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Discussion Starter · #1 ·
Hi to everyone. It's been awhile, but to refresh if needed, I posted my introduction....um.....quite awhile back.

http://www.hondatwins.net/forums/23-member-introductions/26212-all-around-newbie-sc.html

Anyway, here is my current problem.

A couple weekends ago, I decided to begin (finally) messing around with my bike. I had spent the winter building and organizing in my "shop" and when the weather started warming up, thought about doing something to the bike itself.

1972 CB175, 7,000 miles (+/-), open pipes (till I find decent mufflers)

Here's the problem:
The left cylinder misfires in low-mid throttle. After a few miles, it basically goes dead in mid throttle. When I open up the throttle wide, it starts firing and the bike responds quite well, but in the mid range, it misfires and then dies. After awhile, the plug fouls and goes bad. Put a fresh plug in, and it the process starts all over again.

Here's what I've done:
1) Checked compression: 140-145 cold on right cylinder, 150-155 cold on left cylinder. (better compression on the left / dead cylinder?)
2) Checked points for pitting, cleaned them, and gapped them. They are the right gap, but I couldn't adjust them any more even if I needed to because there isn't enough play in the mounting plate. Is that because they are worn?)
3) Set static timing (I still don't know how someone sets timing on these bikes using a strobe light, can someone explain that? Or is there a thread showing how to do that? Do you do it with the magneto cover plate off???)
4) Checked valve tappet clearance and adjusted to .002.
5) Set cam chain tension.
6) Synced throttle valves.
7) Put fresh plugs in gapped to .028 (+/-)
8) Put in ethanol free, high test, with 2oz. Seafoam per gallon to clean things up.
9) Charged the battery.
10) Cleaned grounds just for the heck of it.

When I did all that, it fired right up. I warmed it up, set the idle to 1,200. It idled great, good throttle snap, but smelled like it was a bit rich. Also it fires up cold without the choke so it's definitely rich.

After adjusting the carbs and getting a good idle, I took it down the road a few miles and back. Up to about 45-50 mph. It missed on the left cylinder regularly and after only a couple miles the left cylinder died completely in mid-throttle range.

Got back to the house and pulled the left plug. Sooty black and wettish after only a few miles. The right plug was also sooty but not wet at all and the right cylinder never misfires.

I checked spark on the left wire and it seems to be a pretty strong whitish blue spark. When I put a fresh plug in, the spark on the new plug seems good and if fires good idling.

So I put in a fresh plug and drove it about 10 miles yesterday. With a wide open throttle, the left cylinder fires and I got it up to about 60mph. But when I back off the throttle, the left cylinder misses and it always dies.

It's always the left cylinder even when switching the coil wires. So it seems like it's got to be a carburetor/fuel issue, unless the spark really is weaker than I thought and the left cylinder is the one that suffers as a result?

The only thing I've done so far was to raise the jet needle one notch to the second from highest (second leanest) notch. After I did that I took it for a short run down the road and it still misses in the mid throttle range.

(Oddly when I got it back the second time last night, the left cylinder started smoking a grey smoke. It only did it for a few minutes and stopped.)

If you were going to trace this issue out, where would you begin, and what would you do?

As a side note, I used heated lemon juice on a stove top to clean the carbs last year. Can that erode the jets so that the openings are too large? Just curious if that is a cause for the rich running.
 

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Not familiar with your specific carbs but it sounds like your left carb needs cleaning. Might as well do them both.

Browse or search the forum for tips on carb cleaning, lots of ideas out there.
 

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Discussion Starter · #3 ·
J-T, yeah I'd pretty much resigned myself to pulling the carbs and rebuilding them again. I'm not convinced I did a decent job the first time around, and after learning a bit, it will be good to do it again anyway.

There is a site that sells the Keyster rebuild kits for a fair price.

Keyster Carburetor Rebuild Kit - Honda CB175 CL175 - 1972

Have you (or anyone) had experience with the Keyster name brand, and the website itself?

I think I'll do the rebuild on both carbs, put in a new coil, points, condenser, plug boots, plugs, etc... About $125 total.

Any direction on the timing with a strobe light thing? =)

Also, would you have any thoughts on why it would start blowing blue/grey smoke for a few minutes and then stop? Also from the left cylinder.
 

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Keyster kits are generally not spoken well of around here. Original Honda parts are often still available. If your local Honda dealer is not helpful there are other sources including this one:

Hammond Indiana, Honda, Yamaha, Kawasaki, Suzuki, Sea-Doo, Can-Am, Polaris, Ski, Tucker Rocky, Parts, ATV, Motorcycle, UTV, Accessories, Apparel,

Gasket kit: 16010-304-305

You'll also want:
VALVE SET, FLOAT
16011-355-004


Unless someone has tried to rebuild your carbs with carpentry tools you shouldn't need to replace any hard parts. The aftermarket kits often include jets and metering rods that aren't correct for the carbs you bought them for anyway.
 

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Discussion Starter · #6 ·
J-T, I hear you on the "hard" parts not needing replaced unless they've been damaged right? If that's the case, I think a good cleaning again and blowing out all the ports will be my first option. I had bought a new gasket set for them last year because the float bowl gaskets were bad. We'll see how it goes when I clean everything up real well.

Simo, the floats are good, no holes, float well. I set them as best I could determine to 20mm (I read 19 - 21 mm is correct) and it seemed to help at first. I will recheck them when I put it back together. I thought about the valve stem seal as a possibility on the smoking issue because with compression at 145-150 cold, I thought the rings and such were probably good.

Last night I got a wild hair and decided to take a few things apart, mostly as a learning process. When I took the exhaust off, I noticed that the carbon deposits inside the exhaust port were so heavy they looked about 1/16" thick and had flaked off in spots. Very heavy build up. That made me think it might be beneficial to at least take the top end off and clean everything up really well. If there were such heavy deposits on the exhaust, I can only imagine there are really heavy deposits on the valves and probably in the chamber itself. It's way past running a cleaner through it.

Any suggestions on where to source a good gasket set? I've heard a lot of negativity about after market gaskets and I'm having a hard time finding one for my CB175K6. Also the OEM Honda head gasket costs a mint, but I don't want to shoot myself in the foot by using an inferior gasket set and having to buy and replace it twice.
 

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Discussion Starter · #10 ·
Good deal! I'll look for the country of mfg then when I research for a purchase.
Thx again Simo.
 

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TStephenGaunt, did you ever fix the issue?
 
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