Stab

Heya guys. I am new to the forum but have been lurking for a while now. I recently inherited my grandmothers '83 2wd pickup she bought brand new right around the time I was born. It has been mostly sitting in her garage for the last 15 or so years. It has a 22r, automatic and only 78,800 miles. I started using it for a work truck and am trying to clean it up and fix things as I have time.

The old carb had some problems so I bought the Weber 32/36 kit and installed it last weekend. Since then it has been backfiring/popping while decelerating. I first noticed it on the highway after letting off the gas after I got up a hill. It only seems to be a problem when the throttle plate is completely closed. I can also make it pop a bit if I rev it up and dump the petal in neutral.

Today I installed an inline fuel pressure regulator (set to 3lbs), checked the valves, checked ignition timing and messed with the idle and mix screws a bit. I am running out of ideas here so I am turning to the interweb for some ideas. When I had the timing light out I noticed it was missing every now and then. I did just replace my plugs, wires, cap and rotor so the next place to go on that front would be the points or the coil pack.

Also, just for the sake of being as complete as I can be, Ill add that all the emissions junk is still on the truck but not hooked up, including the egr stuffs. The only other problem with the truck that I have found is a nasty exhaust leak where the manifold connects to the pipe.

Any help would be greatly appreciated. Thanks!

83

Well, a couple things I guess. You don't have points. And by "messed with the idle and mixture screws", do you mean you followed the Weber tuning instructions, or you just randomly played with them?

Having emissions stuff hanging around, possibly connected or possibly half connected or whatever throws a real big unknown into the equation.

Knowing whether you followed Webers tuning instructions will help. There's also a thread here from maybe a year back, filling in the holes in those instructions with some specific tricks.

Stab

I did follow the Weber instructions. I mostly just moved the mix screw a little on the lean side and increased the idle to see if that would help. It did not so I moved them back.

I am working on it again today or tomorow and plan to get rid of all the emissions stuff I can and really carefully check for vac leaks. Might end up ordering a couple things from LC like the egr block off plate.

Thanks for the reply! and I just assumed it was a points ignition so thanks for clearing that up for me.

I gotta say, even with a few little problems, it is so awesome working on a vehicle with no computer BS on it. I am really loving this little truck.

Stab

Alright, I think I have figured out what the problem is. This whole time I thought that it ran rich when the throttle plate was closed but it looks like it is just the opposite. I can move the mix screw about a half turn with no noticeable difference at idle to I set it on the lean side. I noticed that when I had the choke out a little (manual choke) the problem went away which made me think the engine was actually running lean. The popping almost completely went away when I moved the screw out a bit. I live in downtown Seattle so it is hard to adjust a little and hit the freeway over and over again so I will have to wait till I go to work on Monday to play with it any more.

83

Nice. Let us know how it goes.

I had problems with mine popping on decel, and pulling the manual choke out a bit made it go away on mine, too. Tried a lot of adjusting, and using the choke was the only way I could get it to go away.

Since then I've had the head rebuilt, and when I put it all back together and adjusted everything...no more popping. I dunno.

gillesdetrail

iTrader: (1)

Make sure the idle speed screw is not turned it more than it should in the instruction manual, else it will cause fuel droplets to leak in the manifold causing poor idle and popping on decel, mine was too rich and there is no more popping in the exhaust now that I leaned it downed on the idle mix screws.

Stab

Thanks gilles but I have already been down that road.

Looks like I have figured it out though. Tuning the carb did help quite a bit but did not solve the problem. I rechecked the ignition timing today and noticed that it did not advance at all when I plugged the vac line back in. It would, however, advance when I gave it some gas. People seem to have very different ideas about what the timing should be but I am sure it should not sit on 0 with the vac line plugged in. I tried to compensate for it by setting it at 5*. The popping is so faint now that I really have to try to make it happen and probably would never have noticed it to begin with. My guess is that the vac diaphragm has started to leak. If a new diaphragm doesnt fix it, Ill just run it at 5*. It is actually running better than it ever has at the moment and it seems like about half of you guys are running yours at 5* anyway.

Again, thanks for all the help!

Bingle

Hopefully a new vac diaphram fixes everything up. I believe that you should be at about 5° without vac at idle and 8°-10° at idle with vac advance hooked up. If you have a delay timing light your total advance at 3000 rpm+ should be 36° IIRC.

These distributors have a mechanical advance as well as a vac advance so when you rev it you're likely just getting the mech part of the advance or partial advance from the vac. Get a new vac advance and re-time and you should have that truck purring like a kitten.

P.s. I grew up in Lynnwood so I know all about the Seattle/I-5 PITA. I don't miss it at all.
Good luck

jimbyjimb

iTrader: (1)

Your problem is most likely a lean fuel mixture in the idle circuit. Popping through the exhaust on decel is textbook lean. If you haven't jetted your 32/36 they pretty much always need bigger jets for a 22R. It can still be lean after correcting your timing and it's most likely so subtle it's harmless, but jetting is always necessary in my experience.

Your timing was also incorrect which doesn't help. Base timing is 5 degrees advanced. Better is 8-10 degrees advanced. Vacuum advance does nothing at idle OR wide open throttle. Vacuum advance only operates during a low to mid throttle cruise situation to increase fuel economy. If you are getting vacuum from your line to the distributor at idle your idle speed is too high or you are hooked up to the wrong vacuum port. In fact, any factory procedure will have you remove the vacuum line from the distributor and plug it while setting your base timing. I say again, you should have ZERO vacuum advance at idle if you are tuned properly. You might be able to make it run decently that way, but it is not how it is designed to work.

The mechanical advance does all the work operation-wise, the vacuum is there as a low to mid-throttle cruise fuel efficiency supplement and it is NOT required to make an engine work and run properly. It's just a good idea to have if you like saving dough at the pump.

Bingle

Jim is most likely 100% correct on the vac advance at idle, I've been running a mechanical only distributor for the last 10 years or so (DCOE's have no vac port). My memory is a little fuzzy on that. Was under the impression that you unhooked the vac advance when you time it because it does advance a few degrees at idle, but I could be mistaken.

I do agree with his statements about re-jetting the carb for sure.

jimbyjimb

iTrader: (1)

I am unaware of any passenger vehicle past the early 50's, sold in America, that used any vacuum advance at idle. Some old, old cars use only vacuum, but that system never caught in vogue. My guess is simply that weights and springs are more reliable than 1940's and previous vacuum tube and diaphragm material. Could have been to simplify the tuning process. I'm unsure.

In any case, feel free to follow the procedures from the shop manual, which will tell you to remove and plug the vacuum advance line before timing. If your carb settings are correct, this is an unnecessary but wise precaution. The factory makes its manuals for monkeys to use. That's why I like factory manuals.

Anybody have a banana?


This guy drops the edjumakayshun juice more precisely than I'd ever care to:
http://www.camaros.org/forum/index.p...ic=2680.0;wap2

83Toyota88

iTrader: (1)

So when you say the jets need to be larger are referring to the idle jets on the outside driver and passenger side of the carb or the jets inside the carb?

jimbyjimb

iTrader: (1)

Weber has a tuning procedure:

http://www.carburetion.com/Weber/adjust.htm

There are idle jets, main jets and air jets. Search Carbs Unlimited in the link above for detailed descriptions on how to tune a Weber and how a carburetor operates.

Howstuffworks.com is also a useful resource for basic info on how things work. I use it all the time.

Engine tuning is a scientific process. Not an obscenely complex one, but oscientific none-the-less. Doing it right requires a combination of knowledge and experience.