Midget Carb Upgrade

[Loren]

[Loren]

Got the throttle bracket fixed and was able to take the car for a quick test run. Yay!

Running around the neighborhood, it was initially a little hot. I was a little concerned, but once I got the revs up a couple times, I guess I dislodged an air bubble and things immediately cooled down and stayed that way. Good to know the temp gauge works, I guess. I'd never seen it even reach half-way before, and it takes forever to warm up. Today it went beyond half and was getting past 3/4. Pretty sure it's got either a 160-degree thermostat, or no thermostat. (on my list of things to do, already have a 180 to go in it)

After getting past that hurdle, I made a quick run over to the park. Felt good! It was blowing some white smoke under acceleration, which is new. Before, it would blow THICK black smoke on full-throttle acceleration, but never white that I'd noticed.

And it did blow a little bit of black smoke on full throttle, but nothing like before.

But, it ran flawlessly aside from my having set the idle a little too low... it was stumbling down to 600 when I stopped. I was concerned that the 175 might be "too much carb" and not want to idle properly, and/or not behave well under light throttle. I didn't notice any issues at all. Is it more powerful than it was with the 150? Hard to say given that I've not driven it in a month. Probably not, because it's still choked with a complete stock exhaust. But, it started easily, and behaved. What more can I ask for? Very pleased so far.

Once I got home, I started fiddling with the mixture (it's got the bottom-adjustable jet) and idle speed. That's when I noticed that it's leaking oil significantly. It didn't used to do that.

I've read about this, but it's really much more pronounced and immediate than I expected! What I did was remove a functional PCV system (goes through the carb in the original system, but my 175 carb doesn't have a PVC port), and temporarily just ignored it. I put a piece of cloth over the valve cover tube held in place with a hose clamp. I'm guessing that once that got oil soaked, it became an impediment to airflow, and pressure started building up. Oil is coming out EVERYWHERE! Dipstick tube (lots), oil cap, even one of the valve cover bolt holes.

I've already found my 1/8 NPT tap, and ordered a PCV valve that will thread into that. I'll run that to a hose straight to the valve cover... should replicate the original system pretty closely. Put some vacuum on the crankcase and hopefully stop those leaks! I assume that's also where the white smoke is coming from. Lack of negative pressure allowing oil to seep past the rings on the intake stroke.

Also just realized that I have a vacuum leak. I left the hose that went to the EGR valve hanging. Need to button that up.

Lots of little details to tend to. Gotta pull that throttle bracket back off and paint it. Install a PCV valve. Replace some coolant hoses. Plumb the Evap system. Run the choke cable. Get the mixture, idle and choke all adjusted properly. Probably a few other things I'm not remembering. But, she runs! And once I get the PCV sorted, she's properly drivable.

Meanwhile, enjoy a quick video of me ripping around the boat ramp at the park.

[Native]

Nice!

[Loren]

Couple more baby steps today. Took the revised throttle bracket off, painted it and reinstalled it. And got the PCV set up properly.

Just took it for a brief drive. Not blowing oil smoke like it was before, and runs quite nicely. The only issue that I need to look into (of course, I need to really look into tuning it properly after I get the choke cable installed) is that there's a slight hesitation on shifting. Not sure what can be done with that.

As they say across the pond, however... I'm chuffed that my new carb setup is working so well! No leaks, nothing weird going on. All works as it should.

[Native]

That's great!
Must be something about the shift hesitation thing, though - unless they're all like that?

[Loren]

I'm not going to pass judgement until I know the carb is tuned right. It could be as simple as running lean. Hmmm... I also might not have the vacuum advance connected right.

I doubt that it's normal. It feels weird.

Nice and peppy otherwise, though. Good throttle response.

Just need to keep chiseling away at the little details and then figure out how to go about tuning it properly.

[Loren]

Did a little research to verify what I suspected on my hesitation issue. I'm certain that it's vacuum advance.

I hooked it up to the "ported vacuum" (before the throttle plate) port on the carb because that was convenient. The old carb had no such port, and it went to the manifold. This manifold doesn't have a vacuum port. I'll have to T it into my PCV vacuum hose... T is on order.

Ported vacuum is barely there when the throttle is closed. You get a spike of vacuum when the throttle is cracked, and then it's gone when the throttle is open. Ditto when you close the throttle. You get a blip of vacuum as the throttle is just closing, but it's back to near zero when the throttle is closed. There are emissions reasons for having done it that way. We don't care about that. We want performance! A proper manifold vacuum source with pull strong vacuum at idle (which is what the distributor on my car was designed/tuned for), and "some" at partial throttle, thus giving better throttle response. Full throttle, you get "mechanical advance" from the centrifugal weights inside the distributor, but no additional vacuum advance.

So, once I get that sorted, the car should run better, and I can get more serious about tuning the carb. All both of its significant adjustments... mixture and idle speed, other adjustments are idle mixture (which is said to do next to nothing, it's fine-tuning for CO reduction on a new engine, fully closed after break-in), high-idle speed, and a choke stop so that you can't pull more than you need. (I did that today, and it kept me and Steve from driving the car to get lunch... flooded it)

Once you get one of these old cars running properly, especially without any of the complex and "iffy" emission controls, it's easy to see how brilliantly SIMPLE they are.

[Loren]

Got the choke cable connected today. Not the ideal cable or installation, and WHAT A PAIN it is to work with the choke cable at the dashboard! I still need to reinstall the speedo that I had to remove to get to it. Ugh.

Did some fiddling with mixture and such. Still have more fiddling to do after I get the vacuum advance hooked up properly. Currently, it's on a ported vacuum port on the carb. Needs to be manifold vacuum. But, aside from an off-idle hesitation, it's running quite nicely.

Noticed this when I backed out today... I'd used the same cardboard, just turned it over after fixing the PCV. It's amazing what a difference a proper PCV system makes!

With PCV disconnected (the valve cover port is not plugged, just doesn't have a vacuum source):


With PCV connected (most of that is residual oil, I haven't cleaned anything yet):


Still making baby steps. I need to modify and install an air filter assembly. Need to properly mount the fuel pump. Replace some hoses. Reinstall the speedo (and the replacement speedo cable that it's been on the shelf for a couple months). So much to do!

But, I'm getting close to calling this carb swap done.

[Loren]

Today, I properly plumbed the vacuum advance to the manifold. WOW, what a difference!

First thing I had to do after getting it started was adjust the idle speed down. I'm sure I need to re-check the mixture, but didn't bother tonight. After that, I went for a drive, and it was very noticeably better. Acceleration from a stop was easier, and acceleration and shifts were very smooth. It's amazing what a little vacuum advance can do for driveability!

Now, I just need to fab up an air cleaner and get the evap system hooked up.

[Native]