Swapping Carburetors

While the vast majority of Eric’s coupe is original, I decided that it was more important that it was reliable than original. I continuously had issues with it running smooth, and I think it is the carburetor. I decided to get a Summit 560 CFM, which is a more modern version of the Autolite 4100 that came with the car. I knew I would have some fabrication projects to make it work since the stock carb was hard lined in with custom bent tubes for both fuel and vacuum. Not to mention the linkage wouldn’t work. That said, it is an easily doable job, so I went to work.

First, I had a hard rule to not damage anything original. If I didn’t use it, I took it off and put it in a box for Eric. If I needed to modify an original part, like the fuel line, I ordered a reproduction and put the original in the box of parts to save. At any time, Eric can have the original rebuilt properly by someone with more expertise than me, and return it to factory if he chooses. More likely, that would probably be the next owner since he should have no reason to mess with the carb after getting everything working reliably.

I started documenting the starting point so I could see how things were run originally. The two areas of attention are the fuel hard line, which is threaded into the pump and the carb, and the vacuum line, which is also threaded into the carb, and the distributor. Those would need modifying, so I ordered them.

There were many options to choose from for the fuel line. The deciding factor for this one seemed to be the clip on the timing cover, which I have.

The fuel line was a pretty intricately bent part. I would not want to try to bend it myself. Here, you can see the original compared to the NDP replacement from Classic Tube. I generally like their lines, but they usually require a bit of tweaking to at least one of the bends. In this case, the radius off the pump is slightly too wide, and the second to last bend by the carb is off by probably over 20 degrees. Enough to make me a bit nervous trying to correct it by hand since it felt like it wanted to crimp shut. Ultimately, I was able to get it back in shape so it could be used, but it didn’t matter too much, as I had plans to cut the carb side off.

I started with a test fit of the new carb with the provided fuel line in place. It takes up a lot more space, and it looks like its going to be an issue. The heater hose from the thermostat housing is in the way.

Since the heater hose is no longer needed to warm up the choke, I made it fit under the fuel line, closer to the intake. That made more room to connect the fuel hole between the two hard lines.

That also led to the next issue. The stock line was 5/16 and the provided hose connector on the carb was 3/8. So, I had to go to Napa to get a 5/16 adapter with the same thread for the carb side, plus a fuel hose to connect the 2 hard lines together, along with the appropriate hose clamps.

I also picked up some vacuum tubing for the distributor. I used just the last few inches of the repro line, and used rubber tubing to connect that to the carb. I could have gone for something similar to the carb fuel line side, but this works.

I routed the fuel hose around the distributor, similarly to how the original hard line was routed. With the heater hose going down, I was able to make it work pretty well.

Here, you can see it from the other side, just behind the distributor, with only a few inches of rubber hose. I didn’t add an aftermarket filter as the filter is the kind that is screwed to the bottom of the fuel pump. It’s nice to have that out of the way and not be affected by this project.

Next, I did the linkage. All of the modern carbs that I have worked with don’t work with the original S shaped linkage rod and clip. I much prefer the heim joint style I picked up from the VMF board, so I went that route. I used a couple of machined washer/spacers to fill the big hole and adapt to the screw. On the pedal side, I used a bit of hose to compress and fill the hole, similar to how it was originally, but I didn’t have the exact size, so I had to compress it with the screw through the heim joint and a washer. I measured it to match the original length and made sure there was no binding at any part of the travel. I originally had the carb side on the outside, but I noticed the angle was slightly binding, so I moved it to the carb side of the linkage lever and it’s much better.

I also picked up a double return spring kit from the auto parts store. It came with a bracket, which I bolted to the intake for a place to connect the springs. This provides a means ensure failure of the linkage in any way makes the gas shut down, not get stuck open. I also provides good feedback on the gas pedal.

The last piece was the electric choke. When I did this mod on the 67, I took the power from the heater blower motor on the firewall. Evidently, the 65 has a different motor and control. This one has a 3 speed motor with different wiring, so I couldn’t manage to get a 12v lead from it with the blower off. I went to the other option of using the STA terminal on the alternator, even though its only 7v.

It was slightly more involved as I had to take the alternator off, but it’s only 2 bolts. While I was there, I replaced the belt with a new one from Marti Autoworks that is a reproduction of the original. I made a nice, bright red wire that you can’t miss, to tell its not original (I should have used black).

With the wire attached to the alternator, I put it all back together. I couldn’t help but blast the bolts and give them a light coating of oil to clean them up and prevent them from rusting in the near future.

With it all back together, it didn’t take much to get it fired up and tuned. The initial choke idle was a bit high, just over 2k, but the STA lead did the job and it was off after about 2 minutes. You can see it here idling around 700 with just over 20 on the vacuum meter. Too bad about that red wire. The wires out the other side are going to my diagnostics for the RPM, so just temporary.

It fires right up now and seems to run pretty smooth. The last piece is giving it a road test, but my driveway is currently under construction, so I have to wait a few days before I can really be sure this solved the issues. At least it starts up like new now, though.

Oh, and the last piece is the intake threaded stud. The one provided is too long, and the place I would need to cut it is where it’s not threaded. I will have to go to the hardware store to buy a few inches of threaded bar to cut to length and make an air cleaner hold down. With the driveway the way it is, I have time for that it seems.

3 thoughts on “Swapping Carburetors

  1. Kendal Wedan

    My ’67 has a 289 2v Autolite. On a hot day (+90F) idle was very unstable and experienced hard starting when hot. Found a fuel percolation issue which was corrected by installing a 1/2 inch phenolic spacer between the carb and the manifold to insulate it from engine heat. Thought I would pass this along just in case the new carb doesn’t work out. Have really enjoyed reading your posts and used some as a guide for my own repairs.


    1. Thanks. The original carb also had what looked like about an inch spacer that I left on. I may still get a problem though based on how I had to run the line so close to the heater hose. Thanks for the tip though, changing anything on these old cars usually leads to some head scratching troubleshooting.


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