Big cabs can be installed on models that do not have kit parts.!?

Even if you want to enjoy tuning and powering up your car...There are no kit parts on the market.There are many examples. In some cases, even if they exist, they are no longer in print, or are no longer sold, and even if you want to buy them, there are cases where you can not reach them, like treasure parts. Here, the 1974 model of the first generation C90 series = Super Cub Deluxe C90K2An actual example of installing a big carb on a stock engine.Let me report on the

「ポリネシアンブルーメタリック」のC90K2

取り付け実践車両は1974年、昭和49年モデルのスーパーカブデラックスC90K2。
カモメが羽ばたいているような通称カモメハンドルを採用し、左右のエンジンカバー前方にエアー通路がある、通称クジラ型エンジンを採用している。C50やC70と同じボディに見えるが、一回り大きく、フレーム幅も広く燃料タンク容量は1リットル多い。エンジンはS90E系(CS90)のフルサイズ90ccモデル。後のC50/It was powered by an older engine that differed from the 70-based, souped-up 85cc version of the Super Cub 90. This engine is also known as a tough practical engine, which has been continuously installed in the MD90, the postal model postal cub.

Normal engine, so a little bit big carb.

On the left is the Thai Keihin PB20, in the middle is the stock domestic CT110 Keihin PB20, and on the right is the stock seagull C90K2 PB18. the Thai Keihin model has a feature that the float chamber drain faces sideways and is easy to lay out in a tight spot. On the intake side, the stock air inlet is slightly thicker than the stock diameter, but the stomach shape will work. The carb of the Thai Keihin is probably a genuine part of the Thai Cub 110, but I bought it on the Internet auction. The diameter of the venturi is about Φ20mm, but does it really change the driving??

No modifications to the engine, just the manifold.

I removed the stock carb and manifold from the Super Cub 90 engine, and oilstoned the mounting area on the cylinder head side. If the secondary air enters the engine, it will cause the engine trouble. I found the gasket for the CS90 which has the same engine series, so I matched it. I was happy to find that the size was perfect.!!It turned out to be no problem at all. It would be troublesome if the port position was off or the flange mounting pitch was different. If the port diameter is different, I would like to match the step part. ......

Head side flange and gasket size are the same!!

I compared the gasket to the engine side flange of the manifold and it was perfectly fine. You can't see what's going on inside once it's assembled, but if you use the gasket to check both sides, you can clearly determine the port steps. This time, I prepared another manifold for the C90K2 beforehand and decided to use it. If the stock manifold was modified in the first place, it would be troublesome to modify the manifold when returning to the stock carb.

The bumps still occurred on the carb flange side.

The shape of the carburetor flange side is being checked. The shape of the insulating spacer for the Taikehin and the shape of the carburetor side flange match. It is natural to say this, but if the dimensions are drastically different, the power will surely be reduced. When I purchased the Ape 100 early model, I remembered that the intake port hole on the spacer was a half-moon shape instead of a circle. The manufacturer had self-regulated the power output in this area. Next, I checked the step between the insulated spacer and the manifold. The diameter of the manifold side was slightly smaller. Such a step becomes the intake resistance and the acceleration power is decreased.

Cutting steps with reuter + super steel bar

Enlarged the flange port on the carburetor side of the manifold, which had a slightly smaller diameter. The workability is overwhelmingly improved by attaching a long shank super steel bar to an air rheuter (air mini grinder). Not the whole port, but the flange connection part was shaved slightly to eliminate the step. Since cutting with the super steel bar is a rough finish, it is better to use a flap wheel for a slippery finish. Since it is only a small amount of cutting, the processing time is only about one minute. If you were to do this kind of work by hand with an assembled file, you would have to visit ....... It is certain to spend more than one hour probably. The existence of the compressor and the air tool is thankful.

Don't forget to set it up after installation.

Various jet sets for setting were purchased and corresponded. The main jet and the slow jet were removed from the carburetor and the shape and number of the jet were checked before purchasing the front and rear number. Since this is not a tuned engine with increased bores and high camshafts, the number of jets did not change significantly and the engine was set up to be usable for daily use in no time.

As the famous tuner said, "There is no better way to increase power than to increase bore". If you are a fan of horizontal engine tuning, you will probably understand the meaning of this statement. For the horizontal engine series such as the Monkey, Dax, and Super Cub, the 72cc/85cc/88cc/105cc/110cc/Although there are (or were) many tuning kit parts for the 124cc, there were almost no commercialized kit parts for the old horizontal type "full size 90cc engine". By the way, the bore x stroke is 50 x 45.6 mm, 89 cc.

Here is a customization and tuning report based on a full size old Super Cub C90. The theme of this report is the installation of a big carb. When choosing a high performance carb, the air cleaner becomes unusable, the intake noise is noisy, and many other modifications must be made. Since I would like to tune the engine itself in the future, I was wondering if there are any parts that can be bolted on, including the manifold and inlet pipe.　I looked in the spare parts bin in the garage. Then I found a Keihin PB20 for the Hunter Cub CT110 and a Thai Keihin PB20 that I had purchased on an internet auction.

When the new Taikehin carb, which has no missing parts, was fitted to the manifold, the inlet pipe diameter was 1mm larger than the manifold diameter, but from the mounting pitch to the outside dimensions of the carb itself, it was roughly the same and could be bolted on.!?However, I decided to put two insulating spacers in the cab side to cope with the cable connection fitting of the top cover because it hit the frame. In addition, because there was a step in the manifold diameter of the carb side, I decided to process this slight step with an air rheuter.

While going out for a test drive, I attempted to set the carb settings, and since it is not a tuned engine, I was able to easily complete the settings for normal use. However, compared to the stock carb, the low speed torque was not as good as it could be. On the other hand, it seemed to blow well in the higher RPM range. To be honest, there wasn't as much of a difference in feel as I had hoped for, but if it were possible to increase compression and bore with this ......?So, it can be said that this modification is a "tuning setup" for the future. Even without the kit parts, I was able to successfully build a big carb. If I want to install a bigger carb or a different type of carb, I can do it by welding the manifold.