Bike rides "JERKY"

[sparkey]

Just got my used carb rack for my 78 gs750 and did a carb cleaning and bench synced them. Got it to idle decent in the yard. Went to take it for a spin, it has plenty of power but rides jerky like something is out of alignment. Question is: Is this a symptom of ill synced carbs? Or could it be something more serious?

 

[sparkey]

It almost seems like the clutch is off balance.

 

[cowboyup3371]

When does it feel "jerky"?

 

[Big T]

Yes, more info please

Steady throttle?

Accelerating?

Pipe/pods/airbox?

 

[sparkey]

It feels like it when accelerating up to speed or whenever applying throttle. Coasting is better but still does it a little. The main nut on the clutch was checked and is tight also. It feels like something is off balance in the motor. Stock everything no pods, has stock airbox. #102 jets. Stock pipes. The chain was dry and rusted. I wonder if the oil hasnt soaked into it yet, almost feels like it could be the chain binding up when goin around the sprockets maybe.

 

[cowboyup3371]

When you cleaned the carbs, did you use the methods suggested here? You said you bench-synched them, did you also take some kind of a manometer and synch them that way?

Look at the vacuum also from your petcock to the carbs. Could you possibly be having a hose problem?

 

[niclpnut]

If the chain is old it could have some links that are binding or the chain could be stretched on one side.

I had the original 630 chain on my E when I bought it. Was pretty dry, and was binding tight on part of the revolution on the sprockets.

It definitely was causing the engine to work, especially on acceleration, and was a "jerky" ride to say the least.

Put the bike on the center stand and spin teh rear wheel in neutral, watch the chain and see if it is tightening up. Also check the sprocket teeth to see if they are turned/dogeared/worn, and your wheel alignment if the chain looks ok.

For me, the off sync carbs would be easily identified by coughing and spitting, and some missing. You would hear the engine running rough if it's off sync badly enough to cause it to "jerk"

Nic

 

[earlfor]

It feels like it when accelerating up to speed or whenever applying throttle. Coasting is better but still does it a little. The main nut on the clutch was checked and is tight also. It feels like something is off balance in the motor. Stock everything no pods, has stock airbox. #102 jets. Stock pipes. The chain was dry and rusted. I wonder if the oil hasnt soaked into it yet, almost feels like it could be the chain binding up when goin around the sprockets maybe.

If the chain was dry and rusted, it s a 10 to 1 bet it has frozen/galled pins in it and that is your problem. Oiling it will not help because the surfaces of the pins are rough and there is no way to make them smooth again. You're going to need both sprockets also because a binding, jerking chain chews the crap out of the sprocket tooth tolerances.

Earl

 

[Guest]

I'm betting the chain/sprockets are spent as well...

Time for the ol' 530 conversion - chain, front & rear sprockets. Afterwards, the bike will seem like a whole different animal.

Call the guys at Z1, they'll steer you in the right direction.

 

[sparkey]

When you cleaned the carbs, did you use the methods suggested here? You said you bench-synched them, did you also take some kind of a manometer and synch them that way?

Look at the vacuum also from your petcock to the carbs. Could you possibly be having a hose problem?

I did use the methods here to bench sync and I do need to get a carb sync monometer. Thats on the shopping list. I am running it on prime and the fuel pours out.

 

[sparkey]

If the chain is old it could have some links that are binding or the chain could be stretched on one side.

I had the original 630 chain on my E when I bought it. Was pretty dry, and was binding tight on part of the revolution on the sprockets.

It definitely was causing the engine to work, especially on acceleration, and was a "jerky" ride to say the least.

Put the bike on the center stand and spin teh rear wheel in neutral, watch the chain and see if it is tightening up. Also check the sprocket teeth to see if they are turned/dogeared/worn, and your wheel alignment if the chain looks ok.

For me, the off sync carbs would be easily identified by coughing and spitting, and some missing. You would hear the engine running rough if it's off sync badly enough to cause it to "jerk"

Nic

If the chain was dry and rusted, it s a 10 to 1 bet it has frozen/galled pins in it and that is your problem. Oiling it will not help because the surfaces of the pins are rough and there is no way to make them smooth again. You're going to need both sprockets also because a binding, jerking chain chews the crap out of the sprocket tooth tolerances.

Earl

I'm betting the chain/sprockets are spent as well...

Time for the ol' 530 conversion - chain, front & rear sprockets. Afterwards, the bike will seem like a whole different animal.

Call the guys at Z1, they'll steer you in the right direction.

Goin out to put her up on the center stand. It was binding up when trying to roll it around the shop but thought I had a sticky caliper. This thing sat outside for 2 years with no cover. I guess I should consider myself lucky it even runs!

 

[sparkey]

UPDATE: Set it up on the center stand and and ran it in 1st gear. The chain is jumpin around like a Mexican jumping bean on fire!!! Chain and sprockets here I come!
Thanks guys!!!!

 

[niclpnut]

Going to be night and day with the new chain and sprockets, and your engine is going to love you if you go the 530 conversion route, with the weight reduction.

Nic

 

[cowboyup3371]

Congratulations on finding the problem.

 

[earlfor]

UPDATE: Set it up on the center stand and and ran it in 1st gear. The chain is jumpin around like a Mexican jumping bean on fire!!! Chain and sprockets here I come!
Thanks guys!!!!

Whatever you do, do NOT set the chain tension tight. If you do, you will be buying a new chain and sprockets again in just a few thousand miles. On the lower chain run alongside the rear rim, you want to be able to move the chain up and down 2 to 2 1/2 inches total. Thats an inch to an inch and a quarter above centerline plus that amount below. Chains do NOT require tension to function correctly. There is already 70+ HP pulling the chain down, into the sprocket teeth. The tension is useful only to keep the chain from slapping the frame cross arm and to hold the chain tight enough that it can not come off. However, assuming your front and rear sprockets are aligned, how could it come off? When you set your chain tension and you think you have the correct amount of slack, with the bike on the centerstand, (engine not running) spin the rear tire around a half dozen times. If you have the chain tensioner bolts set correctly, the rear sprocket teeth will track in the center of the chain link, never touching the side plates. Tweak your adjustments untii the chain tracks center on the rear sprocket teeth.

I get 30,000 miles on a chain and sprocket set before as a matter of precaution, I replace them. I could probably get another 10k out of a set if I needed to.

Earl

 

[earlfor]

Going to be night and day with the new chain and sprockets, and your engine is going to love you if you go the 530 conversion route, with the weight reduction.

Nic

There are various reasons to do a #630 to #530 conversion, but its primarily for availability and choice of selection. Weight wise, there is about 6 ounces difference between the two. I doubt any 500+ lb motorcycle is going to notice that you're only carrying half a bottle of water instead of a full bottle in you tank bag.

Earl

 

[sparkey]

Whatever you do, do NOT set the chain tension tight. If you do, you will be buying a new chain and sprockets again in just a few thousand miles. On the lower chain run alongside the rear rim, you want to be able to move the chain up and down 2 to 2 1/2 inches total. Thats an inch to an inch and a quarter above centerline plus that amount below. Chains do NOT require tension to function correctly. There is already 70+ HP pulling the chain down, into the sprocket teeth. The tension is useful only to keep the chain from slapping the frame cross arm and to hold the chain tight enough that it can not come off. However, assuming your front and rear sprockets are aligned, how could it come off? When you set your chain tension and you think you have the correct amount of slack, with the bike on the centerstand, (engine not running) spin the rear tire around a half dozen times. If you have the chain tensioner bolts set correctly, the rear sprocket teeth will track in the center of the chain link, never touching the side plates. Tweak your adjustments untii the chain tracks center on the rear sprocket teeth.

I get 30,000 miles on a chain and sprocket set before as a matter of precaution, I replace them. I could probably get another 10k out of a set if I needed to.

Earl

There are various reasons to do a #630 to #530 conversion, but its primarily for availability and choice of selection. Weight wise, there is about 6 ounces difference between the two. I doubt any 500+ lb motorcycle is going to notice that you're only carrying half a bottle of water instead of a full bottle in you tank bag.

Earl

Thanks Earl,

Coool. I will make a decision about what chain I will get. Right now the sprockets look good. I might get a stock chain just for cost reasons. It was tensioned correctly just sat out in the elements too long with no protection.
On a side note I did tighten it up and rode it around the block to try and un-bind it and it did free it up somewhat, but I do not plan on riding it till I get a new chain.


Brian

 

[cowboyup3371]

Replace everything as a set to ensure you don't mess up either even more later on.

 

[earlfor]

Thanks Earl,

Coool. I will make a decision about what chain I will get. Right now the sprockets look good. I might get a stock chain just for cost reasons. It was tensioned correctly just sat out in the elements too long with no protection.
On a side note I did tighten it up and rode it around the block to try and un-bind it and it did free it up somewhat, but I do not plan on riding it till I get a new chain.
Brian

I understand cost considerations. It isn't preferable, but if you need to re use the stock sprockets there is a little trick that will help. When the engine is pulling the chain, the most wear on the sprocket tooth will be on the forward side of the tooth, which is where the engine concentrates the pulling force. If your sprockets are flat, (meaning not having any offset flange cast into them), you can remove the sprockets and rotate them 180 degrees, so that what originally was the front edge of the tooth and taking the load is now the unloaded following/back tooth. It gives you a new front tooth edge. It doesn't help with wear in the valleys, but it will help to increase your chain life.

I'm not sure I'm clear on this point. So, the little drawing is sprocket
teeth. The side/edge that wears is 1. 2 just follows and doesn't do
anything. By rotating the sprockets 180 deg, 2 will be in the 1 position.

/\..../\
--1-2--

Earl