84 250r Gearing Help!

[250r Noob]

Well ive had it for a little while now and gotten to know it more. Um a weird thing is , if you let it run out of gas, just before it runs out on ON position, it revs like mad uncontrolably. The kill switch wont even turn it off.The guy said about it sucking air in and thining the air/ fuel mixture out. Has anybody else heard of this problem? Is their a way to fix it?Also im looking to get a different fron sprocket. i need a little more torque, i was thinking a 11 tooth sprocet on the front. Im still getting used to the race style of trikes.

[Flossyb20]

Well, what you're describing is called the "death rev"...and it means what it says...do not let your engine run out of gas!! 2 strokes love to run lean...but it also means less oil in the engine...doing this will toast your engine. If you really need to drain the fuel out of the carb, then use the drain screw at the bottom of the bowl to do this. As far your front sprocket goes...if you want more torque, you'll need a bigger rear sprocket, not a smaller front. Truth be told, you really shouldn't go smaller than a 13T on the front...it'll put too much strain on the shaft and the chain...or you could also just run smaller rear tires.....

[fabiodriven]

As far your front sprocket goes...if you want more torque, you'll need a bigger rear sprocket, not a smaller front. Truth be told, you really shouldn't go smaller than a 13T on the front...it'll put too much strain on the shaft and the chain...or you could also just run smaller rear tires.....

Putting a smaller front sprocket on will accomplish the same thing as putting a bigger rear sprocket on and at a fraction of the cost. Also, there will be no need to get a longer chain. He may have to shorten his current chain (assuming it's still good).

As far as a smaller sprocket putting more strain on the shaft and chain, that is totally incorrect. I'm not sure where you got that info but it is wrong.

Smaller rear tires would also bring the gearing down as well, but he might not want smaller tires.

[Flossyb20]

Putting a smaller front sprocket on will accomplish the same thing as putting a bigger rear sprocket on and at a fraction of the cost. Also, there will be no need to get a longer chain. He may have to shorten his current chain (assuming it's still good).


You are 100% correct...putting a smaller front spocket on will accomplish the same thing, but when you talk about going down to an 11T on your front sprocket, you may possibly run into problems with the small radius of a sprocket that size, and you'll increase the risk off popping your chain because of it. It really depends on what he wants to do with it. I for one, just kept my gearing stock, and am running 20's in the back, as opposed to 22's...but to each his own.

[fabiodriven]

To sum things up for you Noob, assuming they make an 11 tooth counter shaft sprocket for your R, you can indeed run it with no issues. That is keeping in mind that you have a chain and rear sprocket that are in good shape and you have the chain adjusted to within factory spec.

An 11t sprocket will work just fine.

[Flossyb20]

You should listen to Fabio...he is all-knowing.

[bslama69]

Flossyb20 is correct that you should avoid running out of gas on a 2-stroke, especially at high RPM's. It causes the engine to run so lean that it "diesels", which means that the fuel mixture ignites itself on compression, which is why your kill switch doesn't shut it off. Definitely not good to run like that as there is precious little oil/fuel mixture to lube the cylinder.

As to the gearing I run my '83 stock (100% original bike) and find that is the best gearing combo. I have plenty of bottom end and top speed in 5th is plenty fast enough. I wouldn't personally run an 11T on front. On the project '82 250R that I am building I decided to go up 1 tooth on the front sprocket to a 14 and ran into the problem where there is not enough adjustment to make up for the 1/2 link that I added. 1 chain link = 2 teeth on a sprocket. I had to buy an offset link (AKA 1/2 link) which I don't like to do. Everything on this bike is new, including chain and sprockets, and now I have a 1/2 link that is much more likely to fail on me. If you really want more torque on your 84 I would recommend adding 2 teeth to the rear sprocket or adding 1 to the rear and going down 1 in the front (you should always replace chain and sprockets as a set).

Just my opinion, I could be wrong : )