MGB - Side Draft Carb fun

Today, I return to the little British car: our 1978 MGB, Oliver. Oliver has sat unused for too long. I had been having considerable and increasing trouble just getting him to start and run. So, earlier this year, I removed his carburetor for dis-assembly, cleaning and re-assembly. I did the removal and tear down what feels like months ago, and just completed the re-assembly. So, while this post may feel like a couple of consecutive weeks of fun, it's really a little from March, a little from June and a little from last weekend.

Removal and Tear Down

re-assembled

As is the case with most things on a small car, removing parts requires some flexibility not needed for larger cars of this vintage. Still, removing a carb is not complicated, but I encourage you to take pictures. If your life is anything like mine, you may intend to be back to this in a few days, but days can become months really fast. Anyway, remove the air cleaner. Remove the fuel line (pinch it off first and then plug it). Disconnect the throttle and choke cables. Then remove the carb from the intake. With the side-draft weber (DCOE) and this SK Racing/OER carb, it is held to the intake with 4 nuts threaded onto studs emerging from the intake. The DCOE and SKRacing carbs use the same intake, by the way. Once removed, I stuffed rags into the intake to prevent critters from climbing into my engine, closed the hood and re-covered him. I took the carb over to a bench in the back of the little garage attached to the farmhouse.

At the work table, I started with the most obvious things and worked my way inward. First, the inspection cover and top half of the carb was separated from the main body. I removed every slotted bolt and whatever lay beneath, taking pictures as I went. Last from the top were the air correction jets and then I removed the set screws that held the venturi to the main body. The main body was effectively disassembled, so I shifted to the top half, removing the float, the fuel inlet bits and the choke bits. Last, I pulled the little cover or plate that faces the intake when installed. I am sure someone who does this often would have done it faster, but I needed to chronicle it so I could re-assemble later.

Carb Cleaning

remove from car day

I started like most folks probably do: shooting the carb with rattle can carb cleaner and gently scrubbing it with a toothbrush. I focused mostly on the exterior with the brush and let the carb cleaner do it's magic on the little holes without brushing. Satisfied that I got the worst of it, I pulled out a razor blade and removed all of the gasket bits and rubber seals. Then, put together a ultrasonic cleaner soaking tank with solution designed for carbs. I had read online that some folks will use Simple Green or other things, but I figured the correct solution was far less expensive than a replacement carb in the event those advisers were wrong.

The cleaners, well, the one that I got, but from what I read, many of them have a setting to warm up the solution while doing the ultrasonic. From what I read, there was some level of concern about how well they actually maintain temperature and that sometimes they can run the solution too hot. Since the solution is concentrated (read: need to add water), I decided to use boiling water and when poured into a room temperature solution, the overall temperature would be sufficient. I ran the carb body and all of it's pieces in the ultrasonic cleaner for multiple 20 minute cycles. Once I was satisfied that the carb was as clean as it was going to be, I moved it and the parts into a bucket and rinsed them with water. I then set everything out in the sun to dry.

Rebuild Kit

great kit

Unlike a Weber DCOE, the SK Racing/OER carb is not exactly common in the US. It is not generally sold here; it is much more popular in Japan. So, finding a rebuild kit for an obscure, foreign and old (time is relative) car part was time consuming on it's own. I was able to find a single supplier of a kit, a person in Japan with a storefront on eBay (Bprojects Japan). While I have a healthy skepticism of eBay sellers, deals and parts, I really had no other choice. The kit I received was incredibly well set. It included the major gaskets, replacement air correction jets and springs, new crush seals for the pump jets, a pair of ball bearings for the "pump non-return", a pair of copper crush seals for the fuel inlet and a big collection of rubber o-rings. It really had everything except a manifest indicating what part number each bit was for and the gasket for the jet inspection cover was missing. At this point I realized that I took pictures of the disassembly, but failed to take pictures of the rubber seals as I cut them off.

Re-Assembly

view from firewall

With my laptop open to the SK Racing carb manual, and my phone open to both the pictures I took and a blurry exploded view drawing of the carb, I started putting it back together. I started with the last picture I took and worked by way backwards through them. The only step I took that I had to undo and do again was the placement of the gasket between the top half and the main body. I had assembled the float, but the gasket needs to set above the float, which had I thought about that for a second, it would have been obvious. The float did not fit in the opening in the gasket, nor does it ever need to along its travel path. Also confusing was where the pair of ball bearings and small rectangular rods went. Process of elimination worked well here, choosing to do other things until it was apparent what hole those dropped into.

I used liquid gasket-maker for the jet inspection cover. That stuff makes a dark sticky mess. The instructions on the bottle say to let it dry "for a few minutes" before putting the 2 pieces together which need a gasket in between. I let that sit for well past the recommended few minutes and it was still very wet.. and even after letting it sit in the sun the stuff didn't dry very much. So, I did everything else install-wise and add the inspection cover dead last.

While I had the carb in hand, I decided to add a heat shield to the underside. The header that I installed has a thermo-barrier powder coating on it, but I know from having the hood open after driving it that a ton of heat is still getting into the engine bay. I suspect the source is the header (or the radiator), and the best thing I could do for the carb is to help prevent heat from getting to it. So, I got a DCOE carb heat shield from Pierce Manifolds. The mounting bolt pattern is designed for a Weber DCOE, but the SK Racing/OER is exactly the same in this area. The venturi maintenance holes line up, the cut-outs for the intakes, etc. it all just lines up. The heat shield is heavier and thicker than I expected, but I expect it will do exactly what it is intended to do: block and route-away heat rising from the exhaust.

Install

re-install day

As easy as the carb was to remove, installs always take longer. This bugger was no different. First, the carb mates to the intake with these thin (maybe 6mm thick?) plastic isolator bits between the carb and intake. On each side of the isolator resides a rubber O-ring that is set inside a groove. So, you are managing a carb, 2 isolators and 4 O-rings at one time. That required some dexterity.

I discovered that the heat shield has a small tab on the intake side that would hit the center header pipe. Recall, the MGB has a Siamese head, so the middle 2 cylinders share an exhaust. The PO had a home made exhaust manifold with a center pipe effectively pointed straight down. The header has a more typical curve. So, the heat shield came off and I adjusted that tab to point angled upwards so it did not hit the header pipe, but actually will shield the top-most end of it. Then, I realized that I could not address the lower mounting studs with heat shield installed so I removed it again, re-installing after the carb was nutted down into the intake.

From there, the install was about what you would expect, complete with a dropped bolt under the car. I had to reverse the spring-return arm on the carb as well as flip the fuel inlet. Still, it was relatively smooth, hooking up the fuel line, control cables and air filter.

No Test Fire

By this time, I had sweated my way through most of a summer afternoon and cleaned liquid gasket maker off my hands more times than I'd like to count. As much as I wanted to enjoy the sound of the engine running, I chose instead to take the limited win: Oliver was in one piece. Boo and I went to the county fair instead of test-firing Oliver's engine. Now, Oliver is covered back up, again waiting for me to have a few hours to test fire his engine and fiddle with settings. I sincerely hope the tear down / deep cleaning was what he needed. I'll post an update when I have one.

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That's it for today. Thanks, as always, for following along-