82 GS550 Katana tops out at 65MPH , any ideas?

[tbone]

Last year I bought a '82 GS550M Katana and currently it tops out at 65MPH. The weird thing is that it accellerates quickly but once it reaches around 65 MPH/5000 RPM it and won't go any faster. It almost feels like there is a governor keeping the bike from going faster.

When I had the bike in getting worked on after I bought it they said they did a compression and leakdown test and said it was good, they cleaned and synchronized the carbs, put on new carb boots, changed the spark plugs and plug caps.

They said that the valve clearances were off quite a bit and would need to be adjusted once I rode it for 500-1000km to burn some of the old carbon build up off.
One other thing, the spark plugs have been getting some oily fouling.

Any ideas on what could be causing the max speed to be only 65? Could it be because the valve clearance is way off?

Thanks! Any help is appreciated!

 

[Nessism]

What are the compression numbers? Assuming everything is fine it is unlikely that valve adjustment is causing the problem.

Will the bike rev past 5000 in the lower gears? Can you take it to red line in second gear for example? Does it pull hard or fall flat at high revs? Also, are all the pipes warm when you first start the bike? Check to make sure all cylinders are firing. Report back with more information.

 

[aosmith]

the bike itself could need a valve job, thats probably the cause of your oil fouling

 

[tbone]

These are the numbers I have from my shop invoice, im not sure if these are the compression or leakdown test numbers.
1 - 10%
2 - 8%
3 - 6%
4 - 10%
I'm guessing this is how much compression each cylinder is down but I'm not too sure. Your guess would probably be better than mine.

The bike seems to only rev to a maximum of 5000-5500 RPM in each gear, it's the same for all 6 gears. I could never red line it in any gear.

When I approach the 5000 RPM level and I'm going around 60-65MPH the bike would just feel like it'd max'd out its power, it'll just continue steadly at the 5000RPM level and 60MPH. If I give it more gas the RPM's won't increase and almost feels like it'll get a bogged down feeling, like its getting the extra gas but not doing anything with it.

All the pipes heated up quick so all the cylinders are firing.
I did forget to mention I have a small exhaust leak on one of the exhaust pipes where it connects to the engine block.

 

[Nessism]

Compression is good based on those leakdown numbers. I assume this was checked recently, and the carbs cleaned recently as well. Assuming this is true, the problem could be fuel starvation. I'd check the petcock for proper operation. First thing though you might want to turn it to Prime and see if the problem occurs. Next, suck on the vacuum line feeding the petcock to make sure fuel flows when the lever is in the ON and Res positions.

Good luck.

 

[Jakob]

Long time listener, first time caller...

I have an '81 GS750E that was having the same problems. Only mine was "hitting the wall" at 4500 rpm regardless of gear and had a total loss of power/torque when going up even the smallest inclines. I fought carb probs, petcock probs and spark probs to no avail. Tested the CDI 5 days ago and lo and behold, therein lied my problem. I was getting just enough spark to keep the bike running but not enough to do much else. Found a used CDI at a salvage yesterday (50 bucks !!) and installed it last night and took it for a test run around the airport Top Gun style and WOW/HOLY CRAP/GOOD LAWDY MISS MAWDY where did all this power come from?!? Took a plug out and laid against the motor and got the fattest, bluest spark I'd seen in the 5 years I've owned the bike. The "wall" is gone and I saw an indicated 80 mph before leaving 3rd gear.

If you're unsure about how to do the test then post back and either I or one of the hundreds of other smart people on here will letcha know. Wow, that sounded like I grouped myself into the smart people on here didn't it?

If that is the problem(s) then search high and low for a used one because a new OEM runs just under 400 clams :shock:.

Hope this helped,
~~>Jakob

 

[chiphead]

Jakob, you listen to Howie Carr?
What Jakob said was my first thought when I read your post tbone. It could be off base but it almost sounds like your losing spark advance. Something to consider.

 

[Jakob]

Jakob, you listen to Howie Carr?

Didn't know who that was 'til I did a Google, lol. No, that was a "Frasier" plagiarism.
~~>Jakob

 

[tbone]

Long time listener, first time caller...

I have an '81 GS750E that was having the same problems. Only mine was "hitting the wall" at 4500 rpm regardless of gear and had a total loss of power/torque when going up even the smallest inclines. I fought carb probs, petcock probs and spark probs to no avail. Tested the CDI 5 days ago and lo and behold, therein lied my problem. I was getting just enough spark to keep the bike running but not enough to do much else. Found a used CDI at a salvage yesterday (50 bucks !!) and installed it last night and took it for a test run around the airport Top Gun style and WOW/HOLY CRAP/GOOD LAWDY MISS MAWDY where did all this power come from?!? Took a plug out and laid against the motor and got the fattest, bluest spark I'd seen in the 5 years I've owned the bike. The "wall" is gone and I saw an indicated 80 mph before leaving 3rd gear.

If you're unsure about how to do the test then post back and either I or one of the hundreds of other smart people on here will letcha know. Wow, that sounded like I grouped myself into the smart people on here didn't it?

If that is the problem(s) then search high and low for a used one because a new OEM runs just under 400 clams :shock:.

Hope this helped,
~~>Jakob

Sounds like your bike had very similar problems to mine. Could you explain to me how to do the CDI test, I'm not too sure how to do it. I tried searching for it but came up empty. Thanks!

 

[Jakob]

1. Remove leads and plugs from #3 and #4 (2 on right side of bike if you're sitting on it, assuming you ride facing forward) and put plugs back into leads. Place both plugs against cylinder head making sure both are grounded out (touching head).

2. Remove right side cover and disconnect the blue and green leads from the bottom of the CDI (black box in back). There's one that has just 2 wires (the blue and green) and one that has a few wires. Only unplug the one with 2 wires.

3. Get an ohmmeter and set it to R1 or X1, whichever yours has. This part is critical because if you do it wrong and your CDI was good, it won't be anymore. Turn your ignition on and touch the positive (+) lead from your ohmmeter to the BLUE wire and touch the negative (-) lead from the ohmmeter to the GREEN wire.

4. When you touch the negative (-) lead to the GREEN wire your #4 plug should spark. When you remove the negative (-) lead your #3 plug should spark. Since these bikes have such a poor electrical system to begin with you might want to have someone help you as a "watcher" on this part.

5. If one or both plugs fail to fire then you'll have to replace your CDI, hopefully with a used/good one, because like I said earlier they're almost $400 new.

On mine when I touched the negative lead the #3 would fire and when I took the lead off it would fire again. I never could get my #4 to fire doing this test.

If this is what it is and you have to replace it and want a walk-through in doing so feel free to ask and I'll help you the best I can since it's still pretty fresh in my memory banks.

Hope this helped,
~~>Jakob

 

[tbone]

Thanks for the quick replies, im going to try to get a multimeter and test it out hopefully by the weekend. I'll let you know how it goes.