Topic: Bike broke down...Help

[ANVkevin]

Well, the bike started rough again today. Got 'er going. ran okay. drove about 30 miles, did okay. Started to sputter, abit and bucked really bad in 1st/2nd untill I got on it pretty hard. Missed a few fires. Did alittle better going 55. Hit the next exit and sputtered again in 1st pretty hard, than stalled. Couldn't get it started. It would start for a minute sound horrible and die.

A few notes:

'77 CB750K
Carbs are clean, close to synced and running a fuel filter.
Battery dies pretty quick when it I use the electric start.
Lights don't get brighter when the bike starts or revs.
It will start and run for a minute and die for 5-10. Start and die: repeat.

I'm thinking a may have a bum battery. Or possibly a generator.
I really think its an electrical issue, for what it's worth.

So poor SweetPea is hanging out at a gas station in the city for the night...


Any advice or help would be greatly appreciated.
Thanks!
-Kevin

[Sam Green Racing]

Put a fully charged battery on it and see if that cures it, if it does you have a duff battery or your charging system is not working as it should.

Sam

[mrbreeze]

What do you mean by the carbs are close to synched? They are either synched or not synched!!! How did you determine they are "close"?

[Wheelhorse77]

go get a cheap DVOM--- digital volt ohm meter and check your system. 14.2 is middle of the road, but 13.2 to 15 is acceptable charging.

black to black and red to red and check it at about 2500+ RPMS

[Tom Stark]

Well, the bike started rough again today. Got 'er going. ran okay. drove about 30 miles, did okay. Started to sputter, abit and bucked really bad in 1st/2nd untill I got on it pretty hard. Missed a few fires. Did alittle better going 55. Hit the next exit and sputtered again in 1st pretty hard, than stalled. Couldn't get it started. It would start for a minute sound horrible and die.

A few notes:

'77 CB750K
Carbs are clean, close to synced and running a fuel filter.
Battery dies pretty quick when it I use the electric start.
Lights don't get brighter when the bike starts or revs.
It will start and run for a minute and die for 5-10. Start and die: repeat.

I'm thinking a may have a bum battery. Or possibly a generator.
I really think its an electrical issue, for what it's worth.

So poor SweetPea is hanging out at a gas station in the city for the night...


Any advice or help would be greatly appreciated.
Thanks!
-Kevin

Kevin, sorry for your troubles.  I just put my bike on the road, and was having some fuel and ignition issues.  The carbs need to be synced, the jets are too lean, and the timing is not steady, it has a little "jump" every so often.  Like you I had a fuel filter.  I woudl ride it, and it would starve for fuel.  Pull the line off, no fuel, then a second later fuel.  Put the line back on, ride the bike for a block, (had to kick start it), and then no fuel again.  This went on for a while, and it started getting REALLY bad.  Wind it up to 5 grand, try to ease the clutch out, and it would stall!  Turns out I had a blown fuse in my charging circuit.  The battery was dying and I had not idea.  It was broad daylight, and I could not see my lights from on the bike.  I have since installed a volt gauge.  Got a cheap one at Murray's, $19.  The thing that really fooled me is I did know I had some carb and ignition trouble, and electrical trouble can mimic fuel or ignition trouble.
If it were me, I would put the battery on a charger until it would spin that motor over like a top.  Then I would test the charging circuit.  By the time you hit 4K, it should be putting out all it can.  I recently had to set the core gap and point gap, (as well as clean the points and external connections), on my regulator.  Seems to have helped the output. 
Tom

[stueveone]

Just got back from putting 2000 miles on my old bike from Seattle to San Francisco. I got hung up outside of Sacramento with a bum condenser. Check to see what your points look like. Not sure if that could be it but it's where I would start first.

[ANVkevin]

What do you mean by the carbs are close to synched? They are either synched or not synched!!! How did you determine they are "close"?

I used a manometer. May not be perfect, but its very close.


I have a DVOM, Ill definitely try that. And also check all the fuses.

The points are about 100 miles old. As well as the condensers.

Ill give it a run through and hopefully I'll spot something. Thanks for the help. I'll let you know how it goes later today.

-Kevin

[OldSchool_IsCool]

By "running a fuel filter" I assume you mean an in-line filter in addition to the in-tank filter.

Just a long shot here, but it happened to me.  When I first put my in-line filter on, I simply cut the existing fuel line in half and jammed the filter in place.  This left the filter as the horizontal high point in the fuel line. 

About a month ago, my bike started to have a really bad stumble at around 6000 RPM.  Felt very much like fuel starvation.  Switch to reserve, fill the tank - no help.  Now I'm thinking pull the carbs and clean them because the main jets are clogged - sigh.

While getting ready to pull the carbs off, I happened to notice that the afore mentioned fuel filter was full of air, not fuel.  I close the petcock, drain the float bowls, open the cock back up and .... drip... drip.... drip.... WAY too little fuel flowing!

I could see that the air bubble in the in-line filter was acting as a block causing my fuel line to be severely restricted.  I'm glad the in-line filter happened to be clear so I could see the air in it!

I re-cut the fuel line such that the in-line filter was standing vertically on top of the carb fuel gallery and no longer the horizontal high point.  No way it can trap air now.  Stumble is gone and no issues with fuel starvation since!

[Tom Stark]

So far as in line filters go, you may want to get the Mr Gasket glass filter.  I have one on my bike, it is horizontal, but rather than a paper element, it has a very fine plastic mesh.  This allows the fuel to flow quite easily.  Prior to this I had a regular car filter with the paper element, and it definately starved the motor for fuel.  Had it on for only a short time and had to get rid of it. 
Just a thought.
Tom

[mrbreeze]

What do you mean by the carbs are close to synched? They are either synched or not synched!!! How did you determine they are "close"?

I used a manometer. May not be perfect, but its very close.


I have a DVOM, Ill definitely try that. And also check all the fuses.

The points are about 100 miles old. As well as the condensers.

Ill give it a run through and hopefully I'll spot something. Thanks for the help. I'll let you know how it goes later today.

-Kevin

OK....you used a manometer and they are close so that shouldn't be the problem. Like already said,I would start with a fresh battery and make sure the charging system is up to snuff.I would ditch the in-line fuel filter for now.....make sure tank is clean,in-tank filter clean and vent in cap is not plugged. You say carbs are clean.How deep into the carbs did you go? If all of this good,you may have an ignition prob. but your symptoms don't really point to that. Good luck with getting it going.

[TwoTired]

Put a fully charged battery on it and see if that cures it, if it does you have a duff battery or your charging system is not working as it should.

Sam

X2. 

Also, if you pull the headlight fuse (reducing battery drain), you can probably drive it home to work on in comfort/leisure there.

Cheers,

[ANVkevin]

First off, thanks for help!!!

on to the bike. I trailer'd it home. I know my charging system is fine. Good possibility the battery is junk. It's only 3 weeks old, but ill have it tested tomorrow. I do have the tank and inline fuel filters. My inline is set up horizontal. Which I almost hope is a problem because it may even fix the fact the bike seems to be running really lean. As far as the carb cleaning went I totally disassembled the carbs and installed new gaskets all around. The more I think about it the more I think I could have made a mistake with the slow jets. I know I didn't pull any jets that are the "pushed-in" type jets. I'm starting to see that clogged slow jets cause symptoms my bike has. On the other hand, I honestly don't remember the carbs have anything that resembled the pushed-in slow jets. I could absolutely be wrong, ive tried to search for some detailed pics of the '77 CB750k carbs, but to no avail...

Again, thanks for all the help!

-Kevin