

 

[tfret]

Update: I purchased a rebuild kit which was an expedition in its own since my Qjet has NO ID number on it. Finally after looking closely at all the gaskets in the kits online, and learning everything i could about what year this thing could be, I took a chance and ordered a kit. It had everything I needed. Performed a full rebuild for the first time ever. Everything went together just fine. Got my float adjusted same as the original. at 7/16" Polished the inside of the power piston. Epoxyed the well plugs. Everything is back together, test ran in the drive way just fine, spent all last weekend on the lake and all problems are resolved. A couple notes: One, I never found any smoking gun as to what caused the flooding issue. I have no idea what caused that to happen. None of the 8 items jimmbo pointed out in his post were evident. Two, I did find rust on the power piston spring and accelerator spring. I'm surprised these aren't made of stainless steel to prevent rusting! I can only guess this is due to running mostly pump gas resulting in some moisture in the carb? Anyway, all is well at this time. Just wanted to say thanks to everyone for the valueable feedback.

 

[harleyman1975]

Great to hear!

 

[NHGuy]

Excellent!

 

[boatman37]

awesome!