Rebuilt Carb-Still Gassy

[batsong]

Hi.  I've just rebuilt carb 17059212.  The book was great, and now the carb is idling, cruising and performing much better.  The only problem is that while improved, the gassiness out the tail pipe is still present and fuel economy is still bad.  I used "recipe #3" from the book.  I am working with a 455 with 9.5-1 and a cam with 230 @ 50.  The carb is sucking a lot of air and pulling a vacuum tube makes the engine speed up.  Covering the choke horn causes the engine to die.  The car still has points which is all new, but it will soon be replaced with HEI.  Will this help?  Any more carb work I could do?  Drilling throttle plates maybe?  Was is causing this?
Thanks, Gabe

[batsong]

I just tried drilling the throttle plates, and it did not help.  Still very rich.  The lope came back, it's running alot like it did before enlarging the idle passages (no jerkiness at cruise, though).  Maybe the efficiency is a little better, but I liked the way it ran before drilling.

[Cliff Ruggles]

Drilling the throttle plates is done to lower the throttle angle at idle speed.  The carburetor includes an idle bypass system which does essentially the same thing.

When you get time, list the items from the "recipe" and what sizes you made them.  This includes:

upper idle airbleed:
lower idle airbleed:
main airbleed(s):
idle bypass air:
mixture screw holes in baseplate:
idle tubes size:
idle downchannel:
main jet:
primary metering rod:
fuel inlet seat diameter:
float setting:
incoming fuel pressure:

You also mentioned that pulling a vacuum hose causes the engine to speed up a bit.  Are you able to slow down the engine at idle speed when you turn the mixture screws in?......Cliff

[batsong]

Cliff, here is a list of what I have done so far.  I realize that I did not drill out the air bypass.  I thought that they were already .070.  Drilling the throttle plates with a .094 hole seems to have helped with the fuel economy (I'm getting 12 mpg now!), but I liked the way the car ran better before.  I left the idle screws the way that they are are because they have never been touched and I would have to cut the throttle plate, and nothing else I have done to the carb seems to have cleared up the richness.  In other words, I don't think that I have touched upon the cause of the problem yet.  Your book and the resulting mods to the carb helped enormously in other regions, and I am thrilled, but I am thinking the problem may not be in the carb after all.  The richness is so excessive (I can smell strong exhaust going down the highway with the windows closed)  that I'm thinking that there is something simple that I'm missing.  I tried swapping coils, but the new one I bought turned out to be  defective, so it's taking a little time to return it and get another.  I've got a MSD coming today. 

upper idle airbleed:     (in airhorn) .059     
lower idle airbleed:     stock
main airbleed(s):      stock
idle bypass air:    stock
mixture screw holes in baseplate:    stock
idle tubes size:     .040
idle downchannel:     .059
main jet:      .075
primary metering rod:     later style rod turned .026 at the tip and .050 at the widest part
fuel inlet seat diameter:     .135
float setting:     .375
incoming fuel pressure:    no gauge yet

[batsong]

Just put a gauge on the fuel line.  It's bouncing between 4 and 6.  Put a cheap regulator on too.  I turned it down to 4.5 and even lower but the richness did not go away.
-Gabe

[Schurkey]

The richness is so excessive (I can smell strong exhaust going down the highway with the windows closed)  that I'm thinking that there is something simple that I'm missing. 

First Guess:  You have holes (Rust holes in the underbody or trunk; missing grommets; broken plastic A/C--Heater box; missing drain hose in the A/C box...and there's lots more possibilities) in the passenger compartment that are allowing fumes in.  Seal the holes.

Second Guess:  You didn't do yourself any favors by going to all the trouble to drill throttle blades and modify the carb in other ways--but not bothering to un-seal the idle mixture screws.

[batsong]

It's an old car.  There are a lot of places the exhaust can leak in..  If I smelled normal exhaust in the cabin, I would not worry.  I've tried to plug them up temporarily until I move to that area in earnest
I didn't cut out the idle screws because I've haven't found them to have any effect on this problem when I've had another Q-jet on (they always seem to go back to the way I found them).  I was trying something new.  I have extra throttle plates, I figured no harm done.
All of this is so I can learn and have fun with an old car.  I am trying to improve efficiency and performance so I can drive it to work, but obviously, if there something wrong with the engine, I don't want to drive it for fear of damaging it.  My plugs are normal, and my carb, whether inadvertently or not, seem to be set up o.k.  The oil is thin and gassy, so I think fuel has been walking out along the fuel pump arm.  I'm worried I might wash out my rings.

That's my defense.  I came to this forum not for idle reasons, but because I've exhausted all other possibilities.

Thanks, Gabe

[Cliff Ruggles]

Setting up any quadrajet exactly for an application is like making a batch of chocolate chip cookies.  If you leave out the chocolate chips, don't expect to make good cookies.

I would go into the book, identify your carburetor exactly, and the location of the idle airbleeds, main airbleeds, idle tube, idle down channel, idle bypass air, etc.

Install a set of solid primary throttle plates, pick a recipe that corresponds to your application, and custom tune every area of the carburetor exactly to the specifications listed.

Every "recipe" is street, dyno, and track tested.  The only need to vary much from the recipes would the altitude or climate where you live.  If you send me a note, I can help with that area if needed.

It's quite rare to even find a q-jet with the idle taper proof caps still in place.  Most were removed by dealerships under warrantee due to customer complaints.  Even with the caps removed, the holes under the mixture screws were so tiny on most models that even with the screws backed out 6-8 turns they couldn't get enough idle fuel to the engine!

Also keep in mind that a lean carburetor will "stink" ten times more than one running correctly or even slightly rich.  If you do NOT put enough fuel in suspension for complete combustion, the by-product is some really "stinky" exhaust fumes, as tons of unburnt particles exit the exhaust pipes.  This often fools a lot of tuners into thinking the carburetor is way too rich, when more times than not, it is way too lean......Cliff

[batsong]

Thanks, Cliff, for the tips.  That's cool about the lean mixture being stinky.
I feel bad because I probably should have waited before making any posts on this forum because my post is not really about setting up a carb, but instead about troubleshooting a nagging problem.  I've had limited money and time and was basically trying to troubleshoot by doing quick stuff to various areas to see if anything made any difference.  I intend on doing complete job on the carb, but it's only been about 5 days since I started, and the shop where I plan to cut out the mixture screws is 26 miles away.  I am taking all of your suggestions to heart.
-Gabe

[Cliff Ruggles]

Also keep in mind that getting good results involves exact precision with tuning, stick with the "recipes" exactly and use the one that meets your needs.

Also, it is manditory to use good parts.  Over the counter kits are still using up old stock.  They lack many parts required to do a complete/correct rebuild, and many of the parts will NOT last long in contact with ethonal and/or modern fuel blends.....Cliff

[jamesF]

I feel bad because I probably should have waited before making any posts on this forum because my post is not really about setting up a carb, but instead about troubleshooting a nagging problem.

Dont feel bad about that!
You are in fact trying to: "Diagnose a carburetor problem"
 

[batsong]

Thanks, James, for your comments.
I am getting closer to diagnosing this problem.  It turns out that my cam may be in wrong.
I'll let you know what happens!
-Gabe

[Cliff Ruggles]

One last thing to keep in mind during your troubleshooting and repairs.

Camshafts with a lot of duration and tight LSA's (Lobe Separation Angle) will allow quite a bit of unburnt fuel out the tailpipes.  This is due to both the intake and exhaust valves being open at the same time.  We can clean up the exhaust by allowing more fuel to be available for a cleaner burn, but it is not always possible to get rid of all the "rich" smell.

You never provided the exact cam specs, or where it was set up for ICL.  In any case, a 230 @ 050" camshaft in a 455 cid engine with apprx 9.5 to 1 static compression ratio is going to produce some smell out the exhaust. 

It can be minimized by fine tuning the ignition timing and A/F ratio at idle, but difficult to ever completely get rid of the smell.......Cliff

[batsong]

Thanks Cliff.  That maybe true as the lobe separation on this cam (Crower # 52241) is 112".  I am getting wash down the cylinder walls though.  The oil smells gassy after only one trip, but will not ignite readily.  I have not checked the compression yet.
The car runs great, but it smells like a gas station, as do my clothes after driving it.  I set the timing to 36" all in at 2000 rpm.  I tried dialing back the fuel pressure, even cutting it off, but there is no change.
I'll get to the bottom of this.  I've posted on another forum and researched seating rings, ignition, exhuast valves etc., and it seems to me it's a good car, just that there is something simple I'm missing.
Thanks again!  -Gabe

[batsong]

Just an update.  This morning I went out and took a look in the primary bores while the ngine was idling.  I'm getting big drips of fuel from the nozzles and with the slightest provocation, the accelerator pump quirts gas into the chamber.  It is very sensitive.  If I touch the throttle linkage without changing the rpm's, it'll squirt.  Both of these combined is resulting in gas pooling on the throttle plates.
Thanks again, Gabe