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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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Still have a 73 CJ360 back in the barn. Back, back, back, burner project.
 

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I had some cases of intermittent leakege at needle valves. (but okay, mostly on russian Carbs (Izh Planeta/Jupiter) But there was also a Honda CJ250/360 which dro
ve me crazy with that problem.
A new needle valve and working extremely clean (like in hospital operation rooms...) took care of that......40 years ago. ;-)
Some are a pain indeed.

Last year I found different lengths of floater needles in a CMX450 carb. Drove me nuts/setting the workshop alite!
The thing idled perfectly until the end of days but dropped one cylinder during pulling the higher gears. The longer needle didn't let enough fuel through and dried out that particular side of the carb when power was asked for.

See here;
 

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Discussion Starter · #44 ·
Well, well, well, time for another update. It appears that whatever I touch goes bad, maybe I should rethink being a mechanical engineer. Remember the story of me swapping the spark plugs for cheap Walmart ones intended to replace them?

"Whenever I opened up the throttle past 25%, every few ignitions would feel like a small jolt, and it wouldn't speed up well at all. "

I put the original spark plugs back in, but now it seems that the problem is ongoing no matter what plugs are in there. It was fine initially, but after a day or two I started noticing the jolts again. It doesn't happen from 0-10% throttle, but if I open it any more the bike gets super choppy, it sounds like the engine is fluttering, and I get no increase of power. It's getting worse by the day, I can barely get to 25mph before it refuses to give more.

Stranger still, the bike runs (almost) perfectly on idle. I can open the throttle all the way and it'll rev up, which won't happen in gear. It still sounded like I wasn't getting every ignition though, so I tried to test the cylinders one by one. While running on idle, I pulled the wire to the spark plug (what's this called btw?) for the left cylinder. The revs went down but were still uniformly spaced out and my right cylinder was enough to keep the engine going, albeit barely. I replaced the wire and pulled the one on my right plug and the results were much different. The bike would sputter for a bit and die. I increased the idle speed higher until the left cylinder was able to keep the engine running by itself, and I could hear noticeable gaps in ignitions, not uniform. I take this to mean that I'm losing ignitions on a regular basis, and when I open the throttle I lose an even higher % of them until it maxes out under load.

Keep in mind this is not the original issue, this is a new one that developed ever since I tested the spark plugs at WOT. I really don't see how I could have put them back in wrong, and they were fine before so I don't think the problem is with them. I tested the plugs right after I cleaned the carb and replaced it, and considering the problem is progressively becoming worse over time, I think that's where the issue lies. However, once again, the bike was running perfectly right after I cleaned the carb, and just got worse over time without me doing anything (besides testing the plugs). My only hypothesis is that whatever I did to the carb, I increased the AFR too much so that the plugs are getting increasingly more wet every time I ride it, leading to weaker sparks and failed ignitions. All I did was clean the jets, and reset the pilot screw to 2 3/4 turns out. I'm gonna order new plugs either way (NGK CR6HSA this time), but I think the issue is with my pilot screw setting. I'll mess around with it a bit to see if that fixes anything, but I'm really at a loss as to what happened to cause increased power loss over time. Please let me know your guys' thoughts and ideas.
 

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Drain your fuel tank into a glass jar. Drain your carburetors' float bowls too.

There is water in your fuel from simple condensation on the inner walls of your fuel tank.

That's how the problem seemed to get worse without you changing anything.

The wire to the spark plug is called a 'spark plug wire'

Rule #1 is don't panic. If you're frustrated now, imagine if your bike started acting up when out on a long ride.

The thing you're experiencing is an ignition misfire, sometimes called a 'miss'.

I would drain the fuel from carbs and tank and dump in (1/4 bottle max, just buy the cheapest one) HEET or similar dry-gas type product to absorb any water left at the bottom of your tank after draining, and I wouldn't add any new fuel to the tank until you're ready to work on the bike again, I wouldn't even buy fuel until you're ready to work on your bike.

 

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Yes it's temperature change from day to night. Covering your bike is recommended but that's just to keep rain and snow off the surfaces.

One good practice when storing a bike for the winter is to top off the tank. For a project bike that you won't touch I'd recommend draining it and adding the dry-gas type product, but be sure to drain it out in the spring before adding fresh fuel.

Opinions vary, someone else might say to just fill with fresh gas, but then what if your petcock valve leaks? I'd save that for bikes that are being ridden and you know they won't leak.
 

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Discussion Starter · #48 ·
What's the best way to prevent condensation?

I'm still riding it on a regular basis, planning to for as long as weather permits. I fixed the petcock so nothing leaks. I have no problem emptying and putting in new gas, but is the same condensation going to happen with that tank too?
 

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A full tank will have Less chance of condensation forming than a partial tank of fuel will due simply to the reduced area for it to form on. Water will sink to the bottom of the tank which will make the bottom rust out first, and the water will also be drawn into your fuel system first, causing misfires and rough running.

So yes if you're riding regularly just tank up on your way home every day or top off from a plastic can at home.
 

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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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What I could find is that the CJ360 only saw the light of day from '76 onwards.....
Sorry, I meant CL360. Enduro style! o_O
And, Alan F. sounds like he could be right about water.
You said however, that it is worse on the left side though. Still sounds electrical to me, but try the drain. It really can't hurt.(y)
 

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Oh yeah. That makes it even simpler for the left cylinder to run worse.

With water in the fuel both cylinders will misfire, but on the side stand starting cold,
I'm thinking the left cylinder will probably be gravity fed more water than the right.
 

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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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Again 1 carb. the fluid, be it Gasoline or water, both run through the same jets. this should spread it evenly to both cylinders. Dual carbs... I could see your point. Interesting thought though.
Testing that hypothesis should be easy though. Just hold the bike on the opposite angle, and see if the problem follows.
 

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Discussion Starter · #55 ·
Ok so after a few more days of trying to figure it out, I have a few more thoughts:

Misfiring only happens at higher RPMs, the lower the gear, the higher RPMs I can reach before misfiring, misfiring doesn't occur in neutral. It seems that the misfiring I'm experiencing is dependent on the load the engine is trying to carry. I don't know what exactly this hints at but thought I'd share.
 

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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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Did this start shortly after riding in the rain? The reason that I ask is, that I had a similar situation because of failing spark wires. The higher the RPMs, the higher the spark voltage. Thus, more arcing to ground, misfiring.
Hopefully this helps.
 

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Discussion Starter · #57 ·
It's quite possible, I don't remember well enough to give a definitive answer. Can you help me understand a bit better? If the spark voltage is higher, doesn't that mean stronger spark = less misfiring?
 

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85 CMX 250C, 82 GW Remember that you are invisible, treat all others accordingly. Avoids Road RAGE!
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Yes, as the speed increases the primary voltage that feeds to the CDI increases. Then released to the coil it is stepped up incrementally.
If there is a fault in the wire, it will more easily jump to ground at such an increased amount of power, thus arcing/shorting to ground before ever reaching the plugs.
 

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Misfires can occur for several reasons. Among them are: not enough fuel, too much fuel, not enough air, too much air, weak spark, water in the fuel, and probably more.

I suggest idling the bike while warming one of the plug wires with a hair dryer to simulate a hot bike condition, then spray that plug wire with water from a spray bottle. Do this outdoors, at night so you'll be able to see any blue sparks arcing from the wires to wherever they can ground to. Check the other plug wire afterward.

This also works to check for worn out car plug wires but you won't need the hair dryer to heat things up.
 
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