New motor, rough idle, won't rev.

[SlimKlim]

I swapped in the new motor for the bike earlier this week. It will now start and idle, barely. Idle is very rough, if you give it throttle it won't rev and sounds like its going to die. I took it to the shop and let them work on it, and its more or less got them stumped. Timing is okay, coils are okay. The signal generator seems to be okay. One of the guys had this little timing light, and when he put it up to the plug wires, you can see the spark slow waaaay down when you try to give the bike throttle, even on both sides.

The bike seems to have a good ground. The only possible thing we can think of is a bad igniter, but the book offers no way to test it. I'm trying to see if I can borrow one from a friend tomorrow, but if that falls through, I either need to figure out a way to test the igniter, or buy one and get it shipped ASAP. I'm leaving for school next Monday and it would be nice to take the bike with me. Any suggestions?

[SlimKlim]

Anyone?

[Trwhouse]

Hi there,
Actually, there's not enough info here to help you.
So you put in a different engine.
Did you go through the replacement engine to be sure it is healthy?
Did you adjust the valves and check their clearances as a baseline? All were OK?
I can't imagine you just bolted it in without checking the valve clearances, but if you didn't I'd start there -- despite the spark issues at this point.
Was there any damage on the side cases of the replacement engine? There's a lot of delicate electrical stuff on both sides and that could be part of the problem, too.
There's also the issue of potential carb problems. Did you go through them and clean all the tiny jets and other parts? Did you check the float levels? Did you set the initial screw settings correctly and get everything securely fastened so there are no vacuum leaks, etc.?
Where did you get this different engine? How do you know to trust it?
In cases like this, there are far more questions than answers so you have to go over everything again and see what you find.
Is it possible you missed a ground cable?
Check and recheck and recheck again.
Eventually, you will find it.
Best wishes,
Trwhouse

[SlimKlim]

Hi there,
Actually, there's not enough info here to help you.
So you put in a different engine.
Did you go through the replacement engine to be sure it is healthy?

Took the top end down, cleaned everything, made sure the rings were clean etc, took off the oil pan, cleaned all that out, etc and likewise.

Did you adjust the valves and check their clearances as a baseline? All were OK?

Swapped my old head onto the motor and my valve clearances are all good.

I can't imagine you just bolted it in without checking the valve clearances, but if you didn't I'd start there -- despite the spark issues at this point.
Was there any damage on the side cases of the replacement engine? There's a lot of delicate electrical stuff on both sides and that could be part of the problem, too.

Both case covers came off to fit the engine in, I did use the generator from the replacement, but unless it's somehow shorting stuff out, I can't see how it would cause the motor to lose spark.

There's also the issue of potential carb problems. Did you go through them and clean all the tiny jets and other parts? Did you check the float levels? Did you set the initial screw settings correctly and get everything securely fastened so there are no vacuum leaks, etc.?

Yes, the carbs have been gone through, but there is no way a fuel problem could cause the motor to lose spark, which we know is happening.
Where did you get this different engine? How do you know to trust it?

From a salvage yard in Florida, I've gone through it personally, but mechanically it seems sound, its an electrical issue.


In cases like this, there are far more questions than answers so you have to go over everything again and see what you find.

Is it possible you missed a ground cable?

I thought so too, but the bike seems to be grounded well.

Check and recheck and recheck again.
Eventually, you will find it.
Best wishes,
Trwhouse

Thanks for the troubleshooting, maybe that will help. I found an igniter to borrow today so I can swap it on and see if that fixes it. If not I can move to the stator or triple check the signal generator. Or something. Grarg. 

[Trwhouse]

Hi again,

When you say you "took the top end down" and checked the rings to be sure they are clean, do you mean that you removed the cylinder head amd also removed the cylinders from the engine?
If so, did you replace the rings, head gasket, cylinder base gasket etc. upon taking it all apart?

A pinched wire could cause your alleged intermittent spark issue.

Something could have gotten pinched at the stator cover (there's a rubber grommet there to protect the wires, are you sure there is nothing that is pinched?) or at the ignitor side of the crank.

There are just so many variables, that's why you have to rule them out one by one.

I know that if it's a carb issue it's not directly related to a spark issue, but have you thought that you might be dealing with a spark AND a carb issue?

Never assume it's not one thing until you have ruled out everything.  It will bite you every time.

Best wishes,
Trwhouse

Hi there,
Actually, there's not enough info here to help you.
So you put in a different engine.
Did you go through the replacement engine to be sure it is healthy?

Took the top end down, cleaned everything, made sure the rings were clean etc, took off the oil pan, cleaned all that out, etc and likewise.

Did you adjust the valves and check their clearances as a baseline? All were OK?

Swapped my old head onto the motor and my valve clearances are all good.

I can't imagine you just bolted it in without checking the valve clearances, but if you didn't I'd start there -- despite the spark issues at this point.
Was there any damage on the side cases of the replacement engine? There's a lot of delicate electrical stuff on both sides and that could be part of the problem, too.

Both case covers came off to fit the engine in, I did use the generator from the replacement, but unless it's somehow shorting stuff out, I can't see how it would cause the motor to lose spark.

There's also the issue of potential carb problems. Did you go through them and clean all the tiny jets and other parts? Did you check the float levels? Did you set the initial screw settings correctly and get everything securely fastened so there are no vacuum leaks, etc.?

Yes, the carbs have been gone through, but there is no way a fuel problem could cause the motor to lose spark, which we know is happening.
Where did you get this different engine? How do you know to trust it?

From a salvage yard in Florida, I've gone through it personally, but mechanically it seems sound, its an electrical issue.


In cases like this, there are far more questions than answers so you have to go over everything again and see what you find.

Is it possible you missed a ground cable?

I thought so too, but the bike seems to be grounded well.

Check and recheck and recheck again.
Eventually, you will find it.
Best wishes,
Trwhouse

Thanks for the troubleshooting, maybe that will help. I found an igniter to borrow today so I can swap it on and see if that fixes it. If not I can move to the stator or triple check the signal generator. Or something. Grarg. 

[SlimKlim]

Hi again,

When you say you "took the top end down" and checked the rings to be sure they are clean, do you mean that you removed the cylinder head amd also removed the cylinders from the engine?
If so, did you replace the rings, head gasket, cylinder base gasket etc. upon taking it all apart?

Yes

A pinched wire could cause your alleged intermittent spark issue.

Something could have gotten pinched at the stator cover (there's a rubber grommet there to protect the wires, are you sure there is nothing that is pinched?) or at the ignitor side of the crank.

Yes

There are just so many variables, that's why you have to rule them out one by one.

I know that if it's a carb issue it's not directly related to a spark issue, but have you thought that you might be dealing with a spark AND a carb issue?

You might be spot on there, read below

Never assume it's not one thing until you have ruled out everything.  It will bite you every time.

Best wishes,
Trwhouse

I sourced an igniter to borrow and swapping it out got it the spark sorted out, we tested it by putting that little timing light on it. So I'm trying to get one of those ASAP off of here or from eBay or something. The bike ran better but is still grumpy, and the mechanic thinks its a fuel issue as well, so they are going to go through the carbs for me and double check the jetting. Aside from that, I dont know what else could be making it run rough.

[Trwhouse]

Hi again,

Well carb issues usually mean fuel jets that are clogged from gas that turns into varnish and blocks the tiny little fuel passages.
The jets must be thoroughly cleaned out so you can see light through them -- the pilot jet (the smaller one) is the jet that clogs first because it's so tiny. And guess what? If the pilot jets are clogged (and they are if it has been sitting for a while, believe me!) that's why the engine won't idle or run smoothly off idle.
The main jet is larger and harder to clog, so an engine will usually run better as it pulls from idle.
The idea is that they all have to be cleaned out and cleared, then measure and check float levels and all carb screw settings.
It's not that hard to do yourself, and there are plenty of instructions here on the board if you search.

Best of luck,
Trwhouse 

[SlimKlim]

Hi again,

Well carb issues usually mean fuel jets that are clogged from gas that turns into varnish and blocks the tiny little fuel passages.
The jets must be thoroughly cleaned out so you can see light through them -- the pilot jet (the smaller one) is the jet that clogs first because it's so tiny. And guess what? If the pilot jets are clogged (and they are if it has been sitting for a while, believe me!) that's why the engine won't idle or run smoothly off idle.
The main jet is larger and harder to clog, so an engine will usually run better as it pulls from idle.
The idea is that they all have to be cleaned out and cleared, then measure and check float levels and all carb screw settings.
It's not that hard to do yourself, and there are plenty of instructions here on the board if you search.

Best of luck,
Trwhouse  

The carbs are clean, its definately a seal or over jetting issue. But the guys at the shop are going to sort that out, I've got to get another week of work in and get ready to leave for school. So I don't have time to work on it myself. Hopefully I won't rack up entirely too much shop time.

I have completely gone through the carbs myself several times, checked floats, checked and adjusted jetting, adjusted fuel screws, etc etc. Its something that's genuinely over my head.