Basket Cases

[David Lahey]

What inlet rubber do you run on your Big Bore TY175 David?

Our special TY175 has an RD350 inlet plus boost bottle to try and increase the air flow compared to the original dog legged TY175 manifold.

Lacks power though compared to Greg's 300 engined 240 on the hill climbs at Pacific Park in NSW.

I've got a few different inlet rubbers to choose from and will probably fit a straight one from a DT175A when it goes together. This will require the use of the bigger reed cage (from DT175 or TY250) because the straight inlet rubber has some fairings that fit inside the reed cage that don't fit inside the TY175 reed cage. Previously I had the dog-leg TY175 type on it. Weird design hey?
As for Greg's

[David Lahey]

After Kurt asked about the inlet rubber for my 210cc TY175 I got some different ones out for a look and was quite surprised with a few things.
The photos show four different inlet rubbers that would fit a TY175, some with a bit of modification.
The standard TY175 rubber is sitting on a TY175 reed cage. The other three reed cages are the bigger size that comes in TY250, DT175 and lots of other s.
The issue that is perplexing about TY175 inlet rubbers is that the hole on the rubber doesn't line up fully with the hole in the reed cage. This is a source of drag that on a racing engine would be extremely important but on a trials engine not that important, but maybe something that could be improved upon for people who want to get the best out of their bike.
I'll stick one photo here and identify the inlet rubbers:

20220116_093515.jpg (1.13 MiB) Viewed 920 times

Starting on the left end
TY250 has 434 moulded into it
DT175A no number moulded into it
something with a boost bottle. Could be late model DT175, RD350/400. No number moulded into it.
TY175 has 525 moulded into it
Note that the one with the boost bottle connection is the only one that has the carby positioned centrally.
Some one has trimmed the fairing off the one with the boost bottle connection, presumably so it would fit onto a TY175 reed cage.
The standard TY175 cylinder is too narrow to fit the wider TY250/DT175 reed cage but it is only a few mm too narrow and some people have widened it a bit to fit the bigger reed cage. All the carby connections are the same size ie they fit TY175 or TY250 or 26mm OKO carbys.
Here are the rest of the photos. I've tried to show the misaligned flow path with the TY175 rubber.

[David Lahey]

I noticed a number on the intake rubber with the boost bottle connection 2R9-00
A bit a search points to it being for an RD250/350 and I see that new ones are still available
https://sumorubber.com/2r9-13565-00-carburetor-joint

[David Lahey]

While I was looking at the intake rubbers made by SUMO I see they make air filter cages for TY175 too
https://sumorubber.com/525-14458-01-ty1 ... ilter-cage

[Kurt]

The only reason I can think for the offset was to try and shift the carby away from the exhaust, the RD350 inlet rubber does put the carby fairly close to the expansion chamber.

The reason I asked was being a 210cc I thought you may be looking for ways to improve the gas flow.
The stock airbox being another source of restriction.

Interesting idea for fitting a larger reed cage, do you know anyone who has done this?

[David Lahey]

The only reason I can think for the offset was to try and shift the carby away from the exhaust, the RD350 inlet rubber does put the carby fairly close to the expansion chamber.

The reason I asked was being a 210cc I thought you may be looking for ways to improve the gas flow.
The stock airbox being another source of restriction.

Interesting idea for fitting a larger reed cage, do you know anyone who has done this?

TY175 carby offset: Yes I think the DT and TY250 inlets are also offset for the same reason but at least they did a good job of the flow path streamlining on those. I suspect they were in an incredible rush to get design approval by management for the TY175. The difference in detail design quality between the TY250A and the first TY175 is noticable. Similarly some design details on the TY250B were substandard compared with the TY250A. They couldn't even get the jetting right until after the first TY250Bs came to Australia and some of our sponsored TY riders quickly found something that worked. The problem was the change to the Yamaha-Mikuni on the B from the Teikei Carby on the A was rushed. By the time the next model TY250 (TY250C) came out, the carby was different again and had better jetting compared to what the B model initially came with.

Airbox: Yes I agree and last night I ordered a more sensible airbox from the UK.

Reed cage: I've seen photos on the internet of it done a while back so I know its feasible. I've measured the reed cage compartment on the cylinder and it doesn't need much widening to fit the bigger cage in.

Boost bottle: Did you experiment much with the boost bottle setup? I've read that the length and internal diameter of the tube between the inlet and the bottle is fairly critical for how it functions.

[David Lahey]

At the end of the era, they changed to a reed valve inlet design on their MX bike motors. As you can see the holes in the rear piston skirt are reminiscent of what did many years before.
This is what a reed inlet Pursang piston looks like:

[Kurt]

No I haven't experimented with the boost bottle setup.
Initially it had a large volume bottle say 400-500cc but I found a lower volume maybe 250cc bottle that I thought would suit it better being a low capacity and low revving engine.

I agree though the tube would be important to the scavenging effect.

[David Lahey]

I've been having a big tidy up in my shed during the peak of summer and so far have got rid of one old motorbike, seven bicycles, three scooters and a tricycle. Getting rid of that stuff has allowed two more motorbike frames to be hung up instead of them taking up floor space. The leftover KT250 parts from the work I did on it have been stored away. Getting rid of the camping extensions/attachments that came with my enclosed motorbike trailer freed up some shelf space which allowed me to get three motorbike fuel tanks out of the workshop.
The model 85 Alpina rear wheel in these photos has been sitting patiently waiting to be finished off for a few years now. Today is my RDO and its time has come.
Earlier work:
The rim was vapour blasted.
The hub was vapour blasted except where I painted it black which was dry blasted so the paint would stick.
The brake drum was machined flat and true.
It was respoked with new genuine spokes.
The backing plate is yet to be vapour blasted.
I bought new brake shoes then sent them to a brake shop who fitted 6mm thick super-grippy friction material.
Today:
I plan to machine the brake linings down to fit the drum.
I plan to fit a tyre to the rim.
I hope to find where I put the wheel bearings. I found everything else for the back wheel yesterday.

[David Lahey]

No I haven't experimented with the boost bottle setup.
Initially it had a large volume bottle say 400-500cc but I found a lower volume maybe 250cc bottle that I thought would suit it better being a low capacity and low revving engine.

I agree though the tube would be important to the scavenging effect.

I was originally thinking that this boost bottle might have been off a 1980s DT175 but then I remembered that ITs had them too and even though ITs had a wide range of engine capacity, at the time they all looked the same size bottle to me.