Topic: Finally Admitting I Need Professional Help

[1080]

I had a chain saw that would start and as you gave it throttle it died. Long story short, the tank coating the manufacture use in coating of the insides of the gas tank was separating from the aluminum body ( Gas tank & motor case one piece ). The fuel drawn by the carb was enough to pull the coating away from the tank body and smother the fuel filter in the gas tank. . Several people had tried, even a small engine shop all failed. I could not make it work.  A few years later I looked at it again. Cleaning out the old gas is when I notice a piece bubble away. The coating years later was separating more than before. 
Good luck.

[BomberMann650]

bad condensers have ruined my day before too.  +1 to that

[Don R]

 My brother bought a cb 750 K1 from a mechanic that couldn't ride anymore. We cleaned the carbs multiple times before checking the electrical, the points were loose on one side. duh. And we've been working on these for years.

[70CB750]

Nice progress, I understand your motivation - cherchez la femme  - but with your approach, it will eventually run great.

Keep at it 

I was not as brave as you, I went to electronic ignition first thing to eliminate major part of the trouble getting it back on the road.

[eoddom]

First thing I was advised to do with my recent purchase was clean carbs, and replace points.  These old points ignitions are a pain in the @$$ from what I understand.  If it turns out points are your problem (im hoping they are, for the sake of your sanity) then an electronic ignition should be in your future.

[Airborne 82nd]

First thing I was advised to do with my recent purchase was clean carbs, and replace points.  These old points ignitions are a pain in the @$$ from what I understand.  If it turns out points are your problem (im hoping they are, for the sake of your sanity) then an electronic ignition should be in your future.

No they are a pain in the @$$ from what you don't understand. Easy to work on at 2am a long way from home not so with a  electronic ignition. imho.

[saha6818]

Great input. I'll try all of those things.

Also, I remembered another clue: While the bike was idling in the garage, the bike shut down the instant I turned on the headlight. That happened twice. The battery may have been disconnected at that point, so I didn't think anything of it (dirty electrical signal?). Now that I've cannibalized another bike for a battery, that isn't happening - but I haven't tried it when the bike is misbehaving.

[70CB750]

First thing I was advised to do with my recent purchase was clean carbs, and replace points.  These old points ignitions are a pain in the @$$ from what I understand.  If it turns out points are your problem (im hoping they are, for the sake of your sanity) then an electronic ignition should be in your future.

No they are a pain in the @$$ from what you don't understand. Easy to work on at 2am a long way from home not so with a  electronic ignition. imho.

I am sure every gas station sells correct condensors at 2AM long way from home.  From posts that repeat here on regular basis the main fix for points is to get Daichi, original Honda or whoever makes the best replacement, there is not much you can fix on points that fallen apart as somebody posted not that long ago.  True, you can set points right on the side of the road in the middle of the night, but if you keep up with the maintenance, why would you have to in the first place? 

You may even carry spares and more power to you, but electronic ignition I installed in the K0 in May 2011 gave me zero trouble for 25 000 miles with zero maintenance.

My $0.02 of course, nothing more 

[eoddom]

First thing I was advised to do with my recent purchase was clean carbs, and replace points.  These old points ignitions are a pain in the @$$ from what I understand.  If it turns out points are your problem (im hoping they are, for the sake of your sanity) then an electronic ignition should be in your future.

No they are a pain in the @$$ from what you don't understand. Easy to work on at 2am a long way from home not so with a  electronic ignition. imho.

Completely understandable.  And heck, I'd probably even have an extra set of points and a condenser in my bag.  I did keep two spare coils for my E46 M3 in the glove box knowing that they could go out at any time (and they did, twice).

But knowing how dependable most modern electronics are, I'd take my chances with an electronic ignition failing less often.

[saha6818]

I understand that electronic ignition can improve performance (horsepower and fuel efficiency) in cars beyond factory performance. Is that the case with these old bikes too? From what I'm reading here, it's more a matter of maintenance considerations. (For what it's worth, I imagine light use for this bike - commuting every few weeks to keep it fresh for the girlfriend's occasional longer ride - she wants to do a ~1000 mile trip this summer.)

[70CB750]

Yes, hands down.  Electronic ignition will help with start, idling, everything.  You can even have one and keep the points  as a backup:

http://sohc4shop.com/catalog/index.php?cPath=23  (Hondaman is a local guru)

Personally, I run Pamco:

http://www.cb750ignition.com/

Pamcopete is a member of the forum too.

[saha6818]

Maybe after I look into these other potential issues, I'll install the new points and condensers when they arrive. Then if/when those parts erase the symptoms, I'll seriously consider electronic ignition. Reasonable?

[Gene]

Maybe I'll get me one of those electronic ignitions, I've been futzing with my points for years - it' a matter of pride - but hearing all this praise on behalf of it makes me wonder . . .

[saha6818]

Thank you for your advice, everyone. I replaced the points and condensers, and one of the condensers was discolored. But the problem still exists. When I keep the choke open 50%, the bike will stay running and only misfires when under load. I can ride at least 35 mph, which is relatively good. After riding, the exhaust pipes for cylinders 2 and 3 were much cooler than those for 1 and 4. So I'm thinking maybe I have an air problem. Those air screws are 7/8 turns out - maybe I should back them out more? Maybe I should stay with the electrical theme (if only because I'm so tired of the carbs) and look into the coils?

BTW, I was suspecting 1080's suggestion (recoating material sometimes blocking the fuel outlet) given the recoating job that had been poorly done before, but now I think I'm okay there given I can ride around at a good speed without getting fuel starved. My problem seems only to kick in under acceleration or while climbing a hill.

[Tia813]

Great info given! My old man always preached "Check chain tension, valve adjustment and carbs last."... In case you've done that already before you pull the carbs check float level by using the clear tube method. This way you know where the fuel level sits.. Should be at the bowl/carb body mating surface right?
I'm on my first CB build so if that method doesn't work on these weird (LOL) carbs i apologize in advance.

[Gene]

I can ride at least 35 mph, which is relatively good. After riding, the exhaust pipes for cylinders 2 and 3 were much cooler than those for 1 and 4. and look into the coils?

Check your coils, the Black and White wire coming out of the light bucket - check it at the junction at the coils for 12V.  Again - stupid, I know, but double check the points for gap and timing.  Your not getting fire at 2 and 3 - and they are on their own coil.  So, it could be the coil, but probably the points.  Check plug caps too.

2 & 3 are not firing - you're running on 2 cylinders.  It's electrical, and it's probably points related - even new they need to be checked and checked again and checked again to make sure you're getting fire to those plugs.

p.s. - What kind of points/condensers did you get?  If they're Daiachi - from what I've read - try again.

[saha6818]

I should also mention that I saw a lot of wobble in the shaft that drives the points when the engine was running. I think it's labeled the crankshaft in the shop manual. As in it looks bent a couple of mm. There's no damage to the cover, so I don't know how it could have happened - maybe internally? That could be affecting the contact with the points and causing these problems, I suppose. Fixing that, if needed, would involve digging everything out of the bottom end? Good times. That job would require many beers.

I still have a fair number of other suggestions from this thread to check, so thanks for those!

[scottly]

I should also mention that I saw a lot of wobble in the shaft that drives the points when the engine was running.

The shaft that drives the points is an eccentric cam; it is supposed to wobble. The wobble is what allows the points to open and close.

[evanphi]

I should also mention that I saw a lot of wobble in the shaft that drives the points when the engine was running.

The shaft that drives the points is an eccentric cam; it is supposed to wobble. The wobble is what allows the points to open and close.

Depending on where the wobble is, it might be sending the 2/3 advance out of whack.

OP: Remove the points plate and advancer unit. Is it the tip of that shaft wobbling? That whole shaft needs to be nice and straight. Should have less than 0.002" runout. I had to fix mine.

[saha6818]

Duh. Of course it wobbles, opening and closing the points. Brain fart. I'll start with the coils and wiring. The taillight and one turn indicator randomly stopped working lately, and I haven't been able to track down the problem yet, so maybe there are some electrical gremlins.

[eoddom]

I'm curious to find out what it is when you resolve this problem.  I've also got issues with 2 and 3 being dead in the water.

[mrbreeze]

I went back and reread this from around page 7. You are talking about your points but I don't see any mention of your timing. Could it be that 2-3 are out of range?

[saha6818]

Thanks for the input, everyone. I'm reviewing everything you offer, and I'm also searching and reading lots of other threads in the forum for help. I fixed those lights yesterday (the turn indicator was a nightmare grounding problem taking a couple of hours), and they were unrelated to any engine problems. I removed the left coil running cylinders 2 and 3, and the connection wire is worn and not completely connected any more. I'm hoping the problem is that it couldn't carry much current, and I bought two new coils and some plug wires. I'm not ruling out air problems too, given that the choke keeps the engine running, but I guess I'll tinker with that if/when the coils don't work. Before long, this bike will be as new as the SR400 my girlfriend is threatening to buy. I should have it fixed around when the Seattle rains settle in for the winter.
 

[saha6818]

A quick update: I bought and installed new coils and plug wires. Those seem to work fine (after heavy modification to the stock brackets, which I didn't foresee needing), but I have the same symptoms as before - idling on 3ish cylinders and misfiring or fewer working cylinders as soon as the bike is in gear and/or under load. I played with the timing while the bike was idling, and it wouldn't run any better. Just about everything in the electrical system is new now, so I started unwrapping the central wiring bundle. I found a ground wire with fried insulation. When I isolate that, same symptoms, so I don't think it's grounding anything out. (I'll fix it anyway.) I'm also going to try switching plug wires between #2 and #3 to see if the non-running cylinder (#2) follows the wire. I'll also check various grounds for continuity. I should also check that the alternator generates plenty of voltage. But really I think I'm about done with electrical stuff. Because the bike only runs on 50% choke, I may remove the carbs (literally for the 8th time) and check things out and maybe back out the air screws another half turn to see if that changes anything. Assuming that does nothing, it's time for a professional opinion.
 

Things I've done (engine-related only):
New plugs
New fuel filter and fuel line, troubleshot fuel delivery
Cleaned carbs and checked all passageways, replaced a couple of jets and valves
Cleaned petcock
Adjusted air screws
New air filter
Adjusted float height
New points
Gapped points
Played with timing
New coils and plug wires
New condensers
New (used) rectifier
New battery

[eoddom]

When you cleaned the carbs, how did you do it?


Also you said you changed the coils and wires, but did you put new plug caps on or did you re-use the old ones?

I'm running into the same issues and have come to the conclusion that it is either carb related or the plug caps are shot.  I got a newly cleaned and rebuilt set of carbs today and new plug caps coming tomorrow.