1976 MG Midget

[Native]

I need to sift through my to-do list, re-prioritize it, and try to start getting some things done.

I lol'd.

Oh, and seatbelts are good.

[Loren]

I still haven't fit that air cleaner.

And I dug out a nice tonneau cover from behind the back seat that I want to try out. I've never used one. But, it might just suit my "don't like to mess with the top" persona. Set it and forget it.

But, the big news: Those wheels and tires that I ordered and received 6 months ago? I finally got Carl to mount them and now they're on the car!

5 pounds lighter, 1" wider. 165/65-13 vs. 155/80-13. First thing I noticed instantly is that the steering is WAY lighter. Braking is also better, of course. Acceleration is surely better, but I didn't really notice. And they look great!

[Native]

Those are some sharp wheels. What a great find!

[Loren]

Bought them new on a whim, there are still a few new alloy wheels available for this car.

I figured paying somebody to sandblast and refinish my rusty steelies would probably cost about as much as buying new wheels. I looked briefly into buying a cheap sand blaster kit and refinishing them myself, but decided against it. I generally suck at paint work, anyway.

Based on how they feel, I think I made a good decision!

I think this is going to inspire me to work on suspension sooner rather than later.

[Loren]

Started tinkering with the carb again. My last two fill-ups have netted 15.3 and 15.0 mpg. The first time I thought had to be a mistake somewhere. Second time... well, I guess not. 7 gallons, 105 miles. 15.0 mpg. I knew it was running rich, but not THAT rich!

So, I immediately adjusted the main fuel jet a full turn towards lean. That brought the idle speed up from about 11-1200 to 1500. Otherwise, it still drove the same, maybe even a touch better. It was driving fine before.

That was Wednesday night.

Today, I finally got around to fitting the air filter assembly that I'd modded to fit the new carb. That took longer than it should have. Don't think I'll be removing it unnecessarily!

Then, I started it. Cold start was BRILLIANT. Before, it took a bit of cranking (5-6 seconds) with at least half-choke to get it to fire off, but it reliably did. Today, I gave it more choke (the choke isn't actually a choke, it's a "fuel adder) to make up for leaning out the jet, and it fired right up instantly! Cool.

Once it got a little warmed up, I lowered the idle speed to a proper 1,000 rpm. I'd like to get lower than that, but baby steps.

Drove it around, and found that it mostly drove fine. Actually SHIFTED better because the revs were falling properly between shifts. (I don't think the clutch fully disengages, so that makes a significant difference) Downshifts were VERY nice. But, I did get some low RPM stumbles, and it stalled once when I came off of a 45 mph cruise, popped it into neutral and braked hard. (normally, I'd throttle-blip and downshift) Otherwise, it was okay. Idle would normally fall to around 11-1200 and settle down to 900-1000.

Visited Joe B for a few. While there, we adjusted the idle mixture screw. I forgot about that one because the factory manual says "don't touch it" because it's related to emissions and you "need" a CO meter to properly set it. But, all it does is provide an additional path for air bypassing the fuel metering system and causing it to run leaner at idle. So, I ran it closed about 1.5 turns to see if that helped with the stumbles. I think it did. Seemed to run better on the drive home.

Went out again a few hours later. Another nice cold start. Drove around just fine. I think I smell more fuel than I should, so it's probably still running rich. Next step will be to lean the jet adjuster a bit more. If that causes the idle to go up, I'll adjust that, too. I'll keep making baby steps towards lean until it seems to affect performance.

At least I got the air cleaner checked off the list.

[Native]

...back in my day, we didn't have data logs...

[Loren]

Nothing digital, anyway! Just pen and paper. If I wasn't so lazy, I'd get practiced at the art of plug-reading.

Filled the car up on my way home this evening. Another 82 miles, this time including some highway miles at 65 mph. 4.0 gallons! 20 mpg... which is a vast improvement over 15 mpg. A step in the right direction.

I'll adjust it a bit leaner and see what happens.

[Loren]

Went about a half turn leaner (1.5 turns from where I started), and that gave a really nice cold start. Seems to run fine and actually a bit smoother. But, it's running out of steam before it runs out of revs. 4000-4500, somewhere in there, it just falls flat. I'm assuming that it's going lean up there. But, I'll play with it some more.

I'm going to try leaning it out a bit more. If my theory is correct, it should fall flat at an even lower RPM.

And, I just ordered a cheap wideband AFR gauge. That will answer a lot of questions. Of course... I have to install it, which means I have to weld in a bung for the O2 sensor. I wonder if I have the skills to pull that off?

[Native]

which means I have to weld in a bung for the O2 sensor. I wonder if I have the skills to pull that off?

Well? Do ya?? The bung should be plenty thick, but how thick is the pipe tubing? That's the issue, yes?

[Loren]

Yeah. I've got to figure out how to go about it. The stock manifold has a cat in it, so I need to go pre-cat. It seems pretty sturdy up there. We'll see.

There's a bung where the EGR valve was screwed in. What are the odds that it's the right thread? Wouldn't that be something?

I almost ordered a cheap header last night to bypass that whole question, but I'm not ready to redo the whole exhaust. Baby steps.

I did lean it out some more this afternoon and go for a drive. It still starts up brilliantly, idles fine, and runs just fine if you drive it "normally". But, it seems to run out of grunt around 4000-4500 rpm. And it's got a persistent stumble if I hang a left turn in 2nd at around 3k rpm. Aside from that, it runs just dandy!

Being able to see what the AFR's are doing will be enlightening.

[Jamie]

Steve -- I'm waiting for him to chuck the carb into the bin and put in a Megasquirt setup....

[Loren]

I'm trying really, really hard to stick with the carb.

I've been down the MS EFI rabbit hole before. It was fun, and I enjoyed it. But, SU-style carburetors are so danged simple... I can see the appeal.

Since I have no aspirations to do any kind of competition in this car, and I don't "depend" on it for daily driving (though it is technically me "daily driver"), it doesn't need to be perfect. It just needs to be an enjoyable drive.

Research last night hinted that my left-turn stumble is probably due to float height. Probably a bit too low. If the AFR shows that it's a lean stumble, I'll address that. (gotta pull the carb off to adjust the float)

Then, if my guess is right about what the needle is doing... I'm getting it close to proper at idle and low-medium load. It's going lean on the high end. I can sand the tip of the needle to make it richer there. (could also experiment with different needles, but I like to tinker)

AFR gauge arrived today. Need to see where I can put the bung...

[Loren]

So, I went out to investigate where to put the O2 sensor bung.

Here's the situation:



Cast iron very short runner manifold immediately into a bolt-on (48 year old) catalytic converter. The pipe out of the cat runs around the frame rail and to a flange under the transmission.



Options:

1. Drill out the plugged EGR port on the cast iron manifold and tap it to fit an O2 sensor. (assuming it's not already bigger than that... and, no, it's not already the right size, it's 3/4-16... I had to buy that plug!) I'd have to remove the manifold, buy a big ol' metric O2 sensor tap that I'd never use again, and... meh. Lots of work and spending money for not a lot of benefit.

2. Gut the cat and put the sensor in the cat body. Not the worst idea, but having that big fat open chamber right after the exhaust manifold would surely wreck exhaust flow even more than the cat itself does. Plus, I'd have to unbolt it from the manifold, surely break and replace studs in the process, and on and on. Lots of work, maybe not a lot of money, but not a lot of benefit.

3. Replace the cat with a custom "test pipe". Again, not the worst idea. Would eliminate the cat without adding a big open chamber to slow exhaust flow. Would have to remove the cat flange from the manifold, probably break/replace studs, etc. Would involve a bit of fabrication, and actually be kind of fun. But, I'd have to buy appropriate pipe, fit it all together, etc. Slight benefit of eliminating the cat, though.

4. Bite the bullet and put a header on it! This is something I planned to do eventually, anyway, so it does have appeal. Doing ANYTHING else will ultimately be wasted time and money, because I WILL do this eventually. If I was going for ultimate performance, I'd have to order THE 4-2-1 performance header from UK. It's near $600 plus shipping. Ugh! But, I'm not going for ultimate performance. Just better than 70's emissions-restricted stock. And there's a nice 4-1 header available on eBay for $150.

Sooo... I ordered this:

Benson Tuning 4-1 Header

$160 after tax, free shipping. Should have it late this week.

Fun fact: if this were a Spitfire header (same engine), the 4 tubes would come straight down tight to the block and the collector would run between the block and the frame rail. You have to go there on the Spit because the other side of the frame rail puts you into front tire clearance. The Spit header won't fit the Midget, as that gap is tighter. So, the 4 tubes are angled away from the engine and the collector is just outside the frame rail, same location as the stock exhaust. In other words: This header should fit pretty easily.

I'll still have to weld on the O2 sensor bung and fit it to the stock exhaust. But, this is as close to an "easy button" solution as I'm going to get without spending "throw away money" on temporary mods.

I just have to keep reminding myself that I have no car payment, I only paid $5700 for the car, and insurance is like $25/mo. I can afford to spend a couple hundred bucks on it every now and then.

[Native]

Steve -- I'm waiting for him to chuck the carb into the bin and put in a Megasquirt setup....

Lol.

[Native]

I just have to keep reminding myself that I have no car payment, I only paid $5700 for the car, and insurance is like $25/mo. I can afford to spend a couple hundred bucks on it every now and then.

Right on. Show me a hobby that doesn't cost money.

[Loren]

Header showed up today. Only 4 days late so I couldn't do anything over Thanksgiving weekend. I guess I'd still be waiting for cat parts, anyway.

Check out the giant 2" secondary pipe on this thing! I'm thinking 2" cat and 1.75" pipe. (which is still .5" larger than the stock pipe)



The measurement from the top collector to the bottom of the 90 degree bend is about 7.5". Or 5.5" to the inside of the bend. Now... can I find a cat that will fit in that space???

[Loren]

Options to fit a cat:

1. Put a small diameter cat under the car. Doable, but there's only 4" of clearance to the exhaust as it is, that will take away at least an inch of it. Not good. It would surely get beaten to death, and that's not good for a cat... or good in general.
_____________________________________

2. Try to fit a cat in that space mentioned above, between the collector and the bend. This is the location of the stock cat.

This is about the smallest replacement cat I could find: Walker 82503

Hard to find exact dimensions on it, but based on the 2" pipe diameter, it appears to be about 7-7.5" long. It "might" work. RockAuto says the body length is 4.5", overall length 8.125". If I cut as much of the excess end length off of it as possible, cut the header collector as short as possible and weld directly to it... once I put a 90 degree bend on it, it will hang at least an inch lower than the stock exhaust. It "might" work. But, it's a $130 experiment that I don't want to conduct. Plus... if it's all that tight, I wouldn't have anywhere to fit the O2 sensor into the exhaust flow before the cat.
_____________________________________

3. I just stumbled upon this. They make catalyst inserts for motorcycles. Actually, it looks like the company that sells these is probably the source for a lot of the guts of the cheap Chinese cats. They make them 35-120mm diameter, maybe larger. But, on the list is 50mm. Which would fit neatly INSIDE the 2" collector pipe either before or after the bend. Available in lengths of 80, 90 and 100mm.

Cat insert

This wouldn't be hard to make work. The lengths are 3.2-4". I could make that fit. The only question is... would it be too restrictive? Nobody provides specs on this, so no way to know without doing some kind of flow bench testing.

But, I can estimate...

The area inside a 2" pipe is 3.14". That doesn't really matter, as it's not a target or a goal, it's just how big the collector pipe happens to be.

The ID of the 50mm OD insert, considering wall thickness, is probably about 1.84". So, it has an area of 2.66". Guessing that the cat core takes about 1/3 of that area, so 1.75".

The area of the 1.5" ID stock exhaust pipe (I measured it) is 1.77".

Sooooo... depending on how accurate my estimate of the core density is... it could flow as much or more (or less) than the stock exhaust. I'm gonna say that's "not enough". If I went with a larger diameter, I could get somewhere useful. But, then I'd be completely constructing a custom cat into the down pipe. Seems like overkill.
______________________________________

The conclusion: I'm gonna put it together with no cat. If I don't like the smell, I'll revisit this and see if any of it is worth the effort.

[Loren]

I've got a 2" to 1.5" conical adapter to connect the downpipe to the stock exhaust. Should be here soon.

If I get really motivated tomorrow, I might try to determine the angle that the downpipe needs to be mounted, drill the hole for the O2 and weld the bung in. Maybe.

In other news, I got to looking at the air cleaner I put on the carb. I always thought it looked kind of small, but it was sold for a CD150 carb, which is the original carb for this car. Figured it would be correct.

Found an online calculator that indicates that the size of that filter is probably restricting me to about 40 hp! That's a big part of why it's running out of steam at 4000-4500, I bet! The solution is simple: Remove the 1" tall filter, replace it with a 2" tall filter. That should be good to at least 65 HP and 6000 rpm (this engine generally doesn't live long if you make a habit of revving it past 6k). I doubt that I'll be making much more than 60 HP, so that should be adequate.

Interestingly, the 5.5" diameter 2" tall filter that I found is from a 1966 Pontiac Tempest. (and a lot of other Pontiac/GM cars of that era)

[Loren]

As it turns out, I did find some motivation Friday and got the hole drilled (it's about a 3/4" hole, so it was first drilled, then enlarged with a 1/2" sanding drum... as I don't have a bit that large). I found that my O2 sensor bung is flat... and the pipe is round. So, not a perfect fit-up. I tossed around a couple ideas to get it to fit up better. (flattening the top of the pipe, adding some material to the bung before sticking it to the pipe) Decided to just go for it. My welder settings were pretty close to correct and I was able to get that gap all welded up. It's not pretty, but it's secure and it won't leak.

Got weld spatter all over my polished stainless pipe, though!

Another part arrived today. I had ordered a 2" to 1.5" cone-shaped adapter to go between the header and the stock exhaust. I was on a roll, so I went ahead and welded that on. It was easier to weld because it was a very tight fit-up. I tack-welded 4 places, then spot-welded (alternating from side to side) all the way around at about 1/4-3/8" spacing. Cooled it, wire-brushed it, then spot-welded between all of the gaps. I was rather pleased with the result, and could have just left it un-ground. But, vanity got the better of me and a I took the flap-wheel to it to get rid of spatter and discoloration. Inside looks like I got good penetration. Not perfect, but plenty adequate for an exhaust.

Funny: I was trying to jig up the cone to the pipe so that I could tack it. I've got a bunch of magnets on my welding cart, figured a couple magnets would do the trick. (you see where this is going, right?) At least I know that my stainless steel is REAL stainless steel.

And I thought ahead when welding that. Wrapped a rag around most of the pipe, and put some blue tape around it up to about an inch from where I was welding. Much less clean-up doing it that way!





Final fitment... I stuck the pipe under the car today to eyeball it. Were I not doing an O-sensor (or if I'd placed it elsewhere), the design of this header is pretty good. The downpipe is supposed to angle a little towards the engine and the bracket bolts directly to a bell-housing bolt. I *might* be able to get it to fit that way, but I think the O2 sensor might get in the way. When I marked the location for it, I was thinking that the downpipe would go straight back. So, that's what I'm probably going to do. Straight back with it, the O2 sensor will be right behind the header flange with plenty of clearance to the frame rail.

Oh. The exhaust pipe runs down the left side of the drivetrain on this car. The exhaust comes out of the engine on the right. Why? Because the original MG engine had exhaust exit on the LEFT. The Triumph engine that's in this car was a "production change", so they made it work. As such, the exhaust pipe goes under the transmission to follow the original exhaust routing to the back of the car. I'm sure there are reasons for that, I haven't looked. There's not a lot of room under there to move things around without major re-engineering... which, of course, they didn't want to do.

With the "as-designed" placement of the header downpipe, the angle that's built into the end of it would line up pretty closely to the stock exhaust pipe just before where it has a tidy flange connection. But, while I might get away with "some" angle, I might have to parallel the frame rail with the part of the downpipe before that last bend. That means that I'll have to add a little angle to the stock exhaust pipe to get it to line up properly.

I probably have enough pipe with bits and pieces of the stock exhaust pipe, and I could Frankenstein it together with the original flange. But, who likes welding on rusted metal any more than necessary?

I think I'll go ahead and order a new set of exhaust flanges. Need to get back under the car and see what kind of angles I need to get to fit things together. I guess it would be wise to do that all with 1.75" pipe (will have to mod the 2-1.5" cone adapter to 1.75", no biggie) to make it easier to transition to a full 1.75" exhaust someday.

Might have been easier to put the O2 bung in a different place. I reserve the right to change my mind. I could plug that hole and add another one. I kinda didn't want to go out the side because it just seemed more likely to get in the way, and I wasn't sure what angle it would need to come out at. Doing it the way I did, I knew the sensor would point straight up and be out of the way.

But, if I'm changing the angle so that it goes straight back to accommodate that... I'll need to rework/modify/extend the bracket that attaches to the bell housing. In addition to some rework of the stock exhaust to make it fit. Eyes under the car, that's what I need.

I'll figure it out. Getting better at welding and fabrication (as long as stuff doesn't need to be pretty, I can do it!), so it's just a matter of figuring out what needs to be done, having the right materials, and getting it done.

[Native]

Nice work!