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Discussion Starter · #1 ·
Posting this under engine, as it could be fuel, could be ignition.

CB175 K4. Carbs cleaned, float levels set, original jets and needle position, valve clearances set, new plugs and caps, fresh contact breaker points and condenser, timing set correctly, ignition advance works correctly, checked with strobe light. Air filters rebuilt. Compression 150psi each side, usual proviso about using compression tester designed for larger engine.

Charging system doesn't appear to be working. Just using a new freshly charged battery at present, voltage currently only 11.69v, down from 13v when first installed. Weak spark, going out under load ?

Engine starts easily enough, ticks over correctly and smoothly, picks up on the throttle nicely, bike in neutral.

However, on the road, will only rev to around 6k through the gears.

Any suggestions ? Wondering now if I need to replace the ignition coil. So far, I've had to change the starter solenoid and flasher relay, and I have a new modern regulator rectifier to fit at some point.
 

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Sounds a lot like what Tidler would do when the charging wasn’t working.
Is not just voltage but the current flow needed at high rpm to keep charging the coils at the 12v low voltage side.
P=I*V don’t forget.

Try getting to your 6k point and flipping the lights on, I it dies off even worse then it’s definitely not enough oomph from the battery alone.

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Discussion Starter · #3 ·
Thanks Alex, I'll give that a go.

Annoying, because I'd convinced myself it was simply due to clogged air filters.
 

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This is just an idea. I had a similar experience with a 150cc scooter and it turned out to be that I was one tooth wrong with the timing chain. At lower revs it ran fine, but when it wound up it died. It was because when the spark advance came into play the timing was just too far off. I realize this is a nightmare situation with a CL because you have to take out the engine to check this.
 

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That’s a good call.

As Richard has another running 175, he should be able to check.
With the stator cover off and the mark at T, use your vernier as a depth gauge down the plug hole, see if the two bikes are the same depth.


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Discussion Starter · #7 ·
Thanks for the input folks.

I don't think this engine has ever been apart, so I'd discount the cam timing being out.

I've checked the ignition advance mechanism, and replaced the points cam with a better one, as the one fitted to the engine was rusted and in poor condition. Points gap same on either lobe.

I'm certainly more inclined to think its electrical. At WOT, slides pull up all the way, just running on main jets and needle position then, although I guess float levels would also have a bearing on things.

I haven't checked plug cap resistances yet. I'm expecting a replacement ignition coil to arrive today, that will be an opportunity to check the plug caps. I'm also waiting on some connectors for rewiring my charging circuit.

I have charged the battery ready to try another run, but November weather has set in over here, either wet, frosty, or just cold and wet, not really conducive to road testing, or working in the shed for that matter.
 

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Discussion Starter · #8 ·
With the stator cover off and the mark at T, use your vernier as a depth gauge down the plug hole, see if the two bikes are the same depth.
Easier than stripping engine, just pull the advance mech off the end of the camshaft, check alignment of the keyway on the cam with TDC mark on stator.
 

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Easier than stripping engine, just pull the advance mech off the end of the camshaft, check alignment of the keyway on the cam with TDC mark on stator.
I had similar problem.
My bike had problems at ca 7krpm (5th gear) with headlight (35W) on. With headlight off I was able to reach 9krpm.
I have reduced headlight power to 25 W (as in manual) and problem had been solved.
Try to switch off headlight during ride.
 

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Discussion Starter · #10 ·
Thanks, it all certainly points to battery not charging, ignition failing as battery discharges.

I don't ride with headlight on in daytime, but I could certainly try turning it on to see if it made matters worse.
 

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Have you tried closing the choke to see if it made a difference? It sounds like a lean condition to me.
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Discussion Starter · #12 ·
I know what you mean, and the plug condition would support that, very pale tan colour. Pugs in my other 175, which runs well, are always brown / black. But then, back in the day, plugs in my CB175 K6 were always very pale in colour, a consequence of being continually ridden flat out.

It's just that when I first removed the air filters and went for a ride, it did rev to 10k through the gears, and I thought I'd narrowed it down to blocked air filters. I now think that that was a red herring, and that it was actually due to the battery going flat. If sorting out the charging, coils and plug caps doesn't sort it I'll be looking at the carbs again. Maybe raise the needles a notch or two, it is running all OEM jets, just aftermarket float valves.
 
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