Weird Bumpy Feeling in 85 GPz 550 - Kawasaki Motorcycle Forums
 
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post #1 of 10 (permalink) Old 08-16-2016, 11:19 PM Thread Starter
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Weird Bumpy Feeling in 85 GPz 550

Ok so here goes my GPz 550 story. First of all I'm only 19, and i have never owned a bike or even rode one, Never the less I decided it would be cool to get a project bike. I ended up finding a 1985 GPz 550 on craigslist. It had 50k miles on it, was in a barn and hadn't been inspected for 14 years. The guy I bought it from was able to start it but it didn't move or anything else. It was the first bike I looked at it and I naively bought it for $200.
The crabs had an inch of yellow jello like substance in them and I was amazed it had started at all. I battery didn't work at all(replace that).
Then came the problems....
  • I cleaned/rebuilt the carbs 6 time (sometimes theres a learning curve, the benefit of that is I can take them on and off the bike in less than an hour.)
  • I rebuilt the rear brake caliper and bleed all the lines with new fluid... All new brake pads
  • I had a shop put tires on the rims and replace the stems and wheel bearings
  • I completely dismantled and cleaned the front forks (and replaced all the seals)
  • Replaced the steering bearings.
  • Redid a significant portion of the wiring (a lot of the connectors were not working whatsoever
  • Replaced the spark plug wires and obviously spark plugs.
  • and some other general maintenance
  • Also the 4 to 1 jerker exhaust was completely missing a baffle, all it had was a end cap so I replaced that with a mac baffle replacement

Anyways with all that done and two months of hard work I brought it back to life (and it sounds great) and got it inspected. Theres just one lingering issue that plagues me. (Im gunna have a hard time describing it but here I go). At about 20+ mph it starts to bounce up and down. Not significantly but almost like going over really really small speed bumps. It doesn't get worse when I go faster (I have it at 90 and it has the same rough ride quality), Its most noticeable when decelerating and almost goes away under significant acceleration.
Im inexperienced when it comes to diagnosing the problems and I've relied on a good service manual, some YouTube videos and forums like these to get me this far and I just want to fix this last thing.
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post #2 of 10 (permalink) Old 08-17-2016, 12:21 AM
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Welcome to the forum.

What I'm going to suggest may seem a little odd, but you might as well check your tires first. Cupped tires (from running under-inflated) can show those symptoms.

You said nothing about your tires.
Did you replace the tires?

1) If not, do they show uneven wear?
2) If so, did you inflate per the owners' manual or according to the tire sidewall limits?

Here's a dirty little secret: Owners' manuals almost always recommend pressures that will result in under-inflation (hence uneven wear) and cause the bike to wallow like a whale. Better to inflate closer to the upper limit per the tire sidewall, i.e. a few psi below the upper limit. The bike will handle far better and the tires will wear more evenly.

Anyway, it's easy to check that first before doing anything else. (And tires 14 years old or older should be replaced regardless).

Good luck.
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post #3 of 10 (permalink) Old 08-17-2016, 10:12 AM
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quote: I had a shop put tires on the rims and replace the stems and wheel bearings,,, unquote

Take the bike to another shop. Have them remove the wheels and check balance and take a look
to see if the wheel bearings are actually replaced. Does this bouncing feeling seem to be from the
front or rear of the bike?

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post #4 of 10 (permalink) Old 08-17-2016, 11:30 AM
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One other thing to check might be the chain/sprockets for wear.
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post #5 of 10 (permalink) Old 08-17-2016, 12:15 PM
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I agree with all the advice so far check the tires are inflated to proper PSI as per the sidewall not the manual. Have another shop check the balance on the tires maybe a weight has come off. Check the wheel bearings if you find any shiny spots etc... replace them. Check the chain and sprockets take time to make sure the sprocket bolts are tight and set to correct torque, especially the front. Also check that you have the correct oil and correct level in the front forks. You mentioned that you dismantled and cleaned did you check the fork spring lengths to make sure they are with in spec and both are the same length. Check that when you had the steering apart you put the parts back in the same order and that the torque is correct.
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post #6 of 10 (permalink) Old 08-17-2016, 04:52 PM
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Quote:
Originally Posted by wiredgeorge View Post
quote: I had a shop put tires on the rims and replace the stems and wheel bearings,,, unquote

Take the bike to another shop. Have them remove the wheels and check balance and take a look
to see if the wheel bearings are actually replaced. Does this bouncing feeling seem to be from the
front or rear of the bike?
Sorry, missed that.
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post #7 of 10 (permalink) Old 08-17-2016, 11:01 PM
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Quote:
Originally Posted by Clicker3499 View Post
I agree with all the advice so far check the tires are inflated to proper PSI as per the sidewall not the manual. .
Always use manufacturers tire pressure recommendation. The sidewall pressure is the maximum recommended pressure for that particular tire.
That tire could fit many applications, so recommended pressures could vary according to that application. Go by Kawasaki recommendation.
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post #8 of 10 (permalink) Old 08-18-2016, 09:22 AM
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The rating on the tire sidewall is for maximum load and not what is recommended for everyday riding. Start with the tires cold and inflate to the bike manufacturer's suggestion. they will increase in pressure about 10 percent when fully warmed. I believe most folks who fill tires to max are riding with the tires far too inflated in most cases. If you have the bike loaded to the max indicated on the tire sidewall, then increase the tire pressure.

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post #9 of 10 (permalink) Old 08-18-2016, 10:16 AM
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Quote:
Originally Posted by sfair View Post
Always use manufacturers tire pressure recommendation. The sidewall pressure is the maximum recommended pressure for that particular tire.
That tire could fit many applications, so recommended pressures could vary according to that application. Go by Kawasaki recommendation.

I don't disagree and would normally go with manufacturer recommended PSI, but if we look at the age of the bike and the new tires compounds etc... of today I would in this case not go with the bike manufacturers recommendation. The tires of 1985 may not have even been able to handle the pressure required for the tire that is now installed on the bike. Most tires in 85 worked at or around the 30- 35psi range. However the tires of today depending on the compounds (single or multiple)or manufacturer etc..work any where between 30 and 90psi or even higher . Also in 85 the bike probably did not come with radial tires and that may be what has been installed in this case.
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post #10 of 10 (permalink) Old 08-18-2016, 12:30 PM
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Since the recommended tire pressure on my 81 650 seems kinda low, I choose a pressure between the owner's manual & the tire mfg. then adjust if necessary after riding.

If the problem isn't the tires. when you rebuilt the forks, did you reference the 85 ZX550 Kawasaki factory service manual? There should be a fork spring service limit & fork oil specs. Some say the stock springs weren't that great to begin with & they often times go with a different weight of fork oil.



....

1981 KZ650-CSR. Competition, Sports & Road.
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