1984 Honda 250r revving really high

[jckochan1617]

hey im new to the forum and am having a problem already with my 84 honda 250r. I bought this about as month ago with the engine bored .50 over. Last week i went out to start it and the engine started revving super high to the point i couldnt shut it off. I replaced all my vacuum lines and the air filter is fairly new. The slide is not stuck in the carb and seems to be working properly. Any suggestions out there? thanks in advanced

[shortline10]

Sounds like a fuel flow issue , check everthing related to that .

[jckochan1617]

Can you be a little more specific? sorry im not a engine wizard but have a little experience. And where else would i check for an air leak? Thank You

[badass350x]

How are you checking too see if your slides not sticking? Shortline10 is referring too check your fuel flow coming from the tank all the way in too your carb! Did you change anything? Did you ad a fuel filter? Have you cleaned the carb? But is sounds like it's starving for fuel.

[daledozer]

Check to see if you have a little play at the thumb throttle. Your best bet is to pull it all apart- even the reeds, and put it all back together. If you own it, you should know how to fix it.

[Tri2die]

The 250r is known to rev high when it starts to run out of fuel to the point where even choking it won't shut her down this is either related to the tank possibly in vapor lock meaning its not breathing or the gas tank pet cock being clogged or leaking or the carb itself not performing properly either by jet clog or float sticking in any case it's a fuel starvation issue

[krisx125]

Id check for leaks around the carb. Try sparying carb clean around the rubber intake. If it revs higher, theres your leak.

[SWRWIZ1]

I would bet it is not a fuel delivery problem, it is an air leak, you need to fire it up and start spaying carb clean or starting fluid around the intake boot and where it bolts to the cylinder. if the RPM changes as said you have found you leak, the rubber intake boots are known for cracking and letting to much air into you mixture causing it to run lean and run away with itself. if there is no change you need to spray around the base gasket and then the head gasket, if there is still no change pull stator case and spay around crank seal... that is the long way of doing it, the quick way is to use a leak down tester, put 5lbs of air pressure in your system and see if it leaks, if it does use soapy water and a spray bottle and find problem!! Good luck..

[fabiodriven]

I would bet it is not a fuel delivery problem, it is an air leak

There is no way you can diagnose that with the information provided. The machine will do what he is describing when it is run lean. It could be an air leak, but it could also be a lack of fuel. Either one of these two completely different issues will cause the same problem. The engine running lean. When it runs lean, it revs up. It is very easy to check if it's a fuel problem so there is no reason to dismiss that theory.

Pull the fuel line off and let it flow for a minute. See if you have a nice, consistent flow of fuel. If the fuel doesn't flow well, remove the gas cap. If it then flows well, your gas cap is the culprit. Does the cap have an on/off switch on it? If so, it should be in the "on" position. That is your fuel tank vent.

If fuel flow is bad and cap removal doesn't help then the petcock screen may be clogged or the petcock itself may need some attention.

If fuel flow from the tank is fine then move to the carburetor. Take it off, inspect it, clean it as necessary, and replace any worn parts. During this process you can look for any obvious vacuum leaks.

Do not forget about crank seals. Those are a very obvious culprit as well.

[SWRWIZ1]

I agree that the problem cannot be exactly diagnosed with the provided info, HOWEVER lack of fuel is a long shot on the problem, you will find 100 air leaks on this motor VS. 1 time of a tank vent or petcock being plugged, most notably the bike would start and run fine when it was to let sit for any length of time because the bowl would fill with fuel again. Ever unloaded you bike started it warmed it a bit then took off and got at least a few hundred yards before it ran out of gas, all off of just the bowl... While your theory I feel is not very likely to be the problem you assertion to the fix is spot on, pull the fuel hose off the carb turn the gas on and let it run see if you have a flow, if so fuel delivery most likely is eliminated..

As i pointed out in my first post leak down test would be best way to find problem after you have eliminated fuel flow. you have to pull the carb to do a leak down test, while carb is off give it a good cleaning...

[fabiodriven]

you will find

I'm not new at this.

You can never count on the obvious. The last two lean conditions I fixed were main jet skirts that slid down the main jet body and somehow caused the lean condition. It only covers the main jet, so it didn't really make sense that the bike would lean out with the throttle closed. It did though.

You never know. Start at 1 and proceed from there.

[SWRWIZ1]

I am not at this either been in the business better part of 20 years..

[GoObYdOo]

Do not forget about crank seals. Those are a very obvious culprit as well.

I'm with you on that one!Experienced it on both of my dirtbikes...