Topic: Runs good! Sometimes.....

[cb750f-2010656]

I get paid tomorrow and shoud have enough for a set of plugs.  Anybody have any ideas about my timing issue?  Im going outside in a bit to double check dwell and timing.

[cb750f-2010656]

Just did my idle chop at 1 1/2 turns out.  Way too lean. I ran her from cool, not cold, for about five minutes and all the plugs were clean as new.  As I understand from other posts on this forum they should be black.  And I've been setting points and timing like this.  This engine is probably about burned.  I am letting her cool for now, and have turned the mixture screes to one turn out.  Will post after I have new results.

On a side note, I see there are a plethora of aftermarket parts for K engines, but limited parts for the F.  If I were to build another, should I do a K motor?  It doesn't matter to me if it is a true F, as long as she looks nice in the end, and is pretty quick for an old Honda.

[cb750f-2010656]

Still clean.  3/4 turn run

[cb750f-2010656]

I'm at 1/8 turn out.  Getting a color change finally, but I think it's clear I need to rejet.

[cb750f-2010656]

At 1/8 turn I get the blackness I need, but that dead spot is YUUUUUUGE.  I'm gonna make sure I didn't put those slide needle seats in upside down and if not, drop the needles a step to try to make her limp till I get some cash.  I've never tuned carbs, just cleaned them.  Now's a great time to learn.

[Jerry Rxman Griffin aka MuthaF'er]

I dont have a way to load test it...  But it turns out that I drained it while resetting the points and timing and I guess there just wasn't enough voltage for that field coil to properly supply the stator.  After charging the battery the votage gets to 13.5 ish with the high beam on so its cool.  I was freaking out a little though.

I set the points perfectly the first time but after a few weeks the dwell angle increased to abiut 106.  I figure parts wearing in, so i do it all again.  Two weeks later my dwell hasn't moved but my 1-4 timing was WAY retarded.  My 2-3 breaker had a sharp peak and wouldnt fire the coil but every once in a while.  I filed it down, set dwell and timing.  Now heres the kicker:  my plate is advanced almost all the way to time 1-4 and my subplate to time 2-3 is fully retarded, leaving 2-3 still firing a touch before F.  Advancer is still working.  Wonder what could be upsetting my timing.

If you have an Advance Auto store put a full charge on it and take the battery there for a load test. You can show good voltage but still have a weak battery. Low voltage and it's not going to run right. 

[evinrude7]

I dont have a way to load test it...  But it turns out that I drained it while resetting the points and timing and I guess there just wasn't enough voltage for that field coil to properly supply the stator.  After charging the battery the votage gets to 13.5 ish with the high beam on so its cool.  I was freaking out a little though.

I set the points perfectly the first time but after a few weeks the dwell angle increased to abiut 106.  I figure parts wearing in, so i do it all again.  Two weeks later my dwell hasn't moved but my 1-4 timing was WAY retarded.  My 2-3 breaker had a sharp peak and wouldnt fire the coil but every once in a while.  I filed it down, set dwell and timing.  Now heres the kicker:  my plate is advanced almost all the way to time 1-4 and my subplate to time 2-3 is fully retarded, leaving 2-3 still firing a touch before F.  Advancer is still working.  Wonder what could be upsetting my timing.

If you have an Advance Auto store put a full charge on it and take the battery there for a load test. You can show good voltage but still have a weak battery. Low voltage and it's not going to run right.

Jerry what if the timing is so completely off that he's just got a poor running bike?  cb750f-2010656 loosen your timing plate and set it in the middle of hard left and right.  then torque the screws down.  then adjust your points to what the manual recommends,  then set your timing with something like a light or a dmm that beeps to static set the timing.  crank the bike up and check it with a strobe light.  right then it should make sense to you how to get better at timing the bike. worked for me after about 6 attempts.

[cb750f-2010656]

I dont have a way to load test it...  But it turns out that I drained it while resetting the points and timing and I guess there just wasn't enough voltage for that field coil to properly supply the stator.  After charging the battery the votage gets to 13.5 ish with the high beam on so its cool.  I was freaking out a little though.

I set the points perfectly the first time but after a few weeks the dwell angle increased to abiut 106.  I figure parts wearing in, so i do it all again.  Two weeks later my dwell hasn't moved but my 1-4 timing was WAY retarded.  My 2-3 breaker had a sharp peak and wouldnt fire the coil but every once in a while.  I filed it down, set dwell and timing.  Now heres the kicker:  my plate is advanced almost all the way to time 1-4 and my subplate to time 2-3 is fully retarded, leaving 2-3 still firing a touch before F.  Advancer is still working.  Wonder what could be upsetting my timing.

If you have an Advance Auto store put a full charge on it and take the battery there for a load test. You can show good voltage but still have a weak battery. Low voltage and it's not going to run right.

Jerry what if the timing is so completely off that he's just got a poor running bike?  cb750f-2010656 loosen your timing plate and set it in the middle of hard left and right.  then torque the screws down.  then adjust your points to what the manual recommends,  then set your timing with something like a light or a dmm that beeps to static set the timing.  crank the bike up and check it with a strobe light.  right then it should make sense to you how to get better at timing the bike. worked for me after about 6 attempts.

I think the batts fine.  I can only kick-start her anyway.

About the timing, I have a digital timing light with rpm, dwell angle, etc. She runs bad, but when the timing gets off, she's worse.  There is a noticeable improvement every time I have to adjust it.  But my bottom engine case is broken on the front of the points cavity.  Just open to dirt and moisture and fork oil.  It'll prolly never stay right.

[cb750f-2010656]

I double checked my slide needle seats and they are in correctly.  Double checked slide needles and 3 were fourth notch from top.  Moved them to the third notch, reassembled and rest ran the bike.  Now it has a very high idle even with the mixture screws seated.  Lean popping can be heard from the muffler.  I have decided to go no further till I have the carbs sonic cleaned.  I just hope she doesn't burn up before I get another bike running.....

[evinrude7]

I double checked my slide needle seats and they are in correctly.  Double checked slide needles and 3 were fourth notch from top.  Moved them to the third notch, reassembled and rest ran the bike.  Now it has a very high idle even with the mixture screws seated.  Lean popping can be heard from the muffler.  I have decided to go no further till I have the carbs sonic cleaned.  I just hope she doesn't burn up before I get another bike running.....

if you move the slide needles up don't you have to go back and bench sync again?

[cb750f-2010656]

Is it true that burned valves would make an engine idle lean?  Thanks.

[cb750f-2010656]

Ordered on sonic cleaner.  Good ol ebay

[cb750f-2010656]

I got my sonic cleaner.  It's a $98 Vevor just like the one we had at a quad dealership I once worked at.  From what I remember it performed welll, but I know those cheap ones are hit-and-miss.  It has a 30 day warranty though, and I have have a bunch of stuff i can run through it and make sure it works.  I'm just trying to decide what solution I should use.  From online research I learned that anything I put in there to attack the rust may be too harsh for pot metals, so is guess I'll just use regular carb cleaner and just let the vibes to their thing for a while.

[cb750f-2010656]

I'm testing my sonic cleaner now.  I put some aluminum foil in it and those little holes and dents appear.  I have my rebel carb in there now.

[cb750f-2010656]

Out of necessity I have been working on Old Girl again.  Dealership ordered the wrong front sprocket for Little Girl (the Rebel), and I had to have something to take me to work Monday, so I ultrasonic cleaned the 750 carbs and replaced the o rings for the air mixture screws.  Drives like a completely different bike.  No flat spots or hesitation.  There is a noticeably weak cylinder, but overall driveability is great.  I have not done a plug chop yet, but today is payday.  Maybe I can spring for some new plugs.  Again.

[cb750f-2010656]

I guess I'll perform a leak down test next.  As of right now I cannot determine which cylinder is weak.  All of my header pipes seem to be the same temp after a ride.  I may be worried about nothing.  I think it has too much of a growl.  And my idle isn't smooth no matter how I try to sync the carbs.  How is a 76 CB750F supposed to sound?

[cb750f-2010656]

Just heard a very nice one on YouTube and yeah, my bike definitely still has something wrong with it. 

[cb750f-2010656]

So I was googling stuff and came across a tip to diagnosing valve trouble.  I read you could hold a dollar bill to the exhaust pipe to check for burned or sticking exhaust valves.  I observed the bill intermittently being sucked back towards the muffler.  Not always at the same rate.  I assume I have one hanging and closing ever now and then allowing her to sound and feel like an SOHC 750 should sometimes, and doodoo other times.  I haven't verified this with a leak down tester, but I am really done with fighting her anymore.  After my carb job Sunday I have regained just about all lost driveability, I just now have an SOHC 3-1/2 for now.  I definitely can't afford an overhaul anytime soon, and will reserve Old Girl for redundant transportation only.  Thank you to all who pitched in to help me with this, and I'm sorry I drug it out this long.