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Augoose

2007 CRF250r valve lash measurements

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All,

I am going over a new to me 2007 CRF250r. The seller claimed that the upper and lower was rebuilt about 5 hours ago. We bought the bike yesterday and it started fine when I inspected it (I checked the exhaust and it was cold) but after getting home its been really difficult to start. 

I checked the compression w/out disabling the auto-decompression and it read 60 psi after about 5-6 kicks. 

The left intake was .152 mm, the right intake was .178mm, the left exhaust was .254mm but the right was .152mm. 

 

I'm going to re-shim the right exhaust obviously but I have a few questions:

1) The service manual calls for 57 psi of compression at 800 rpms. Sorry to sound like a noob, but is this inferring that the kick should turn the engine over at 800 rpms? The service manual was pretty vague on directions for checking the compression.  

2) Can anyone confirm that the tight right exhaust could be causing the hard to start condition? 

3) I've read that the amount of resistance you want on the feeler gauge is similar to dragging the gauge out from the bottom of a phone book. Is that consistent with opinion? 

4) For both the intake measurements, a .203mm gauge wouldn't slide under. A .178mm was really sticky on the left while the .178mm was more smooth on the right. As a result, I decided that the .152mm on the right was ideal while the right was .178. Should I drop the right side valve down a bit? 

 

Thanks!

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*found this in another thread....
intake .005 plus or minus .001 inches or .12 mm +or- .03mm
exhaust .011 plus or minus .001 inches or .28mm + or - .03mm

As far as compression test, I'd do 10+ kicks with the throttle full open.  60 does sound about right since the auto decompression mech is working at kicking speeds.

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Posted (edited)

Thanks for the feedback. I ended up re-shiming the valves based on what felt like the appropriate amount of drag. The bike is still hard to start in that it takes a very strong kick to get the engine to fire. On the other hand my '04 CRF450r starts with much less kicking effort. We went on a 12 mile or so trail ride today and the bike ran great - nice low end power, good open throttle response, idles nicely as well once started. 

I have a 42 pilot jet and I'm currently at 1.25 turns out on the fuel screw based on where I had the highest and smoothest idle. Service manual however calls for 2.25 turns out. The bike did not seem to like 2.25 turns and I felt as if it were already rich at 1.25 turns. Plug was not wet but it was a bit black which wiped off on a cloth. I'm on the 3rd clip position on the needle with a stock main jet. I plan to check the timing and clearances again tomorrow, maybe I'm off a tooth on timing? Should I go against the service manual and try a 40 pilot? 

Only other issue we had was what I think was vapor lock. The fuel line out of the bottom of the tank makes a sharp turn towards the radiator and into the petcock. While riding, the engine stopped suddenly and visually we could tell no fuel was passing through the fuel filter. After cooling for a few minutes, fuel began to pass on its own. Fired the bike back up and rode again for 5 minutes, same issue again and same resolution after cooling. I picked up some new fuel line and will re-route away from radiator with a more sweeping bend to the petcock. 

Edited by Augoose

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Is the gas cap vent line clogged up?  If it happens again, you can simply unscrew your gas cap and see if fuel begins to flow.  Your tank already has a fuel filter built in.  Is it necessary to have another one in the fuel line?  The Honda fuel line is not expensive.  Buy the OEM one that is made for the bike rather than some autoparts store line.

Its been my experience that the 450's start easier than the 250.  Less effort at the lever.

I like to start my jetting with what ProCircuit uses...  

Pro Circuit 170mj, 45pj, NKBT 3 (clip),  1.5(fuel screw),  45 leak

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Posted (edited)

Garage Dog, I did unscrew the gas cap and it didn't make a difference. Regarding the fuel filter, that's a great question. I'd like to not run one but I was worried the screen could pass gunk that the filter would stop? 

So I was just checking the valve clearances again today after riding yesterday and I had a forehead slap moment. Here's what I found....

I think that the PO when he "rebuilt" the head, he installed exhaust shims which were too small (1.77mm). The shims sat inside the retainer and are below the rim of the retainer itself. So when I used my feeler gauge, I was getting a clearance between the rocker arm and the rim of the retainer instead of between the rocker arm and shim.

image.png.5228a91be0265582df645a0778f4a80e.png

When I use my finger and rock the rocker arm up and down, the gap between the rocker arm the surface of the shim itself seems to be about 1 mm instead of .28 mm. 

image.png.cf29061fe620915ed026478b284f1373.png

I took a video of the amount of play I currently have. https://drive.google.com/file/d/1bwNUTlUedlsKpaBPWdRaFcmT7HIHoJFQ/view?usp=sharing

Can anyone confirm that these shims are indeed way too small? 

Secondly, I'm assuming that this is really a good thing, correct? I was a bit worried that a newly "rebuilt" head was already at 1.77mm shims on the exhaust. 

Lastly, this most certainly would cause the hard to kick/start condition, correct? I would imagine the exhaust valves are not opening when or as far as they should? 

Edited by Augoose

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It does look like you have a problem with at least the one side exh valve and that needs attention. I would be checking all the other valves and shims as well, meaning remove the cam and buckets to make sure the intake side is assembled properly also. Apparently the PO didnt know how to check and properly shim adjust the valves.

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On the CRF250R, you have to use a feeler gauge that's reduced in width so you dont end up measuring the lash between the spring retainer and the arm on accident. That's what's happening here.

Those shims are only 7.5mm in diameter. A standard feeler is like 12-13mm...

right now, you arent getting good data to make decisions from.

You need one of these

https://bikemaster.com/bikemaster-feeler-gauge-sets.html

Once you get that nailed down, you need to dial the fuel screw when the engine is fully warm. Also, if the bike has been sitting for more than about a month, I can almost guarantee you that the pilot jet is getting clogged.

If it's me, I replace the pilot jet just to save time. You need the feeler gauge anyway.

 

image.png.df3dedba9d5da95580fdb4e1886fd4a2.png

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My new feeler gauge came in today. Here's where I think I am:

Left Exhaust - 2.25mm shim = .28mm +/- .03mm    (up from 1.77mm shim)

Right Exhaust - 2.15mm shim = .28 +/- .03mm        (up from 1.77mm shim)

Left intake - 1.89mm shim = .12 +/- .03mm             (up from 1.82mm shim)

Right intake - 1.87mm shim = .12 +/- .03mm          (up from 1.82mm shim)

The bike is MUCH easier to kick now vs when the exhaust clearances were huge.

Fuel screw was at 2.25 turns out and I'm at about 1/16" on the idle screw. Started third kick with choke. After warming up for 10 minutes, started better and easier with choke than without, so I'm still a bit lean despite going out to 3 turns on the FS. Pilot jet was replaced and carb is clean. I'm thinking my hot start might not be seated or the threads on the lock down nut are loose. Have an aluminum replacement nut on the way. 
Thanks for all the help. 

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Your "10 minute" warm up time is alarming.  These "R" bikes do not have fans to move air past the radiator.  You are going to cook your engine!  I would not let a bike idle more than just a couple of minutes.

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It'll take 10 min to heat soak the head properly to adjust the carb. But there needs to be some air flow through the radiators. Putting around in 2nd gear or something is fine.

But it's not too lean, it's too rich.

The idle is probably too slow because it's way too rich on the fuel screw.

With the engine warm, you need to dial that fuel screw in, until you get to the highest idle speed, then turn it back out 1/4 turn.  You're done. THEN reset the idle speed with the idle speed screw.

If the pilot is correct, it should need the choke to start on a 70F day, with a kick or two. If it's cold, like 40F, it'll probably want the choke and a twist or two of the throttle (accelerator pump) to prime.  Then it should again start on the first or second kick, maybe three.

The assumption of lean...I have no idea where this comes from. But 90% of the time when someone brings me something that runs like shit when warm, but fires right up when cold..it's almost always got some ridiculously large pilot and the screw out to 2-3 turns out. It's also why they dont want to start easy when they're hot.

 

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Posted (edited)

If it starts easier with choke, how can it be too rich?  I'd expect it to just flood and refuse to start with a wet plug.

 

Personally, I'd make sure that the fuel level in the bowl is spot on.  You can check if it's too high by just leaning the bike over, if it starts pissing out of overflow at fairly moderate lean, it's too high.  Too low is not as easy to detect, just need to open up and see how the needle valve is set up.  It's a bit of a bear to do with the carb in the bike, but if you aim for the float to be parallel to the bottom of the carb at the exact time the sprung little nub on the plunger bottoms out, you'd be pretty close.

Edited by dakh
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Posted (edited)
5 hours ago, Shawn_Mc said:

It'll take 10 min to heat soak the head properly to adjust the carb. But there needs to be some air flow through the radiators. Putting around in 2nd gear or something is fine.

But it's not too lean, it's too rich.

The idle is probably too slow because it's way too rich on the fuel screw.

If the pilot is correct, it should need the choke to start on a 70F day, with a kick or two. If it's cold, like 40F, it'll probably want the choke and a twist or two of the throttle (accelerator pump) to prime.  Then it should again start on the first or second kick, maybe three.

The assumption of lean...I have no idea where this comes from. But 90% of the time when someone brings me something that runs like shit when warm, but fires right up when cold..it's almost always got some ridiculously large pilot and the screw out to 2-3 turns out. It's also why they dont want to start easy when they're hot.

 

Thanks all, this is really interesting. I replaced the hot start nut with an aluminum one and it seated nicely. I wonder if the old one was leaking a bit and I noticed it didn't have an o-ring.

We did ride the bike around for the warm up and didn't let it just sit idling for 10 minutes, as I agree it would over heat quickly. My service manual calls for 2.25 turns out on the FS and a 42 pilot jet which is where we started. I verified the float when I cleaned the carb. With the engine cold and the ambient air temp around 75 F, I rolled the throttle 4 times and it started with choke on 2nd kick. At the time I thought rolling the throttle a few times was appropriate as that's what my 450 seems to like. We rode around the yard for about 10 minutes and then stopped the bike and immediately tried to kick it. Three kicks and it didn't start. Turned on the choke and it immediately started, which led me to believe at the time I was lean because I thought the choke enriched the pilot circuit? I then went to about 3 turns out on the fuel screw, rode around a bit, stopped and then started the bike - started 2nd kick, no rolling of the throttle. 

I had a hard time trying to hear rpm changes from 1/4 turn adjustments to the FS, and I was worried if I sat there idling too long I'd begin to overheat. Seemed that the bike did not respond to FS adjustments between 2.25 and 3 turns out - idle stayed the same best I could tell. What was noticeable was a hanging idle if I had the idle screw up a bit too much. The bike is running SO much better now and my 14 year old son can finally start it himself, so we are ecstatic compared to where we came from last week with the valves so far out of adjustment. 

I would like to get more proficient at tuning the carb so please keep the replies coming - greatly appreciated!

 

Edited by Augoose

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That's unusual.

What fuel screw is in it?

It almost sounds like it wants a 45 pilot...The fuel screw should settle in at 1.5-2 turns out... The fuel screw adjustment is doing almost nothing beyond 2 turns. And they'll want to fall out from vibration at 2.5. Just kind of keep that in mind.

But, if it works, it works.

The "choke" opens up a third circuit all its own.

The only way to really get proficient at carb tuning is to just do it. But to be good at it, you need to accept the results with an open mind. Doing X Y and Z doesn't always work. IE..My 450 had a hanging idle issue, was lazy in the middle, just off the very bottom, hard as hell to start when hot...I dropped from a 42 stock pilot to a 40 and it was perfect. it could be on the edge of boiling over and start on the first kick.

:cheers:

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The fuel screw is one that came in an "all-balls" kit. Not the greatest quality. Thanks for the reminder about the fuel screw falling out - that happened on my DRZ and my 450. 

My 14 year old son and I went riding today and the bike did great. We tried to get a routine going with the starting - choke, no choke, twist of the throttle, etc. We don't have enough time on the bike to really define it yet but we are darn close to being at ideal settings I think. At first start (cold), we turned on the choke and gave the throttle 4 twists. The bike started within 2-3 kicks. After trail riding for quite awhile, we tried starting both with the choke and without. Early on in the 4 hour ride, the bike seemed to start better with the choke (1-2 kicks) but by the end my son was able to start it (hot) no choke, no throttle, within 1-2 kicks. Very happy and his confidence is building. 

Thanks again for the help!

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Posted (edited)

Unless it's a freakishly cold day, no point in even trying to start a warmed up bike with choke.  In fact, from my experience, trying to start an otherwise well adjusted, pretty hot bike with the choke on can wet the plug and require the "air out" procedure to start again.

I have one now and had a couple before, a really well set up carb will get you a bike that starts with a half-assed weaksause kick almost every time (in neutral).  I had one freak bike that would pretty reliably start  in gear too, but I can't replicate that.  All these bikes had a heavier flywheel though.  I think it's just a matter of experimenting.  If everything in the carb is consistent/reliable (no air leaks, float level is correct, etc.), it's just a matter of finding the perfect fuel screw and idle adjuster position.

Edited by dakh

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5 hours ago, dakh said:

Unless it's a freakishly cold day, no point in even trying to start a warmed up bike with choke.  In fact, from my experience, trying to start an otherwise well adjusted, pretty hot bike with the choke on can wet the plug and require the "air out" procedure to start again.....

 I think it's just a matter of experimenting.  If everything in the carb is consistent/reliable (no air leaks, float level is correct, etc.), it's just a matter of finding the perfect fuel screw and idle adjuster position.....

I agree, a warm bike should not need the choke and finding the best mixture setting is exactly what I'm trying to do. I am trying the choke, trying the hot start and just plain old kicking it (one test attempt a time) and seeing what works best helps determine if I'm lean or rich on the FS. 

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