72 cb350 twin points problem (searched) - Ive tried it all

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o2sensorheating

New Member
So like the title states, Ive spent days and weeks on this forum searching for my particular problem with no such luck for a solution.

Notes before my question:

- Good compression on both cylinders
- Brand new electonics including Sparck Moto harness, new antigravity 4cell, reg/rectifier, dyna 3ohm coils, condensor, new plugs and new wires.
- I own the clymer manual and saw no help for my problem
- Running velocity stacks and straight pipes
- Carbs rebuilt and running two needle spacers and 85/140 jets for each side
(diaghrams are good)


Ok so I got this bike running and driving about a month ago and it always had a problem breaking up at higher RPMs, so I supplemented that with more fuel (bigger jets) and the problem changed where the bike would basically shut itself off under load in a way that i deem could only be electrical and was running a capacitor at the time. My thought was that the capacitor was just not giving the plugs enough spark. So i swap out the OG coils and the capacitor for the dyna coils, new plug wires, new condensor, new plugs (gapped correctly), and a 4 cell antigravity battery. I checked spark on both sides and it looked good.

I try to crank the engine and i get nothing but a cough smoke occasionally out of the right side carb while kicking starting it and one back fire out of the left exhaust. So i then decide the timing must be way off, i pull the alternator cover off, replace and gap the points at .013 and have at it. With the ignition on and the test light on the left point and a ground, i see no light at all after multiple times rotating the engine with my wrench. To be sure i wasnt crazy, i tested the other point and did get a light (not where i wanted, but thats a part of the reason im down there).

What would cause a point not to get power regardless of where the crank is at? From what Ive provided, please help! I want this bike firing!

Thanks!!!


- Joe
 
Check continuity on the left points points wire and ground, when the points are open. You should have none. Repeat with points closed and you should have continuity.

If you have continuity with points open and closed, then your points wire is short circuiting to ground. This is not an uncommon problem after a points or points wire replacement. The metal circlet terminal on the end of the points wire can't be touching ANYTHING except the bolt that hold it in place and there are often plastic washers to help keep this from occurring.
 
Matt is correct, the first time I changed out my points on my GL I missed the washer and it acted retarded. I was grounding out sometimes and not others, I pulled my hair out for hours until I grabbed a parts fiche and checked all the parts to find I had missed the washer and it was allowing the wire to ground out randomly. Another time I had tightened down the spade connector and it turned just enough to touch the cover that one was fun, bike ran great minus points cover, put it back on and ran like shit. took a while to find that one too. Good luck.
 
So just an update here.

Here is a list of things I've tried since I last posted:

- removed points cover
- rechecked the points gaps which now gives me power to my test light on both sides as it should
- rechecked the timing
- swapped the two coil wires and back to test if the timing was 180 degrees out
- tested spark with both a capacitor and a 4cell antigravity battery and both plugs had spark each time
- sprayed start fluid in both cylinders
- rechecked the float heights
- rechecked the plugs and made sure they were gapped correctly ( note - no matter how many kicks with or without throttle opened the plugs were dry and clean)



I have done quite a bit of research on advancers lately and know they can be rebuilt incorrectly causing the timing to be 180 degrees off as well. I never removed or rebuilt the advancer so im not sure that applies to my situation. I have good compression in both cylinders.


I am also noticing a lot of pressure back on the kickstarter occasionally almost like its firing against me. At this point I am absolutely stumped. Any help would be greatly appreciated!
 
o2sensorheating said:
I am also noticing a lot of pressure back on the kickstarter occasionally almost like its firing against me. At this point I am absolutely stumped. Any help would be greatly appreciated!
Click to expand...

Classic symptom of overly advanced timing.

I'll venture a guess and say that your timing, though it has been rechecked, still isn't correct.

Do you have a strobe light?
 
Hey Sonreir,

Any classic problem is good news at least, haha. I do not have a strobe, just the test light I made. Anything I can do to test this without a strobe?
 
Yup.

Pull the spark plug on the left side of the engine. With the plug still in the plug wire, the ignition switch on, and the kill switch set to run, hold the plug against the engine case while turning the crank counter-clockwise with a 14mm wrench. You should see a spark on the plug when you pass the LF mark (every other rotation).
 
Ah ok, understood. So, assuming its not sparking on the LT is it just a matter of rotating the points plate until it does? If so, will i have to regap the points after the fact?
 
Points are gapped first to .015" and then timing is set by rotating the points plate. If you gap after you time, you need to repeat the timing.

Timing should be set on the left cylinder first, and then the gap can be readjusted on the right cylinder to time it (if it's off).

But, yes. If the spark is coming in at the wrong time, the goal is to rotate the points plate so that you get a spark just as the LF mark on the rotor reaches the line on the stator.
 
Next time you time the points try these instructions done up by Steve over on Honda Twins. They are by far the clearest and foolproof way of timing.

How to time a Honda Twin
  • When you set the gap on the left points, you should do it when the points are at their widest opening (the "follower" is on the highest "bump" on the breaker cam of the advance unit)
  • Lock the left point screws down to keep it at the .014 gap on the plate
  • Then, with crankshaft now rotated and held on the LF index during the left compression stroke, rotate the entire plate to get the left points to just open (light the light) and lock down the plate
  • The plate MUST remain where it now is, no further adjustments are made to the plate
  • Rotate engine to the F index of the right compression stroke
  • Set right points to just break
  • Lock the right points down
  • Now you check the right points gap by rotating the engine until its follower is on the biggest bump
  • If it is anywhere within the spec range, you are done
  • Don't adjust the right gap (or anything else) further
  • Gaps do NOT have to be any certain amount or even, just within the spec range
 
Sonreir, I did as you said and without touching the points or the timing plate I saw that the left plug fired exactly when the rotor passed the index mark at "F" and the right plug fired when the rotor passed at "LF". I could have sworn I timed this correctly the first time (did not do the spark check then, though). I also swapped the blue and yellow coils wires a week ago and saw no improvement.

With that info, what do you think?




Thanks HerrDeacon, I'll give it a shot after my other theory becomes defunct haha.






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LF stands for "Left Fire", so if your right cylinder is firing at the LF mark, then the wires are backwards. Swap them and try again.
 
So a little update here, SHE RUNS!!

I swapped the coils and she fired for me then eventually was able to hold an idle. I am able to keep it running at one full turn out on each mixture screw but am getting a LOT of backfiring when trying to rev it. Am I still too lean?


Sent from my iPhone using Tapatalk
 
Been a while since I've looked in the manual, but I seem to recall that the starting point on the mixture screws is two turns out? Not enough turns out would definitely cause a lean condition.
 
Hello,

Update here, I pulled both mixture screws out two turns from closed and unfortunately no matter what the setting I can't find myself being able to ditch these backfires. I rechecked the points and timing, checked the ignition switch, the battery to make sure we had a good charge, carbs look very clean, floats set right. I pulled the plugs and they were horribly carbon fouled after running like that so I cleaned them and out them back in. Started it back up and again it would idle but any reving it was breaking up and back firing.

Any ideas?


Sent from my iPhone using Tapatalk
 
back firing could be a sign of being too lean yes. Could also be stuck valves or valve seals not in sealing anymore. or in the worst case, piston blow by.

My 550 fired up like new as soon as I replaced the points with nos tec points.

You're getting a lot of solid advice. I would do spark plugs as well and much like the points, gap them accordingly.

If your points are toast or need replacing i should have nos points for a 350 in my shop. But if they can clean up or at least have something left on the inside faces your good.

Sonreir, so you're able to do the timing without strobe? I've heard of people using the static method with a light bulb. Super tip man.

Cheers
 
Hey Cxman, I've checked for air leaks and silicone'd the intake boots to double checked for leaks with starter fluid.

Seventeescycle, the points are brand new and gapped correctly and I can see them firing with the cap off while it's running. I used a static light to check the timing on it. Any way for my to check for a stuck valve? I think the only reason it might not be that is because it ran fine last month only about 25 miles on the bike prior to this issue unrelated.




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