QuestionQUESTION: Hello! Thanks so much for contributing to a site like this. I have enjoyed reading your comments about other hondas, and you have shared some links to several insightful websites. Please keep it up!
My problem lies with my 1971 Honda CL175 K5 that I have been restoring for the past 10 years. I have done just about everything you can possible imagine to this bike, and I'm almost finished. I've rebuilt the entire engine, and this summer have been trying to get it running smoothly. My problem is that it keeps fouling spark plugs within about 10 minutes or 3 to 5 miles. It used to only foul the right cylinder, but now it is fouling both. I just installed carburetor rebuild kits, and have checedk the levels on the floats MANY times (right now they're sitting at 19.5mm). I had the floats sitting at 21mm but for some reason that is too close of a tolerance, and the left carb would not take on fuel at all. So, I pulled both carbs and reset the floats to 19.5. All three of the books I have (including the factory shop manual) disagree on the height of the floats. God bless Honda. So for now I have them at 19.5 at that seems to be working. Both carbs get fuel, but yet fuel does not overflow out of the carbs. I also installed new jets and float valves and seats. Basically, everything in the carburetor is new except for the main piece of metal.
I have checked and rechecked, and then rechecked the ignition timing. Initially I set up the timing with a closed loop circuit with a light bulb and battery, aligning the timing to the "F" mark, the way the manual says too. Then once I got the bike running I used a timing light and removed the crankcase cover. The timing seems to be perfect, but yet it keeps fouling the plugs. I tell you, if I was the kind of man who ripped his hair out in frustration, I wouldn't even have eyebrows anymore!
I have raised the clip on the needle jet in the right carb in an effort to get it to run more lean at intermediate throttle...but there was no positive change.
I've replaced the condensor with a new one, and noticed no change. Then I swapped the old one back in, and still no change.
I've checked the gap on the points (no less than .012, no more than .016), and then rechecked it. And then rechecked it again. I can't figure it out! Obviously, either the mixture is too rich, or there isn't a big enough spark to detonate the fuel, right? So, does this mean there is something wrong with my coil? This bike has a single coil, and it's probably the only thing I haven't replaced. I have wondered about the air filters, but you cannot find replacement filters anywhere (at least ones that aren't used), so it's kind of a moot point. I don't think they're clogged though, because if you hold them up to your mouth it's very easy to draw a breath in through them. I'm not sure just how "valid" that test is, but it seems to indicate they are not the source of the problem.
I've put an voltmeter on the battery while the bike is running, and usually it reads right around 13 volts. I'm running premium fuel in it, that I put in it a couple weeks ago at the fuel pump. Since putting the fuel in, I have filled and emptied the carbs several times while installing the carb rebuild kit. There is no varnish build-up of any kind on any of the carb parts.
If I put brand new NGK D8HS plugs in the bike (gapped to approx .026), it runs like a charm at first glance!!! All I have to do is literally tap the starter button and it comes to life in a heartbeat! It idles smoothly and slowly, and is very responsive to the throttle (which I have a restraining hand on because the motor has only 54 miles on it since I rebuilt it). It's enough to make a man's heart melt with joy! But after 10 minutes of riding it down the road at about 45mph in 5th gear and 4500 to 5500 RPMs, and the next thing you know it won't idle anymore and stalls out. I have to keep my hand on the throttle to keep it alive (around 2000rpms). Turning in the throttle stop screws doesn't do much beside making it "idle" at 2K rpms. Eventually, it just doesn't want to stay alive at all, and keeps stalling. Then when I pull the plugs, they have a very distinct black carbon build-up on them, an almost powdery, NOT oily dust that wipes off easily the first time. The black carbon coating covers the entire exposed part of the plug. The left cylinder (that did not have this problem before I installed the carb rebuild kit) has a slightly lesser amount of carbon on it, but it is still fairly fouled nonetheless.
One time, I decided to hook up the timing light to the right cylinder after I got back from one of my ten minute rides. I just hooked up the light, and turned it on, with it pointed at the ground. I watched the light to see if it blinked steadily indicating that the right cylinder plug was firing consistently. It wasn't. The light would come on and go off in a completely random manner, clearly showing that the plug was only firing every now and then. I pulled that fouled plug and put in a new one, and ran the same test with the timing light. This time, the light fired every single time, just like it should. The test didn't tell me what was wrong with the bike, but it did help me clarify that the plug was fouled.
If you haven't noticed already, I humbly feel that I am intimately familiar with this bike, but I'm certainly not an expert. I have the shop manual as I said, and I have the parts microfiche as well (on my computer). I also have a somewhat decent parts bike (with a not-so-decent coil on it). The parts bike is the same year and same model. If you have any thoughts or suggestions, I would love to hear them. I can't explain how tired I am of seeing my wife hop on her bike and go for a ride, and I'm stuck in the garage fighting with this thing!!! At the same time though, I was really hoping to find some help that won't cost me $60 an hour (I've already spent WAY TOO MUCH on this bike in the first place). Thanks in advance! -Ian R
ANSWER: Ian, thanks for your kind comments on my contributions to this site. You certainly have lavished a lot of time, money and care on this vintage Honda. I read all of your comments and what you have done, but I don't see the part where it says, "I put the carb slides in with the cutaways towards the air filters." Carb slides are left and right handed, so if you put them in backwards, the engine will flood out very quickly. Check that first....
Now, if for some reason the slides are in okay, then the next question is where did you get your carb parts from? If the answer is KEYSTER, then you may have calibration problems due to their known inaccuracies of parts dimensions and specifications. Their float bowl gaskets tend to be cut too wide, so the edges tend to rub against the floats, causing the bowls to overflow because the float valve isn't closing and/or causing the float to stick closed and not fill the bowls.
All this assumes that you put the camshaft in properly and that the spark advancer is working as designed. If the cam timing is off a tooth, one way or the other, the engine will run, but poorly and the resultant loss of intake vacuum signal strength will confuse the carburetor metering a lot. Sticking spark advancers will cause similar changes and mismatches of vacuum signals in the intake tract.
Hopefully, this will give you an opportunity to go "AH-HA," fix it and go for a nice break-in ride. All that excess fuel can wash down the cylinders, causing a loss of lubrication to the cylinder walls and rings. Drain the oil and put in a fresh refill, to reduce the fuel dilution issues.
Bill Silver
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QUESTION: Thanks so much for your input Bill. Although I'm not sure I've got the cause of the problem nailed down yet, I believe your suggestions are helping to narrow it down.
In any case, I apologize for not mentioning the carb slides. Unfortunately, I can completely relate to having the carb slides accidentally swapped, because I've done it twice now. Can you believe that?! Twice! The first time it happened I couldn't figure it out for a while... but the second time I did it I knew what was wrong immediately. Talk about wanting to shoot oneself! There's few things worse than making the same mistake twice. So, yes, I have checked (and rechecked) to make sure the carb slides are in correctly, with the cutaways facing the rear of the bike. When I had them in backwards, the bike would not idle at anything below 2000rpms, and I had to keep my hand on the throttle. However, as I said before, the bike runs like a top if I put new plugs in it.
So here's my follow up question for you: If the bike runs REALLY smoothly with brand new plugs, but craps out after a few minutes of riding, can it really be the camshaft sprocket being off a tooth? Or a bad spark advancer? To paint a better picture, the last time I put new plugs in it, I could get it to idle at about 600 to 700 RPMs. Not bad eh? And, when I took it out on the road, it had tons of power (for it's age and size) and was very lively...keep in mind I am not riding her hard or hot-dogging her. Seriously, for the first mile she really had some get-up-and-go in her!!! I was so happy with her performance I started to think that I had solved all the problems! However, after the first mile she started to idle too low (maybe 350 to 400 RPMs) and then after that she would just stall when I sqeezed the clutch in. The only way to keep her running was to keep my hand on the throttle and keep the RPMs up around 1700. Even if I move the throttle stop screws all the way in, she would still stall. Then when I pull the plugs out, they are covered in carbon.
I guess what confuses me is how it can run so smoothly and powerfully at first, and then go to pot? If the camshaft sprocket was off one tooth, wouldn't it idle really poorly? Or have poor power on the street? And if the spark advancer (which I have examined carefully in the recent past) was bad, wouldn't it lack power and run poorly once I got above 1000 RPMs?
I don't want to discount your experience and knowledge in these matters, but I can't help feeling that this is still a carburetion problem. Yes, my rebuild kits did come from KEYSTER. I was highly disappointed in their inability to make a quality gasket. It took some considerably tedious trimming to get the gaskets to fit correctly without rubbing the floats, but I did get them to work. As far as the jets go, I held each one up to the one it was replacing, and the holes looked to be the exact same size. Of course the human eye can be misled, but I don't have anything else to measure the holes with. As far as the pin and seats go, I ran several tests with the carbs unattached to the bike, to see if the floats were functioning properly. The first test I ran was with the carb bowl off, leaving the float exposed. I connected the fuel line to the carb while I held it in my hand, and manually raised and lowered the float. It worked just fine, allowing fuel to flow as it was lowered, and finally cutting off all incoming fuel as it was raised to the top. For the second test, I connected the carb bowl, and turned on the fuel again. This time I just waited to see if the carb would overflow or if fuel would run down the throat of the carb, headed for the cylinder. Neither happened. The carb just sat there, as it would if it was problem-free. I gave it a little jostling and whatnot, (to imitate the bumps in the road) and still nothing. To confirm that the carb really was full of fuel, I shut off the fuel valve and carefully removed the bowl to find it full of fuel (as it should be).
If, after all this, you still strongly believe that the camshaft might be off by one tooth, then I am prepared to remove the engine to check.... but it is quite a bit of work to do that, and each time I risk scratching the new chrome and paint. Are there any other signs or symptoms that might be manifest by a camshaft sprocket being miss-set? Honestly, I feel that I took great care in lining up the cam when I put it together, because the replacement timing chain did not have a master link with a clip in it (the way the old one did). The new timing chain had a master link that had to be peened on, making it somewhat permanent. In order to change the alignment of the cam sprocket and crank sprocket, the old master link will have to be cut off and then the new one pressed on. Not an easy task! I wish they still made a timing chain with a master link that had the clip in it, but despite all my searching I can't find one.
Please keep in mind that it used to only foul the right cylinder. But after putting in the carb rebuild kits, it now fouls both plugs.
Well, I've probably bored you to death with all this, and I pray that you do not find my questioning disrespectful. I am very grateful for your suggestions and thoughts. Thanks again! -Ian R
AnswerHome followup.... all carbs have 21.mm float level from that time period. Carbs are stamped CBD, CLS, 306A, 644A, 653A or 306B and all have varying calibrations. Main jets vary from 90, 92 to 98, idle jets are #35 or #38, needle clips are 3rd or 4th and idle mixtures range from 1 to 1.5 turns out. Idle speed is 1200rpm, warmed up.
Bill Silver
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Ian, I only put out the possibilities on what may be causing your problem, not condemning your work. You can verify the cam timing by 1) checking compression...if about 175, then you are fine. 2)Noticing of the point plate is about in the middle of the slotted area, rather than way to one side or the other. (3 If you turn the motor to TDC, then gently feel if the engine wants to center itself forward or backwards of that point. The idea here is that the cylinder with valves on overlap, which normally occurs close to TDC will stop the crankshaft from rotation when both valves are opened equally in the overlap phase. Got it? I know that one is a bit esoteric, but I use it as a quick test. You can also rock the motor back and forth, with a wrench, to verify if there is any slack in the camchain, as there will be a little slack before the camchain tightens up.
I would round up some OEM parts, if you can, for your carbs.
If you think about having to change the cam timing, you can always just loosen the camchain tensioner, remove the two cam support bearings, lower the camshaft enough to run one link over the top in one direction or the other, then put the cam bearings back on again!
I am at work so don't have the exact recommended float level settings handy, but if you have the level off 1.5mm (21mm vs 19.5mm) then the idle circuits and main circuits are going to run richer, drawing fuel more quickly than when the level is a little lower. Remember that the float height is in inverse proportion to the fuel level in the bowl. Higher the float setting, the lower it sits in the bowl, shutting off fuel earlier and running leaner. Assuming all that all the passages are open, then the calibration of the needle, idle jets and main jets are all in question.
With a double ended coil, the timing isn't going to be a fault causing only the right side to foul, unless you have a bad spark cap on that side. The only other factors are carburetion or oil fouling due to a broken ring, rings not seating or some other kind of mechanical condition causing oil consumption, in conjunction with the fuel metering issues.
Bikes with cam timing issues can run good at idle, then crap out at high speeds or the other way around, depending on if the cam is advanced or retarded.
Bill Silver
