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Discussion Starter #1
I was recently contacted by a buddy that I've done a little trading with. He was giving me first dibs on a '72 Honda CL175 on which he is throwing in the towel. Initially, I declined. Too many irons in the fire.
The bike is a nice looking little twin that he went through a couple of years ago. Tank lined, new petcock, sorted the brakes, tires, etc. He actually had it running and said it ran well.
Then the seemingly impossible happened: He lost spark in the RH cylinder. That, technically, shouldn't be possible on a Honda 175 twin.


He says he's tried everything; different plugs, coils, points, etc. Even had a guy that used to race CB350 twins take a look at it and he proclaimed "This isn't possible".
He drained the gas and oil and it has sat for two years. Complete, titled, once running bike. Now with a dead battery and a mystery "No Spark" in one hole issue.


After he got dicked around a bit when trying to sell it, he told me "Make and offer and I'll even deliver". I did, he accepted, I take delivery around Tuesday. I have yet to actually put my hands on it.
I will first check valve clearances, compression and maybe even the carb on the RH side. And a new battery, of course. He SWEARS it's a spark issue. But with one set of points, one condenser, and one dual output coil, that shouldn't be possible. You shouldn't be able to get fire in one hole but not the other.


While I await it's arrival, any guesses or suggestions on what to check?


And because everyone likes pics:




 

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^^^that, and... nice survivor, it looks to be in really nice shape with original paint. You should probably re-route that points wiring away from the exhaust though
 

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Discussion Starter #4
He says he's tried all of those things. I will, of course, start afresh.


I plan on:


-Fresh battery
-Valve adjustment
-Compression test


- Then start from the mechanical advancer and work my way all the way to the plugs. Checking for continuity, bad grounds, loose wires, etc. I will check the parts that come with the bike, but new caps and plugs are always one of the first things I do anyway.

And ancientdad, I think he just has stuff laying loose after his last attempts. I'll have everything in the right place.
 

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Discussion Starter #6
He says he's tried multiples of all the ignition components and will include everything with the bike. My guess is, that's how the bike was when he gave up.
 

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Discussion Starter #7
Bike arrived yesterday and I'm very happy with the overall condition. The tank and side covers are still all original and in great shape. No dents on the tank at all, very solid with shiny paint and stripes and only a few minor scratches. Overall, the entire bike will shine up pretty well, I think.


I adjusted the valves. They were all loose, by my standards. Adjusted the cam chain. I pulled the carbs and gave them a soak in Simple Green and hot water, followed by carb cleaner. Didn't find any smoking guns there. One of the floats was a little lower than the other (the floats look brand new, BTW). I set the odd one to 22mm to match the other and set the mixture screws to 1 turn out. Do those sound right, to you?


Next up, I'm going to go over the ignition parts that came with the bike and bench test/ohm out everything. I'll try using what I have with the fresh battery, which should be here tomorrow.


Oh, I also pulled the exhaust, mostly so I could install the LH side cover and check out the air filter(s). The LH filter has a torn rubber boot and it's been jury rigged with some rubber and a hose clamp. I might look around and see what's available out there.
I also want to take a closer look at the tips/baffles someone has installed. Maybe try to come up with something a little better there, too.
 

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It is not necessary to Turn the motor over to check for spark.

You can simply apply power to the Hot Lead of the Coil then remove it with the Plug End "NEAR" - within a 1/4" of a good ground and it should produce a Spark.

The Coils Charge when the points are closed, this energizes the Primary Coil Windings, when the Power is Disconnected (the points OPEN) that field collapses and the energy is discharged to the Plugs.

If the above test does NOT produce a spark then you most likely have a bad coil.
 

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It is not necessary to Turn the motor over to check for spark.

You can simply apply power to the Hot Lead of the Coil then remove it with the Plug End "NEAR" - within a 1/4" of a good ground and it should produce a Spark.

The Coils Charge when the points are closed, this energizes the Primary Coil Windings, when the Power is Disconnected (the points OPEN) that field collapses and the energy is discharged to the Plugs.

If the above test does NOT produce a spark then you most likely have a bad coil.
So, turn the ignition on, wait, and then disconnect the coil power wires with ignition still on, this would produce spark on a grounded plug, if the coil was good?

I have a 450 twin that I need to diagnose a no spark condition on.
 

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Discussion Starter #11
It is not necessary to Turn the motor over to check for spark.

You can simply apply power to the Hot Lead of the Coil then remove it with the Plug End "NEAR" - within a 1/4" of a good ground and it should produce a Spark.

The Coils Charge when the points are closed, this energizes the Primary Coil Windings, when the Power is Disconnected (the points OPEN) that field collapses and the energy is discharged to the Plugs.

If the above test does NOT produce a spark then you most likely have a bad coil.
I was waiting on a fresh battery. I had nothing to give the bike 12V. I also needed the battery to set the timing, using my test light.
 

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Discussion Starter #12
Fire in the hole! Fire in the hole!


Cleaned a BUNCH of connections, including the main frame ground. Went through the standard tune up stuff. Re-used the stock coil because I liked the ohm readings on it better than the brand new coil. Fresh AGM battery. Set points to fire right on the F mark using my test light.
Turned it over with each spark grounded on the head and I have fire!


I also cleaned the carbs, and I ordered a replacement LH air cleaner since this one has a torn boot (and of course, it's the one you MUST put on before the header pipes).
As soon as it gets here and I get the exhaust on, I'll add gas and see what happens.


I have NOT tried to get spark with the points cover on...could be a short there, when it's installed.
And, I found a double female connector right off the main harness that I'm not happy with. And it's for power to the coil and to the horn....Hmmm, possibly the culprit all along?
It's split inside and even after I crimped it with pliers, the coil wire isn't as tight as I'd like. I'll probably dig through my stash and find a better connector to splice in.
 

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If working with twin coils it would be a MUCH better idea to disconnect both Power lines to the coils so you don't fry one.

There is no need to wait for it to charge.
All you have to do is apply power and remove it to charge then cause the coils to discharge.

Think about the time required to charge the coils.
The cylinders fire every other stroke.
At 2000 RPM this happens 1000 times per minute. (you can't move your hands that fast)

If you have to wait for the coil to charge then it is definitely bad.

The condenser plays a BIG ROLE in a Points system. (the following is an OVER SIMPLIFICATION but basically accurate)

When you make and break electrical contacts they SPARK.
There is no difference between that spark and ARC Welding, it is just a much smaller scale.

The Condenser suppresses the ARCING that occurs when the Points Open & Close.
Other wise they would wear out extremely fast as small bits of metal transfer from one contact to the other creating Pits and changing the Gap.
The condenser is the ONLY Ground point in the primary ignition circuit.
The Spark Plug in the Head is the Ground for the secondary Circuit
A Shorted Condenser can cause the COILS to NOT Charge correctly as the current gets shorted (fastest Route) to Ground, and it doesn't charge the coils.
The condenser needs to absorb SOME of the Power & Current but If it is shorted and sucks it all to ground = NO SPARK.

That is why I say to just By-Pass the Points and Condenser to give the coils a Basic Test.
BTW - It is NOT a definitive they are good test.

It is still possible for them to produce a spark that is capable of jumping a 1/4" gap when not under compression.
What happens inside the Compressed Space of a Cylinder is a whole different set of variables.
But it will get you on your way to determining what is going on.
 

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I have NOT tried to get spark with the points cover on...could be a short there, when it's installed.
depending on how you attach the points wire connector when you replace the points, it can touch the cover when you put it back on. Just be sure it's turned so the fat part of the connector (where the wire is crimped into it) is away from where it could touch the cover and of course, keep the wire connector on the outside of the fiber insulating washers so it isn't grounded to the metal frame of the points, which would obviously kill your spark
 

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If I were you I'd probably get my wife to donate an Old stocking and wrap it over the intake just to see if it would fire up while I was waiting of a proper air cleaner.

I understand the pipes would also be off but it either fires or not.

I wouldn't run it for more than a few seconds but I'd be really curious - I'm not sure knowing the history it has if I could wait.
 

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Discussion Starter #19
Well, I rode it today. It's DEFINITELY running on both cylinders now!


It still needs some tweaking, though. I can't get it to idle properly. I have to use the throttle to keep it running. I tried changing the mixture screws (from 1/2 turn out all the way to 1 3/4 turns out) and the idle screws. I actually went all the way IN on the idle screws and it still didn't want to hold an idle. I also adjusted the free play at the throttle grip.
One of the bowls is leaking around the gasket and...you guessed it...it's the LH side, the one behind the high pipes. I *THINK* I can install a new bowl gasket without R&R'ing the carb, but I also feel like maybe I should address the float heights again, too.
I tried to sync them the best I could, by checking the gap in the closed position, W.O.T. and watching them open together.
Just needs more carb work, I guess.


I also feel like it would be wise to check the timing again now that I've had it running. And normal tweaking and tuning, too....clutch adjustment, etc.
 

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Discussion Starter #20
Started to drain the gas tank this morning so I could pull the carbs and take them to Rick at OldSkoolCarbs. That's when I noticed a couple of odd things...


I noticed that I wasn't getting even flow out of the petcock outlets. And the one that was acting funny was the side that I was using to feed the RH carb.....Hmmm...
Then, as I wiggled the lever around, I noticed fuel coming out of the petcock body. Also, Hmmm...
Then, as I removed the crossover tube from the gas tank (hate those things), I noticed gas still in the LH side but nothing in the RH side. Triple Hmmm.....


Pulled petcock apart and cleaned it well and tested it by sucking through the outlets and spraying carb cleaner. Didn't really find anything.


Found the crossover tube nipple plugged up on the RH side of the gas tank. Fixed that.


Then I moved on to the carbs. I wanted to check operation of the slides/cables. I also wanted to verify that the slides were in correctly. I kept them on the same side of the bike I removed them from. BUT, I had read several threads about the slides being in backwards causing a "no idle" issue. Pulled them out and, guess what!? Yep...in wrong. The throttle cable was also routed incorrectly.


Fixed all that and hooked up my I.V. bottle for gas. Fired right up, I was able to adjust the idle and it revs MUCH better now!
I'm still waiting on bowl gaskets and a new throttle tube.
Inching closer and closer!!
 
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