Cb175 running to rich

Hello everyone, I am new to this site and have a problem with my 1973 Cb175. The right cylinder is running very rich and fouling plugs while the left cylinder is running somewhat normal. I have put new plugs in, checked the points and timing, and switched the spark plug leads. I also cleaned out the carbs several times and adjusted the throttle and pilot screws. I also moved the needle jet down a notch and then again another notch and no difference.
When I put new plugs in the bike runs fine but then after about 50 miles the right cylinder is fouled and the left is in ok shape. I don't know what is fouling out this plug. Is it electrical, or a carb problem, or something else I'm not even considering? If anyone knows anything or had similar problems I would really appreciate the help. Thanks

Sounds like your carbs are out of synch. There should be an adjustment screw in between them to adjust this. You'll need a set of synch gauges to do this, if you don't have them and aren't familiar with the process you can have a shop do it for you. Shouldn't cost too awful much. What this does is to ensure that both carbs are spraying the same amount of fuel. From all the other things you've done, I'd say this should fix the problem.

Thanks for your reply.
I guess I don't understand where to hook the sync tool up to. There are the throttle and idle adjustment screws and the fuel line hook up. I didn't see any vacuum hook up port or anywhere else that a hose could be hooked up to. Or do I hook it up to the fuel line port on the carb or somewhere else?

I strongly recommend you look for CB175 shop manual for carb adjustments and sync. Troubleshooting without it may be very difficult.

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When you say "fouling plugs" on the right cylinder, do you mean oil deposit ?

Have you performed a compression test on both cylinders to make sure piston rings and valves are in good shape? It is quite common to see 35 years old valve seals fail, interfering with valve motion, even if they are not worn out. Your valves may simply be out of adjustment too.

Cylinders pitted with rust will make piston rings fail. If your compression test reveals less than 100 psi or a difference over 15 psi between cylinders, it may be impossible to properly adjust your carbs. An obstructed exhaust pipe may also produce such problems.

Good luck

Martin

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Here is a quote from Honda CB360 won't start HELPP MEE!!!! - FixYa
The CB360 is about the same age and very similar to CB175, so it may inspire you...

SYNCHRONIZE THE CARBS
Remove the air filter and rubber fittings to allow you to see into the throat of both carbs. You may need a mirror to see inside. You need to be able to see the slides go up and down when you twist the throttle. Now turn the fitting where the cable goes into each carb such that there is just a bit of slack in the cable, 1/16" is plenty. Lock ONE of the cable adjusters down tight. All further adjustments will be made on the other carb.

With the motor turned off twist the throttle very slowly while looking at the slides. Both slides need to begin lifting at the exact same moment. If the slides don't raise at the exact same time then slowly twist the throttle until the locked adjuster slide just barely starts to move. Hold the throttle still and turn the adjuster on the other carb so that the slide on that carb just barely starts to move also. Now recheck the slide movement timing. Do this process until the slides on both carbs begin to raise at the EXACT same moment. Lock down the loose adjuster and re-check the slides.

BALANCE THE CARBS
Turn the throttle screw on the LEFT carb one half turn inward. Now start the engine and get it warmed up. With the engine running, remove the RIGHT spark plug wire. Adjust the idle speed on the left carb to the point where the engine just can't quite stay running and dies. Now put the loose spark plug wire back into place.

Now turn the throttle screw on the RIGHT carb one half turn inward. Restart and rev the engine. Next, remove the LEFT spark plug wire. Adjust the idle speed on the right carb to the point where the engine just can't quite stay running and dies. Now put the loose spark plug wire back into place.

Turn the idle screw on each carb EXACTLY ONE QUARTER turn outward and restart the engine. The engine will be probably be idling very fast. Adjust both the idle screws equally from this point to get to the desired idle speed. Congratulations, you have just synchronized and balanced your carbs

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thanks iamimartin,

the compression is the next thing i will check. I don't have a gauge but i was looking at getting one anyway. i will try your sync and balancing procedure after i check the compression.

I checked on Ebay, I found several compression tester kits that include adaptors for ATV and motorcycles. Price and shipping included is about 40$.

If your compression is too low or uneven, any carb balancing will have to be redone.

In the meantime, I suggest you check your petcock and clean it from gum and rust deposits.

Every fall, I use fuel stabilizer and every spring, I use a few shots of Seafoam fuel treatment... great stuff to clean up light gum deposits and tune up.

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so if the compression is out of whack, all the carb tuning in the world won't matter?

If you engine breathes, it is not dead, but its health level must be measured before you invest time and money to make something useful out of it. Attempting to balance your carbs is indeed a waste of time if the compression test fails.

My advise is to make sure you have a chance to win your bet BEFORE you start ordering carb rebuild kits and spare parts. Only a compression test will tell you if your engine is healhy enough or needs an overhaul.

I did buy my CM400T 1980 just with a road test, sound of the engine and looking at the spark plugs. Everything looked so nice, it had low mileage, I bought it. Later, I found out the odometer had been changed and the bike real mileage was probably much higher. A low compression test could have given me a warning, but not necessarly on a vintage bike. Consequently, I did not pay much for the bike, but I now consider it would have been smarter to get compression test prior purchase.

Not even a month and 2000 miles later, I lost compression on the right cylinder, the bike became hard to start, used a lot of oil and made a big cloud of gray smoke for about 5 minutes every time I started cold...

Piston rings had failed. How could I tell ? I had 125 psi on the left, but only 70 on the right one. If I added a spoon of engine oil by the spark plug hole, compression came back up to 100, but not for long. If the valves were leaking (out of adjustment or damaged) a adding oil on the piston would not help. So I now faced the fact my engine needed an overhaul.

I made another mistake: I got it repaired. Cylinder head overhaul, new pistons and rings, honing the cylinders... It did cost me over 700$ in parts and labour. I could have purchased a CM450 engine with a 3 months warranty for 450$. Three months later, the new gasket at the base of the cylinder block failed and leaked oil. So the whole engine overhaul job had to be dissembled and reassembled again for a stupid 5$ defective gasket. In the meantime I had purchase an identical bike for 250$ just for parts, so I swapped the engines to save my season. I have all parts, tools and knowledge to try to do the failed engine repair and reassembly, but until I have the time, I can ride on the spare engine for a few years if I have to.

You don't have a spare engine handy to cover for bad luck. You have to know now if it is worth betting on such an engine that keeps a spark plug fouled. Only a compression test could tell if it is worth trying to tune it up. Valves out of adjustment must be corrected first, for instance. If a valve is not adjusted properly it breaks or overheats, destroying piston, cylinder and possibly the crankshaft too. A compression test has good chances to tell you if valves and piston rings are heathy enough to start tuning up the engine.

Betting on a vintage engine is already a risky bet. If something can be done to minimize the risk at a reasonnable price, do it. If things turn sour, a compression tester will tell you if it is time to let it go or to get deeper into your pocket.

CB175 1971 was my fist bike, when I was 18. I loved it. The CM400T I now ride is just a little better in terms of pleasure and just as easy to handle. Instead of 55 miles an hour with the wind on my back, I can now exceed legal speed limits whenever I want to, but I don't even want to. Riding at 50 mi/h on a scenic country road is still my favorite type of ride. I wish you some years of fun if you can restore your CB175. I do.

Good luck

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