81 GS850G Won't Rev over 4000 RPM

[GS850GFan]

I only mention valve timing because, if you have one too many pins between the intake and exhaust cams, no matter what you do on the carb side, the engine will not rev beyond a certain point, period. I spent 3 months chasing the problem that you have. I could be wrong though.

V

Oh man...that doesn't sound fun....well, there is only one way to find out!

 

[GS850GFan]

All parts ordered, be here on Saturday!

 

[GS850GFan]

Weather striping in the air box!

 

[gustovh]

Well how about an update, the suspense is killing me.

V

 

[GS850GFan]

Well how about an update, the suspense is killing me.

V

I wish I had something to report. Still waiting on parts, should be here on Saturday. I haven't taken the valve cover off yet as I want to verify that I have the correct gasket before I take it apart.

I did look into the snorkel for the airbox, the junkyard didn't have it. I'm going to hold off till all this other stuff is done.

In the box of extra's that came with the bike, I did find some small bags from the carb kit the PO did and it had all the old O rings, so at least I know those are new.

Other than that, I have been cleaning and preparing for work on it this weekend.

 

[londonboards]

Anything like this:

For me the problem was the needles incorrectly installed in the throttle slides. Main jets not able to deliver fuel.

See my blog posting: Who put these main jets together?

And also the needle valves in the floats needed replacing.

Just another idea.

Greetings

 

[GS850GFan]

Anything like this:

For me the problem was the needles incorrectly installed in the throttle slides. Main jets not able to deliver fuel.

See my blog posting: Who put these main jets together?

And also the needle valves in the floats needed replacing.

Just another idea.

Greetings

Wow, that was an interesting read. I have had these carbs off and on a few times looking for problems but haven't pulled the needles out.

I didn't mention before that in neutral the bike will rev to redline it's only under load that it will not pass 4,000 rpm.

BUT, since I have to deal with the carbs again I will have a look to verify I don't have the same problem.

The guy I bought the bike from was a nice guy, but not a great mechanic. I have found nuts and bolts loose all over the place (clutch cable lock nut, choke cable lock nut, air box mounting bolts, headlight mounts). Old rubber parts that should have been replaced (like intake manifolds and air box tubes). But they used it a few times a year on vacations. They put it on the back of their camper. I understand that he probably didn't want to spend the money to fix all this stuff. So I am doing it.

I only paid $750 for the bike and i think when all is said and down, it will work out to the right amount of money for the bike and what I have spent

Thanks for sharing this thread!

 

[GS850GFan]

OK, Here's how the weekend went. Got the gaskets and intake manifolds on Saturday.

Installed the new intake manifolds with new O rings
Re-Installed original 115 main jets
Replaced bowl gaskets
Had to replace all screws on float bowl because they were warn out and the heads were stripped
Cut drilled and shortened stretched out intake boot clamps. Before they wouldn't tighten all the way, not there is 1/4 inch left after they are tight.

I DID NOT adjust valves because I realized I didn't have my torque wrench here, I lent it to a friend.

The finished product:

Not too different! It will still only rev to 4,000-4,500. But what IS different, if I let up on the throttle just a little it will then go to 5,000 rpm.

Tomorrow I will get my wrench back and do the valve adjustment and check cam timing. I'm also going to check the ignition timing again with a dead light, not just with the timing light.

Maybe the ignition mechanical advance?

Here is the plug:

 

[ShadowFocus603]

Plug is showing lean but the caveat is did you actually do a chop or just let it idle then shut off? If the latter then the plug doesn't tell you much. When you cleaned the carbs did you uncap the fuel mixture screws and remove them before dipping the carbs? If no that would be the next course of action. You will have to remove the carbs anyways if you got the o-ring kit from cycleorings. Be careful as the screws tend to be stuck. Once you get them out dip the bodies again and reset the needles to 2 1/2 turns out. Doing this and installing the new o-rings will remove two more links in the chain and get you that much closer to finding the culprit for being lean. By the by, if you have a thermometer of the laser variety you should temp all four head pipes at idle and see if they are all around the same temp. This will give you some indication if you have any spark or carb issues as well.

 

[GS850GFan]

Plug is showing lean but the caveat is did you actually do a chop or just let it idle then shut off? If the latter then the plug doesn't tell you much. When you cleaned the carbs did you uncap the fuel mixture screws and remove them before dipping the carbs? If no that would be the next course of action. You will have to remove the carbs anyways if you got the o-ring kit from cycleorings. Be careful as the screws tend to be stuck. Once you get them out dip the bodies again and reset the needles to 2 1/2 turns out. Doing this and installing the new o-rings will remove two more links in the chain and get you that much closer to finding the culprit for being lean. By the by, if you have a thermometer of the laser variety you should temp all four head pipes at idle and see if they are all around the same temp. This will give you some indication if you have any spark or carb issues as well.

I did ride the bike about 3 miles and it runs great below 4,000. Best it's ever run...

Which brings me to this...

As previously mentioned...The bike came with a small box of parts, carb kit bags with the old O rings, a set of multi air cleaners, a set of 130 main jets, a box with the K&N cleaning kit and in the bottom of THAT BOX I found some tappets and a tappet tool!

So someone was in messing with the valve height.

As previously mentioned in this thread "Check the Valve Clearance". So tomorrow I will be doing that. I ordered and have the valve cover gasket and tomorrow I will go pick up my torque wrench so I can put the valve cover back on right.

According to the "Official Manual" page 3-5 which talks about tappet / valve adjustment and that if the tappet height is to low, you have a low power situation, basically the valves aren't opening wide enough.

Either way, I'll be going over your list above, checking the tappet / valve clearance and reporting back!

 

[49er]

I doubt that your valve clearances are too loose. They are really noisy when the engine is run that way. They are shimmed buckets and the clearances get tighter with use. Suzuki recommends they are checked every 6000 kms (4000 miles).

Have you fitted a snorkel to that inlet window yet? If not, that will be causing some leanness at mid range to WOT.

Try partially blocking the window by placing masking tape over 80% of the inlet area. If your performance increases, you'll have confirmed the need for a snorkel.

Are you running an extra inline fuel filter? Some filters don't flow well and if there is excessive fuel line looped too high, the carbs will get starved of fuel when under load. Are the carb butterflies fully opening when the throttle is wide open?

No major flow restrictions in the exhaust system?

Just some other areas to check.

 

[GS850GFan]

I doubt that your valve clearances are too loose. They are really noisy when the engine is run that way. They are shimmed buckets and the clearances get tighter with use. Suzuki recommends they are checked every 6000 kms (4000 miles).

Have you fitted a snorkel to that inlet window yet? If not, that will be causing some leanness at mid range to WOT.

Try partially blocking the window by placing masking tape over 80% of the inlet area. If your performance increases, you'll have confirmed the need for a snorkel.

Are you running an extra inline fuel filter? Some filters don't flow well and if there is excessive fuel line looped too high, the carbs will get starved of fuel when under load. Are the carb butterflies fully opening when the throttle is wide open?

No major flow restrictions in the exhaust system?

Just some other areas to check.

The valves are not overly noisy, but will check anyways since someone had mentioned checking the cam timing. Might as well check it off the list.

I have not fitted it with a snorkel and you're right, I do need to cover that opening. The guy at the junkyard said the same thing, forgot to do that.

No extra fuel line filter. I did rebuild the fuel petcock and cleaned the fuel filter (it was already clean).

Fuel line is short, no loops, straight from the tank to the carbs.

Butterflies open all the way.

I pulled exhaust system, inspected and reinstalled with all new gaskets.

I will go test the snorkel first, since it is the simplest and post back!

AS ALWAYS, THANKS EVERYONE FOR YOUR IN PUT!

 

[salty_monk]

check the ignitor... That can act sort of like a rev limiter when it goes. I chased jetting for ages on the 1000G until I figured out the ignitor was shot.

 

[GS850GFan]

check the ignitor... That can act sort of like a rev limiter when it goes. I chased jetting for ages on the 1000G until I figured out the ignitor was shot.

Another item on my list to check.

A bit of an update:

I haven't been able to test the bike because two other issues came up.

1) I have had an on going issue with fuel overflowing the carbs. Thought it was the float levels, pulled the carbs a few times, readjusted them a few times. Turns out there was a faulty part in the petcock rebuild kit I used. There is a diaphragm with a small disc in the kit. It regulates the flow of gas from the tank to the carbs and shuts off the gas when the engine is not running using the vacuum off the carbs. But I kept coming out to find gas on the ground. A new part has been reordered. Will be here in a week.

2) It turns out the previous owner had the wrong brake handle and master cylinder. It was at the wrong angle which caused brake fluid to leak, which got on the little window to see how much fluid is inside. I went to wipe it clean to check the fluid and the window broke! Also the top screws to open the lid were stripped. LAME. So I spent a few days tracking down a suitable replacement which will keep the fluid at the right angle. Also had to rewire the brake light switch.

Currently, there is a pair of vice grips on the gas line from the tank to the petcock. Once I can resolve that issue, I can start working on getting back to checking things off my list to find why this engine won't rev.

More to come...

 

[Steve]

1) Your best bet will be to order a new petcock, not replacement bits and pieces for the inside.
The success rate for petcock rebuilds is very low.

2) I have always been under the impression that BOTH sides of the view window would be impervious to brake fluid. :-k
Evidently not. You can use a piece of Lexan that is cut and shaped to fit the hole then epoxied into place to replace the broken window, but evidently you just had the wrong master cylinder anyway.

.

 

[DanTheMan]

check the ignitor... That can act sort of like a rev limiter when it goes. I chased jetting for ages on the 1000G until I figured out the ignitor was shot.

I second what Dan said. I chased the carbs and fuel guesses for a good six months on my '83 GS1100G, and it turned out to be the ignitor. Luckily I had an older ignitor from the '81 GS850G to replace it with. I had to put it in a different spot, and make a jumper cable to attach it all. New ignitors cost around $450.00. I'm glad I had one that would work.:nightmare:

 

[GS850GFan]

OK, Now I have to ask (noob) what is the ignitor?

 

[Steve]

The "ignitor" is the little box that has a few transistors in it that takes the place of points in the ignition system.

It is a poor choice of names, as it does not "ignite" anything, but we are pretty much stuck with what Suzuki calls it.

You will find it on the left side of the battery box, right there with the starter solenoid and the fuse panel.

EDIT: it is the larger black box on the left.

.

 

[GS850GFan]

The "ignitor" is the little box that has a few transistors in it that takes the place of points in the ignition system.

It is a poor choice of names, as it does not "ignite" anything, but we are pretty much stuck with what Suzuki calls it.

You will find it on the left side of the battery box, right there with the starter solenoid and the fuse panel.

.

OK, and how do I test it?

 

[Steve]

There is a procedure in the service manual that is rather easy, but must be followed EXACTLY, or you can blow it up.

It involves connecting a flashlight battery (D-cell) to the input leads, but it must be done with the correct polarity. Remove the spark plugs from the engine, plug them into their wires and lay them on the engine so they can ground out. When you connect the battery, one coil (two plugs) will fire. When you disconnect the battery, the other coil will fire. Consult your service manual for details.

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