'83 250R carb swap

[red_russian1]

Good evening! About 6 years ago, I acquired my brothers 250R (the one in the pics). I stripped it down to the frame, rebuilt/repainted nearly every part and bored the cylinder out to about .070" over (I'm guessing because I don't recall off the top of my head). I also installed a set of Boyesen Pro Series reeds and Moose torque spacer. After I broke in the rings, I found a guy that was selling a larger carb off of a supposed '84 or '85 250R. I think I paid $40 but never installed it because I wanted to put a kit in it and I also would've needed to remove the air box and install a filter directly on the carb.
Well, 6 years later and after the trike has been sitting for 4 of those, I decided to dust it off. Choke is broken, right tire is flat and a mouse nest in the air box but it started after about 5 kicks!
So, my question is; has anybody installed this larger carb on their trike? I'm just looking for some info on what jets to install, air filter to use, etc. Thanks in advance!

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[yaegerb]

Yeah you can, may require frame mods but I have put a 41 TMX in an 83 before. Just need to take measurements. I would go with a modern carb like a keihin pwk or mikuni tmx.

[red_russian1]

Yeah you can, may require frame mods but I have put a 41 TMX in an 83 before. Just need to take measurements. I would go with a modern carb like a keihin pwk or mikuni tmx.

Modern because of parts availability? Will I notice very much difference with the one I planned on using?
I remember chatting with someone when I first got the bigger carb about which carb adapter to use. They said I should be able to heat the '83 adapter to stretch it over the larger bore and still be able to run the factory air box...

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[barnett468]

I also installed a set of Boyesen Pro Series reeds and Moose torque spacer.

Why did you put the spacer in it?

[red_russian1]

Why did you put the spacer in it?

It's supposed to change the power curve to give it better low end. It does have tons of low end now but I think I might pull it out if/when I change the carbs.

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[atc300r]

Its hard to do but posible.I stuffed a 38 mill carb with esr reed block 13 mill reed spacer and a DG intake in my 300r. Im using my stock airbox with lid removed.

[barnett468]

It's supposed to change the power curve to give it better low end. It does have tons of low end now but I think I might pull it out if/when I change the carbs.

Well, actually, the majority of the time they REDUCE hp and soften then hit. They were originally designed for the 1978 YZ400's. These bikes and even my 1981 YZ465 have a boost port in the rear that is partially blocked by the reeds, which renders the boost port less effective. The 78 400's and the 80 465's also had a very abrupt power hit, so strangely enough, this spacer softened the power hit but still increased the power. It sounds a bit contradictory but that is what they did. I had a 1978 YZ400 in 78 (I also have one now) that I raced in the Pro class, and the engine was stock with the exception of an ANSWER silencer, and I was always an extremely good starter, but after I got this bike, I went from getting 1st thru 4th place starts, to getting 6th and 7th place starts against the same people, and when it came on the pipe, it would get squirrely, so I called Dave Miller, whom had a shop called Miller Mano at the time (now called DMC), and whom sponsored me in 1976, and told him what was happening, and he told me to get the spacer and install a 2 tooth larger rear sprocket, which I did, and the spacer reduced the abrupt hit so the bike was more controllable even though it now had a larger rear sprocket, and the very next race I got a 3rd place start and finished in 3rd even though my rear brake rod came off in the first turn, and every start and finish was much better after that.

Since the mold was already made for the spacer and the mfg still wanted to sell as many of them as they could, they simply gave it a fancy marketing name like "Reed Valve Tourque Spacer" which suggests that it increases an engines torque, even though it actually reduced hp on nearly every bike at the time except for the 1978 YZ400, lol.

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[atc300r]

On the 250r the reed block covers part of the ports .I use them on my aircooled 250r and 300r so the aftermarket reed blocks will and not bottom out.

[red_russian1]

On the 250r the reed block covers part of the ports .I use them on my aircooled 250r and 300r so the aftermarket reed blocks will and not bottom out.

So, leave it on?

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[barnett468]

So, leave it on?

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No, you need to test it, so simply try it with and without the spacer, but I can guarantee you that if you are looking for a fairly noticeable increase in low end, the spacer will not provide it. Also, the rear boost ports still function without the spacer, and to improve their function a little, the bottom edge of the port closest to the cylinder can simply be radiused a bit to unblock them some more.

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[red_russian1]

No, you need to test it, so simply try it with and without the spacer, but I can guarantee you that if you are looking for a fairly noticeable increase in low end, the spacer will not provide it. Also, the rear boost ports still function without the spacer, and to improve their function a little, the bottom edge of the port closest to the cylinder can simply be radiused a bit to unblock them some more.

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Did you have any pics of how these ports should be modified? I might tear it back down someday to do it but at this point, I'm just looking at swapping carbs out.

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[barnett468]

On the 250r the reed block covers part of the ports .I use them on my aircooled 250r and 300r so the aftermarket reed blocks will and not bottom out.

I'm not very familiar with this exact model but doing a quick Google search I found 3 cylinders that all sellers claim to be from an 83 250r and 1 has a boost port and it is red, and the others do not and they are black. Obviously the cylinders could have been repainted a different color but my bet is that the boost port cylinders are actually from an 84 and, and if so, there is no boost port for the reed valve to block in an 83 cylinder unless someone removed the bottom of it to open it up which I think is the case because I saw 2 82 cylinders that had the boost port.

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The black cylinder

[barnett468]

Did you have any pics of how these ports should be modified? I might tear it back down someday to do it but at this point, I'm just looking at swapping carbs out.

I do because I did the same thing on my 1981 YZ465 around 4 weeks ago but I will have to find them.

[yaegerb]

Modern because of parts availability? Will I notice very much difference with the one I planned on using?
I remember chatting with someone when I first got the bigger carb about which carb adapter to use. They said I should be able to heat the '83 adapter to stretch it over the larger bore and still be able to run the factory air box...

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Yes, easier for parts and better technology.

[red_russian1]

Yes, easier for parts and better technology.

So, any idea which carb or size to run? I'm not really looking to dumping a bunch of $$$ into a new carb if this PE will work.

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