Troubleshooting a Rochester Quadrajet...need help!

[ClydesdaleKevin]

I started a new thread because its not quite related to my last one, Bad Rebuild From Holley, and I couldn't find the answer searching around the site.

Here is what we have and the weight we pull:  1977 27 foot Itasca on a P-30 Chevy chassis, with a 454 big block, and a Turbomatic 400 transmission.  Not sure of the gear ratio on the rear end.  We are pulling a fullsize 2000 GMC 2500 Savannah van behind us, loaded with our workshop etc for the business, with a total weight just shy of 7000 lbs. 

When we first bought the Itasca around 5 years ago now, we were pulling an even heavier 1985 Dodge van, loaded with even more crap, for an even higher total weight.  The RV drove fine, we got great gas mileage, around 7-9mpg on the highway on average, and lots of power up hills.  I kept it around 55-60mph for the best gas mileage, but she wanted to go faster, and I could pull all but the biggest hills at 55 without downshifting and with no problems.

Over the years the original carburator just wasn't running the same, less power more than anything, and wanting to stall at traffic lights, so I went to change the fuel filter in the carb and discovered that a previous owner had cracked the carb body at the fuel filter and patched it up with something like JB Weld.  I couldn't get it to reseal and it was leaking fuel everywhere, so I ordered a "new" rebuilt carb from Summit Racing, professionally rebuilt by Holley.  It was a crappy rebuild and problematic from day one, but really got bad on our way out to Arizona from Florida.  It started dumping gas into the manifold, wanting to stall even at normal highway speeds on flat roads, and we limped into Arizona barely keeping it running.

I found some great mechanics in Arizona, and they took my old carb, which I saved, and the rebuilt carb from Holley, and Frankensteined a working carb from the two, using new gaskets etc.  They tuned it in the campground for me, and all seemed well. 

Then we got on the road today.

At first it was running great!  As good if not better than when we first got it!  On the way out here we were only towing a 5x8 trailer loaded with our stuff, probably weighing 2000 lbs or less.  And it could barely handle that. 

We left Apache Junction, and that area is fairly flat.  Small hills and gentle grades, and I drive slow anyway.  We left on I-10 headed east.  It was running great!  Drawing a good vacumm, maintaining 55mph without holding the peddle down far, and all in all running as good or better than it used to when we first got it.

Then we started hitting the big hills around Texas Canyon, AZ.  Trying to maintain 55mph meant flooring the pedal...and then I started getting what I thought was vapor lock.  If I released the pedal and then floored it again, it came right back...but there was this one constant point that it would bog, when the RPMS were just at the right point and the pedal was pushed down to just the right point.  It took me a while to realize that it would bog once the secondaries opened.

I pulled off the highway to check things out when the fan was on for what I felt was too long a time, and it stalled.  I was able to drift off the road, so I checked everything out and all seemed fine.  Fluids were fine, not too much heat coming off the engine, etc.  But she wouldn't restart.  The starter would turn...I heat shielded the crap out of it after going through 2 starters on the way out here...but she wouldn't catch.  Again I thought it might be vapor lock from heat, but when I tried to start it with starting fluid, it took a while and I then realized that it had flooded out!

She finally fired up, cleared out the extra gas, and it was back on the road.

The roads flattened out a bit, and then we hit more big hills, long grades heading into New Mexico.  Since this was a new carb, I had to relearn its ideosyncracies.  As long as I don't have to depress the gas pedal very far and keep the speed low, its fine!  55mph it runs great, unless I come to a steep grade.  As long as I don't push down the pedal enough to drop the vacumm below 5 on the guage, it runs like a champ, even if that means dropping the speed down to 50, or downshifting on very long grades and doing 45 or even 40.  If I push the pedal down beyond that point, it starts to bog, acting like vapor lock, and if I let it stall, it takes starting fluid to bring her back to life, but not easily.  It is definately flooding when the secondaries open up.  Once she starts back up, she runs just fine, AS LONG AS I don't give her too much gas. 

And we have El Paso coming up, with the steepest hills on the trip!  We pulled in for the night at the Flying J in Lordsburg, New Mexico, 300 miles into the trip.  We haven't topped off the gas tanks yet, but we are still running on the front tank, so that means we are getting a respectable 6 mpg at least, so overall the carb rebuild is much better than before the rebuild, but its not right!

I'm going to call my mechanics in the morning and see if they can walk me through troubleshooting the new symptoms.  Maybe there is a way to adjust when the secondaries open...maybe they are opening too early?  Or maybe Summit sold me the wrong carb with too high a CFM rating?  I have no idea what rating the original carb had.  And the mechanics only used the top plate off the original carb...the one from Summit was toast to begin with...but they reused the Summit/Holley rebuild main body and lower body plate. 

I think the ultimate solution is just to get a NEW Edlebrock made for this big block, the one they make for best fuel economy with all the adapters, but we don't want to spend too much in case something else goes wrong on the trip.  We have a decent amount for the trip, but the buffer isn't all that high.  Once we get to Georgia I can invest the money during the show, but not right now if it can be helped.

Oh yeah...it might not mean anything, and I'll update this in the morning once I top off the tanks, but when we pulled off the exit for the Lordsburg Flying J, after pulling the steep upgrades at low speeds and downshifting with no problems beyond a low speed and having to use the flashers, she stalled out trying to make it up the hill from a standstill at the exit.  I had to pull the doghouse and air cleaner cover and literally run her up the hill using the fluid!  I switched it to the back tank halfway up the hill, stilll spraying in the starting fluid, and at the apex of the hill the motor came back to life and we drove the rest of the way to the Flying J on the back tank with no problems.  Its possible we simply ran out of gas in the front tank at just that moment...and I'll know for sure when I fill the front 50 gallon tank in the morning.  It was getting close, being just at 300 miles, to being empty if we were getting 6mpg.  It was only another mile on the back tank, which is running the genny right now as I type this.

So those are the symptoms, the history, and what we have and tow.  If anyone is very familiar with Quadrajets and can give us an opinion on the troubleshooting of the symptoms it would be very much appreciated!  I'll call my mechanics in the morning and ask them too...I didn't want to disturb thier Easter, and it will wait until morning.  I'm really hoping its just a simple adjustment!  Like when the secondaries open, or mixture etc. 

Worst cast scenario, I can disconnect the van when we get to the really bad hills near El Paso, reconnect the driveshaft, and have Patti drive that over the mountains carefully while I drive the unloaded RV up the mountains, but that would suck!  I want a non-stressful easy trip after the last one from hell!  Worst worse case scenario is pull into an autoparts place and see if they have the right Edlebrock and adapters, but that is money we really can't afford to spend right now, and time we don't want to waste if possible.

Help us out with your knowledge if you can!

Kev and Patti

[tiinytina]

hey ho. clueless and put a call into my mechanic but he's busy...
but started googling

http://www.mako.com.au/buick/html/qjet_tips.htm

http://www.bob2000.com/carb.htm

http://www.arkansaspontiacs.org/techstories/RockyQ-jets.htm

http://www.florida4x4.com/tech/quadrajet/500cid.com/Quad.htm

http://www.realoldspower.com/phpBB2/viewtopic.php?p=397184&sid=8550f62b4a765784bcd30910166f240a

just glancing at a few of these sounds like it may be your accelerator pump.... but like I said i'm a clueless wonder on carbs...

Tina

[ClydesdaleKevin]

Problem solved!  After reading the whole 78 page Quadrajet manual that someone so graciously posted, I decided that the secondaries weren't opening at all or very little for some reason.

After talking to my mechanics I determined that there is a little cam under the choke that contacts a small rod on the end of the secondary throttle valve shaft.  It is supposed to be a safety lockout to keep you from being able to really rev up your engne, ie. open up the secondaries, until the engine is warmed up.  Because the carburator is a Frankencarb, it didn't quite disengage after the choke opened. 

Simple low cost solution!  I just bent the rod out of the way...and now have full power again!  No bogging, no flooding, great vacumm unless I homp on it, and then it goes right up the hills at 55 pulling the van.  NOW its running better than when I first got it!

The primaries deliver fuel and air at lower demands and idle.  When there is more demand, the primaries deliver even more fuel, AND the secondaries open up with thier own metering rods and jets, delivering even more fuel, and even more importantly to keep it from flooding, a lot more air! 

Problem solved! 

Then it was back on the road again!

And then we had two more unrelated non-engine problems that I'll put in my On the Road to Georgia post.

We made it as far as Los Cruses, NM...and are stuck at a rest stop for the night...but that's another story!

Kev

[DaveVA78Chieftain]

Your welcome for the Q-book
That lever is a secondary lockout adjustment, pdf page 38, Fig 11.

Also, did you make sure all the carb adjustments are correct?  As you discovered, the little things can bite you big.  BTW, that 5Hg vacuum point is where the power mode kicks in.  Holley uses a power valve.  Quadrajet, Edlebrock, and Thermoquad use a power piston/spring arrangement.  Vacuum falls off (under heavy engine load or heavy pedal) and the spring pushes the piston up pulling the rods out of the jets.  If enough pedal has been applied, the throttle linkage opens the sec throttle plates allowing manifold vacuum to act on the big air valves (top of carb).  Manifold vacuum overrides air valve spring presssur allowing them to open up.  The air valves create a low pressure area  that allows gas to be pulled from the secondary jets.  All these things have to be adjusted so that the carb reacts properly.

Here is a 10 page Q-Jet T/S document.  Based on component failure but gives the symptoms for the component failure.  You may have to find the symptom to find the failed component.
http://www.florida4x4.com/tech/quadrajet/qjtshoot.pdf

Accessed through here (more info):
http://www.florida4x4.com/tech/quadrajet/index.php

Dave

[ClydesdaleKevin]

LOL!  After reading the manual, I actually understood all of that!  And thank you VERY much for posting the link to the manual.  It was invaluable!

Kev

[GWINGER]

Type "Quadra Jet rebuild" in your search engine and a lot of free info comes up.
J