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Discussion Starter · #1 ·
Hi, I posted some two years ago about my CB175 blowing gaskets. Well it's taken me this long to make the final push and get the bike on the road, and I nearly did...

The bike is running but keeps 'breaking' new spark plugs, in other words causing them to arc from the electrode to the plug body. The spark isn't jumping the gap, and once it happens the plug never seems the same. Plugs (non resistor NGK), HT leads and caps (resistor NGK) are new. I reckon it's an ignition coil, as I mistakenly left the ignition on once and flattened the battery. Oops.

What's unusual is the bike is running two sets of points (on one plate), two separate ignition coils, and two condensers. Now, I quite like this setup because I was able to time the ignition for both cylinders accurately, but does anyone think this would put more strain on the charging circuit? I'm definitely not an electrics whizz, but did test the voltage when test riding and it was getting as high as 14v.

I'm going to renew the ignition coils as they are old and suspect, but wanted to know if it would be more reliable changing to the standard single coil - single points setup. I'll take some photos if anyone wants to see them.

Cheers, Chris
 

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Has the spark advancer been fitted with a single lobe points cam or does it still use the two-lobed cam? If it is still using the two-lobed cam that means the coils are each firing at the top of every revolution. Nothing to be gained,doing that, you have a wasted spark on the exhaust stroke just like the original setup. You would be wasting some watts of electricity to run two coils instead of one. Sounds like the plugs are being gas-fouled because of a weak spark.
 

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Discussion Starter · #4 ·
I'll try to get some photos later today and have a good close look at the setup. Thanks for your thoughts.
 

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It'd be intriguing to see a picture of the bike itself. Just squinting at the little pic in your avatar, looks like CB175 pipes and side panels, and almost looks like a Cb200 tacho drive fitted instead of the CD175 blanked off part ?

PO obviously enjoyed some time in the shed. :p
 

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Discussion Starter · #8 · (Edited)
IMG_3510.jpg IMG_3511.jpg

It's been ages since I posted pictures - hope these show up.

I meant to update a few days ago but family duties took priority, we're all ill! So as you can hopefully see here are the twin points, on a possibly homemade plate. It looks like a good bit of engineering to me if it is. I took the centre bolt off for the second photo to show the profile of the cam. There is only one 'dip'. Would this indicate that this is still a wasted spark setup? When I rotate the engine the plugs are sparking alternately which would suggest otherwise. I will need to test this again more thoroughly, as I wasn't testing this aspect at the time.

I gave the spark plugs a good clean and the spark was jumping the gap again, though it was a bit erratic. Bearing in mind what Mike said earlier about fouling plugs I was disheartened to find fresh oil on the cooling fin on top of the L/H cylinder barrel - the bloody head gasket again. I was now wondering if the plug was oiling up and arcing.

Another question; can a head gasket blow but the engine still run as normal? Can it just blow a little bit?!

Anyway, these are the ignition coils it's running, one each side. Possibly old Yamaha XS.

IMG_3509.jpg
 

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Discussion Starter · #9 ·
Richard, here are some better photos of the bike. I changed the tacho drive back to a CB175 one - very well spotted by the way. When I bought the bike some 15 years ago it was considerably uglier than it is now. I fitted the CD bodywork. Points of interest include 2 into 1 exhaust, ported head, and plastic mudguards, of which I have no idea of their origin. And of course, the twin points setup. It's certainly seen some tinkering in it's time.

IMG_5738.jpg IMG_5739.jpg
 

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Those do look like stock xs650 coils. The factory xs coils are considered, by the xs650 crowd, to be crap and are usually the first thing they like to replace.
 

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seems to me if you have just one "dip" and two sets of points and two coils, you would get an alternating spark assuming one set of points is connected to just one coil and one spark plug. on a factory set up-one dip, one set of points, and one coil connected to both plugs.
 

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Thats no longer wasted spark, but you are running 2 x 12v coils off of a 6v system and some of the dwell is going to be charging both coils at once.
Considering the stator can't even output enough to keep things charged at idle even with the headlight off I'm guessing your system is draining more than the stock system
 

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Discussion Starter · #13 ·
I should have mentioned that this is a 12v system. The bike is really a CB175 with CD175 bodywork on it, with a few minor modifications. At idle I'm only getting about 11.8v and it does seem to gradually drop, then charge when revved/ridden.

The bike has been sat for a year, and initially it wouldn't run if the voltage dropped below 9v. I have charged the battery since then of course, but I want to replace it with a gel one. It's a lead acid one and I also ran it flat by mistake last year.

I think you may be right about the twin coils being more of a drain, considering the low voltage at idle. I have read that this bike's charging system is not the most powerful.

As much as like the uniqueness of this bike, perhaps I should revert to standard single coil, for reliability's sake.
 

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These little bikes ALWAYS have had the battery discharging at idle.....
Most of the period Hondas need to be revved closer to 1800 or 2K before the alternator produces as much re-charging power as the bike is consuming...
A good, fully charged battery to begin with,(12.6 to 12.7V) is needed.....
Any less than 12.2 V on a "resting" battery indicates replacement is due....

Changing back to a single coil will not improve the situation UNLESS the current coils EACH draw significantly more "juice" per coil as the 360 degree engine has no dwell overlap...... Firing the two separate 5 Ohm coils one at a time is no different (as far as electrical draw) than firing one 5 Ohm coil twice in the same rotational period......
 

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Discussion Starter · #17 ·
Thank you for your thoughts guys. I have been friends with these bikes for some 15 years and I still have a lot to learn. Progress is slow at the moment, with family and work commitments, but I have a tinker in the garage if I get an opportunity.

A small update, then; after the engine deteriorating to the point where it wouldn't even start I went back to the fundamentals and discovered that both of the points gaps had closed past spec. Hmm. After adjustment the engine started and ran, but not smoothly. I strongly suspect ignition timing and will strobe each cylinder when time allows.

Before that though the points plate will have to come off, as one of the pivot screws has stripped it's threads. The spring tension as a result has then allowed the points to close up.

IMG_3511a.jpg

So at this stage I will definitely still buy a new battery, but I think the two ignition coils are still working normally, and not draining the system excessively. Ideally I only want to replace things that need it, as it helps me learn why the bike isn't running as it should. Scientific process and all that...

Simo, I have a single-points cylinder head knocking around and will have the points and cam off to compare.
 

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ANCIENTDAD..... Doesn't matter what the breaker cam came from, only that it has only one low spot allowing the points to close
The 180 positioning of the points' cam followers assure the required two (and ONLY two) pulses per full cam rotation...
It would be nice for the advancer baseplate and weighted throw arms to be appropriate to the engine however.....
 

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Excellent observation Steve, as I would have expected from you - the points are positioned 180° from each other, precluding a problem with the breaker cam and it does provide one break per points set each revolution. "point" taken :D
 

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Discussion Starter · #20 ·
It’s been ages but I have been very busy with the little Rat Bike. In brief it’s now on the road and being ridden daily. I grew up on these bikes so I’m grinning like a teenager every time I open the throttle… I’m not finished yet though. I hope this long update makes up for the long gap.

IMG_4743a.jpg

To continue from my last post, I had the points plate off to check which thread had stripped and fortunately it was the screw, leaving the plate intact. Phew. Inspecting the points themselves showed considerable pitting, and I was glad that removal was necessary, as this would have caused problems later on. I cleaned them up with a fine file with the intention of replacing them later. I also removed the points from my other donor engine to compare the two. The advancer could possibly be from a bigger Honda twin from the same era? It seems to do the job well.

IMG_3574.jpg IMG_3575.jpg
IMG_3572.jpg IMG_3573.jpg

This whole time though I felt nagged by a weep of oil collecting on the top L/H cooling fin of the barrel and a bit too much smoke from the exhaust. Early on Mike in Idaho suggested gas/petrol fouling of the spark plugs, and my subconscious kept telling me that perhaps the left plug was oiling up. I had to find out. One of the aspects I love about these bikes is it’s possible to remove the engine and lift it by hand onto the bench in under an hour.

IMG_4698.JPG

The head gasket looked like new, mainly because it was. Even so there was no sign of a broken seal or any damage, but I must mention that after rebuilding again with new gaskets the engine ran considerably better. I’m not sure if it’s possible but perhaps the head gasket had only partly blown. If not, then I felt I still needed to have a second look, so not a wasted effort. It also allowed me to check the piston rings. It was during the second rebuild that I also fitted new condensors and spark plugs.

By this stage the bike was running reliably enough to make it road legal. I was pleased and relieved to get an MOT certificate on the first attempt, and was now able to undertake proper shakedown tests. These tests showed that:

*The L/H cylinder was running rich, and required a 35 pilot jet and the needle dropping one slot. R/H is still 38 pilot and needle on middle slot
*The ignition timing chooses the worst moment to move; in my case heavy city traffic!
*The carb float levels are crucial
*The battery definitely needs replacing – turn on the lights and I could hear the idle speed drop and stumble
*3 oil seals are leaking
*I need to be careful when cold starting with the choke, or it fouls the plugs
*Most importantly, the bike is an absolute joy to ride!

In summary then, I was troubled by the different air mixture setting needed, but further testing showed that this was what the engine was happy with. I tried a different L/H carb but it still ran rich. I also tried the weaker setup for both cylinders but the R/H side ran rough. I can only guess that perhaps the porting job the previous owner gave it is causing this? I’ll monitor the colour of the plugs.
It’s worth mentioning too that unlike other bikes I have ridden care has to be taken when using the choke on cold mornings or you will be removing the plugs to clean them.
The ignition timing at some point had moved, which on a little engine like this was very noticeable. I have come to realise that having two sets of points is great for accurate ignition timing, but also twice the maintenance. In fact I have a suspicion that it’s the points that were giving some of the problems with the fouling plugs. With that in mind I have contacted Hondaman about his transistorised ignition system.
I’m going to buy a new gel battery today — turning on the lights would actually slow the idle to an eventual stop, and turning them off again would allow the idle to speed up again. I believe the stator is charging normally, the problem is a lead-acid battery which was stood for over a year.

A few fairly minor fixes left and then I’ll have the bike from my youth which I bought 15 years ago for 75 quid, but with the added qualities of reliability and practicality. I am so pleased to reach this stage; this forum has been absolutely invaluable and I want to thank its members for their knowledge and time. Thank you.

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