gs1000g now starts but still running rough at high revs

[DaveWatts]

Hi,

With the new starter motor my GS now starts right up and ticks over nicely. trouble is when revving to higher revs when it sputters and almost back fires. I know the bike isn't charging, (even with a new polaris reg/rect!). I swapped the ICU with a spare and it is exactly the same, I cleaned out the carbs and put a new set of original diaphragms in them, there is some mechanical noises and maybe the previous owner got the valve clearances wrong, he said he had the engine apart and I saw a new base gasket. Maybe the next thing I'll do, get the strobe out, an easy check. 2nd thing check the valve clearances.

Anything else to look for?

Cheers

Dave

[fixmybrokecomputer]

I'd make sure the cams were timed properly.

[Dogma]

Correctly adjusted valves will make some noise. If they're not making noise then you're out of clearance and in danger of burning valves. So, a little noise is a good thing. Most often the sound is compared to a sewing machine.

How is everything else? Stock airbox, exhaust and jets?

If the battery is weak, you may not have enough voltage to build a good spark at high revs. That happened to me once. I don't remember if I had enough power to crank it. Not charging could point to a mess in the wiring, or just a stator burnt by the previous regulator or even just dirty connections and grounds. Cam timing could be wrong, since it was apart. Mechanical noises could be an incorrectly installed tensioner.

The bad news is, you have a bike that doesn't run right and the PO had the top end off. That means you have a basket case. The good news is, if you methodically check everything, build a list of what's wrong, and then fix everything on that list, you'll have a great bike. I recommend this course of action, because we don't know what the PO did wrong, so we can't tell you what to fix.

Make sure the cam chain tensioner is working and not locked up. If it's installed incorrectly, cam timing can jump. I'd start there.
Next, take the cam cover off and check valve clearances. You can check the cam timing during that process. You don't need the strobe.
Since it runs, you can check the stator to see if it even generates power.
I'd normally suggest cleaning the carbs, but instead I'll ask how. There are some wrong ways that can leave problems behind.
Etc.

[chuck hahn]

Valve clearances, timing, and a good vacuum gauge carbs syncing are all needed to eliminate the "easy" ones.

[DaveWatts]

Yes, that is a good point, it could well be that he messed that up when putting the engine back together. I'll check the clearances and the cam position at the same time.

[DaveWatts]

Correctly adjusted valves will make some noise. If they're not making noise then you're out of clearance and in danger of burning valves. So, a little noise is a good thing. Most often the sound is compared to a sewing machine.

How is everything else? Stock airbox, exhaust and jets?

If the battery is weak, you may not have enough voltage to build a good spark at high revs. That happened to me once. I don't remember if I had enough power to crank it. Not charging could point to a mess in the wiring, or just a stator burnt by the previous regulator or even just dirty connections and grounds. Cam timing could be wrong, since it was apart. Mechanical noises could be an incorrectly installed tensioner.

The bad news is, you have a bike that doesn't run right and the PO had the top end off. That means you have a basket case. The good news is, if you methodically check everything, build a list of what's wrong, and then fix everything on that list, you'll have a great bike. I recommend this course of action, because we don't know what the PO did wrong, so we can't tell you what to fix.

Make sure the cam chain tensioner is working and not locked up. If it's installed incorrectly, cam timing can jump. I'd start there.
Next, take the cam cover off and check valve clearances. You can check the cam timing during that process. You don't need the strobe.
Since it runs, you can check the stator to see if it even generates power.
I'd normally suggest cleaning the carbs, but instead I'll ask how. There are some wrong ways that can leave problems behind.
Etc.

It doesn't sound like a sewing machine unfortunately. Everything is stock (except the exhaust). Battery is good but not charging, could also be the coils though. Good advice with the cam chain tensioner, the mechanical noise could be chain slap. The carbs have been cleaned and new stock diaphragms installed. So cam chain, valves & cams, then stator (i should get the AC multi-meter on it), then timing.

Cheers

Dave

[salty_monk]

You should also check the Ignitor. I had one that went bad on a 1000G and it only manifested at 6,000+ rpm. It failed the Clymer test (hook a AA battery up to a couple of the pins & measure voltages). A Dyna S sorted it out as it replaces all that. The triggers don't usually go bad...

Coils would tend to make it miss (and only on 2 cylinders unless both were shot).

Most Carburation problems are electrical....

[80GS850GBob]

You should also check the Ignitor. I had one that went bad on a 1000G and it only manifested at 6,000+ rpm. It failed the Clymer test (hook a AA battery up to a couple of the pins & measure voltages). A Dyna S sorted it out as it replaces all that. The triggers don't usually go bad...

Coils would tend to make it miss (and only on 2 cylinders unless both were shot).

Most Carburation problems are electrical....

So, does that theory work in reverse as well....
Most electrical problems are the carbs?.....lol

[DaveWatts]

You should also check the Ignitor. I had one that went bad on a 1000G and it only manifested at 6,000+ rpm. It failed the Clymer test (hook a AA battery up to a couple of the pins & measure voltages). A Dyna S sorted it out as it replaces all that. The triggers don't usually go bad...

Coils would tend to make it miss (and only on 2 cylinders unless both were shot).

Most Carburation problems are electrical....

I swapped out the ICU and it sounded exactly the same so I don't think its that, the electric ignition pickup could be suspect though, that's why I thought maybe a strobe would be good, to show up any problems at higher revs (I get problems about 3500 and above).

[tom203]

So this is a 1980 model... Problems above 3500 rpm...Check the mechanical advancer in case it's frozen.
You said... you put in "a new set of original diaphragms" in carbs

Is the hole thru each vacuum piston still oriented correctly?

[DaveWatts]

So this is a 1980 model... Problems above 3500 rpm...Check the mechanical advancer in case it's frozen.
You said... you put in "a new set of original diaphragms" in carbs

Is the hole thru each vacuum piston still oriented correctly?

"Check the mechanical advancer in case it's frozen" is that something that happens often? it would explain things.

The diaphragms were the thin rubberised canvas originals and were installed directly on the slide cylinder, the diaphragms also had the tang for locating in the carb housing, I think they are ok.

I want to check the chain tensioner as well, Are there any good resources out there, the manual pages are a bit confusing?

With checking the value clearances, the lobe should be sticking up perpendicular to the shim face for maximal clearance, right? I've seen some videos where people have the exhaust cam lobe facing forwards and in line with the rocker cover gasket surface, it also says that in the manual, but that doesn't make sense to me, does anyone know why Suzuki specified it like that?

[tom203]

Try this..

http://members.dslextreme.com/users/storagecliff/images/engine_odds-n-ends.html#A06

if you remove the tensioner, and hold/fiddle it in your hand, you'll get how it works very quickly

[80GS850GBob]

"Check the mechanical advancer in case it's frozen" is that something that happens often? it would explain things.

The diaphragms were the thin rubberised canvas originals and were installed directly on the slide cylinder, the diaphragms also had the tang for locating in the carb housing, I think they are ok.

I want to check the chain tensioner as well, Are there any good resources out there, the manual pages are a bit confusing?

With checking the value clearances, the lobe should be sticking up perpendicular to the shim face for maximal clearance, right? I've seen some videos where people have the exhaust cam lobe facing forwards and in line with the rocker cover gasket surface, it also says that in the manual, but that doesn't make sense to me, does anyone know why Suzuki specified it like that?

To have a lobe facing up is good for checking that cup but to have two lobes facing outward allows two to be checked at the same time...its just faster that way. A lobe dead 90 away is still off ramp enough to check clearance.
I'd suggest pulling the timing cover and checking cam alignment on #1 firing position just to make sure one of the cam sprockets isnt off...it's one of those "while your in there" things for peace of mind.

[80GS850GBob]

Oh, I'll add this much too....did you check the plug caps on an ohm meter? Should be 5 ohms. Unscrew each plug cap from each wire and test them...as they age they can get a higher read and add more resistance. I dont know if they're bad or if itll help your situation, but it can't hurt to check them too. Sometimes its not one thing that causes a problem, hut a few lil things that add up...

[DaveWatts]

Oh, I'll add this much too....did you check the plug caps on an ohm meter? Should be 5 ohms. Unscrew each plug cap from each wire and test them...as they age they can get a higher read and add more resistance. I dont know if they're bad or if itll help your situation, but it can't hurt to check them too. Sometimes its not one thing that causes a problem, hut a few lil things that add up...

A good point, they are not expensive, I'll get a new set of plug caps.