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Valve Clearance Problem?

  • Thread starter Thread starter 78gs1000
  • Start date Start date
7

78gs1000

Guest
Ok, I have a backfire when I run the engine hard, especially at higher rpms about 4-5k range and up. This has not happened before, and just started out of nowhere. Also a noticeable loss in power during acceleration, and its harder to keep it at a certain speed while cruising.

Things I have done, 1. Took apart and cleaned the carbs 2. Checked timing, its good 3. Power to all the spark plugs/coils are good. 4. Resynchronized the carbs.

Just today I checked my valve clearances, the #2 Exhaust shim needs to be changed from a 2.9 to a 2.85. Also on the #2 Intake shim needs to be changed from a 2.7 to a 2.75. #3 Intake shim as well from a 2.75 to a 2.8. All others are within acceptable clearance range.

**Ok there's the info.
***NOW, would the valve clearances on those 3 shims cause the issue reported above? Or do you have another idea for something I could try.

Thanks!
:confused:
 
I don't think so but what were the actual clearances ?? May need to further clean the carbs ? Could have a weak valve spring, a damaged exhaust system ???
 
SqDancerLynn1 said:
I don't think so but what were the actual clearances ?? May need to further clean the carbs ? Could have a weak valve spring, a damaged exhaust system ???
Click to expand...

Ok, my clearances are as follows: (In MM)
Exhaust ** 1- 0.05 ** 2- 0.025 ** 3- 0.05 ** 4- 0.05
Intake ** 1- 0.075 ** 2- 0.1 ** 3- 0.125 ** 4- 0.05

As you can see the intake 2, especially 3 is pretty off. Exhaust 2 isn't too bad.
 
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Just an update, rechecked the carbs, the pilot fuel screws tips got broke when I put that back, but I don't notice any differences and the same problem is occuring.

** So is this a valve clearance problem?

I am going to order the shims I need tonight as well as the valve decompressor tool from Z1 Enterprises. Let yall know what the outcome is
 
Save your money on 'the tool', just use zip-ties. :D

Some claim to be able to use 'the tool' successfully, I'll believe it when I see it. :p

If it were my engine, I would DEFINITELY change that exhaust shim, but leave intake #2 as-is. #3 is loose enough that it should be changed.

.
 
Thanks Steve, I looked up the "zip tie" method and really just don't understand it... You fold it over, crimp the part you folder about an inch from the end, and then hook it on the valve through the spark plug hole? I wish I knew someone that lived nearby the area to show me :o
 
Hi,

I don't think your issue is related to valve clearances. Although I am not a zip tie apologist, the clearances should be set to the correct specifications. I run mine on the loose end of spec. As of my last adjustment, all of my clearances are in the 0.07 - 0.11 mm range. Sometimes I'll even swap out a shim on a 0.05 mm clearance to get 0.10 mm. But that's just me.

Providing the carbs are properly cleaned and adjusted, I would lean toward an ignition issue with those symptoms. Do you have the stock ignition? Is the spark advance working properly? Do the coils spec out? Have you tried installing new points and condensers? Have you insured the points are clean and properly gapped?


Thank you for your indulgence,

BassCliff
 
Ok BassCliff to answer your questions, Do you have the stock ignition? No I have aftermarket. ** Is the spark advance working properly? Yes, i am getting a fluent reading of power from the spark plug and coming out of the ignition, spark advance. ** Do the coils spec out? What exactly do you mean spec out? They are giving an accurate power reading. Have you tried installing new points and condensers? No I haven't but the ones I have are tested power wise to be functioning. ** Have you insured the points are clean and properly gapped? You mean spark plug gaps? They are all within range.
 
78gs1000 said:
Thanks Steve, I looked up the "zip tie" method and really just don't understand it... You fold it over, crimp the part you folder about an inch from the end, and then hook it on the valve through the spark plug hole? I wish I knew someone that lived nearby the area to show me :o
Click to expand...
That's pretty much it.
shrug2.gif


After measuring your clearances and recording them (by the way, I know a guy that offers a dandy way to do that :D), rotate the cam so the valve is fully opened. You can see the edge of the valve through the spark plug hole. Slide the folded end of the zip-tie under the edge of the valve, rotate the cam so it's pointing away from the valve. You now have enough room to move the bucket around to find the notch, then lift the shim out for inspection and/or change. Insert the shim, make sure it's fully seated, rotate the cam, pull out the zip-tie, move to the next valve.

I have had 'the tool' slip sideways off the side of the bucket too many times to be comfortable with it.
Had it happen on one of my previous Kawasakis, and this was the result:
IMG_4064.jpg


IMG_4065.jpg


It took about an hour of fishing with a magnet and another hour of assembling the jigsaw puzzle before I was comfortable turning the crank any more. I figured that small chip on the back side was not going to present enough of a problem to worry about, so I continued.

After having the Suzuki tool slip off the edge of a bucket and seeing how easily it did so, I switched to the zip-tie method and have enjoyed valve adjustments ever since. :D

.
 
Ok, so everything has been done, and its running FABULOUS all the way until I hit 5500rpm. then the engine gets really loud and I have to really force her to go higher. Is that a sign of weak valve springs? Or what else?
 
Not valve springs. Lean mixture or weak spark would be my guess.
 
Hmm possibly a lean mixture, it's still wanting to backfire slightly until its heated up some then I hardly notice it, if I have a helmet on I don't notice it.
As far as the spark goes, everything there checks out fine.
 
I suspect if you put your fingers in your ears you wouldn't be able to hear it either; but that doesn't make the issue go away.
 
MAJOR UPDATE :)
So I finally got my shims in the mail (took forever Z1 Enterprises as many know are out of New York.. and the hurricane delayed thing) Replaced 2 of the 3 needing replacement, Exhaust #2, and Intake #3. I still have to order the shim for Intake #2, I was going to swap out the shim that came out of Intake #3 but it was not what I thought was in there. Anyways got everything squared away..

NOW TO THE GOOD PART :) Bike is running SMOOTH throughout the rpm range(no I don't red line all the time), before like I noted at about 5k rpm it wanted to get loud and not function at optimum performance levels.

BAD PART.. It is still backfiring, maybe more then it was before, also stripped the #3 spark plug hole but managed to get it back in correctly, I'm going to replace the shim on order, and might take apart the carbs....again...

**Could a broken needle jet (fuel mixture screw) just the tips from screwing in too far cause backfire? My carbs still synched fine. Regardless I don't think I'm too worried about it since the bike is running beautifully. I changed my oil while I was bored waiting for the parts as well.

Thanks guys!
 
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With respect to backfire the Dynojet instructions are quite clear:
1) verify there are no vacuum leaks (on the inlet side)
2) verify there are no exhaust flange gaskets leaking ( most common issue)
3) if those things check out, try turning the mixture screw out 1/2 turn, making sure you have a good stock idle.

Hope this helps?

By the way what's the exhaust on your bike?
It looks like a CBR 900 RR?
 
78gs1000 said:
Ok BassCliff to answer your questions, Do you have the stock ignition? No I have aftermarket. ** Is the spark advance working properly? Yes, i am getting a fluent reading of power from the spark plug and coming out of the ignition, spark advance. ** Do the coils spec out? What exactly do you mean spec out? They are giving an accurate power reading. Have you tried installing new points and condensers? No I haven't but the ones I have are tested power wise to be functioning. ** Have you insured the points are clean and properly gapped? You mean spark plug gaps? They are all within range.
Click to expand...

I don't understand your answers here

Do you have a Dyna S electronic ignition?

Some other points set up?

Did you check the advance mechanism with a timing light? Manually?

Did you use a VOM and test your coils to make sure they meet specifications?

Do you know what points and condensors are? How could you have aftermarket ignition and points?

The symptoms you describe could be ignition, but most likely bad jetting or air leaks in the intake system.

What size jets are in your carbs??
 
John Kat said:
By the way what's the exhaust on your bike?
It looks like a CBR 900 RR?
Click to expand...

The problem ended up being my my valve clearances entirely, just letting yall know, and John, I was told by the guy I got it from it was from an early model GSXR. But after looking upt he cbr900rr it does look VERY similar too it! Thanks for that heads up that bike has a 4 bolt flange like mine, I can easily find an adaptable exhaust system now :)
 
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