Figured why gs750 not starting

[baz666]

While waiting for a friend to bring over a 30mm socket to open up the cam chain tensioner adjustment assembly, I had a look at the carbs. The butterflies were shut absolutely tight, not space for a hair to get between the butterflies and the carb body. So I did a bench sync and used the soft wire from a bread tie as a measuring tool. Now all butterflies are open the width of the bread tie wire when at rest. I'm thinking that having the butterflies shut tight was another reason the bike wouldn't start but I guess I rode it this way last year so who knows.
I had a look at the carb internals and no clogged jets. The floats were a little high at about 24mm. They're supposed to be at 22.4, give or take 1mm so I adjusted them. The float valves appear clean and aren't deformed in any way.
thanks,
baz

[Mekanix]

When your all done and its up and running good, Remember that float adjustment if you notice it doesn't run as good as it did last year.
There may be a lean spot or trouble idling/low speed.

[baz666]

One question about the carbs. There are little rubber stoppers that go on top of one of the jets. Can anyone clue me into why this is and how it works? Why are they stopped up?
thanks,
baz

[Big T]

One last thing, a local bike mechanic keeps insisting it's got to be bent valves.

I'm wondering if this guy knows what he's talking about. Sort of glad I never took a bike to him.

Any comments would be much appreciated.
thanks,
baz

I think you've already found the answer to that - never take your bike to him. He doesn't even understand the basics of engines. Is this the HD guy, or another one?

[baz666]

Yep, he's an HD guy, telling me, "Those Jap bikes are too complicated for their own good."
Uh, okay.... so much for his expertise.

Anyway, I'm beginning to figure out what happened. Ever since I got this bike, GS750ES, I've noticed some old oil gunk behind the cylinders and down on the top of the gearbox. I thought it was the two oil lines leaking. I took them off yesterday and they seem fine, pretty new actually. Then I noticed some old gunked up oil around where the tensioner attaches to the back of the engine. It wasn't until I got the entire tensioner apart that I realized it works on oil pressure. The rubber seal that locates the shaft of the adjustment assembly is pretty shot, along with the 21mm rubber seal that fits onto the threads of the big 30mm bolt. The setscrew rubber seal is also flat and kind of chewed up.
So what I'm thinking is that oil was leaking from this area, and the tensioner didn't have enough pressure to operate properly.
Am I on the right track here? Is that how the tensioner operates, off oil pressure and of course, the spring?
thanks,
baz

[Mekanix]

HD guys :P Saw a group of them passed by a Bergman scooter once. Not easy to look bad-a$$ in that case :P


The tensioner works on locking spring pressure..

It gets oil splashed on it from the cam chain throwing oil around.


That spring pushing the tensioner's plunger out is just there to push it out a bit. Not to hold the cam chain tight.


When the plunger moves out, the knob on the side rotates clockwise and actually moves into the tensioner.

Its actually moving in and pushing on the tapered end of the plunger.

that locks the plunger from moving back.

So its completely automatic


That oil you found underneath it is quite normal for aging GS's

It requires a replacement of the all the seals in the tensioner to stop it from leaking.

Hope this helps

[tom203]

One question about the carbs. There are little rubber stoppers that go on top of one of the jets. Can anyone clue me into why this is and how it works? Why are they stopped up?
thanks,
baz

Those plugs cover access to pilot jets- farther up column is a port that connects to main jet area to feed the pilot. These small jets clog real easy, especially after a bike sits unused and this is why folks tell you to do a thorough cleaning. When you put the fuel bowl back on the stopper is held in place.

[baz666]

Thanks Mechanix for the explanation about how the tensioner works and thanks Tom for the explanation about the little rubber stoppers in the carbs.

So about the tensioner, I'm guessing that since it is actually spring operated, it is critical to make sure the spring behind the knurled knob is turned at least 1 complete revolution before putting on the nut that holds the knurled knob in place. But when I rotate that spring, it seems to go off center, like it's being wound too tight.
Also, about the nut that holds on the knurled knob. How tight does it go on if the knurled knob is still supposed to move freely?
In the bwringer instructions, it says to use Loctite on that nut. So does it torque down tight enough to allow the knurled knob to turn but not to lock it in place?
Potentially dumb questions, I know, but any help at all is much appreciated.
thanks,
baz

[Big T]

Thanks Mechanix for the explanation about how the tensioner works and thanks Tom for the explanation about the little rubber stoppers in the carbs.

So about the tensioner, I'm guessing that since it is actually spring operated, it is critical to make sure the spring behind the knurled knob is turned at least 1 complete revolution before putting on the nut that holds the knurled knob in place. But when I rotate that spring, it seems to go off center, like it's being wound too tight.
Also, about the nut that holds on the knurled knob. How tight does it go on if the knurled knob is still supposed to move freely?
In the bwringer instructions, it says to use Loctite on that nut. So does it torque down tight enough to allow the knurled knob to turn but not to lock it in place?
Potentially dumb questions, I know, but any help at all is much appreciated.
thanks,
baz

Just make it snug - the Locktite will hold it in place. You don't want to overtighten and snap it off.

[mike_of_bbg]

I don't think one turn of tension on the spring is enough. I'm thinking 2, maybe 2-1/2. If it's too loose it's going to rattle.

[baz666]

DOh! The instructions I'm looking for were staring me right in the face on page 81 to 85 of the shop manual, how to reassemble the cam chain tensioner. It says 1 complete counterclockwise revolution of the adjustment assembly spring, put on the knurled knob then attached the lock nut with 6 to 7 lbs of torque, and use loctite according to the bwringer instructions.
So hopefully the seals will arrived from Suzook soon and I can get the tensioner back on the bike, check the timing chain set up and see if that helps with the lack of compression.

It takes me a while to figure out the obvious so thanks to everybody for your help and patience.
baz

[koolaid_kid]

You do realize we are helping you because expect and require pictures, don't you? Especially when you start riding it...

[Big T]

You do realize we are helping you because expect and require pictures, don't you? Especially when you start riding it...

And a video of it starting up once you're done

Did you resolve your cam timing?

[baz666]

It's a deal.
I'll take some pics of the bike with the valve cover off and the disassembled cam chain tensioner. I haven't set up the timing yet because the tensioner is off the bike and I don't want to mess with the chain before putting everything back together. It took a while, and lots of 'splaining by wiser forum members, but the fog is finally clearing about how the tensioner works. I even have a glimmer of hope the bike will soon be running again - and I'll shoot some video to show her off!
Much better than the gloom and doom scenario of a week ago when I thought the bike was toast.
thanks again,
baz

[Big T]

It's helpful to set the cam timing before you reset the tensioner - easier to pull the cams and turn them as required

Once they're in place, reinstall the tensioner (before you rotate the engine again)

So:

1. Crank to T 1-4
2. Set exhaust cam with arrow parallel
3. Set intake cam 20 pins back
4. Install tensioner

Rotate a few times to confirm the cam timing

Your spark plugs should be removed for steps 1-4