[Solved] Left Cylinder Misfire - Bad Petcock - Valves too tight

[crazydred]

EDIT: The issue is Solved - the problem was the bad petcock diaphragm and valves set too tight
Read on if you want to repair it yourself
Notice that I had no experience with the engine before buying this bike.

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After posting this video about my bike on another topic:
http://gstwins.com/gsboard/index.php?topic=70686.0;topicseen

I decided to create my own since I've made some progress diagnosing more issues.

[crazydred]

So, I found out that the fuel tap/petcock diaphragm was leaking gas to the vaccum system which is connect only to the left carb (causing rich mixture? black wet spark plug on left side, backfires and left not firing at all)

After removing it and cleaning the carbs again, I started the bike without the petcock by pinching the vaccum hose and connecting a fuel bottle to the fuel line.

The bike ran fine with a bit of choke and both cylinders ran at about 220ºC. <- some progress right here 
The choke is needed because the air box is not connected resulting in too much air entering the carbs

However, occasionally the left carb spitted fuel backwars through the pilot air jet marked on the picture (I don't know its function)
I will provide a video soon (uploading)

[crazydred]

EDIT: has I wrote bellow (Reply #13)
I had negative gaps (calculated by doing the maths) on both Intakes that caused carbs spitting fuel backwards because the valves were not closing all the way.
Also the exhaust ones were too tight.

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Here's the video that shows the issue:

[crazydred]

So, today I checked the valves. I found that I maybe I need to replace both intakes because my smaller gauge 0,05mm won't fit.

Also I found that there were only 17 chain pins between the number 2 and 3 cam notches.
I was like wtf? Manual says 18 pins...

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EDIT: this happened because I turned the engine without the cam chain tensioner installed, don't do it!
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I took the intake shaft out and placed the number 3 pointing the 18th pin, also on the exhaust shaft the number 1 should be horizontal (pointing fowards) and the number 2 vertical (pointing upwards), they are not.

If I rotate the engine so they are (1 horizontal, 2 vertical pointing up)  the RT ignition pickup mark goes out of alignment.

As you can see in the images below:

[crazydred]

Please help, any opinions would be helpful 

[crazydred]

I will try this method, I found on the forums

Resetting the cams is always tricky and their is an art to it.  that left exhaust lobe is a PITA.

the way I do it is to leave the cam chain tension installed but backed all the way off. Place and start tightening down the cam holders as per the manual, but before the left exhaust lobe starts putting pressure on the valve, let the tensioner out so that if (when) the exhaust cam slips it takes the intake and crank with it so they all stays in time.

yeah and ALWAYS rotate the motor around by hand a few times to make sure you have it right, though you can have it wrong by one tooth each way and it will still rotate, but it won't run or will run like crap.

Good luck, I hope you didn't damage the motor.

[gsJack]

I see the 2 and 3 arrows pointing to the pins but can't see the #1 arrow you refer to as being horizontal.  The #1 arrow should line up with the top finish of the cylinder head.  Assuming the picture of the rotor is positioned as it is with the #1 arrow lined up properly that might be as close as you can get it timed.   

I pulled my 02 head to replace a broken valve and when I retimed the cams that #1 arrow was a bit above the finish but to change it a link would have put it further below so it was as close as possible and ran great for another 80k miles. My rotor was right on the top center mark while installing the cams.

[crazydred]

Here you can see the #1 and #2 nothes marked in red and green lines representing vertical and paralel references to the engine.
It is impossible to rotate the shaft more to the right because the cam lobe hits the exhaust port (it would be a bit open already).

Also I have a question which is when I turn the engine with the 19mm wrench I feel normal resistance but at some point it rotates by himself like half turn (I guess this is engine counter balancer?). Is this ok?

[gsJack]

When your turning the engine with a wrench it jumps forward a half turn when a piston goes over the top and starts down on the power stroke if the plugs are left in, the counter balancer has nothing to do with the movement.  Are you paying attention to the notches on the ends of the camshafts?  My engine timing diagram:

[crazydred]

It is impossible to rotate the shaft more to the right because the cam lobe hits the exhaust port (it would be a bit open already).

The exhaust valve on cylinder #1 (left) needs to be pushed down a bit so the camshaft is assembled properly.
This is impossible imho.

My new approach will be setting the signal generator roughly 15º degrees before the RT mark, assemble the camshafts and hopefuly, when I rotate the generator back to the RT mark the exhaust camshaft will be exactly as shown on your diagram.

[gsJack]

It was 11 years ago when I timed the cams on my 02 GS but nearly as I can recall I put the crank on the RT mark and left it there until the cams were timed and the cam chain tensioner was set.  Rather than fight the left exhaust valve I took the sprocket loose and timed it to the marks and after cams were done I turned the exhaust cam forward and rebolted it to the sprocker compressing the valve. 

[crazydred]

Today I assembled it all, but it still spits through the left carb air jet.

I just ordered a small feeler gauge set from china because my 0,05mm would not fit into any of the valve gaps.
I hope I dont have negative gaps 

Anyways the shims mounted are:
LEx 270 | REx 265
LIn 255 | RIn 260

[crazydred]

Update:
Feeler gauge just arrived, aswell as a brand new 250 shim so I can swap the shims around and take 0,05mm from each valve.

going from:
LEx 270 | REx 265
LIn 255 | RIn 260

to:
LEx 265 | REx 260
LIn 250 | RIn 255

But I gotta re-check the gaps with my brand new chinese feeler gauge first 

[crazydred]

So yeah a little update on this so future readers can enjoy the whole story.

Last week I finished the valve job going down 0,05mm on each shim.

old shim sizes mm:
LEx    (gap)| REx (gap)
270    0,02 | 265 0,015
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LIn     (gap)| RIn (gap)
255   -0,01 | 260 -0,01

new shim sizes with gaps in mm:
LEx (gap)  | REx (gap)
265    0,07| 260 0,06
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LIn (gap)   | RIn(gap)
250    0,04| 255 0,04

Notice that: LEx means Left Exhaust and LIn Left Intake
The gap must be set between 0,03-0,08mm
I had negative gaps (calculated by doing the maths) on both Intakes that caused carb spitting fuel backwards because the valves were not closing all the way.
Also the exhaust ones were too tight.

Also notice that with some luck I managed to set higher gaps on Exhaust side as recommended by @gsJack
I only bought a 250 shim from eBay (8€), swaping the used ones to the other buckets.
You don't won't a big gap or you will get that awful valve ticking noise 

Important Note: As I had no Suzuki valve tool and the zip tie method was not working for me I disassembled the entire cams to change the valve shims. I do not recommend doing this because it's really hard to time the engine again with the RT mark!

I had to turn the engine backwards about 15º degrees, tight the cams and re-align RT mark (rotating the engine forwards) hoping that cam notches would face each other and #1 was perfectly horizontal / #2 vertical (you can see the diagram above posted by gsJack).

[crazydred]

So, I found out that the fuel tap/petcock diaphragm was leaking gas to the vaccum system which is connect only to the left carb (causing rich mixture? black wet spark plug on left side, backfires and left not firing at all)

How did I found out that the petcock diaphragm was bad?
- First I removed it and connected the carbs to a bottle filled with gas and the bike fired right up (both cylinders) dispite the backfire shown in the 2nd video on this post (valve problem)
- Second I placed my mouth on the petcock vacuum connection, filled the ON connecting with water and sucked -> water came to my mouth -> I was like WTF you are leaking!
- Disassembled the petcock and spent 30min understanding its fundamentals
- Pointing the phone's lantern right under the rubber diaphragm showed some tiny holes where gas would be sucked into the vacuum system.
- I tried to repair the diaphram with glue with no success and it would fail again anyway 

Note that the vacuum only connects to the LEFT carb -> LEFT cylinder, so only the Left cylinder was getting bad mixture!

So, following this issue I bought a used petcock from eBay for 18€ from a 1995 GS500 which is working perfectly.

I also found out that the last owner had the hoses connected to the petcock the wrong way so the ON positing would not work at all, the RES was using the PRI tinny hole (causing fuel starvation under full throttle) and PRI was fine working backwards 

Finally I replaced all the hoses with new ones for about 5€ (except vacuum one  )

[crazydred]

Finally I equalized the carbs using my home made tool, using glass bottles and sealing the hoses and caps properly with hot glue!
Note: If you don't seal it right one bottle will always rise, you can diagnose this by switching the hoses connected to the carbs, if the same bottle rises you have a leak.




-> Checked the carbs float heigth using Kerry's method: http://www.gstwin.com/float_height_check.htm



But you can also use the proper engineer's recommend method: http://gstwins.com/gsboard/index.php?topic=26604.0
Set at 14.6+-1mm



-> Installed 2 new spark plugs - 3,30€ each

The bike now runs like a clock and I am proud of my work.
Looking back I did it with passion and I learned alot by getting the hands dirty (use some rubber gloves).
Thank you gsJack and Grupo Gs500 Brasil for helping me 
I hope that in the future this post helps anyone with the same left cylinder misfire problem or valve job.

[SirHansford]

Well done man    Enjoyed reading your thread and seeing your progress.  Learned a good deal from it as well.  Lots of satisfaction fixing a problem yourself and not having to pay someone to do it for ya!  Thanks for sharing.