81 honda 250r advice needed

[Deathrocket]

ok folks I have been wanting to post this for a while so here it goes. got this trike about 2 months ago and I am trying to figure out what I've got, and where to go. the first question is what carb does it have. its a mikuni with the air inlet side about 4mm larger than stock, and the idle mixture being set by rotating the choke knob. I've talked to 2 shops and only one guy knew about this carb. anyone know anything about these things? most people look at me sideways when i tell them about this carb. next the bike has plenty of get up and go but its just not fast enough for me. (clocked at about 60mph top speed) is that about right for this trike? and if so how much could I gain if i had the jug ported? and will that carb support the increased flow? also are aftermarket expansion pipes / mufflers worth it? they are pretty pricey and I dont want to drop a chunk of change on them unless there going to get some noticable gains. and finally how much bigger can I make this engine with out having to sacrafice reliability? I think thats about it. thanks y'all

[portland250r]

with the majority of engines when you build one thing like boring the jug you have to re tune the bike itself.
if your looking to go faster my idea would be to bore the top end and get it ported and polished after that run the bike and see weather you need to adjust the carb.
ask a shop about this or someone on here may be an expert at this kind of work.

[jadleybray]

You will not see any noticeable gains from boring that cylinder. Unless you need to clean up the cylinder wall, there is no gain in boring, obviously you are not a hardcore dragracer. Pipe, very much worth it, and imo the 1st purchase you should do, along with reeds. You will see and feel gains, then step up to porting to compliment the additional air/fuel in and exhaust out.

[dcreel]

Is the Mikuni a flat slide carb? Got any pics?

[southtexas250r]

you dont really need to bore it... i have a 82 and i just had a wiesco piston dropped in... i also removed the stock air ox and filter and put a replacement k&n that mounts straight to the stock carb... i have very noticable power & speed gains.... so a higher compresion piston and k&n are probably your cheapest bet to start out with.... and also you could go up a tooth on your front sprocket for more top end

[Deathrocket]

nope not a hard core drag racer at all.. just a rider who likes to go fast. I was noticing when i was tuning the carb (went to a higher elevation) that there was a considerable amount of blow back from the intake. I checked all the reeds and they are all intact and seal like they should however i would tend to think that would lead to a small loss in compression thus loosing some latent power. that about right folks? I love 2 strokes but I really don't know much about them and I'm trying to learn as much as I can. thanks again.

[TheRealFatShady]

Better option - what I'm doing - is buy a 1982 or 1983 CR480 honda engine from a dirbike. Supposedly you can use just the top end and mill the stock air cooled R's cases to fit it, also.

I got my engine for $200, the adapter plate set is a little under $200 (still need to pick mine up), then just need to figure out where to put a pipe.

Then you will have a 480 2 stroke as opposed to a 250.

[Yamaha_Rules69]

I dont know how much faster top speed you will gain by doing these modifications above... One thing they will deffinatly do is much faster acceleration. If you want to gain more top end speed you could always change the gearing by getting bigger/smaller sprockets. A bigger front sprocket will provide faster top speeds, and a smaller rear sprocket will give you even more. Changing the gearing for top speed, you will notice a loss in acceleration. Another thing that makes a big difference is tire size. What size are your tires? A 22inch rear tire will allow you to have faster top speed than a 20 or 18 inch rear tire. Usually when a smaller tire is put on, gearing changes must be made, because with a 18 inch tire, it would lose at least 10mph when using the same gearing as a 22 inch tire, but the smaller tire would offer much greater acceleration. Hope this helps!

[Deathrocket]

I'd like to apologize by meaning faster i really meant more acceleration top end is nice but if I had to choose id pick acceleration and I like that top end idea I am going to have to check that out.