Another Carb problem (sigh)

[Stripe]

Okay, when taking pics looking for ID markers, I discovered this tube.  I think it has rusted through.

Here is a pic or the tube.

I think that is a hole in the green circle.

The tube itself comes from this...

And goes down into the engine.

Can anyone tell me if this is a hose for vacuum, or is fuel supposed to be going through this.


Thanks for any help.

Fredric

[ClydesdaleKevin]

I know this one!!!   

Your carburetor uses a "hot air" choke.  That tube goes from the manifold to the choke and introduces hot air to the choke so that it will open when it warms up.

Same setup on my old 77 Itasca.

Not sure if the hole in the tube will hurt anything, because I don't know if the tube goes into the manifold vacuum section.  If it does, then it will be a vacuum leak you'll have to deal with.  But I don't think it goes into the manifold vacuum section, since the choke isn't sealed vacuum tight.  Not sure though.

Kev

[DaveVA78Chieftain]

There is no vacuum on the heat tube.  It simply provides a path for heat to be directed to the bimetal coil in the choke assembly. You can either replace it or convert to electric choke.
http://www.ebay.com/itm/JET-Performance-Electric-Choke-Conversion-Rochester-Quadrajet-with-Heat-Tube-Kit-/390609024600?pt=Motors_Car_Truck_Parts_Accessories&hash=item5af21cb658&vxp=mtr#ht_1438wt_978

Dave

[Stripe]

Okay then, I will have to research this, like how does the electric choke know when to adjust when the old one used hot air.  Is there a thermostat, etc.. 

Thanks a lot you guys..  I do appreciate the help!

Fredric

[DaveVA78Chieftain]

Electric choke is a timed function not a temperature function.

Dave

[Stripe]

So what sends the signal to the electric choke to tell it to do its thing?

[ClydesdaleKevin]

Ignition positive.  You'll have to run a wire to the choke from a positive ignition source (12 volts + when key turned on).  Since you have a hot air choke, there won't be a wire already, so you'll have to run one if you plan on converting to electric.  Nothing wrong with the hot air style though, so if it ain't broke, don't fix.  In other words, if your choke is functioning, opening when warm, leave it alone.

Or get an Edlebrock and be done with it...lol!  Rochester Quadrajets are arguably the best carb ever made, IF all is working perfectly and adjusted perfectly...and there ain't nothin' simple about setting them up right.  After much trial and tribulations, we went with a simple Edlebrock 1411...I just couldn't wrap my head around the QJ and finally gave up.

Kev

[Stripe]

Ok, not sure yet if choke is opening when warm, but I do know that what I took a snap of is indeed a rusted out hole.  I have a bead on a rebuilt Carburetor for US$178 from http://www.guaranteedcarburetors.com/category/CTMH/CHEVY--GMC-TRUCK-and-MOTORHOME-8Cylinder-4-Barrel-Carburetor/1.html  which has THE lowest price I found on rebuilts and It's not far from Mark, lol. I remember the one I got for the Coachmen and it STILL runs like a bear, (Right now it's more like whinnie the pooh, but as soon as I put a voltage regulator back in there, it should go straight to Kodiak maybe even Grizzly level). So, what I think I might do, is see if I can find a source for new tubes, if not, I will figure out where there is a ignition engaged +12v power source.  Again, thanks!

Fredric

[ClydesdaleKevin]

If it works out, great.  Otherwise, get an Edlebrock.  We LOVE ours...or at least I do.  Patti could care less as long as it runs well, we get decent mileage, and I'm not under the doghouse constantly trying to adjust things...lol!

Kev

[RockwoodMike]

On your intake manifold, there is a passage for exhaust gasses to pass back and forth from the left bank of the engine to the right..It is just like a tunnel leading to exhaust heat from the exhaust ports..This helps the carb to warm up and helps the engine warm up faster..That tube of yours is right in the middle of that tunnel.. it gets hot from the exhaust..In your picture that shows the black cover with "carburetor"..that has in it a curled up spring and it is attached to the choke cover shaft..it snaps the choke close when the engine is cold..As it heats up, either with air heat or electric current, the spring grows longer and it rotates the shaft of the choke plate, slowly opening the choke as the engine warms up..

To draw air into that area where the spring is, there is a direct manifold vacuum passage..but it is a very small vacuum passage...  pin hole size...and it sucks in warm air from that tube..to heat the spring... to open the choke as the engine warms up.

Your tube is broken..so it doesn't draw in as much heated air from the manifold and so it takes longer for that spring to heat up and open the choke plate..That wastes gas!!..The sooner the choke opens up and your engine warms up, the better for gas mileage..Because if the choke plate doesn't open up all the way after the engine is warm, it dumps excess gas in..and the engine can't get enough air to breath..

The problem is finding a tube that can replace your broken one..That's why it is easier to convert it to an electric set up and eleminate that tube all together..When you turn your key on , 12 volt power starts to warm up that spring..

You either find a cap to close off that tube or put a drop of epoxy glue inside that area that has the spring..to plug up that vacuum leak at that pin hole size port..

[Stripe]

Great info guys. Okay, so in the meantime would it be okay to temporarily plug the hole till I get a new choke?  I sent an Emilio to the carb guys to see if they have or know of a source for the tubes. If so I will just replace the tubes. Otherwise I'll get that electric conversion.
Again, thanks!

Fredric

[RockwoodMike]

I would not plug that tube up..just leave it as is..Because if you plug the tube, then no heat gets to that spring..At least right now, you are getting some heat. Until you get a new tube or convert to electric choke setup..just leave it alone..But in the mean time,  just understand that it is taking longer for that choke plate to open than it is designed to do..

I think that it is better to go the electric route..the problem with the tube system is in side of the tunnel were exhaust gasses pass, it builds up with carbon and soot and pretty soon it just doesn't work very well because it (the tunnel) gets all plugged up and no heat really gets moved through there..But the electric system will always open it up (the choke)..

The engineers that designed the engine, put that tunnel near where the carb is to help the carb warm up faster too..When the carb gets warm, it helps with preventing icing and it warms the fuel in the float bowl to help it burn better on a cold engine..

The problem with the tunnel with all of the exhaust heat, is after the engine is hot, it over heats the carb ..causing the fuel to boil off and dieseling in extreame cases...

[RockwoodMike]

That Ebay link that Dave gave on the third post of this thread is the way to go..You drill out those rivits and tap a thread into the holes where the rivits where with the given tap..Then I would cut that tube where there is about an inch left from the carb and with a pair of vice grips, just pinch that tube tight to close off that vacuum leak..

[Oz]

... I have a bead on a rebuilt Carburetor for US$178 from http://www.guaranteedcarburetors.com/category/CTMH/CHEVY--GMC-TRUCK-and-MOTORHOME-8Cylinder-4-Barrel-Carburetor/1.html  which has THE lowest price I found on rebuilts and It's not far from Mark, lol...

If you do go that route or get something from G-teed Carbs, LMK.  I can pick it up and send it to you.  It's right on one of my daily routes home.

[Stripe]

Hehe , groovy,  thanks  Mark! I'll let you know!