Idle's fine, boggs down with high rpms

[CMGoldie]

Hi, first time posting here, not the first time I have came here for information though. I have a question.

I have an 81 cb750f. I just recently had some started issues, which I found out was a broken wire in the headlight. I got that fixed. Before I fixed that I had tried starting it for a while (I am still not the most engine savvy) with starting fluid and I kept spraying a little more not realizing it wasn't getting spark. Now that I have gotten that fixed and got it started, it runs terribly. It idles fine, but now you rev it up and sounds off. It doesn't necessarily bog down while it is in neutral but when you run up the rpms it doesn't have the same pitch/sound as it did before. Now in 1st gear that is a different story, you pull on the throttle the pitch still sounds off and then it boggs down and backfires all to hell when you are accelerating. Does that in all the gears as you accelerat through them.

Ok so here is what I have done so far. I had a short in my cable from the battery to the solenoid starter, replaced that. I have checked all grounds and etc. Made sure all wires were in butt connectors and not shorting out. I have just pulled my carbs and cleaned them again.

Here is what I think the issue may be. I am looking for suggestions, or if anyone else has had a problem similiar problem. I have done a bit of research on this.

I had just replaced the battery when I broke the wire in the headlight. So I am going to test the voltage on the wires. I had a problem with the choke cable. I am going to work on that get the tension out of it so I don't have the choke on while I am riding it. I got the carbs cleaned out, checked them for gunk, I didn't rebuild them because I did that right at the beginning of spring. One of the website I saw said check for wet plugs, idk what that means. So I am going to pull them out and check for fouling, etc.

The thing that really got me was that the pitch just sounds so different. I am worried to death that it might be somehting with the engine because I want to ride it not pull the engine off.

Thanks guys, Matt

[trapper]

Hard to really tell cuz none of us here can actually hear what your bike is doing but I'll take a shot. There's a lot of great techs here so, hopefully we can help ya trace it.
I'm not leaning towards an electrical issue. Though not impossible, seeing as it idles fine and revs better (but not good) in neutral but not as well once under a load (in gear) I'm still going to lean towards carbs.
Sounds like you may not be getting enough fuel.
You say you cleaned them but, a real cleaning should involve pulling the jets and tubes and really cleaning them out. Take a small wire, an e string from a guitar works great, and poke it through all the holes in the tube gently. do this until you can put the little hose that comes with a can of carb cleaner, spray it and see a steady spray coming out of all the holes. Make sure you spray through all ports and clean the bowls completely. Any little bit of schmeg can clog up a jet. Next, after you assemble them and get them back on work on your pilot screw adjustment. This puts more or less fuel in your crabs. I believe stock on these are 3/4 turns out from gently seated. Do this, clean your plugs then take it for a quick ride. Then check your plugs again. If they are white you're running a little lean. Turn the screw out a little. If excessively black you're a little rich. Turn them in a bit. You'll have to adjust each carb to how the coinciding plug looks. Of course, getting them properly sinced will help a lot too.
Try this and let us know how it turns out.
One step at a time my friend. But no, it doesn't sound like you'll have to go as far as pulling the whole motor out. :)
Good luck  

[CMGoldie]

Ok, got the carbs back on and synced. I started working on the tuning. I also noticed when checking my plugs that they were not fully in. I got them tightend up, along with my headers. We tightened down the screws to adjust the fuel. It seems to run better, didn't get much done after that. I ran it down the highway to see how it would do. It ran better but still didn't run very good. It seems like rpms get higher now before it bogs down. 1st and 2nd gear were bad about it. 3rd was too but not as bad as the other. I didn't get the rpms high enough in 4th and 5th. It seems to be happening when you are accelerating hard. I am going to work on it again later this week.

 

What is blowing my mind, is that it ran fine before I changed batteries. The carbs were still synched when I put them back on. I don't understand how it would go from running fine, to running as fast as a 3 legged dog, by changing the battery and sitting for three weeks. It sat all winter and didn't have any problem with running. My theory, I am not a mechanic, is that the battery could have something to do with it. Or the wire that we ran pass the coupler and spliced together. My friend, who is a mechanic, told me I am wrong. So I will continue to work on the carbs and adjusting them.

 

Also I don't know how good the sound quality is. I made this prior to adjusting the pilot screws.

 

http://www.youtube.com/watch?v=PnUuV6Twvzo

On Fri, Jun 28, 2013 at 5:48 PM, trapper [via Honda CB750'S] <[hidden email]> wrote:

Hard to really tell cuz none of us here can actually hear what your bike is doing but I'll take a shot. There's a lot of great techs here so, hopefully we can help ya trace it.
I'm not leaning towards an electrical issue. Though not impossible, seeing as it idles fine and revs better (but not good) in neutral but not as well once under a load (in gear) I'm still going to lean towards carbs.
Sounds like you may not be getting enough fuel.
You say you cleaned them but, a real cleaning should involve pulling the jets and tubes and really cleaning them out. Take a small wire, an e string from a guitar works great, and poke it through all the holes in the tube gently. do this until you can put the little hose that comes with a can of carb cleaner, spray it and see a steady spray coming out of all the holes. Make sure you spray through all ports and clean the bowls completely. Any little bit of schmeg can clog up a jet. Next, after you assemble them and get them back on work on your pilot screw adjustment. This puts more or less fuel in your crabs. I believe stock on these are 3/4 turns out from gently seated. Do this, clean your plugs then take it for a quick ride. Then check your plugs again. If they are white you're running a little lean. Turn the screw out a little. If excessively black you're a little rich. Turn them in a bit. You'll have to adjust each carb to how the coinciding plug looks. Of course, getting them properly sinced will help a lot too.
Try this and let us know how it turns out.
One step at a time my friend. But no, it doesn't sound like you'll have to go as far as pulling the whole motor out. :)
Good luck  

It ain't a custom till you have customized it yourself.

1981 CB750c (current daily ride and build)
1980 GL500 (Stripped and rebuilding)
1981 CM450 (Stripped and rebuilding)

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[Johnnylevi]

did you check your charging system? If that is weak you won't be able to go very high on your rpm's I think somewhere around 5k

[trapper]

I see your problem, your gremlin bell is to high. It's gotta be lower to scare 'em off of even the low parts of the bike.

Seriously though. Johnny has a good point. Get a volt meter and put it to the positive and negative terminals while it's running. Just a shot in the dark but if you're pushing low voltage, the bike will run rough.
The bike should idle around 12 to 12.5 volts. When you rev it, it should jump to 14 or so...

A poor connection or a weak stator can cause this. If you don't have one already, go get yourself a Clymer manual. They are available here on the forum for download but, I find it's good to have one you can have nest to you while working on the bike.
It will give you a good run down on how to test your stator for resistance and voltage.

[Truck]

I have a similar issue going on with my 900. A mech friend looked the bke over and found that the stator had gone bad. Might be worth the time to check out. Is you battery charging ok?

[TOOLS1]

It definitely sounds like an ignition problem. Check the plug wires, ignition coils, and the cdi unit.
TOOLS