Full rebuild after low-side; troubleshooting idle/running problems.

[Al Capwn]

Hello everyone! Long time lurker, first time poster. First, I want to thank everyone here for all the excellent advice and information. About a month ago, I ended up low-siding on my 2006 GS500F. Typical noob mistake of target fixation combined with lazy turning. I managed to escape with only some scrapes and a sprained right thumb; I was wearing all my gear except for wearing blue jeans. Side note: blue jeans do not count as protective gear. 

At any rate, the bike ended up going sideways into a pole, crushing the tank and into the frame. It was declared a total loss. However, I was not going to go quietly into that gentle night - there was a gentleman who was selling a 2007 GS500F parts bike. I jumped on it as it was a great deal, and ended up having most of the parts to fix the damage to the bike.

Prior to the crash, I had removed the stock airbox and dropped in a K&N lunchbox, and rejet to 20/65/142.5. Adjusted the mixture screws a bit, and everything was peachy. Cold-blooded nature decreased, and starting with choke would cause the bike to start ~1200RPM to warm up to ~4-5K RPM.

Well, after the crash I ended up building the bike from the frame up. I took the time to upgrade the suspension with a Katana 600 rear shock and .80 Sonic Springs + 15W oil, new ZG windscreen, new tires, etc. Needless to say I learned quite a bit on how the bike is put together. However, the way it is running is not like it used to be. Something is certainly "off" in the way it is behaving. Initially there was some backfiring into the carb body, and there is some extra "puffing" in muffler (guessing fuel detonating inside of it). However, there is no smoke in the exhaust, so that is good.

The symptoms and condition of the plugs in very similar to this post: http://gstwins.com/gsboard/index.php?topic=60286.20

The left plug is cream-brown (normal) while the right plug is black and fouled; usually indicative of an overly rich condition just like the post above referenced. Additionally, my right exhaust pipe (same side as the black-fouled spark plug) began glowing cherry red after maintaining 5k RPM for 3-5 minutes. I believe it could be intake manifold boots, valve clearances, timing or exhaust leak, since I did not install new exhaust gaskets. I am guessing this may be causing an improper seal. However, would that cause the black carbon build up on the spark plug?

Here is what is happening:

With the fuel on the ON position:
Idles without choke @ 1100 RPM.
Choke does not increase RPM as expected; it does very little.
Bike bogs down with increase in throttle.
Bike will run for roughly 1 minute before dying out.
After that, will not start on ON without choke.
Bike will barely start with choke on ON.
Switching to RES will cause bike to idle at 1100 RPM until throttle applied - then will stay @ 5000 RPM (with no choke, and throttle closed).
Right-side exhaust glowing red after ~3-5 minutes @ 5k RPM.

What I have already done:
Cleaned the carb body and jets.
Checked float needles and height.
Checked carb diaphragms.
Checked carb vacuum line.
Replaced carb->petcock fuel line.
Checked for kinks in line.
Replaced the entire carb body with one from the parts bike.
Installed brand new jets.
Sprayed to check for vacuum leaks; nothing noticeable.

I have ordered new exhaust gaskets, and plan on replacing the intake manifold boots with the ones from the donor bike, just in case there are any cracks. However, does anyone have some insight as to what would cause this behavior? Any troubleshooting advice would be greatly appreciated.

[1034am]

no expert here, but, it sounds like a gasket leak.  possible head or intake. with the bike running spray wd-40 on the side in question (around the gaskets.) if the rpms pick up, then it's a leak.
if not at least it rules it out.

[W201028]

You say the bike will run for roughly one minute before dying, that tells me its fuel starvation. One cylinder hotter than the other tells me its an individual carb, not the total fuel supply. Run it until it stalls, then open both float bowl drains. If one has less fuel or no fuel (probably the right carb) then look to the fuel supply to that carb, maybe the float needle/seat, or the splitter that sends fuel into the bowls. If both have about equal fuel, then I would look for air leaks, most likely intake side, as exhaust leaks dont heat the pipe that bad.

[Al Capwn]

If both have about equal fuel, then I would look for air leaks, most likely intake side, as exhaust leaks dont heat the pipe that bad.

So I bit the bullet and took off the old intake manifolds and put the donor bike's manifolds on. I did not notice any leaks, cracks or problems with the originals. However, I did notice the carb seats more snugly in the new intakes. Perhaps there was a weak seal somewhere. So far so good - seems like there is a big improvement from the small test I did. 

Idle is stable, and when revving, it does not stay at one particular RPM. It also did not die out, but that was on the RES setting. I will try it out tomorrow purely on the ON setting and see if that makes any difference. Though I cannot imagine it would unless for some bizarre reason there is some starvation with the ON fuel line or something in the petcock.

I still am going to replace the exhaust gaskets as well, just as extra insurance since they should be replaced anyways.

Last issue I am having, and I *think* I know what it is - when revved, it will slowly return back to idle speed (slowly drop from ~4k to 1.2K). Since I put on a new carb body, I never adjusted the air/fuel mixture screws. Since I have different jets/lunchbox, I am assuming this may be what is causing the slower return to idle speed? Either that or carb sync based on this? http://gstwins.com/gsboard/index.php?topic=69127.0

Also, choke still seems to be almost completely unnecessary and does little. So question for those with similar jets: When your bike is warmed up, does applying the choke cause the bike to bog down or just rev higher? Just curious if maybe because the idle jet is larger, applying the choke is making it too rich and bogging it down.

[Al Capwn]

Update: Wellll, I was wrong. I thought I had her fixed, but I have at least narrowed down the problem. It is only firing on the right cylinder.

Tested this by pulling the left spark plug wire, and no change in idle speed. Pulled the right plug wire, and it immediately died. Tried swapping the plugs, and no dice. Checked to see if I am getting a spark, and I am - a solid blue line.

Found out about the "right pipe hot, left pipe not" problem and I guess that means there is a problem with the left side, which makes sense now that  that side is not firing. Also, would probably make sense why it was dumping gas and running rich on one side, since it was doing all of the work. The part that confuses me is that I have tried two different carb bodies and brand new jets, and the same problem persists. That leads me to believe that it isn't carb related.

Did some searching on the forums and came back with the following Blue's Clues...
http://gstwins.com/gsboard/index.php?topic=43834.msg491466#msg491466
http://gstwins.com/gsboard/index.php?topic=45018.0
http://gstwins.com/gsboard/index.php?topic=60716.0

So potentially still an exhaust leak, but I don't know.

So, here is where we are at:

• Replaced intake manifolds.
• Checked plugs - both good.
• Tried different ignition coil; no change.
• Getting spark, but pulling left-coil while running changes nothing during idle.
• pulling right-coil kills bike.

Any ideas? 

[Al Capwn]

Guessing this is bad too...intakes look like there is a black paste build up.

Left Intake:


Right Intake:

[W201028]

Do a compression check, if you have a tester. If not, pull the carbs off and hold your hand over the intake boots one at a time. See if the left pulls any less than the right. Not a very scientific check, but Im guessing you are going to find a big difference. That black goo looks too dark to be purely fuel, I am thinking oil too. If you can, pull the pipes and look at the exhaust valves, I wouldnt be surprised to find the one on the left doesnt have as much buildup as the right.

[Al Capwn]

Well, things keep getting better and better (or worse as the case may be).  Decided to check the valve clearances and the right intake and right exhaust were in spec. However...



...left intake's gap is over .457mm.

No, I didn't miss a .0 in there. That seems like a lot to me, unless I am reading it wrong.  What can cause a gap that large, and how do we correct it? I don't think that number is shim-able is it? Or am I just bad with math?

Also, plan on doing a compression test and I will pull the exhaust as well, but not looking too good at the moment with the valve clearance.

[Krav]

My uneducated guess with a clearance that high is very conservative timing. So powerloss. Thats the theory i can think of. I don't think its particulary harmfull, but then again, im no pro at this shizzz.

[gsJack]

A sticking bucket can cause a valve clearance that large cold and loosen up as engine warms and have good compression warm when it had little or no compression cold.  Had a sticking bucket on my 02.  Check compression with engine both cold and hot.   Check if you can turn bucket with finger with cam turned away from bucket when cold. 

[W201028]

Sticking bucket or serious cam wear are the only things I can think of. Unless a prior owner ground the stem too short.

More likely I think, is all that gunk in the intake side causing the valve to be unable to seat. This would also cause power loss and possible lack of fire on that side. I think youve found your problem.

Pull the carbs again, pull the spark plug from the left cylinder, and shine a bright flashlight into the intake boot. Look through the spark plug hole andI bet you see light in the cylinder.

[Al Capwn]

Ok, I will go ahead and clean up the intakes and the valves and  try that light test. I have some Seafoam intake cleaner spray I picked up just for this reason. Somewhat dumb question: If the valve is not seating all the way, would this affect the clearance values I am seeing?

[Al Capwn]

So I did the light-through intake port test, and sure enough I could see the light coming through. However, to be fair, I haven't ran the engine yet and I have the starting pickup at the R.T. I will attempt to fire her up and see if the light is visible after the valves are in their completely closed position.

Then the question is, how do I fix it? I am going to try and clean up the valves as best as possible, but what is the best way to clean out all the carbon and gunk?

[Al Capwn]

Update: We have compression, so that is good. Downside is that it is most certainly a valve problem. With the air filter out, the engine will turn over and run on a single cylinder and spit misty gas back through the left carb. Basically, the compression stroke is blowing through the non-sealing valve and sending gas back, instead of igniting. 

Verified this by running some air through the spark plug hole where the valve was in its most closed position - air shot out of the intake manifold. Guess I am taking apart the head this weekend, and looks like I am going to have to continue this project in the Projects and Builds section of the forums. 

Thanks to everyone's suggestions and inputs, and if anyone has any wisdom on swapping out the heads of the bike, let me know.

[W201028]

It could still be a sticking bucket holding the valve down, but yes the valve not closing is why you say such huge valve clearance. Its tough to clean a head on the engine without throwing all that carbon and gunk down into the cylinder. Before you pull the head, try and turn that bucket like jack said, and if you cant, theres a chance the bucket is stuck and can be fixed from the top. If you can turn the bucket, I would say for sure that it is the valve staying down under its own power, whether from the seat being filthy or maybe even a broken valve spring.
Either way you will be pulling the cam to get to the bucket or pull the head, so read up on timing the engine, and set it at TDC before pulling anything further apart.

[Al Capwn]

I was able to spin the bucket freely, without any resistance, so the bucket did not appear to be the issue. At that point I figured "in for a penny, in for a pound" and watched BaltimoreGS's video on top-end rebuild. Set the engine to TDC and pulled the cams and head off. After removing the head, it is pretty clear that there is a gap in the valve, but I won't know why exactly without pulling the valve out, like you said.

So I have an extra head+cams from the parts bike I bought - the crank was toasted, but everything else seems to be fine. Would I be able to replace the gasket and place the new head+cams on without messing with the current pistons and cylinder block? Or is the head married to the bottom cylinder block in some way?

I.e. can I swap this part out...


...from this engine?

[W201028]

I cant say for a swap unless they are the same year, but someone else will know more than me. I seem to remember 04 and up having either bigger exhaust valves or exhaust ports. If the ports are bigger, they may not fit your pipe. If its valves, maybe piston clearance? Not sure.
As far as head and block being married, I have yet to see this on any production machine. One head to rule them all, so to speak.
Do look at the stuck valve though, is the gap all the way around, or just half way? Any damage to the top of the piston?

[Al Capwn]

So the original bike was a 2006, the parts bike is a 2007 - I can't imagine an engine change between the two years, but stranger things have happened. So if a head swap is possible, I will just do that while I investigate what it going on with the head with the stuck valve. I have the parts bike's cams so tolerances shouldn't be a problem. There is no noticeable damage to the piston heads. Just some black carbon coating.

The valve has has 3/4 gap around; the rear portion that is next to the exhaust valve is seated, the front and sides have a gap. Guessing that means buildup on the valve seat or potentially a bent valve?

[gsJack]

If my memory is correct the 2nd air was added to all US bikes in 07.  It was already on California F models in 04-06.  Can't think of any other changes between 06 and 07.

[W201028]

Secondary air shouldnt be a problem, as many people block it off anyhow. Look around the exhaust ports, I think the SAI is above the ports. Should be a direct swap other than that.
Id love to know what caused a 75% seating problem on an intake valve; Ive never seen or heard of this without further damage. I was thinking maybe the motor sucked a throttle plate screw or some other solid part, but I believe you would certainly see a knicked piston and/or exhaust valve damage. Also, Ive never heard of anyone burning an intake valve due to poor jetting, timing, or any other reason.
Good luck on the swap, and when you get to look into the old head, post some pictures of the valve before and after disassembly. Could be good educational material.