Help.. starts and idles well but skips and pops and is sluggish

[demenacer]

Background:  Hello!  I am excited.  I bought this bike for 600 bucks.  I am not a mechanic at all.  I am learning, but this problem is way over my skill set.  The bike is a 1980 CB750F in good condition.  It starts and runs very well.  First 3-4000 RPM's is fine if you are slow on the throttle.  If you hammer on the throttle or you get past 4k RPM it spits and pops.  

The guy I bought it from said it need the carbs synced and it would be fine.  Um... not true.  My buddy and I synced the carbs and it still ran horrible.  The gas tank was filled with rust flakes from the sea foam.  I cleaned out the tanks, shook rocks around in them then cleaned them out.  Still bad.  

So now I pull out the big guns and request the help of another buddy that just got out of two years of motorcycle school.  He is a bit young, but he has tinkered all of his life and 2 years of school, so he is way above me.  He took the carbs a part and dipped them, checked compression, put silicon in the boots to make sure they were sealed and basically looked through everything he could think of.  We replaced one air cut off valve and the accelerator pump just because they were a little crusty.  Mikey went through everything from the air box to carbs and he is stumped.  Anybody have any idea?  

[Re-run]

Have you ever checked what your plugs look like? You can learn worlds of info just from reading fresh plugs.

[demenacer]

Yes.  Plugs are fine, but thank you for the tip.  I read a post last night that had a problem something like mine.  I forgot which one it is.  ANYWAYS!  The good news is my buddy thinks he knows what it is.  He thinks its the plug wires.  He was going crazy ripping apart the carbs.  He trimmed one of the wires and it is running smoother.  I am going to buy new wires.  I can make my own right?  Isn't it just a matter of cutting and crimping?  I forgot to ask him before I left.  I have another question, but I am going to make it in a separate post.  Thanks for the reply.

[Mike CB]

 Hi Mate,

  You might find replacing your H.T. leads is not quite as simple as you first think, on some models the leads as permantly fixed into the coils ,trouble is they look like they come out, you may find one or two loose just to add to the confusion,don't be tempted to pull them out otherwise you will end up knackering your coils and have to buy a new set (not cheap) you can replace the plug caps and chop a bit off the leads at tis end,the new caps just screw into te end of the leads,so no fancy tools required just a pair of wire cutters.lets keep these great machines running !!

[Re-run]

What color where the plugs? I have a hard time seeing how the plugs were ok if your buddy cut off the end and it ran batter. If that was the case, then the plugs would NOT look fine. Most likely your buddy is wrong about what is fine and is not fine on plugs. Starting in 77, honda leaned out the bikes and in most cases, the plugs should be a VERY light tan, more like a dusting.

Also, did you test the ohms on the caps themselves? most resistor caps should be about 5k ohm.

remember, your buddy might have gone through bike school but ask him what ages of bikes he worked on. most never go older than the 90s and if that is the case, he is only flying somewhat less blind than you are.

Also, the rust in the tank should be a big clue. You MUST drain that gas out and then either clean the fuel filter or replace it. Those flakes are likely plugging the filter.

[woodsrider250-2]

Also make sure there is an air cleaner in it.  If it has not filter or pod filters installed it will give up right where you're talking about.