Large Valve Clearances

[Dreef1999]

The Suzuki method is probably also the Clymer method, but I don't have a book in front of me to verify.
Using the Suzuki method, one of the two cam lobes on one side of the cam will be pointing UP. The other will be pointing forward or backward, depending on whether you are working on the exhaust or intake cam. When the lobes are in this position, you can measure BOTH valves under THAT cam without moving anything. Rotate the crank 180 degrees (using the 19mm nut on the right end of the crank), check the next pair of valves. Rotate another 180 degrees, check another pair. It is very easy to determine which pair valves are ready to be measured as neither lobe will be pushing on a valve. The hardest part is following a pattern. If I remember correctly, I do Exhaust 1&2, Intake 1&2, Exhaust 3&4, then Intake 3&4. Just checked the Suzuki manual, that is the correct order.

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That is all understood. It is clear to me how the suzuki method works.
I have one point though.

Half of my measurements still satisfy the suzuki method where neither lobe is pressing on a valve and one is pointing up. Those 4 measurements shouldn't be called into question based on the method and all 4 were large, though not the largest.

The possibility that the other 4 measurements are skewed is ok with me but it unfortunately doesn't help explain all of my clearances.

[Wallowgreen]

I had a similar experience with my 850. I've just done the first valve adjustment in hopes it would fix my inconsistent firing problem on #1. I still think I have a pilot circuit issue I haven't gotten to the bottom of yet. However, when I took the cover off and took cold measurements all my exhaust side clearances were huge. The largest was 0.28mm - yes I said 0.28mm. All were around 0.2mm but in order were 1-0.20mm, 2-0.18mm, 3-0.28mm and 4-0.23mm. The intake side were all within tolerance, all four intakes having 2.75 shims.

I understand this should be a reason for further investigation but there is some confounding information that leads me to suspect the previous "person" may have been doing what he could with what he had at the time.

- by looking at the numbers on paper it could be the exhaust clearances were adjusted to be centered on 0.20mm, all four that far out and around the same number... hmmm?

- shims I wound up with exhaust side are: 1-2.80, 2-2.70, 3-2.85, 4-2.75 so on the large side but machine only has 30k on the clock. Sound about right?

- 7 out of 8 shims were 29.0mm diameter not 29.5mm (indicates the quality of the last valve adjustment me thinks!)

- three out of the four cylinders run really well at all speeds

- when pulling at anything above pilot circuit rev's #1 comes in and the engine performs really well to red line

- all the plugs look ok

Only thing I haven't done is a compression test, I don't possess a device to measure it with but I will get that done. Frankly, I don't expect to find anything awry there I think I'd get worse performance with poor compression.

If I've missed something drastic here someone please shout up so I can avoid more heartache. Other than that, I figured I'd continue with the #1 pilot circuit diagnosis whilst running the machine for a few miles then check the clearances again.

[Steve]

... shims I wound up with exhaust side are: 1-2.80, 2-2.70, 3-2.85, 4-2.75 so on the large side but machine only has 30k on the clock. Sound about right?
...

It does not really matter whether your shims are 2.30 or 3.10, as long as the clearances are correct.

... 7 out of 8 shims were 29.0mm diameter not 29.5mm (indicates the quality of the last valve adjustment me thinks!)
...

That tells me a lot about why your clerances are so large. Somebody that either did not know or did not care about the different shim diameter would stand a good chance of not knowing how to do the job correctly.

... when pulling at anything above pilot circuit rev's ...

There is no such thing as "pilot circuit revs". The different carb circuits depend on throttle position, not engine speed.

... I figured I'd continue with the #1 pilot circuit diagnosis whilst running the machine for a few miles then check the clearances again.

I don't remember seeing where you have cleaned the carbs yet. No sense in fighting it when you can simply remove the carbs and check it out in a matter of a couple of hours.

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[jpaul]

I have had valve clearance open up for me, on my 78 GS750. The vast majority of the time they will close up over time, though. I don't know why, and I really don't care. If your bike was running reasonably well before, I doubt if any valves are bent. Swap out the shims necessary to bring everything into spec, and enjoy the rest of your riding season. I would probably recheck the valves over the winter if I were you. I used to do that every winter when I had my 78, just so I wouldn't have to take off riding time for maintenance during the riding season.

[Wallowgreen]

Steve,

That tells me a lot about why your clerances are so large. Somebody that either did not know or did not care about the different shim diameter would stand a good chance of not knowing how to do the job correctly.

That's exactly the conclusion I came to!

There is no such thing as "pilot circuit revs". The different carb circuits depend on throttle position, not engine speed.

Quite right, my mistake, I meant throttle position. When open more than slightly cracked #1 comes in full steam and the machine takes off. If I bumble around the subdivision constantly just off idle #1 is in and out all the time.

I don't remember seeing where you have cleaned the carbs yet. No sense in fighting it when you can simply remove the carbs and check it out in a matter of a couple of hours.

Dude, I've had these carbs off the machine as much as on it in the last six months. First time was over the winter, before that I don't remember any issue with the performance that's why I think it's a carb issue (someone better than me at this may have been able to mask it though). Anyway, I spent time over winter, stripped them all, dipped everything overnight, installed new o-rings (carbs and intakes), reassembled with new gaskets. Inspected the intake boots while I had them off but didn't replace them because they seemed ok but this is a question. Ed was kind enough to supply me with a couple of brass parts that were missing.

After that, 3 of the 4 were leaking from around the bowl gasket. Can't remember who sussed that but it was someone here, maybe renobruce. Whoever it was asked the magic question if it was only while the machine was on the side stand. Evidence round the bowls supported that so I took the carbs off once more to replace the boogered bowl screws with new ones I could tighten better. While they were off, I went through all four again, redipping and cleaning (the bowls needed it anyway). I paid particular attention to the pilot circuit on #1 and am sure all those passages are clear. I posted high res pictures from our microscopy lab of the float needles and seats. HampshireHog was impressed with the pictures but reckoned they were too close up to tell if the needles were worn. I decided to set the floats again to spec then before fitting the rack on the machine I connected the fuel line and checked the gas height in the bowls using a clear piece of aquarium air tube shoved into each bowl drain plug. Bit messy but it showed me the level was within spec so I convinced myself the needles and seats were good. Been proved so now I guess, no more leaking from the bowl gaskets.

Used my manometer I'd gotten from that Irish mob for the first round and synched them on the machine. Used the highest revs method to set the air screws and found another difference. #1 has highest revs when only 1/4 turn out from seated. I also got a colortune so I used that and easily set #'s 2, 3 and 4 but could never get #1 rich enough for the flame to turn yellow.

Another thing I've noticed is the header on #1 is cold enough to hold whilst starting on choke. I get burnt after a few seconds with the other three. Soon as the choke is off, #1 starts to warm.

Been messing with it ever since, the next step was to do the valve clearances.

I figured my best bet now was to get a spare set of carbs and start swapping parts. I wonder if the passage the air screw sits in has been damaged by the bent screw but guessing. Been chasing up Pablo for the set he has, have dibs I think but haven't heard anything from him since.

In the end I just want to get her running like I know she can but I'm running out of ideas.

EDIT: Forgot to mention I also cleaned, painted and sealed the airbox and installed new airbox boots over the winter as well.

[Steve]

OK, you might have mentioned the carb work in another post, I just didn't see it mentioned here.

If it were my bike, I would pull the carbs (again) and look very closely at the cleanliness of the 'choke' pickup tube and the pilot circuit in #1. Along with the 'choke' tube, check the passage in the float bowl that it fits into. If the exhaust pipe remains cold when using the 'choke', it makes me think that it's not getting fuel, so look for an obstruction in the supply. If #1 remains cooler than the others when the 'choke' is turned off, it sounds like the pilot circuit is plugged. Since you cleaned the carbs quite well rather recently, you might get away with spraying some cleaner through the passages against the normal flow. Remove the mixture adjustment screw, cover the outlet holes in the carb throat and spray into the hole where the adjustment screw came out. If you are able to pressurize the flow a bit, you might be able to flush whatever is blocking the line.

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[Wallowgreen]

No worries, that's cool. Wanted to post up here so our mate that started the thread knew it's possible to have large valve clearances and probably have nothing to worry about.

Not trying to hijack the thread here but I really am all ears for some useful suggestions on what I can try next. I'm pretty sure all those choke pipes, pickups and passageways are clear in #1. I was real particular because I knew it wasn't working right, in fact that was one of the reasons I stripped them in the first place. I ran a guitar string through all the places I could like the pick up tube then sprayed cleaner through. Always possible I missed one I suppose, I didn't go to the length of comparing it with another working one to see if spray came out of somewhere in a working one and not in the duffer.

I've also swapped the plug and HT supply with #4 with no change so I'm still back with a fuel issue somewhere.

[Dreef1999]

No worries, that's cool. Wanted to post up here so our mate that started the thread knew it's possible to have large valve clearances and probably have nothing to worry about.

And I do appreciate the info.
I went in to check my shims because #4 was running noticeably more lean(light plugs, slow to warm up) than the other 3 cylinders. Turns out #4 was the closest to 'spec' with intake within tolerance and exhaust just a bit out.

Hopefully shuffling things closer to spec all around will help.

[Wallowgreen]

Most certainly will not do any harm!