Getting rid of the catalytic converter...will that cause problems?

Maintenance/Repairs
41

Jad2007, there are a lot worse issues out there than the converter on your car, or the lack of one. You are not going to have someone from the Feds coming after you if you can the converter. A shop won’t do it, but you can.

Cars of this era, both domestics and Asian, were bogged down with computer controlled carburetors, air injection, miles of vacuum hose, thermovalves by the case, etc. and often there were so many problems due to this stuff, and coupled with the de-tuned state of the cars anyway, a converter problem is a minor issue.

If you wanted to spend some time doing it you could remove most of those vacuum valves, hoses, air injection, computer controlled carb, etc. The carb could be replaced with an earlier non-CCC version, the ignition timing bumped up a few degrees, and both performance and mileage would probably improve. To go even further, a camshaft change would make a very noticeable difference. If you ever did this I would advise keeping the EGR circuit intact; that pays big benefits.

Give you an example here. Some years back I had a Subaru 4WD wagon that was outfitted with the always trouble-prone Hitachi carburetor. These carbs were near junk new and went downhill from there.
This car, just like all the others, got 27 MPG on the highway. I made an adapter plate and installed a one barrel carb from a 200 cubic inch Ford 6. One would think that would be too much carb for the Subaru motor and I expected to have to do some tweaking.
Not. That car would fire right up hot or cold, idle smooth, and most amazing of all - it got 38 MPG. The first time I checked the mileage I just knew that I had somehow made a mistake. Follow up checks showed it to be true - 38 MPG.
Kind of baffling, huh?

So did I screw up the environment here by eliminating the original carb and some of the garbage on top? I would like to think not since the vehicle would go 10-11 miles further on a gallon of gas than it did with the factory carb.

I also had an old carbed 70s era Monte Carlo and after a few months of some modification and wrestling I had that car (350/4 barrel) getting 21 MPG on the road with the A/C running. Not too shabby, if not environmentally conscious.

Civil discourse from Jeremy? After the horse comment and especially the “laying off the crack” comment? Jeez.

42

Ahhh sounds good…will the new cat just bolt on then with new brackets?

43

Thanks for your post, OK…excellent as usual.

That’s amazing what you did with the Subaru…and must’ve been fun too! I’d love to do stuff like that, especially with this older, easy to work on car, but I just don’t have the know-how or someone close by to guide me through it.
But 38 MPG…that’s a huge jump from 27, and I agree…any emissions increases would have been outweighed by the benefits of the new mileage.

Mind if I ask what kind of modifications you did to the Monte Carlo?

That comment on “laying off the crack” was my favorite too… :slight_smile:

44

How about the opposite…installing a cat in a vehicle not originally designed for one? Specifically, I’d like to know if it’d be feasible to run one in a '92 Honda Nighthawk 250. The “moral high ground” I’d like to occupy is tarnished somewhat by “sure, you get 65mpg, but it’s a stinky carb’ed catless thing!”

Incidentally, what amazes me is that, on my cross-country ride, I looked into leaning my bike in the high desert and was told (per the owner’s manual) I’d need to re-jet it, only to recently learn I could’ve optimized mixture via a screw-type device that the EPA requires to be sealed so the operator can’t use it! (Presumably under the “Heck, if we let you mess with it, you’ll just foul it up” philosophy.)

45

Those saws NYBo mentioned are great, but the electric ones seem better than the air saws whose blades aren’t as long. Snap-On makes a nifty hand pipe cutter that’s better than the plumber’s type. You can kind of “ratchet” the handle so it never has to go up against the body. You’ve gotta get the new cat and it’s pipes in hand before you figure out where to cut the old cat. Pep or any place has like 6" or so pipe adapters (1 1/8 X 1 1/4, for ex.) Good luck, and thanks for the compliment. I think I’m better explaining things than actually fixing these damn cars sometimes. Back to the grind in 8 more hours…

P.S: If you just need a length of pipe period, go to a muffler shop. They always have scrap pieces laying around, maybe like for a few bucks.

46

On the Monte Carlo it was a series of things that evolved over about a 4 or 5 month period. Change the distributor advance weights, several intake manifold changes, with several carb changes and jet/metering rod tweaking. This Monte Carlo also had the TH350 transmission (no overdrive and a 3:42 axle ratio) so the 20-21 MPG was a bit of a surprise. Before getting it ironed out it would get about 10-12 in town and 15-16 or so on the open road.

On the Subaru I can’t really explain that to this day. The vehicle had a 1.6 engine and the Ford 6 was about 3.2 Liter so my assumption when I was doing this project was that the gas mileage was going to suffer, the car would run rich, etc.
It never happened. The carburetor never had to be touched.

The Subaru Hitachi carbs were prone to warped body sections which would cause them to suck air and/or leak gasoline internally. Erratic starting, rough idle, bucking and surging were common symptoms. Repair it properly, install a new kit, and within a year it was back to square one.
The Ford carb swap was done because of the last straw with the factory Hitachi carb.

A week after I did the carb swap I made a 250 mile road trip with several fillups and the mileage astounded me. I just KNEW I made an error in filling the tank but after several months of following it closely the mileage was at a legitimate 38.
It’s not mechanical genius on my part at all; just sheer luck with the moon and stars aligned just right is all.

47

I don’t know so much about a '92 but those capped mixture screws only provide so much adjustment. Normally meant to make minor adjustments to get the engine to run right based on the factory equipment and EPA mandates. Anyway, the newer bikes are already leaned out significantly IMO. My 2001 Intruder was so lean I had to richen it up to get decent performance out of it. The jetting is selected to favor this lean condition and so most of the time you have to change jets to improve the performance at the expense of efficiency. Anyway, a small drill in a pin vise can be used to make a small hole in the middle of the cap, Then use a wood screw inserted a bit into the hole in the cap and pull it out with a pair of pliers to gain access to the mixture screws.

Catalytic converters must run very hot to keep them lit. This means they need to be located very close to the engine. Where would you stuff this monstrosity on a typical bike not designed for it? The excessive cooling, a byproduct of the design for air cooled motorcycle engines, would also make it tough to keep the cat hot. Never fear, I’m sure the CARB mandates will eventually produce bikes that are choked down even more and fitted with O2 sensors and cats. Then the rest of the nation will follow suit like rats behind the pied piper…

48

The entire engine management system has to be designed to work with a cat. If not, excess emissions will eventually overwhelm the cat, plugging it up.

49

If I were in your position, I would look into an exhaust pipe made for your bike that meets California emissions standards. You might already have it. The new Honda Nighthawk 250s sold in California might have a cleaner exhaust than the ones sold in other states. Honda’s web site reads “California version meets current CARB standards and may differ slightly due to emissions equipment.” Since this is an air cooled bike, the exhaust probably gets hot enough to keep the emissions equipment running right. If you are really serious about this, ask your local Honda dealer if the exhaust used on Nighthawks sold in California are any different. If they are, see if they can get one for you.

50

Thanks again Karl, that makes sense to get the cat before I figure out the rest…then at least I can eye ball it and see what’s needed. Will let you know how it goes!

51

Probably not. As long as the muffler is good, the back pressure will be enough to keep the exhaust valves from running hot.

52

The “sealed, screw type devices” variant of the idle mix screws that are mentioned have been around for 25+ years. These are the idle mixture adjustment screws and they have nothing to do with the air/fuel mix at cruising speeds. They only affect the mixture through the idle and off-idle ports in the carburetor.
Whoever told the poster that adjustment of the idle mixture screws would solve an alitude problem is wrong. Altitude modifcations will require jet changes, timing changes, etc.

Also, the catalytic converter works, in conjunction with the EGR, to beat down NOX emissions. If you’re driving a car or motorcycle with tuning problems, oil burning , etc. then the HCs and CO are still going to be way high.

53

Wish I could do that kinda stuff, just don’t have the knowledge or tools. Spent too much time as a kid on computers, not cars!

What did you end up doing with the Subaru? I wonder if that project was done again if it would work as well as it did back then.

I’d love to make my Cutlass get even 21 MPG…don’t think it’ll happen.

54

Wound up selling the Subaru cheap and let someone else worry about it. It had developed a serious problem in the ring/pinion gear in the transaxle. I could not find another 4WD transmission around anywhere at the time and since high mileage meant a complete overhaul I decided that it was just not worth my time and money to mess with. Overhauling a Subaru transmission is a bit tricky and time intensive not to mention repair parts are obscenely overpriced. One oddball mainshaft bearing is about 150 bucks by itself.

Can’t complain; I got almost 300k miles and 11 years of use out of it and it only cost me 700 bucks to begin with. The car had been towed into the Subaru dealer with a serious engine knock. The owner did not want to repair it and traded it in on a new Mazda. Since the car was like new inside and out and the dealer was going to wholesale it out anyway I bought it for wholesale price. I already had a new engine built just waiting for a car to put it into and voila!
(The original engine was trashed because the owner had taken it to an independent shop for tune-up. The experts there did not read the sticker on the hood about setting the ignition timing properly. The owner hit the highway with it and after about 75 miles a couple of pistons started disentegrating due to the timing being too far advanced.)

55

That’s a pretty good return on 700 bucks.

I didn’t realise setting ignition timing improperly could cause that much damage! Is that on any engine or just that specific one?

56

It’s true of any engine with a distributor and adjustable timing. Running a couple degrees more advance on your Cutlass won’t hurt anything at all and should perk it up a little along with improving the fuel mileage a bit.
The problem is when the timing is advanced from around 7 to whatever more degrees than it should be. Running timing too retarded will cause loss of power and overheating.
In the case of the Subaru I bought (which had several loud engine knocks in it) the timing was verified when I pulled the first cylinder head off and saw 2 mangled pistons and gouged cylinder walls.

Since I knew this damage was a timing problem I put what was left of No. 1 piston at top dead center and checked the distributor position. This showed the timing to be advanced by 10 degrees too much.
I sincerely miss that car and if I run across another clean one I’m going to buy it. The problem so far is that most of them have been beaten or rusted to death, or both.

57

Hmmm good to know. 10 degrees, that’s a lot.

Rust is a terrible thing…hope you find one in decent condition someday. Thanks for all the info!

58

I didn’t realise setting ignition timing improperly could cause that much damage! Is that on any engine or just that specific one?

Just do a google images search for “pre-ignition piston damage”. You’ll see lots of pictures showing what too much timing advance can do.

59

The economy leaves some struggling to make ends meet. Some see the rediculousness of wasting a great deal of their income to impress their fiends and neighbors with expensive automobiles. For those so inclined, the feedback carburator automobiles of the early and mid 80s offer safe, reliable, easily repaired transportation with the proper knowledge to economically re-engineer them. At best, an 81 Caprice with a 305 will get 20 mpg. But if driven less than 1,000 miles per month with only liability insurance and no payment operating it may be much cheaper than a 40 mpg econobox with it’s payment and full insurance.

60

Hmm interesting point. I wasn’t thinking that way when I bought my 85 Olds Cutlass for $500 and spent $3000 fixing it up, buying a second set of wheels, and repainting it and getting all the body rust repaired…I just thought it was a cool car (when not “pimped out”) but that I’d be spending a fair bit on money on gas. I guess since I don’t owe any money on the car, and have been able/will be able to do a lot of work on it myself, it is saving me money overall compared to a 40 MPG econobox that I’d have a payment with and full insurance. Plus I could never drive an econobox, no matter how economical it would be. No soul!

Anyway, thanks for pointing that out!