Topic: cutting out at constant speed

[blackhog02]

Finally got the 71 cb750 out on the road.  It starts fine with little to no choke and seems to accelerate fine but at a constant speed it is cutting out.   I have adjusted the valves, static set the timming (can't get my light to work), and synced the carbs today.  Bike idles ok not great and every now and then surges up and won't come back down.  All 4 plugs look sooty.  Cleaned gas tank and put in inline fuel filter.

Open to ideals to check next - thanks

also any ideal how to seal up the plug that the altanator wires run thru?  I think that is where my big oil leak is comming from.


Bike is stock with 4 into 1 pipe.  
http://www.mptrackclub.com/photos/cb750_k1/cb750_k1.htm

[MotoMartin]

Cutting out sounds like an electrical problem. Verify that the fuses are held tight in the fuse box, also make sure that the electrical connection at the ignition switch is tight.

[blackhog02]

I'll  check the electrics but I think it is more of a carb fuel issue.  - I guess a better word to describe it would be surging or running rough as it is not dying. If I accelerate it seems fine but if I am just crusing and holding the throttle steady it acts like it needs a carb sync.

[Johnie]

Have the carbs ever been gone over, cleaned, etc.?  I cleaned my carbs on my K1 and it still did not idle that good.  Then I bought new slow jets and what a nice difference.  It is tough to get all the crap out of those small slow jets.  Where are the air screws set?  I also had the miss at a constant speed and it turned out the sync was off a little.  Got it spot on and the miss is gone.  I used some anerobic gasket maker on my stator wire rubber grommet.  Do not use to much and you will be OK.
http://forums.sohc4.net/index.php?topic=53027.msg567751#msg567751

[blackhog02]

I went thru the carbs when I got them but I did not look at the position of the needle jet.  The carbs had been taken off and stored inside for the last 15 years and they were in great shape minus a few spider webs.  I am going to check the float height again.  I know one was leaking out of the overflow tube when we shut the bike off after syncing it up.

[Johnie]

I went thru the carbs when I got them but I did not look at the position of the needle jet.  The carbs had been taken off and stored inside for the last 15 years and they were in great shape minus a few spider webs.  I am going to check the float height again.  I know one was leaking out of the overflow tube when we shut the bike off after syncing it up.

I hear you...it is just the process of elimination to find the problem.  Do you have the brass floats in yours?  One of my floats had a leak in it so it was sinking.  As long as you are going to check the floats, take each one off and shake it.  If you hear gas in there replace it.  Lets us know where your needles are set and if you have the 120 jets in there. 

[BlackMax]

cutting out at a level throttle usually indicates too lean; but, you say the plugs are "sooty".   I would look towards an electrical issue, as others have mentioned.

I have had something like this happen with a bad coil, but it could be a number of things.

[Mdub]

Too rich will all make it miss at midrange as it loads up, fires and loads up again.
Try to quickly accelerate, if it hesitates and wants to die, it's probably lean.
If applying a little choke helps it is more than likely lean.

If choke doesn't help, it's probably rich.
If it just just bogs it is probably rich.
If your air cleaner is very dirty it could be rich.

Sounds rich to me.
Check your air cleaner if you haven't.
Then, do a high speed plug chop to get in the ball park.
After you have proper plug colors on the main jets (high speed) then you can fine tune
the response through the rest of the throttle range.
Good luck!

[Johnie]

Just to clarify what "cutting out at constant speed" means...are you saying when you get going like around 65 and level off it completely stops?  Or do you mean at that higher constant speed it misses and sputters a bit?