Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem

New rebuild leaking fuel

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Stitch:
Sorry this is kind of long.

This was my first time ever rebuilding a carb.  Got Cliff's book to get me started in getting the right knowledge.  I learned a lot, but I still made some rookie mistakes.  I used Cliffs kit so I knew I had the best parts, therefore all errors are on me.

The quad is a 4MV, I think.  It's a 1970 CA model, that's about all I know off top of my head.  It's sitting on a 350.  I finished the rebuild, which wasn't as bad as people make it out to be, but maybe it wasn't so bad because I didn't do so good a job.  I put idle mixture screws out 4 turns, and tried it.  I didn't expect it to work, but it fired right up.  However, I noticed after a short time, the gasket between the bowl and the throttle body was leaking fuel.  It wasn't dripping, but it was wet right at the rear passenger side corner under the secondary bore.  All I had done was start the engine, adjusted the fast idle a bit, revved it a little, got it warm enough for the choke to pull off and then revved a little bit more to look for leaks, which I was hoping not to see.  At this point, I was thinking maybe I didn't get the throttle body screwed onto the bowl tight enough.  I thought maybe it was leaky well plugs somehow getting fuel back there, but looking at it now, that doesn't seem like where the fuel would go if the plugs were leaking that badly.  And I did do the soap test twice to be sure they were good.  Then, I saw the gasket between the air horn and bowl was also getting wet front driver side, right in front of the accelerator pump.

Called in to Cliff's yesterday when this happened, left a message.  Impatiently, called again today but got voicemail.  Okay, I'm on my own until I hear back.  Not complaining, Ray was really patient and helpful with me when I called in yesterday morning. I'm sure they are busy over there, so I thought I'd post here while I wait.  So I just pulled the carb off and started taking it apart. 

Throttle body screws were snug enough, I think.  The diagram shows 3 screws, my model only has 2.  I read around that people use loctite on these, maybe I'll do that next time around if anyone here recommends it.  Throttle body appears very flat, as does the bottom of the bowl.  Although, when I put them together, I do see the side have a little light showing, like the bowl can sort of rock on the throttle body side to side a little, making that gap where fuel was coming out.  But a straight edge shows nothing out of flat and I think when it was together, everything looked really snug.

Moving on to the leak between air horn and bowl.  Major rookie mistake I made was to not check the parts before assembling them.  Just looking at the air horn, I can see its warped with my eyes.  A straight edge shows it even more clearly.  The front corners of the air horn where the long manifold bolts go are clearly bent downward from overtightening.  Now, I got it pretty tight, but I just checked a spare air horn I got from the previous owner of my truck, and the spare is bent the same way.  So I am assuming this one was already bent, but maybe I made it worse, because I don't recall a leak there before the rebuild.  However, the little ridges seemed to make a good impression on the gasket.  Just looking at the gasket, it looks like there was a good seal.

Stitch:
It's so long I had to split it....

Finally, just right now while I was typing this, I flipped the throttle body over and out fell a little stud.  It was the stud that locks it into place on the bowl.  It only had one to begin with, didn't even realize there was supposed to be two because the other one was already broken off cleanly.  Seeing as I had one stud in the right place and everything assembled well, I don't think there was any way the parts were out of alignment.  But could that missing stud have caused that leak?  Now that the other one is broken off, can I still use the bowl?  I've got spares, but they're not the same models.

So now I am wondering what to do.  Should I try heating and gently bending the air horn back to straight?  Could the front drivers side air horn bolt have been tight enough that it made a gap on the opposite, rear right corner of the bowl/throttle body?  Or is it something else entirely?  I tried calling in to Cliff's one more time this afternoon to see about maybe just sending it in to have them fix it, but I really don't want to wait that long, and I really don't want to be defeated after I got this far doing it myself.  Last question, if I just rebuilt the carb yesterday and only had it together for about 24 hours, can I reuse my gaskets if I figure this out?

Again, sorry for the long post, but I wanted to provide as much information as possible.

Stitch:
Just wanted to add:
float height is 5/16".  My untrained eye thought there was more fuel in there than what I expected to see.  I have not checked fuel pressure, maybe I'll try and do that next while I wait for a response.

429bbf:
if you use your hold down bolts for alinement you can get it straight without the tabs . if the air horn is not bent to bad you can use a thicker gasket which i believe comes in the kit ,or you can file down the high spots and give her a try . don't over torque the bolts the hold it to the manifold thats what causes most of the problems in the first place .appox 20 lbs max.check fuel press and make sure you didn't hook the needle in one of the holes on the float.you may also try lowering your float a tad .i know 5/16 is not much ,and a lot are set apox.1/4 . patience is the name of the game and fuel pressure is the key. hth

Stitch:
Thanks so much for the reply, it's nice to have some advice!

Ok, good to hear the alignment isn't that big of a deal.  I wasn't sure if there was anything critical that needs to be just right. I was considering drilling the old spots and trying to fit new studs in there, but I'll leave that be for now.

I probably put more than 20 lbs on the bolts, but I don't think I went too crazy.  Maybe, I'll grab a torque wrench to be sure I don't go too tight.

On the air horn, I hadn't considered removing metal as an option, I was thinking only about moving metal.  But I can see how it could go bad in a hurry trying to bend this stuff.  I'd hate to mess it up either way, so I will consider both options.  I did not get any more gaskets in my kit, just the one. 

This carb has been on this truck for who knows how long, maybe 30 years.  Before the previous owner got old and sick, he knew what he was doing.  He neglected the truck when he got older, but I think he maintained it very well prior to that.  I'm pretty sure the last time he opened the carb to adjust anything or installed a fuel pump, he knew what he was doing.  So I trust the fuel pump is probably right, but I'll check it.  I don't have the tools to do it and the fuel line is all metal with a compression fitting, so I'm not sure how to test it yet. 

The only leak I knew about on this quad was from the primary shaft, which is why I installed the bushings.  But now that I look at the photos of it before I cleaned it, it looks like these areas probably were leaking and maybe just got gummed up and sealed themselves from filth.  I don't even know if that's possible, but you can see what I mean in these pics. 

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