Topic: Frustration got the best of me...input needed...

[Thor's Hammer!]

Sorry if this is long winded...

Well, got my 78 CB750F about 6 months ago or so.  My bike was and still is pretty rough by my standards, not by others perhaps though.

I've never ridden the bike as it didn't run when purchased, but I was able to get it running in the garage after a cleaning of the carbs (off a newer model nighthawk).  Lots of smoke, perhaps bad valve guide seals or too much raw gas?  Anyhow, I had the bike running on three occasions, about 5-10 mins each time, with lots of smoke and the wrong carbs.

Trying to figure out my plan of attack, I decided a factory like restore was what I was going to go after.  Knowing I had the wrong carbs, I thought (perhaps incorrectly) that I should get the correct carbs for the bike, get it running again and try to establish what caused the smoke.

I got some PD-42A carbs, spent a while getting them cleaned and assembled, bench sync'd and re-installed.  My hope was to get the bike running, take it for a short drive to see if the trans checked out and whether a full engine tear down and rebuild was going to be required.

This was the plan until this last weekend.  Upon getting the carbs installed (major PITA), I tried to start the bike...no love at all.  Back firing, lots of fuel, the occasional spark.  I played with the carbs for hours.  Could get the bike to start even briefly.

I have been delaying a complete tear down because I thought getting the bike up and running would be best to diagnose the condition.  But after meeting with  failure to get the bike running again...in a moment a of weakness, I decided to hell with my carefully thought out "approach" to the restore.

Started tearing down the bike, found a loose wire on the rectifier (likely the reason for no start or run).  I know I should have walked away when I got frustrated and the loose wire illustrates that perfectly.

So...what do you guys think.  Should I continue with the tear down, working from the ground up, or go back and start at the top and go down...(make sure it runs, then tear it down).  I know this is all highly subjective and i have read several projects which were start from either direction and seemed to have turned out just fine.

What do you all think?

Thanks,

Mike

[kghost]

Rectifier doesn't have anything to do with the bike getting spark.

Just won't charge with a wire busted off the rectifier.

But the bike will run without charging off a good battery.

[Patrick]

When I start a project, first I check for compression and spark before I decide whether to tear down the engine. If I have both, I try to get it running so I can figure out how much and what needs to be done. I once rebuilt a whole engine and reinstalled it before I got it running. When I did I discovered I had no first gear and had to pull it and split the cases again.

Of course, on other bikes I have torn down the engine before I did anything else just because I like to tear down engines and build them back up.

If it was my project, I would get it running before I tore it down just to gauge the extent of its needs.

Patrick

[Thor's Hammer!]

Rectifier doesn't have anything to do with the bike getting spark.

Just won't charge with a wire busted off the rectifier.

But the bike will run without charging off a good battery.

OK...I just looked at the manual.  What I was calling the rectifier (rectangular gold colored box with wires) the manual calls a regulator.  Perhaps it was of no consequence at all...as you said with the rectifier.  The reason for my posting was to get input on planned "approach" I took and whether I was foolish in abandoning it in a moment of frustration.

[kghost]

Well Opinions vary.

Be aware thats what your asking for.....Opinion.

Personally I like to have them Running, Shifting, Charging before I take them apart.

Example: Wiring.

Wouldn't it be nice to know it worked when you took it apart? Seems theres always something with the damn colored spagetti.

Example: Engine

The 750 is a pretty robust design. Many have been Resurrected from sitting. Every one I've brought back to life has smoked some. While sitting cylinders corrode, Rings stick, Valves and seats corrode.....etc etc. Most of the time a bit of running seats everything back in.

Sometimes not.

Good thing to know before taking it apart.

[Hush]

I always get my "barn finds" running first so I can ride them a bit and see if I want to do a full rebuild or just on sell them a a runner.
If I like what I find I'll get them running as good as I can and ride them while adding bits and improvements.
So far I have been very lucky with 3 parked up bikes having strong motors, I need to do the head gaskets and base gaskets on both my 650 and my partners 400 but that can wait till winter, we are having far too much fun riding them right now.

[TwoTired]

The 78 Cb750F black engine was notorious for wearing out valve guides prematurely.  Oil smoke is typical with this failure.  Honda put bigger valves in the 77-78 F head and changed the valve angle and cam lift.  The rockers then put heavier side loads on the valve stem.  See what your adjuster to valve stem interface surfaces look like.  If they are grooved, oblong, mushroomed, etc., You probably have valve guide problems, valve wear problems, and valve seat wear problems.  These would show up in a good compression test and even moreso with a leakdown tester.  Fixing this isn't exactly cheap.

Good on you for getting the correct carbs.  But, more than a few people have had issues getting these properly cleaned to function correctly.  The pilot jets are pressed in and this scares people off from their removal, yet, it is necessary.  Also, the accelerator pump mechanism/circuit seems to challenge some rebuilders.

I would certainly prefer to identify problem areas to address before a full disassembly.  It would seem that unless you were intimate with all the details of the subject machine, it would be easy to overlook something that would need addressing later, meaning yet another tear down.

As an example, I got a CB550 with hopes to restore.  I did enough to get it running and found that the engine ran well but the trans sounded like a box of rocks being shaken.  Yup, it's a parts bike, now.  Can get an engine for $100 if you shop around.  The internal parts to repair would be far more than that.

As was mentioned, opinions vary, but that's what I think.

Wouldn't it have been nice to put on carbs that you knew worked after going through the engine?  Now you have yet another variable when you put it back together, instead of knowing a run issue has to be elsewhere.  When solving problems, I like to minimize the variables.  But then, some people think that the more difficult the mountain is to climb, the more satisfying it is to stand at the top.
Just how much of a challenge are you seeking?  

[Thor's Hammer!]

Thanks fellas!

I appreciate the opinions and suggestions.  In term of tear down, I only removed the wiring harness, coils, gages and controls.  I can get it back to where it was in a couple hours i think.  Once back together, perhaps I'll use the Nighthawk carbs initially to make sure all the electrical bits are sorted, then switch to the PD-42A's afterward in hopes of then establishing if my day of frustration was the result of a carb problem or something else entirely.

The slow jets were a PITA to get cleaned!!...the center holes were very hard to clean.  It's very possible I did something wrong somewhere, maybe with the needle jet/jet needle holder/main jet and relation to jet needle.

 

[Thor's Hammer!]

Well....I am here to confirm that yes...indeed I shot myself in the foot.  Let this be a lesson kids...when frustration get the best of you...promptly step away...before you do something you will come to regret.


I put the wiring harness back on the bike today, certain I had it the way it was when taken off.  Well, something isn't quite right.  Bike won't kick over any longer.  No starter action.  I suspect a bad connection somewhere.

Off to chase it down.  One the bright side, I needed to learn some basic electrical theroy anyway

[edbikerii]

Two questions for you:

When you say "won't kick over" are you saying that the kickstarter doesn't turn the engine over, or that the engine simply won't start with the starter?  Dead battery or seized engine?


When you say that the pilot jets "were a PITA to get cleaned!!..the center holes were very hard to clean", do you mean that you pulled the pilot jets out, or that you just tried to clean them in place?  The pilots on these later model carbs have cross-drilled holes that also must be clear.  They cannot be cleaned without pulling the pilot jets and deliberately cleaning them.  When I first pulled mine, I couldn't even see that there were supposed to be holes, they were so clogged.  So, I didn't clean them, and upon re-assembly, the bike still ran poorly.  Second time I pulled them and cleaned them out thoroughly.  After re-assembly, the bike ran like a charm, seemingly on the first revolution of the starter!

[Thor's Hammer!]

Thanks edbikerii for responding.  I appreciate your help.

Please see answers inline below.  I should have been more precise in my statements.

Two questions for you:

When you say "won't kick over" are you saying that the kickstarter doesn't turn the engine over, or that the engine simply won't start with the starter?  Dead battery or seized engine?

The starter will not turn the motor over.  Battery just came off the tricle charger.  This bike previously ran.  The motor should run, it is not seized.  That start is good as well, the problem is my reconnection of the wire harness.

When you say that the pilot jets "were a PITA to get cleaned!!..the center holes were very hard to clean", do you mean that you pulled the pilot jets out, or that you just tried to clean them in place?  The pilots on these later model carbs have cross-drilled holes that also must be clear.  They cannot be cleaned without pulling the pilot jets and deliberately cleaning them.  When I first pulled mine, I couldn't even see that there were supposed to be holes, they were so clogged.  So, I didn't clean them, and upon re-assembly, the bike still ran poorly.  Second time I pulled them and cleaned them out thoroughly.  After re-assembly, the bike ran like a charm, seemingly on the first revolution of the starter!

I removed the press in pilot jets, boiled them in Yammalube and then very carefully cleaned then with an extremely smaller wire brush.  The pilots are very clean and all holes are clean as should be.  The center holes on each of the 4 jets was very hard to get clean, but after finding a small enough wire, I was able to clean each one using compressed air and the small wire.

[edbikerii]

Sorry, I have no idea what you reconnected improperly in your wiring harness.  That will just require you to go over all the connections again.

I hate to be a jerk, but you still have not answered the question about the emulsifier tubes.  Yes, the center hole in the jets is a pain in the butt, but did you clean out the horizontal, cross-drilled holes in the pilot jet?

Thanks edbikerii for responding.  I appreciate your help.

Please see answers inline below.  I should have been more precise in my statements.

Two questions for you:

When you say "won't kick over" are you saying that the kickstarter doesn't turn the engine over, or that the engine simply won't start with the starter?  Dead battery or seized engine?

The starter will not turn the motor over.  Battery just came off the tricle charger.  This bike previously ran.  The motor should run, it is not seized.  That start is good as well, the problem is my reconnection of the wire harness.

When you say that the pilot jets "were a PITA to get cleaned!!..the center holes were very hard to clean", do you mean that you pulled the pilot jets out, or that you just tried to clean them in place?  The pilots on these later model carbs have cross-drilled holes that also must be clear.  They cannot be cleaned without pulling the pilot jets and deliberately cleaning them.  When I first pulled mine, I couldn't even see that there were supposed to be holes, they were so clogged.  So, I didn't clean them, and upon re-assembly, the bike still ran poorly.  Second time I pulled them and cleaned them out thoroughly.  After re-assembly, the bike ran like a charm, seemingly on the first revolution of the starter!

I removed the press in pilot jets, boiled them in Yammalube and then very carefully cleaned then with an extremely smaller wire brush.  The pilots are very clean and all holes are clean as should be.  The center holes on each of the 4 jets was very hard to get clean, but after finding a small enough wire, I was able to clean each one using compressed air and the small wire.

[Thor's Hammer!]

>> Yes, the center hole in the jets is a pain in the butt, but did you clean out the horizontal, cross-drilled holes in the pilot jet?

Yes.