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I recently rebuilt a 22r and I deleted 100% of the emissions items with block plates and plugs. I'm trying to determine exactly which basic element of the emissions system I could selectively choose to reinstall just to eliminate this slightly obnoxious exhaust popping. It pops from the tailpipe when you're engine braking. It's really not too big a deal but it would be nice to have it silent again as it was before. I have a good cat converter and muffler and fully solid sealed exhaust system which was not popping like this at all before the rebuild.
I'm thinking that perhaps I could reinstall one of the minimum "Air Suction" systems to cure this. The one pictured here is from 1983/1984 Federal and Canada trucks. Later years and California trucks had more elaborate Air Suction or "Air Injection" systems - some with those large belt driven smog pumps. Perhaps this minimal setup could silence the exhaust popping? This is a guess on my part though. I'm guessing this because perhaps the exhaust needs a bit of fresh air added to it to eliminate the symptoms I'm experiencing? Does anyone know for sure the cause of this exhaust popping and how to cure it?
Perhaps the exhaust popping can be corrected through another element of the emissions system other than possibly the Air Suction system? Such as the Deceleration Fuel Cut? Or the Mixture Control Valve?
Is the problem when you just let off the throttle while coming to a stop or when you are actually using the engine to slow down like when you're going down a hill?
Does your carb have a working dashpot?
Is the problem when you just let off the throttle while coming to a stop or when you are actually using the engine to slow down like when you're going down a hill?
Does your carb have a working dashpot?
My carb did not have a dashpot previously. So we can rule that out.
The popping is most pronounced and audible when slowing down and actively downshift/engine braking down through 3rd, 2nd, and 1st gear. It is also mildly audible just when you let off the gas pedal and are coasting while in 5th gear. When you are actively applying gas and driving along it sounds perfectly fine.
For example, if I were to coast down a hill at like 45mph and I put the tranny into 3rd gear and engine brake down the hill the tailpipe would be popping like mad. As soon as I apply a bit of gas it goes away. And if I shifted into neutral and coasted down the hill it also goes away.
I'm not a tuning guru, but I would suspect that your carburator tuning needs to be changed after removing the emissions junk.
Maybe your idle mixture?
How is your idle speed?
Have you checked your plugs to see if you are running rich?
I'm not a tuning guru, but I would suspect that your carburator tuning needs to be changed after removing the emissions junk.
Maybe your idle mixture?
How is your idle speed?
Have you checked your plugs to see if you are running rich?
I'll check out the plugs. I have 2 1/2 turns out on the mixture screw which I have heard somewhere along the way is the factory standard setting.
Are you saying that exhaust popping/cracking/snapping is not normal after doing a full desmog? Does everyone who does a full desmog experience this exhaust popping upon engine braking/deceleration? Or is it just me?
I'll check out the plugs. I have 2 1/2 turns out on the mixture screw which I have heard somewhere along the way is the factory standard setting.
Are you saying that exhaust popping/cracking/snapping is not normal after doing a full desmog? Does everyone who does a full desmog experience this exhaust popping upon engine braking/deceleration? Or is it just me?
"Factory standard setting" aplies to "with all the emissions junk".
I don't know if the popping/cracking/snappling is normal or not after a desmog.
I am just assuming (and correctly I think) that the carb is tuned to account for the smog control equipment and if you mess with one you should mess with the other as well or take what you get.
EGR valves recirculate exhaust gasses through the intake, so it will mess with your mixture if you delete it.
I have never done an emission delete, I figure if it runs right don't mess with it.
I also don't buy California emissions vehicles, (not many up here in Alaska anyway)
"Factory standard setting" aplies to "with all the emissions junk".
I don't know if the popping/cracking/snappling is normal or not after a desmog.
I am just assuming (and correctly I think) that the carb is tuned to account for the smog control equipment and if you mess with one you should mess with the other as well or take what you get.
EGR valves recirculate exhaust gasses through the intake, so it will mess with your mixture if you delete it.
I have never done an emission delete, I figure if it runs right don't mess with it.
I also don't buy California emissions vehicles, (not many up here in Alaska anyway)
If you've ever done an engine removal, rebuild and reinstall of a 22r motor then you might also omit all of the emissions equipment. To me it didn't feel right to bolt on dirty emissions equipment with well over 250,000+ miles on it to a brand new motor. It also didn't feel right or necessary to buy all brand new emissions equipment. Mostly because most of it doesn't exist new anymore. And it's incredibly nice to have a very clean and simple engine bay on these old trucks. It makes maintenance easier and makes troubleshooting any issues much easier. I also do not live in a state where these items are required. So it made perfect sense for me to eliminate it all. I can always add things back on should I decide there is a particular need for a certain element.
Maybe many people do not notice or care about this exhaust popping/cracking/mild backfiring/afterburning whatever you want to call it because they use their rigs for for off roading and don't care about the exhaust noise? Mine is a daily driver street rig so I'd like to try to get it to quiet down. Someone on here must have knowledge about this topic.
Yes I meant to say let the throttle slam closed. Open the hood, and work the throttle by hand. It will probably sound more like a muffled popping sound.
If you've ever done an engine removal, rebuild and reinstall of a 22r motor then you might also omit all of the emissions equipment. To me it didn't feel right to bolt on dirty emissions equipment with well over 250,000+ miles on it to a brand new motor. It also didn't feel right or necessary to buy all brand new emissions equipment. Mostly because most of it doesn't exist new anymore. And it's incredibly nice to have a very clean and simple engine bay on these old trucks. It makes maintenance easier and makes troubleshooting any issues much easier. I also do not live in a state where these items are required. So it made perfect sense for me to eliminate it all. I can always add things back on should I decide there is a particular need for a certain element.
Maybe many people do not notice or care about this exhaust popping/cracking/mild backfiring/afterburning whatever you want to call it because they use their rigs for for off roading and don't care about the exhaust noise? Mine is a daily driver street rig so I'd like to try to get it to quiet down. Someone on here must have knowledge about this topic.
I can understand the motivation, I am convinced that any engine smog legal or not can be dialed in with proper carburator tuning and your issue should be correctable even if it requires a different carburator due to the emissions removal.
popping in the exhaust sounds like you may be running rich and unburnt fuel is igniting in the exhaust pipe.
I would bet that someone good at dialing in a carb could work wonders with it, I can rebuild them all day long, but getting them to run just right is an art that escapes me.
I can understand the motivation, I am convinced that any engine smog legal or not can be dialed in with proper carburator tuning and your issue should be correctable even if it requires a different carburator due to the emissions removal.
popping in the exhaust sounds like you may be running rich and unburnt fuel is igniting in the exhaust pipe.
I would bet that someone good at dialing in a carb could work wonders with it, I can rebuild them all day long, but getting them to run just right is an art that escapes me.
Well there is only one adjustment screw (the mixture screw), on these carbs so it shouldn't be too hard. I have adjusted it in the method that you are widely advised to adjust a carburetor mixture screw - 1: Adjust the mixture screw to wherever you get the highest idle. 2: Then adjust your idle screw for the appropriate idle of about 700 RPM. That's it. Following this method put the mixture screw at about 2 1/2 turns out on my truck.
Ok you know what, scratch what I said before about 2 1/2 turns out on the mixture screw. I just went back and really took my time and paid close attention. It took a full 5 1/2 turns out to get the best highest idle speed. With the idle screw out this far the exhaust popping is hugely diminished. It's still there but minor enough now that it's not really much of an issue. It's a big difference. If I go all the way down to only 2 turns out on the mixture screw the exhaust pops and crackles on deceleration something wicked. I never would have guessed this but it is an overly lean mixture that is causing the popping and a richer mixture cures it. I'm going to have to research this because I also would have assumed that such a thing would be caused by an overly rich mixture. I'm glad that I don't have to reinstall any of the archaic emissions equipment to solve this.
This reddit post explains exhaust popping from running lean real well. Total news to me. Glad to learn it. 5 1/2 turns out on my mixture screw does seem like a lot though. Possibly I need that much because of an intake leak...
This reddit post explains exhaust popping from running lean real well. Total news to me. Glad to learn it. 5 1/2 turns out on my mixture screw does seem like a lot though. Possibly I need that much because of an intake leak...
That link does make sense, if you don't find an intake leak or similar you only other adjustments would be to rejet the carburator (or maybe adjust the choke). I have always left that to someone who knows what they are doing better than I do.
But, once again, that carb was set up to run the engine with the smog stuff.
If you have any hesitation or any other indicators of lean/rich conditions (fouled plugs, pinging/clatter under load, hard starting, sooty exhaust etc.) you should get with a carb guru since you mixture screws only adjust the "idle mixture" and the mixture at all other throttle positions is controlled by the jets adding more fuel to that idle mix as the throttle opens.
If anyone knows better please correct me, but get out the crayons and explain it to me!
That link does make sense, if you don't find an intake leak or similar you only other adjustments would be to rejet the carburator (or maybe adjust the choke). I have always left that to someone who knows what they are doing better than I do.
But, once again, that carb was set up to run the engine with the smog stuff.
If you have any hesitation or any other indicators of lean/rich conditions (fouled plugs, pinging/clatter under load, hard starting, sooty exhaust etc.) you should get with a carb guru since you mixture screws only adjust the "idle mixture" and the mixture at all other throttle positions is controlled by the jets adding more fuel to that idle mix as the throttle opens.
If anyone knows better please correct me, but get out the crayons and explain it to me!
Do you (or anyone else) have any idea if these stock Aisin carbs came with different jet sizes from the factory depending upon where they were sold? Or did they all come with the same jet sizes in every state? I did buy this truck in Washington State and I now have it in Maine.
I think that you are partially right about the mixture screw. The slow jet is always being drank from by the carb at every throttle position. But only so much fuel can travel through that small jet. At idle it is only the slow jet being used. At any other throttle position it is the slow jet + the main jet. So the mixture screw and jet size of the slow jet does effect performance at all throttle positions, not just idle.
If you want to tinker you can get a couple of spare jets and carefully drill them out slightly over sized. They're brass, so easy to drill. You'll need a numbered drill set with finer size steps than the normal hardware store boxed set.
Back in the day (70's), I've decreased the jet size (for high altitude operation) by filling the hole with solder (solder bonds well with brass) and then redrilling it to a smaller size.
If you want to tinker you can get a couple of spare jets and carefully drill them out slightly over sized. They're brass, so easy to drill. You'll need a numbered drill set with finer size steps than the normal hardware store boxed set.
Back in the day (70's), I've decreased the jet size (for high altitude operation) by filling the hole with solder (solder bonds well with brass) and then redrilling it to a smaller size.
I have a pack of main jets for my motorcycle that range from 90 to 140 in increments of 2.5. The difference in size between one to the next is barely visible to the naked eye. Yet one size difference hugely effects performance. I definitely won't be taking your advice. haha Maybe I'm wrong but it just doesn't sound like I could do it accurately. But that's cool you used to do that.
An interesting note is that with all of the emissions equipment installed it hides this exhaust popping on deceleration. The Air Suction, Fuel Deceleration Cut, and Mixture Control systems definitely eliminate this popping caused by running too lean. Before I rebuilt my motor I had been experimenting with unplugging some of the emissions equipment and seeing how the truck behaved. Just out of curiosity really. And I remember the exhaust popping after unplugging the Air Suction system. This is why I instinctively thought that the emissions equipment was needed to cure this. When in fact it was actually a simple too lean condition with the motor. So while the emissions equipment arguably is useful and helps the engine run more efficiently, it definitely clouds things and can make tuning the motor itself more difficult.
06-06-2019, 09:50 AM
