Uneven rough idle

[mastroiani]

Hi, I got a 1979 CB750 10th Anniversary Edition  couple of months ago and have been fixing it ever since.  I changed pretty much most electric stuff:  CDI, alternator, stator,  starter,  etc.  Before these replacements the battery wouldn't keep charge.  Now it keeps charge and seems to be running ok.

The only electric part I didn't replace is regulator rectifier.  But it seem to work fine without it.

I took it out for a ride today and mostly it runs great!  But I noticed that the idle is uneven.  When the bike warms up and idles, it seems like sometimes it wants to cut off and die, then resumes the idle.  Then again.  Sometimes, it's more severe and other times less.  It doesn't actually die right away, I think idling goes on for about 30 seconds or more and then it seems like it will cut off any second.  If I open up a throttle couple of times, then it begins to idle again normally for about 30 seconds and then same thing begins all over again.  When pulling away in the 1st gear I have to open up throttle more than usual so I can ride away, otherwise the engine cuts off.  Happens on and off.  Sometimes it takes off fine.  Also, when riding in low gears at a very low speed I could swear I feel some hesitation and I have to open up the throttle...

in high gears or high speeds it seems to have no problem and rides very strong.

Do you guys know what could be the problem?  Carbs were also cleaned and rejetted...  

I don't know whether this is electric problem or problem with too much or too little gas or proper carb synchronization?

Thank you very much in advance.  Any advice is greatly appreciated.

[brcree]

  Well, you had the carbs redone and cleaned......well it doesn't take much to clog up the idle jets. These jets have extremely small holes. It could be some trash in your tank that has made its way into them. I run a fuel line filter on my 76 cb750 k6. Also you do need to sync your carbs......runs much better all around if they are. Your fuel air mix may be out............hope it helps.  

[Re-run]

Why were the carbs rejetted? The stock jets should have been fine. If you were rejetted, I would guess your engine is loading up on fuel, as in running too rich. I would pull your plugs after it dies when idling and check to see what they look like. If they have a lot of black on them or are very dark, then the carbs are too rich.

[mastroiani]

Thanks a lot for your replies.  I'm not sure why they were rejetted.  Prior to my purchase, the bike has been standing for a long time and seems like it was substantially abused...  There is some kind of after market, 4-into-1 gutted exhaust without a baffle etc.  So when the mechanic started work he suggested that carbs should be rejetted.  I don't know much about mechanics so I just went along with whatever he said.  He actually changed the jets couple of times, because once there was too much gasoline and the other time it wasn't enough (or something like that).  

So I guess from your replies it's either of the two: either too much gas or too little because of dirty jets.  Mechanic told me he'd come back and sync the carbs and take a look at the problem. he doesn't speak English very well, but I think he said "mucho gasolina"  :)

I was also thinking of running a bottle of carb cleaner through a full gas tank.  Just in case there is some dirt?  Do you think it's a good idea?

Thanks again

[Re-run]

Rarely do exhaust changes by themselves require a rejet. Granted you are running a different bike than I but in most cases, some tweaking with the idle mix is all that is required. As the mechanic does not do english very well, maybe he knows his stuff but it would be good for you to fine a manual for your bike so you know what is going on too.
If you want to run some cleaner through, I suggest seafoam.

[mastroiani]

UPDATE
=========

So I decided to try SeaFoam and ordered it online since none of the local stores carried it in stock.  But while I was waiting for Seafoam I saw another carb cleaning product called Berryman B-12 at a local Walmart and thinking it was a very similar product bought it as well to try before the SeaFoam arrived.

Well, I put about a quarter of the bottle into full tank and I think I either did something terribly stupid or something terribly wrong.  Instead of slight uneven / rough idle that I had prior, now I the engine sounds really terrible.  The engine dies right away unless I keep it on high choke or rev it up real high.  I can still ride the bike on high RPMs but anything lower than 4-5 it dies.  It began to backfire and then engine feels like its grinding something inside and something is muffling it and choking it.  I think it also lost 50% of it's torque and power.   It's just really really bad.

Whats happening?  What did I do wrong?

[Re-run]

Well having to rev high sounds like the cleaner clogged the idle jets. As for the grinding and such, that should have nothing to do with the berryman. I would check your oil and see if there is metal in it. A dirty carb would never cause a grinding from the engine.
Drain the float bowls and see what comes out. You might need to drop the bowls and pull the jets out and clean them.

[swiffer]

Have you looked right under the motor behind and down from the carbs and seen the black knob that adjusts the idle?That is on  dohc.Plus a manual is a must for any bike .