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  #1  
Old 12-16-2007, 09:37 PM
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Default Honda XR250R

I just recently bought my first dirt bike it is a Honda XR250R. I am having problem starting the dirt bike. I am finding that is is taking about 15-20attempts to finally get the bike started. I have been an automotive mechanic for about 7 years now but I am not familiar with carbs (electrical and cpu has been my main focus) so anyways I do know a little. I pulled the carb and it was gummed up, along with the fuel filter in the tank. So I cleaned everything so diligently made sure all ports were clean and brake cleaner could go through and put it back together and got the bike to crank in about 3 tries, ran fine for 2 mins than I noticed the exhaust pipes were glowing red. Bad news!!!! This usually means lean condition so I turned my idle screw to no avail. So I got this brilliant idea and decided to adjust the valve, simple to do right done 100s of Honda cars. Adjusted valves to .003in IN and .002in EX. Now I can't get the thing started. Before I did all this crap the bike was popping out the exhaust real bad and the only way to keep the thing running was to keep the choke on. How many turns should my idle screw be turned out? Please help...................
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Old 12-16-2007, 11:53 PM
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Default Re: Honda XR250R

Kind of a tough one for me, even though I own and XR250. (I never used the stock carburetor on it).

Dont worry too much about the glow. I have quite a few air cooled 4 strokes. you are more likely to get that at idle when they are rich to be honest. Mine all do it if it is dark enough to see it.

are you sure that you set the valves when they were really on the compression stroke?
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Old 12-17-2007, 12:21 AM
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Default Re: Honda XR250R

My thoughts too -- maybe not on the compression stroke.

Also, I would check for a leaking header pipe once you verify the valves.
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Old 12-17-2007, 01:13 AM
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Default Re: Honda XR250R

The glowing header is normal, I am guessing you might have a 96 to 04 XR250? On these models they use thin wall stainless steel for the header, so they tend to want to glow if there is no air movement over them (it is also really noticable at night). As for the valve adjustment, not exactly sure with the 250, but on my 400 I have two hex caps located on the flywheel case cover. The larger one is for the crank bolt to turn the crank and the smaller one will have an index mark on it. I am sure the 250 is more than likely the same as the 400, but there should be a "T" mark on the flywheel, you wshould rotate the crank until this "T" is in the index mark. This is "TDC" and the cam lobes should be pointing down towards the ground, this will give you the true valve clearence.

When i had my stock carb I had my idle knob tightend til all the tension was taken out of the cables. When I would go to start my bike, I would turn the knob in to increase the idle and help with starting, once the bike was warm, I would turn the idle back down.

As for the carb, it almost sounds like it is on the lean side. I know the XR's tend to come from honda on the lean side and the Cali XR's are even leaner.

A little tidbit to improve exhaust flow, if you ever get bored and are searching for a little better throttle response, remove the header pipe and grind down the weld on the inside of both small openings of the header where it meets the head on the header. These welds restrict the exhaust flow quite a bit. When I did mine, they were probably choked up to half the size of the pipe. I ground them down almost all the way, no problems in 5 years.
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Old 12-17-2007, 03:39 PM
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Default Re: Honda XR250R

I am not to sure if I am on compression stroke, I am going to go outside tonight and mess with it some. On a car it being a 4 stroke and this bike being a four stroke I would have intake compression power and exhaust. So on the T mark which is the compression stroke both valves would be closed which they were last night. If what I am doing is wrong let me know, cuz like I said dirt bikes are a new world for me.
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Old 12-17-2007, 05:00 PM
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Default Re: Honda XR250R

Thanks yall (with a southern draw) I went outside tonight and checked my valve clearance and to my surprise they were off. In my defense I was mad and it was cold and I tried to start the bike a few times before I did the original adjustment. LoL. I drove it around the yard last night and it rode well but it is popping out the exhaust real bad, sounds almost like a backfire. Whats with that, am I running to rich? Also can old oil cause a hard to start condition, almost to the point of being to thin making the bike loose compression? I know it has been 20 questions but one more, how often should I perform an oil change? I have 3 acres of land and plan to ride the bike often.
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Old 12-17-2007, 11:45 PM
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Default Re: Honda XR250R

Oils cheap, so if in doubt change it. But it shouldn't -- to my knowledge affect the running of the bike as long as it's doing it's job.

I have no idea how often -- maybe every 10 hours?

If it's backfiring a lot, 2 things come to mind.

Does it backfire when you are on the gas, or just on decel?

If it backfires when you give it gas, you are lean. If it backfires on decel it could be either.

And depending on how bad it is, the exhaust to header gasket could be leaking.

Some backfiring is fine. A lot indicates you need to do some jetting work, or fix a leak.
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Old 12-18-2007, 10:08 AM
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Default Re: Honda XR250R

Quote:
Originally Posted by monkeywrench67 View Post
I am not to sure if I am on compression stroke, I am going to go outside tonight and mess with it some.
Simple way to tell if it's on TDC on compression stroke. Take your valve cover caps off and watch the intake valve. It's the one closest to the carb. Turn the engine over without the plug in (the correct direction of crank rotation....)
when the intake valve opens and then closes, look for your timing mark. Bingo TDC....
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Old 12-18-2007, 11:57 AM
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Default Re: Honda XR250R

Yeah Monkey,, look for the intake to be closed about 160 degrees before the T mark comes up if you used JLO's method.

FYI, on the backfiring, that carburetor (which I stated I never used) has a little air cutoff valve. I have had other similar rigs that had that same cutoff valve. It is to help keep the engine from doing just as you indicate yours is doing.
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Old 12-18-2007, 12:00 PM
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Default Re: Honda XR250R

By the way, the fuel screw is in front of the float bowl on the engine side at the 6 oclock posistion. stock setting on an 88 is 2.25 turns out if that helps with anything.
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Old 12-18-2007, 12:20 PM
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Default Re: Honda XR250R

Quote:
Originally Posted by ossagp View Post
Yeah Monkey,, look for the intake to be closed about 160 degrees before the T mark comes up if you used JLO's method.

FYI, on the backfiring, that carburetor (which I stated I never used) has a little air cutoff valve. I have had other similar rigs that had that same cutoff valve. It is to help keep the engine from doing just as you indicate yours is doing.
oops forgot about that part
after the valve closes don't stop turning it over until you see the mark!
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Old 12-18-2007, 01:48 PM
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Default Re: Honda XR250R

Usually on that one, I just look at cam position (lobes should be straight down) but the JLO method is good. just dont expect to see the closing too soon :-)
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Old 12-18-2007, 02:57 PM
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Default Re: Honda XR250R

ok I am positive I got the valve clearance right although with the specs .004 intake and .005 exhaust I have a little rattle nothing excessive though. The bike is running great I still have a little backfire but I am going to wait until I run this tank of gas out before I worry about it, because I put a can of injector cleaner that you would use on a car in the tank.
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Old 12-18-2007, 03:27 PM
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Default Re: Honda XR250R

even in the best of tune you can get them to do it at odd times. enjoy. i like mine. i should put it back together. what year is yours?
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Old 12-18-2007, 11:31 PM
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Default Re: Honda XR250R

Yeah, I wouldn't worry too much about a little backfiring. It's going to happen if the bike is moving and the engine is sucking fuel through the pilot circuit with the others circuits closed.
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