Hard Starting Hot 1997 XR250

[crwiseman]

Recently picked up a super clean low hours 1997 XR250. When I crash and burn at slow speed (<5 MPH) on a HOT day, bike usually end up on top of my leg or slightly upside down, Of course, I am overheated and out of breath on some horrible single-track side of a cliff goat path in direct sun, no room or traction to bump start. This is the moment the darn thing is an absolute biotch to kick start. It's all stock except for the silencer core removed from the muffler.

I can only assume that it came really lean from the factory as I have to keep it revved up on full choke starting from cold or it will not idle. Any solid-proven jetting/etc. suggestions out there. I would even like to add a full after market pipe system on it without doubling what I have invested in it. Thanks you guys.

 

[TJSCOTT1977xr75]

first off i would get that "Core" put back in, your bike is probably obnoxiously loud without it. dont worry about it not idling cold, because my bike barely does and i end up adjusting the idle screw to make it. as for it not starting after you wreck it, you have usually flooded it, so just take a break and let it sit for about 10 minutes or so and then try and start it.

 

[dirt bike dave]

If you have flooded it, put it in neuetral and open the throttle all the way and kick it over a bunch of times. DO NOT open and close the throttle - hold it wide open the hole time. The air coming in is what is needed to clear the motor out.

Also, check your valves. Overly tight valves are a very common cause of hard hot starting. When the valves wear on these bikes, the valve clearances tighten up.

Basically, when the motor heats up, the clearances get even tighter. If you are too tight to begin with, the valves are not quite closing all the way. This can make for great difficulty on a hot start.

 

[crwiseman]

Thanks guys, since I am new to the bike, I am not all that familiar with all the "tricks". I was trying to clean it out by not touching the throttle, pulling in the comp. release, and holding down the kill button while licking a few times. So holding the throttle wide open is better as it holds the intake open wide?

 

[dirt bike dave]

If you have a manual compression release, keep it open as well as the throttle to help clear the motor out.

If you have the throttle closed, you get a much higher vacuum through the carb, which sucks in more fuel. With the throttle wide open and the motor at very low rpm from the kickstart, there is less vacuum.

Many four strokes have accellerator pumps. So if you constantly open and close the throttle, you will get a shot of fuel each time. By leaving the throttle open you avoid the accellerator pump squirt.

Many four strokes are hard to start hot, especially if they were dumped and laying on their side. So even perfect technique is no guarantee for a quick restart. There's a big reason electric start is so popular, lol. If you crash, try to keep the motor running by pulling the clutch in if possible. Improved jetting might help, too.

 

[crwiseman]

Dear DBD: That's funny, trying to keep the bike running, ha ha. I'll have to give that little XR a lot of credit because it actuals idles away in gear laying completely horizontal for a minute or two before it quits. When I dump it, it's on an expert single-track trail that even a snake would have difficulty getting through. Does anyone have a re-jetting solution for me?

 

[bwood]

If the bike is stock, rejetting may not be the answer. I would check the valves as suggested before. These bikes are easy to check and adjust and will need periodic adjustment. As they wear the distance between the valve stem and rocker arm get closer to a point where they stay in constant contact. Once this happens the valve don't close all of the way causing a lean condition and decreased compression. Also make sure the decompression lever is adjusted properly. Improper adjustment may cause it to stay engaged all of the time (too tight) and too loose would not allow it to engage all of the way. I would also make sure the carb is jetted close to factory. These bikes should idle, they are simple air cooled 4 strokes. They are like tanks and when properly maintained they will last forever. Also make sure your vent tubes on the carb are all clear. Make sure you idle is up where it needs to be, I'm not sure of the exact RPM, but a decent service manual would be a great investment.

 

[rmc_olderthandirt]

If you have the throttle closed, you get a much higher vacuum through the carb, which sucks in more fuel.

No, it doesn't work that way.

With the throttle closed the manifold vacuum will be higher. The "throttle" is the valve between the carburetor venturi and the manifold, and when the valve is closed the carburetor doesn't see the vacuum.

An engine "floods" because an excess amount of gas made it through the carburetor and is now sitting in liquid form in the intake manifold. This can happen easily when the bike falls on its side. Before the engine will run again all that raw gas has to evaporate and get flushed through the engine. The easiest way to do that is to provide as much air as possible to get the gas to evaporate.

Rod

 

[crwiseman]

Does anyone have a link to a do-it-yourself valve adjustment site? And no, I don't have a repair manual, just the owner's manual.

 

[dirt bike dave]

I see the distinction. The key thing is to keep the throttle open.

 

[crwiseman]

Actually, without the "core" in, it's not really too loud. Now it sounds like a motorcycle and not a sewing machine.