72 CL175 no throttle response

NJ72CL175

NJ72CL175

New Member
After messing around for a couple weeks on my bike I thought I finally had everything together after I rebuild the carbs. Now I find that it is only running on one cylinder (right side) and anytime I attempt to give it throttle while it moves it sputters and dies but reacts to the throttle when stationary. I just replaced the battery this morning. The float bowl on the left is dry and will not fill with gas unless I take it off and hold it underneath the carb (obviously why that cylinder isnt running). The right side is running extremely hot as well. I have been experimenting with the air mixture screw but nothing seems to help at all. Im at a lost of what to do at this point and the manual is little to no help. Any help would be greatly appreciated. Thank you.
 
You have a combination of issues.

First up, double-check the float heights on your carbs (the left, especially). It could be out enough to prevent any fuel from getting into the bowls. Once you have fuel in the bowls, you may not be out of the woods, but that's the first step, at least.

You're also fighting a timing issue. Get a strobed timing light onto the bike and I'd be willing to bet you see that your timing is retarded by quite a number of degrees.
 
The height of both floats are 21mm, I had just checked those yesterday. Just to be sure, you must turn them upside down and measure from the lip to the top of the float correct? and the timing suggestion sounds dead on as this is the first time I have timed ANYTHING and read it straight out of the manual and felt as if I had done it incorrectly. I have a strobe light but am unsure how to perform this maintenance. I believe my manual is from 1970 and it kind of hard to understand. What is the dumbed down version to timing this bike? Thanks for for your help Sonreir
 
Floats are usually set with the carbs on their side so that the float only just contacts the needle, rather that putting too much pressure on it.

For timing, hook the strobe up to a battery and then the inductor from the strobe gets clipped onto the outside of one of the plug wires. If your strobe has a setting for timing advance, make sure it is set to zero. Next, remove the stator cover from the side of the bike so that the rotor and stator are exposed (you may need an oil catch pan for this part). You should be able to see lines on the rotor with letters like 'T' and 'F'. Those will match up to an indicator on the stator (in the 10 o'clock position) during certain times of the crankshaft's rotation.

The 'T' mark indicates that the pistons are at Top Dead Center (or close enough for government work). The 'F' mark is where the spark is triggered when the engine is set to idle speeds (1200 RPM or less). So at this point, you want to get the bike idling and check things out. The beauty of the strobe approach is that you can use it to check timing while the engine is running (which is the only sure way to do things). The strobe flashes every time a spark is triggered and the human eye/brain views the rotor as standing still. You can see exactly where the marks all line up and you can see if you need more advance or not.

Once the timing at idle is set, you want to verify the timing advance. Get someone to rev the bike to 4000 RPM and hold it there (or slightly faster, but not slower than 4000 RPM). The spark will advance to the point where it is now triggered between the two lines that are maybe an inch along the rotor, in the counter-clockwise position.

Make sense?
 
Yes, Thats makes a lot more sense than my manual. I'm gonna try this tonight and hopefully remedies my problems. Thanks again
 
Re float bowl. Is the gasket binding on the float when you install the bowl? If I understand you correctly, fuel flow into the carb when the bowl is removed but not when it is installed. To me this idicates that something is binding on the float and that this could be an illfitting gasket.

Brian
 
I'd check your petcock and tank. These old cocks get real shitty after all these years. Replace the fuel lines if you haven't already.
 
So I set the timing, turned out it was advanced a little too far. I rechecked the point gap and it sparks exactly on "F" and reset the cam chain on the "T" mark. but now the right cylinder is not firing. I put the timing light on the right plug wire and the light was not flashing so I assume there is no longer spark to the right cylinder.
 
Sounds like that assumption is correct. Double check the plugs, caps, and wires for that side.
 
Well I just timed (or what i believe to be timed) correctly with the timing light I have. I finally got both cylinders running and I still am having the problem of no acceleration even though I have throttle response when stationary. I'm not sure if i did not understand the timing or what. I ALSO just bought a new throttle cable NOS and replaced it right around the time I started having these problems. It maybe unrelated but important nonetheless.
 
Well I went out and bought a compression tester and being the newbie I am I bought it without the correct size adapter, which I would assume to be 12mm. So as I await for the adapter I ordered to arrive is there anything else I can check that could get the ball rolling? I understand if my compression is messed up then its not worth tinkering with other stuff but when I first got the bike I got it running and drove it around quite a bit so compression might not be my issue. Then again, what do I know ha.
 
Do you have a video recorder available? If so, you could shoot a video of your ignition timing (checked with strobe light) and we'll let you know.

There are a lot of videos on youtube though and I suggest you check them out. Ignition timing can be a bit confusing at first, but there will be a point where it "clicks".
 
Forget timing for the moment and get both carbs working correctly. If one carb will not fill unless the bowl is removed, either the float valve is partially blocked or a float is hanging up for some reason. Next, clean out the slow jets and the passages they discharge through. There is a tiny hole just in front of the slide through which the slow jet discharges. That is frequently blocked on those carbs.

When you are 200% sure the carbs are perfect, get a new pair of plugs and plug caps and shorten the HT leads by 1/4" and then test for a spark on both sides. That bike has one double ended coil and they do age over time, but if it's sparking on both, leave it for now.
 
So I just adjusted the float level on the left side to a about 17mm and now the fuel runs fine. I start it up an it drives like there was no problem at all. This leads me to believe the timing was done correctly and that corresponds with the other day after I timed it and it ran decently well (as in a little more throttle response). Thank you for your help. I couldn't have done it without you guys.
 
My only question now is how hot the engine should be running. In the above described "run" I came back to the garage and the engine was extremely hot. Now this is my first bike and I am fairly foreign to them so I was wondering if it is actually suppose to be burning hot. Thanks again
 
After a spirited run, you should just be able to touch the fins and then remove your hands without any lasting damage.

If you have an infrared gun (pretty cheap at Harbor Freight), surface temps of the jugs can be as high as 400°F, but should be closer to 300°F.
 
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