Jump to content
Sign in to follow this  

Overly-loose valves causing tough starting?

Recommended Posts

So im back on this bike again. Cleaned the carb on it and put it back together. So it takes me about 2 rounds of 18 kicks each the first time which I suppose is normal after it has no gas. But when it stalled on me and I go to start it again, it wouldnt start. At one point I flipped the choke off and it sputtered, twice, but I couldn't get on the choke fast enough to keep er going.

So I figured the valves might be tight. So I pop the valve cover off and measure the valve clearance. Intake were about .15 MM, maybe a bit looser. Now I know the service limit for these bikes is +/- .03 MM per valve, and perhaps this is just a tad over the service limit. I know if I dropped the shim size by .05 (smallest adjustment) it would bring my measurement down to about .10, which although its still in the limit its tighter rather than looser. And valves only get tighter, ive heard its better to have them looser.

Exhaust was the same thing, .28MM was loose so I slid a .30MM in there (not .31. No .31 MM feeler on my gauge, its more inch friendly rather than metric) and .30 still felt just a little loose. Down one shim size would make it about .26 or maybe even .27 or .25 MM clearance.

So does my problem lie here? Loose valves? Anyone think it would help if I ran them a bit tighter?

EDIT: From my memory, the shim size is in the 2.25-2.75 range, I believe. I was last to touch the shims. Figured id add.

Edited by lethalweapon100

Share this post


Link to post
Share on other sites

If it's the stock pilot jet, 42, then the fuel screw needs to be about 2 1/4 turns out. You could check that you have a good spark and the plug isn't groady looking. You also need the pilot jet clean and all the parts on the fuel screw: o-ring, washer, spring. You also might try just turning the idle up a bit, but it sounds like its not getting the right amount of fuel. My wild ass guess. It's hard to figure without knowing more about the jetting.

Share this post


Link to post
Share on other sites

If it's the stock pilot jet, 42, then the fuel screw needs to be about 2 1/4 turns out. You could check that you have a good spark and the plug isn't groady looking. You also need the pilot jet clean and all the parts on the fuel screw: o-ring, washer, spring. You also might try just turning the idle up a bit, but it sounds like its not getting the right amount of fuel. My wild ass guess. It's hard to figure without knowing more about the jetting.

Here's where im at. Checked valves, okay. Checked spark, good spark. New plug as of last november with only a few hours on it. Checked resistance of TPS, 5 Ohms, which is smack in the middle of the service limit. Started cold in about...10 solid kicks, 4 from TDC. Now idling in my yard was...odd. choked, it idles nice. After about 45 sec of choke, back on normal idle, it sounds like it wants to die. It doesnt idle smooth either, it backfires sometimes (lean?). Tiny blips of throttle bring it back. After about a minute of that, I snapped the gas a few times. It missed every time. Now every time it missed, once I let off the gas, the idle rose a little bit then fell right back on its face. Slowly rolling throttle on results in good revs. So I turned up the idle almost a full turn with no results which was odd. So going down my street, I really got on the gas. Hard revs through 1st, 2nd, and 3rd. That was fine. Once I got off the gas from those the idle was a bit high. So I roll up in my yard and cut it. After about 45 seconds I kick it again, nothing. Use the hot start, not even a sputter. So I try to pop it, nothing.

Once it cools down ill turn the air screw out 1/4 turn, sound good?

EDIT: Everything is complete in terms of O rings and stuff. I've done enough FCR Carbs to know what to look for.

Edited by lethalweapon100

Share this post


Link to post
Share on other sites

Yeah, the problem you described isn't getting resolved by a 1/4 turn. You can have backfiring from an air leak as well as lean pilot and even sometimes a coil will do that when the motor is hot and coil going bad. I would look into the carb first, verify the pilot jet # and that it is clean. Take a look at the ap diaphragm and make sure it doesn't have a tear, see below. Ap diaphragm going bad just seems to make everything erratic.

 

Slowly rolling throttle on results in good revs. 

Share this post


Link to post
Share on other sites

Yeah, the problem you described isn't getting resolved by a 1/4 turn. You can have backfiring from an air leak as well as lean pilot and even sometimes a coil will do that when the motor is hot and coil going bad. I would look into the carb first, verify the pilot jet # and that it is clean. Take a look at the ap diaphragm and make sure it doesn't have a tear, see below. Ap diaphragm going bad just seems to make everything erratic.

 

Okay. Which is the AP Diaphragm? The one on the throttle slide plate? Because that one was O.K.

 

Its not backfiring like a traditional BANG BANG BANG either. Its more a small pop. It only happened once when it was still cold and I touched the gas, so I dont think theres an air leak. 

 

Any way to verify that the coil is alright? 

Share this post


Link to post
Share on other sites

Three screws on the bottom of the carb. There is a plate there with o-rings, diaphragm, and spring. Easy to lose an o-ring, be careful. There is info in the owners manual on how to test the coil and all electrical, ohm meter. Still sounds like the carb, get the pilot jet number and how many turns on the fuel screw. 

Share this post


Link to post
Share on other sites

It also sounds like you had the slide plate out? Make sure that went back in correctly?

Share this post


Link to post
Share on other sites

It also sounds like you had the slide plate out? Make sure that went back in correctly?

All those O rings are correct and in place. The diaphram is good too.

I just made a video. It started doing something new. Idle is low, then high like its choked. then low after a throttle snap...then high. Vid uploading now.

Air screw is at 2 and 1/4 turn out, thats what it was before i cleaned the carb.

Ill see if i can get the pilot jet # tonight...is there an easy way to get to the jets without removing the carb? I really dont want to pull the whole subframe again.

Edit: slide and slide plate is okay too

Edited by lethalweapon100

Share this post


Link to post
Share on other sites
It also sounds like you had the slide plate out? Make sure that went back in correctly?[/quote

See video

http://youtu.be/lPma_dGoiW0

 

It was somewhat cold still when I did this, I think thats why it didnt react very well to gas. Now that youve seen it, any guesses? My mind is back on airleak...

Edited by lethalweapon100

Share this post


Link to post
Share on other sites
The carb needs to come out to check the AP-Diaphragm.

 

You can get to the pilot by taking off the front sprocket guard and loosening up the carb and tilting to the right. The remove the bolt from bottom of carb bowl. Long screw driver can get to the pilot. View the pilot through a loupe, it should have a perfect concentric circle, no distortion.

 

It sounded like a carb issue. You can also verify that the carb is aligned in the boot and nothing is clogging the boot at the air jets behind the filter

  • Like 1

Share this post


Link to post
Share on other sites

The carb needs to come out to check the AP-Diaphragm.

You can get to the pilot by taking off the front sprocket guard and loosening up the carb and tilting to the right. The remove the bolt from bottom of carb bowl. Long screw driver can get to the pilot. View the pilot through a loupe, it should have a perfect concentric circle, no distortion.

It sounded like a carb issue. You can also verify that the carb is aligned in the boot and nothing is clogging the boot at the air jets behind the filter

Working on that now.

Not to be a total PITA, but please check back regurally, I really need this bike done.

Share this post


Link to post
Share on other sites

Ha, I am vacationing on TT while unemployed. Hopefully not much longer.

Share this post


Link to post
Share on other sites

Ha, I am vacationing on TT while unemployed. Hopefully not much longer.

Haha, okay. So I got the carb off in record time.

42 PJ. (Pic is the PJ, yes? Checking for brain fart...also the light I can see through the PJ is minuscule. I compared it with a brand new 45 PJ and its about the same...I also have an old 40 PJ)

Air screw a tad over 2 1/4 turns out.

O rings in place, diaphragm came out as pic shows.

Working on coil now.

1399933035260.jpg

1399933063295.jpg

Share this post


Link to post
Share on other sites

Ha, I am vacationing on TT while unemployed. Hopefully not much longer.

Also, I have an idea where the airleak might be. I think its where the carb meets the air boot. I have no way to make sure thats on there all the way, I cant see a damn thing in there. Any way to sucessfully reinstall subframe so that all carb connections are solid?

Share this post


Link to post
Share on other sites

I spray the boot with WD-40 and line it up and push on the swing arm. then I give a tug on the tab at the bottom of the boot. With the air filter off, you can run your finger around the inside of the boot and carb inlet to check for a gap. Make sure the front carb boot lines up on the head at the right side.

 

Am running out of ideal btw.

Edited by restukey

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Reply with:

Sign in to follow this  

×