Compression and throttle question

[Ian Donahue]

Hi everyone. I bought a 1983 GS850g in January and I'm having a hard time getting it running right. Here's what I have done:

Replaced air intake boots, clamps and o-rings
Cleaned carbs and replaced gaskets and o-rings
Cleaned the carbs again with a full dip
Checked the diaphrams and replaced one
Bench tuned the carbs with the basscliff paperclip under the butterfly technique
Set the mixture screw to 2-1/2 turns
Replaced airbox boots
Rebuilt the airbox using basscliff technique (new weatherstripping, cleaned and oiled the air filter, etc.)

Sooo... I start the bike, and it purrs like a kitten, until it warms up, then I get an idle increase, and a hanging idle when I blip it. This has been happening all along, hence the usual attempts at fixing. So I let the idle climb and just kept dialing down the idle until it was purring. All set. But then I can't get it started even with the choke. Not surprising. So yesterday I picked up a compression test kit. Good news - all 4 cylinders are with 5 psi. Bad news is 60psi. Very bad news is that it does not increase when I open the throttle all the way up like you are supposed to do. 60 psi either way.

Naturally the next step is to shim the valves. I ordered the tool and feeler gauge last night (and a set of real o-rings from cycleorings.com). But in the meantime, what do you all think about the compression issue? Am I wasting my time here? Is there an engine problem? Do you think my valves are too tight and everything will be better after the adjustment?

Any advice would be great. Thanks everyone!

 

[Big T]

I'm guessing that your bike sat for a long time before you bought it.
Chances are good that your rings are stuck in the grooves and not sealing fully

So, adjust valves, complete the carb rebuild and sync them.
Ride the heck out of the bike and see is compression comes back up

Many people recommend putting some Marvel Mystery Oil into each cylinder for a few days and rotating the motor to free up the rings

 

[Nessism]

I'm surprised you didn't just do the valves straight out.

 

[Steve]

Yep, first suggestion is check valve clearance. (Your spreadsheet has been sent.) After that, open up the mixture screws another 1/2 turn for a total of three turns, just to make sure it's not running too lean until you can verify other issues.

How long has it been since the bike has been run regularly? If it has been a while, you might also need to do an Italian Tune-up.

.

 

[Ian Donahue]

Yeah, I was afraid of the 3 of you, since I knew I would get my pee pee wacked for not doing the valve clearances. Opening the engine is a little scary for some of us, and I also did not want to create more variables into the system. But like every other tutorial on the basscliff page (thank god I bought an 850) it's really not that hard once you just put the wrench to the bolt. I appreciate the support that I'm on the right path, and just need to "complete the road". The carbs are busted down and waiting for "real" o-rings (cycleorings.com) and my tappet depressor and feeler gauges will be here on Tuesday. I'll do the mystery marvel thing just to dot my "i"s. For carb syncing I was going to purchase the dial type, since they are half the price of the mercury type. Any warnings there?

 

[Ian Donahue]

Steve - I'm not sure how long the bike was sitting (bought it from the son, the owner is deceased), but it was registered 2 years ago, the son claims it was on the road last year. Best part of the bike was the storage condition - rust free, every machine screw I have touched has come right out. I don't think this bike has ever spent a night outdoors. It's in great shape, I'm excited to make it run and look great, I just want to get over this hump and see it run, then get into the smaller items and the polishing. But I got all winter for that right? Italian tune-up is hysterical, I got that suggestion from a couple of buddies yesterday! Now I know the name!

 

[Steve]

For carb syncing I was going to purchase the dial type, since they are half the price of the mercury type. Any warnings there?

OK how much money are you talking about there?

For a decent set of dial gauges, you are going to spend at least $100.

Where can you still get a set of mercury gauges?

The forum favorite is the Morgan Carbtune. It comes from Great Britain, so it is priced in Pounds, the current exchange rate has it at $93.59 USD. MUCH better unit, and a LOT safer than Mercury.

EDIT: For what it's worth, I have a Carbtune, a Mercury gauge, a Motion Pro "blue liquid" gauge and the official Suzuki gauge with the balls. The only one I don't have is a dial-type, and there is a reason for that. :-\\\

.

 

[Steve]

Italian tune-up is hysterical, I got that suggestion from a couple of buddies yesterday! Now I know the name!

The concept is rather simple. For an engine that has been stored a while or run rather gently, the cylinder walls might have oxidized a bit or the rings have gummed up a bit in the pistons. Running the engine vigorously for several hundred miles (with fresh oil) stands a good chance of freeing up the rings and re-burnishing the cylinder walls, which can bring the compression back up to spec.

Of course, that assumes that the valves are properly-clearanced.

.

 

[Ian Donahue]

$93 US is less than I expected for the gold standard, but 10 days... This is the dial type I mentioned:

https://smile.amazon.com/AlphaMoto-...TF8&qid=1492990951&sr=8-2&keywords=carb+tuner.

Here is the Motion Pro I can get from Amazon overnight:

https://smile.amazon.com/Motion-Pro...TF8&qid=1492990951&sr=8-1&keywords=carb+tuner

Is this equal in quality to the Morgan or crappy facsimiles? Should I suck it up and wait the 10 days?

 

[Steve]

Let's just say that even if you manage to tame the needle bounce to where you can actually get some information from the dials, there is the need to check calibration on them every time you use them. If you happen to do anything in the way of bumping them just a little too hard, you might affect the calibration (some claim they are very rugged, I have found otherwise).

The blue liquid one from Motion Pro is a decent gauge, but let's face it, it has liquid in it. You have to be very careful how you handle and store it. The one I have developed a leak and lost fluid in one of the columns. I will repair it some day, but I have others to use in the meantime.

The Carbtune will be there in 10 days or less. If you have not yet checked your valve clearances, it will take you that long to check your clearances, determine what shims you will need, order the shims, receive them and install them, so what's the problem? :-k Yes, it's worth the wait and the few dollars extra. Splurge, make sure you get the case. That is included in the $95 cost that I mentioned.

.

 

[Ian Donahue]

Well, you all have been right every time I tried to take a short cut, so I just bought a Morgan. Wish me luck.

 

[Ian Donahue]

Update: I have removed the valve cover and checked the current valve clearances. ALL 8 were too tight for my .03mm feeler gauge. I found that hard to believe so I slowly rotated and checked at many positions around the cam travel just to make sure I was doing it right. So... do you all think it's possible that all 8 were too tight, or am I doing something wrong? Question 2: Using the spreadsheet, I put in .01mm for the clearance. ( all the shims could rotate, indicating they aren't actually jammed under the cam, but I think the oil might make that not true...) Do you think I should assume .01mm for the clearance, or drop another size down for each shim?

Hey BTW you guys weren't kidding about the tie-wrap trick. That's $15 I'll never get back.

 

[Nessism]

The valves tighten with mileage, that's why it's so critical to adjust them. After enough neglect the clearance goes away completely, the valves hang open, and then the valves and seats burn.

It's hard to say what shims you will need but I'd plan to be able to move each valve two steps. Take an inventory of the shims you have and then order as appropriate. If you don't need the shims right away you will at a later date. The Shim Club is also a way to get shims for cheap. Try searching for info if you don't know what I'm referring to.

 

[Ian Donahue]

I have already reached out to Ray about shims, thanks. How do I tell if the valves and seats are burned?

 

[Steve]

Well, you all have been right every time I tried to take a short cut, so I just bought a Morgan.

Congratulations. :clap: :clap:
We often say that every shortcut taken is just another opportunity to do it RIGHT.

Do you think I should assume .01mm for the clearance, or drop another size down for each shim?

Have you ever noticed the wisdom offered in Nessism's signature?

To measure is to know.

Never assume.

Do an inventory of your shims. You are likely to have several different sizes in there. Take one of your thinnest shims out, put a quarter in its place. Move that shim to the other spots that have thicker shims, see if there is enough clearance with that thinner shim. If you find one that has too much clearance, it's much easier to determine how much EXTRA clearance you have than it is to guess in the other direction.

Hey BTW you guys weren't kidding about the tie-wrap trick. That's $15 I'll never get back.

Yeah, some guys think it's a bit too "fiddly" and there is too much crank turning, but that is only for this first time, when you have to inspect (and likely change) all eight shims. Next time, you might only have one or two to change, so the "fiddliness" is not really a factor.

How do I tell if the valves and seats are burned?

Unfortunately, unless you remove the head and physically inspect the valves, you will have to wait until you do your adjustment, then evaluate performance. When everything is working properly, a compression check should give you a pretty good clue, too.

.

 

[JTGS850GL]

I have already reached out to Ray about shims, thanks. How do I tell if the valves and seats are burned?

The best way to verify valves is, after you've completed the adjustment procedure, do a compression and/or leak down test. If you have a burnt valve the compression will be low and you'll have excessive leak down. If the compression tests are bad then add a teaspoon of oil to each cylinder and do the test again. If the numbers come up then it's rings. If no change in compression figures then the valves are the problem.

Compression tests are easier to do but a leak down test will not only tell you that you have a problem but will also tell you where the problem is by listening to where the air is escaping. If you hear the noise in the intake or exhaust then valves are suspicious. If the sound is in the crankcase then rings. Don't forget to do the leak down test with each cylinder at TDC.

 

[Ian Donahue]

Embarrassing update: So... I thought all my valves were too tight because my .03mm feeler was stuck to my .04mm feeler (tell me you've never done it!). With a remeasure, 7 out of 8 are good, between .03 (I4) and .08 (I2+ I3). E4 is below .03, but my "feel" is that it is just below. So I will fix that one. I do not need to fix the other ones right? .04 and .04 are within spec, so that shouldn't cause my idle issue.

Question: I got this from another post:

Exhaust lobe on #1 facing forward: check E1 and E2
Exhaust lobe on #4 facing forward: check E3 and E4


Intake lobe on #1 facing perpendicular: check I1 and I2
Intake lobe on #4 facing perpendicular: check I3 and I4

Why so finicky? Why not just check each valve one at a time with the lobe perpendicular to the shim?

Anyhoo, looks like I'm narrowing my issues to the carb, but at least I can swap out the one shim and button it up (with my new reusable gasket that is coming on Monday!), and continue with the Bikecliff carb rebuild. Any thoughts?

 

[Steve]

Why so finicky? Why not just check each valve one at a time with the lobe perpendicular to the shim?

There are two reasons for this, one is the happy coincidence of convenience, the other is much more important.

You will note that in those positions, neither valve on that side of the cam is being depressed. That will keep the cam in a more or less neutral position in the bearing. There is a very slight clearance in the bearing to allow oil flow. If you push the cam sidways by depressing a valve, it might give you a false reading at the other valve.

.

 

[Ian Donahue]

There are two reasons for this, one is the happy coincidence of convenience, the other is much more important.

You will note that in those positions, neither valve on that side of the cam is being depressed. That will keep the cam in a more or less neutral position in the bearing. There is a very slight clearance in the bearing to allow oil flow. If you push the cam sidways by depressing a valve, it might give you a false reading at the other valve.

Totally right again Steve. With this technique, each valve was about .01mm - .02mm tighter, so I now have a more accurate spec. Ray hooked me up with new shims and I'm hoping to get them before the weekend and get this buttoned up. I bought this thing for my 50th birthday (Saturday) and I'd love to see it run right for a birthday ride!

 

[Ian Donahue]

Update #3: I am dutifully following the carb rebuild outlined on the bikecliff page. For the float needle seats, I found this:



So if you can't see it, there is a thick hard gak on top that is blocking the passage of air (or gas obviously). That is #4. #3 looked the same, the separated gak next to it is from #3. During this whole process #3 and #4 were not warming up like 1 and 2, maybe there's a connection?

Anyway, on the carb rebuild PDF, the picture shows a half-dome screen under this piece. I don't have that on any of these. Is it required?

Thanks again for the help so far. How come no one told me to do the carb clean the right way? ;-)