Choke problem?

Anytime my 72 riv starts after sitting for 4+ hours it takes a full 10 minutes to "warm up" (in the words of the previous owner). Until then it's without power and will pop and sputter, seemingly not firing on all cylinders. However, after it's "warmed up" once it'll run fine all day long.

My best guess is that this is some type of choke or carb problem. Thoughts?

BTW, i'm a noobie here and though not a pro mechanic I'm hoping to tackle issues like this on my own when possible.

 

This could be a choke issue, an ignition issue, if, for, example, something in the ignition got damp, or it could be an issue of the heated air cleaner not operating correctly. The fall and winter air is both cooler, and denser, requiring additional fuel, or heated air. ANYTHING causing a lack of vacuum at the flap will cause it to unload in the open position, leaning the mixture. It is also possible for the exhaust crossover to be blocked by someone seeking that last hp, and blocking the passage. This can be checked by touching the passage directly below the carb within about 30 seconds after a start. Be aware that, if the passage is not blocked, you could get burned.
The heated air cleaner can be checked by grabbing the snorkel, close to the air filter case, about 1 minute after a cold start. It should feel warm, but be prepared to get burned as well if is working VERY well. These sensors typically provide air at about 120-150 degrees. Let us know... Ray

 

I should clarify here that i'm in Hollywood, so the weather is still pretty nice, though it is about 20-30 degrees cooler at nighttime now. As for the other things, I grabbed the snorkel close to the filter case and it takes about 5 minutes to heat up and never got too hot to touch in the first 10 minutes that the engine was running. When I took a look at the air filter some of the rubber on the bottom was coming off but I don't think that's a huge issue. I think i'll probably get a K&N for it soon.

The other thing I found was odd was that there is a vacuum noise from the engine that turned out to be a tube with vacuum on it but no hose. I'm not familiar enought with the engine to know what it is and they won't let me post a pic till i post 10 times so i'll try and describe it. It's a index finger sized hole in a tube that's on the right side of the air cleaner but not on the air cleaner and just forward of where the hose on the air cleaner that connects to the valve cover is. Shouldn't this thing have a hose on it?

Another thing I noticed today while driving was that when I push the gas to the maximum power without kicking in the four-barrel it sometimes will lose all power and pop. It also does this if I give it a very small amount of power when I start from stopped. If I give it more gas it's fine.

 

Here's the picture of the hoseless vacuum hole:

 

Thanks smartin. I capped that opening.

I also took a look at the condition of the vacuum tubing leading to the carb and found that a lower vacuum tube leading from the front of the carb back to the manifold was medium stiff and easy to pull off of the front of the carb, so I put a hose clamp on it as a temporary fix until I can replace the tube. The bad news is that when I did this the tube running from my valve cover to my air cleaner broke (it was brittle and old), so i'll have to replace that soon too.

Here's the pic of the clamp I put on the front vacuum tube. It seems to have had an immediate effect on the performance of the carb so i'm happy for now. I'll see tomorrow if it's shortened the "warmup" time.

 

Looks like this helped the problem a bit but it's still taking like 10 minutes for the vehicle to run right after it starts up. Even if I just start driving it'll bog a bit until that 10 minutes is up.

 

Checked vacuum lines and followed to termination. Replaced one questionable line and all others seem okay.

Checked Fuel Filter and it was bad, like very bad. It had some grit in it, so i replaced it, bought a new fuel pump, and I plan on removing and boiling my tank today. After that's done i'm going to fill the fuel line with carb cleaner and let it set for about an hour then blow the line out with some compressed air. Am I missing anything here? I want to make sure the fuel system is CLEAN.

I've thought about removing the carb and cleaning it but am curious if this is a good idea for a first-timer. I've done a few motorcycle carbs but have heard that the Q-jet is very intricate. Advise on this? I certainly wouldn't mind taking this to somewhere in LA if anyone knows someone who's good, and the last thing I want is to take it apart and have springs fly everywhere.

Also, after this work i'm planning on checking timing and regapping the plugs. I checked one and it was at .042 and a little twisted, so i'm planning on doing them all.

For now, the car's running noticeably better than before but still seems to need the time for warmup.

 

Is the engine slow to start cold, and does it fast idle? Two things can cause this condition. Either the choke is not closing properly, or opening too fast, or the choke pull off is misadjusted, opening the choke too wide when the engine starts. Try this... With the engine cold, or not driven after about three hours, open the throttle either with your foot or your hand, and note the choke. It should close completely, especially when overnight cold. There should be some tension trying to keep it closed when you attempt to open it with your finger. Then try compressing the choke pull off with your hand, seating the plunger and note the choke opening. The distance should be about 1/8" between the choke blade and the primary opening. Before starting the engine, either using a vacuum pump of your mouth, try to open the pull off with vacuum. Not only should it open the choke smoothly, it should hold the vacuum with continuous vacuum applied. Many of these pull offs have a bleed valve incorporated in the system to allow the pull off to close the choke should the engine stall. We'll start there... Ray

 

Thanks for your response Ray. After checking this whole thing out I don't think that the choke is the problem.

At this point I've completed a lot of work. I removed the gas tank, had it boiled and coated at Burbank Radiator shop. At the back of the car there was another fuel filter that was full of grit so I removed it and put a straight hose there. I removed and replaced the fuel pump cause i'm guessing it was pretty contaminated with this grit just like everything else was. I replaced the fuel filter at the carb too.

I removed the carb, ripped it apart and cleaned the jeepers out of it. It was so full of brown stuff coming out that i'm guessing it was a miracle the car was running at all. I'm guessing that the carb was also tuned so that it'd run even with the dirty carb. One way or another the theme of this so far has been neglect.

At this point in time i've got the system back together and clean but I still need to get the carb tuned. My pops got me a full shop repair manual for the car and I haven't gotten it yet, but when I do i'm planning on giving the carb a fresh tuning and then working from there.

In addition to all of this I'm planning on checking timing next, but I really feel that my carb is **** and that I should just find a better example to clean and get on the car cause i've found some "rigging" on the carb from where a tab broke off that holds the rocker arm to the actual gas control at the front of the carb. Now that rod has had some wear on one side that I don't like.

As far as the running of the car, it runs way better now, but died twice when decellerating. It starts harder now, and takes the pedal to the floor to do so (making me think it's running too rich). It warms up in about 4 minutes now but still glugs a bit until warmed up. I'm guessing that the tuning and possibly a new carb would help all this out. I've also got the choke completely disengaged at this point in time.

I think i'm on the right track here, so thanks all for help, and if anyone sees anything screamingly obvious that i'm missing, then feel free to chime in.

 

"At this point in time i've got the system back together and clean but I still need to get the carb tuned."

http://www.cliffshighperformance.com/buy_book_2.html

This should help....Cliff

 

Nice! Thanks. Bought this book and since went through the carb once again, this time honing the accelerator pump area and re-examining components. Decided not to remove the idle tubes due to lack of skill level, but am leaning towards having a professional rebuilt or finding a new carb cause mine's obviously been rebuilt and seems to be in poor shape. For now though the car is driving much better than before. Still some problems starting and warming up.

 

Continuing work

Got Cliff's carb book in the mail and went through my carb again, this time going to a carb shop and finding a new top plate and installing a new acceletor pump with a blue rubber on it. I also bought and installed a new vacuum for the front side of the choke.

At this point i've got the carb running well, but i'm concerned that when I floor the pedal the secondaries don't jump in. After working with the choke-side linkages i've found that the secondary has a shutoff piece on the lower back choke-side of the carb. Is this controlled by vacuum and if so which one inlet/outlet on the carb and where do I get that vacuum?

I think after I can figure this out i'm good to go.

 

Depending on the carb you are using, there is typically a link, called an "upset tang" that keeps the secondary throttles from opening. This tang is pushed aside when the choke opens completely, and is operated by the choke thermostatic coil. Things that can keep the choke from opening include a leaking housing gasket, if you use that type of carb, an inoperative or bypassed heated air cleaner, or a sticking or mis-adjusted linkage. If you are using the choke housing type choke, the air coming into the air cleaner provides the initial heated air; the choke housing will not receive sufficient heat otherwise, and the choke will not open completely.
If you are using an open element air cleaner here, you might consider using an electrically heated coil. With the "divorced choke," it may be that the housing over the coil is missing, the crossover is not being properly heated, or, again, you might need to free or make adjustments to the linkage. The divorced choke system was more trouble-prone than the "integral choke," but the latter was not trouble-free either. One other thing to check with the integral choke system was the calibrated vacuum leak in the housing, which pulled in the heated air. If this passage became blocked, the resulting lack of air flow through the housing precluded the choke's unloading properly. Ray

 

Thanks for your response Ray. Upon further examination the linkage isn't engaging the secondary cutoff and needs adjusting. Just got my Chassis service manual and this process looks pretty extensive. I'm going to give it a shot anyway.

On a side note I went to the valley and found a 72 electra for a couple parts. When I forced the trunk open I found a bag of GM NOS hoses, clamps, and a full set of wood handled Craftsman tools. A fun find.

 

Finally killed this problem with a big hammer!

Got a rebuilt carb from Burbank Carburetor. Costly, but it was well worth it. After I got done installing it, the car ran a bit better, but still not the best so I decided to keep looking.

Next thing I checked was the distributor. Took it out and found all the bushings gone and the vacuum advance plate rusted so it wouldn't move! I then installed a new distributor, cap, rotor, wires, and plugs. Gapped the plugs correctly and set timing, dwell, and idle speed with a timing light, dwell meter, and tach meter and now she's running better than ever! Finally it'll smoke the tires down the street!

The other thing I did was advance the timing just a bit to compensate for timing chain loosening and that helped the performance a bunch.