Bike sputters at different RPMs in different gears

[Guest]

My bike will sputter and not die but wont go past different RPMs in different gears. So in in 3rd gear i can get it to 6k then it wont go past that and will just sputter no how much gas i give it. In 5th it wont go past 5k rpm and sputters, and in 6th wont go past 4.5k rpm. And It is exactly each of these RPM numbers, right on the number/and or line. Sometimes i can hear that the left cylinder stops firing because i dont hear anything from the left exhaust. Notes: Otherwise carb runs good I think, only 28k miles. New battery, new spark plugs, checked the cables to the spark plugs and are good. So any ideas?

 

[Cipher]

Check plugs and plug caps.
Swap caps to see if prob moves

 

[cowboyup3371]

What maintenance (last PROPER carb cleaning, valve adjustments, carb sync) has been done? Is this bike new to you or you've had it for awhile? Inquiring minds need to know

AND MOST OF ALL, what bike is this?

 

[Rich82GS750TZ]

We also don’t know what motorcycle you have, whether you are using stock intake and exhaust vs. individual pod filters. Did this bike ever run good for you? If so, what changed?

Please put your bike year and model in a signature. Go to settings at the top right of any page, then look for signature links on the left side.

 

[Guest]

Sorry, it's a 87 gs450l. The bike is new to me, the bike is stock mechanically. As for carb cleaning, syncing and valve clearance I don't know if it's ever been done. Guy I bought it from was going to use the engine to put it on a bicycle till I rescued it. I did put a new petcock in. And from what I can tell the bike runs good and smooth up until those mentioned rpms

 

[cowboyup3371]

Since you don’t know if that has been done, please read through the Top 10 Newbie Mistakes thread (https://www.thegsresources.com/_forum/showthread.php?171846-Top-10-Newbie-Mistakes) and take a look through Basscliff’s site (http://members.dslextreme.com/users/bikecliff). Taking time to do all of the basic maintenance will give you the best baseline to start troubleshooting this instead of just throwing darts at it

 

[Cipher]

Sorry, it's a 87 gs450l. The bike is new to me, the bike is stock mechanically. As for carb cleaning, syncing and valve clearance I don't know if it's ever been done. Guy I bought it from was going to use the engine to put it on a bicycle till I rescued it. I did put a new petcock in. And from what I can tell the bike runs good and smooth up until those mentioned rpms

Yeah wow a 450cc bicycle would be a head turner.
Now check the plugs cap and wires
Pull plugs to see what color they are.

 

[Rijko]

I am working on a 87 GS450L from a buddy atm.

It would start and run up to approx. 4500RPM and would go no further.
I did all the leg work to exclude possible causes : dipped/cleaned/synced the carbs, shimmed the valves, cleaned up corroded connections in the wiring loom, spark plug caps and coils swap/test, etc.
Did not find a mechanical advancer under the ignition groundplate which i do not yet understand.
In the end i had to suspect the igniter box.

Opening this box is easy, the backplate comes off easily.
The print underneath clearly showed burn/melt signs.

Just for giggles i have hooked up an igniter box from a GS500E and the bike would rev way better.
At least that confirms the suspicion the original igniter box is toast.

 

[Who Dat?]

I am working on a 87 GS450L from a buddy atm.


Did not find a mechanical advancer under the ignition groundplate which i do not yet understand.

Starting in '83, Suzuki did away with the mechanical advance and went full-electronic, it's all contained in the ignitor.

 

[Rijko]

Starting in '83, Suzuki did away with the mechanical advance and went full-electronic, it's all contained in the ignitor.

I am not familiar with the ignitor systems : until now i thought the GS bikes either had contact points (and mechanical advancer), or signal generators with an ignitor and mechanical advancer.
The ignitor being a 'dumb' amplifier of pulses, whereas a CDI would have extra 'intelligence' to also do things like advance.
Apparently there's at least 2 generations of ignitor, learning something new here again, thanks !!