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Discussion Starter #1
Hello all. I'm looking for a fresh angle on my 75' CB360T.
Here is my issue: from about 2000 to 4000 rpm at steady cruise, low load, the engine runs a little rough. If I give it more than half throttle it will pull through it. Anything above 4k rpm it runs just fine. When I pull the plugs, the right looks good but the left is black sooty. They both still fire.

Here is what I have done so far. I started by cleaning the carbs and verifying what metering is inside. I verified that all passages are clear and replaced all rubber gaskets.

Before reinstalling the carbs, I checked the cam chain adjustment, adjusted the valves, cleaned the points and static set the timing. After the carbs were back on, I synced the carbs and adjusted the pilot screws. The bike has always idled perfect and smooth. I put about 200-300 miles on it and the problem still exists.
I pulled the carbs again ( three more times) and checked and rechecked everything I had done. I have the floats set to 18mm as per the shop manual.
At about the 9000 mile mark, I finally replaced the factory ( yes, factory) points and condenser. At the same time I installed a Hondaman Transistorized ignition. I verified the advance dimensions to make sure it didn't have too much end play and shimmed it to get the correct endplay. At this time I static set the timing and checked it with a timing light. I was able to fine tune the hell out of it! It has always been a three kick bike, now it usually starts on the first kick. The advance comes in and works as it should now.
The problem still exists. I gave up on it for about a month to clear my head. Yesterday I started thinking about an ignition problem and how to trouble shoot it. I Pulled the gas tank again and rewired the coils so that I could switch which plug they would fire. I figured if it was loosing a coil, the spark plug on the right side would now show a sooty plug instead of the left. Took the bike for a 30 mile loop with the same problem occurring. After the bike cooled I pulled the plugs to find the left cylinder is still the issue. I pulled the carbs this morning when I decided I needed someone else to maybe chime in with a new idea of what could be going on.
It appears to be a fuel issue and I am at the point of frustration, HELP!
 

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Sensei
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Your problem is you are in too high a gear....Cruising, regardless of actual speed, you should be nearer the peak of the power/rev curve for whatever gear you are in (about 70 to 80% to redline)....
At 2000 RPM, you are BARELY off the idle circuit (which tend to be set richer than the main circuits)... If I'm only going to be going 45/50 MPH or less, I never get out of second gear.....On the 360, you might be in third at 55....
 

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I'll agree with Steve, I try to stay around 5-7k RPM all the time. I get above 4k as soon as I can, doesn't hurt them at all to be reved they are designed to do so.

Bike is also NOT charging at 2k with the lights on and you are running on battery at that time. It is interesting that the side stays the same, how is the compression on both sides?
 

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To join in, at 2K RPM, the battery is slowly discharging. Low battery voltage = rough running.

Even Ducati's don't run well under 3K RPM.

Keep the RPM 3500 RPM or higher...that's why there are 6 gears, to keep the motor in the best RPM range.

4K RPM is my lowest to use RPM....Battery is kept fully charged, the motor is smooth, and responds to throttle quickly.

These motors are not large displacement car motors....Most cars have a 5K-6K red line. The Cb360 has a 9200 RPM redline. You are just entering the real powerband at 5K rpm.. Above 8K RPM, the torque/HP starts to diminish, I usually shift around 8500 RPM when accelerating fast....More than that is a waste unless your engine has serious modifications to the cam and timing, intake and exhaust passages...

A lot of people seem to tun these motors at too low of an RPM, not sure why....
 

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Discussion Starter #5
I understand about the charging system and I don't lug the engine. Most of my bikes are under 400cc so I realize nothing is gained at low rpm. Like I said it is at steady cruise with little load. I can get it to happen at 2k, but the time when I experience it the most is usually at speeds where I am cruising along in slower moving traffic at about 45 mph, @ about 4K rpm in 5th or 6th. I am concerned that it is possibly running too rich on the left side.
 

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How about a pic of the plugs? Maybe the lean side is the issue.

Are the carbs synced well? Using a vac gauge? Out of syn carbs give poor throttle response off low low....That can explain the difference between the 2 cylinders....

Are you using the stock air box and filters? or Pods? What kind of pods? The cheap Emgo's are nasty for tuning. The Uni and K&N are higher quality, but require rejetting most times.

Hows the fuel feed? Sometimes the petcock doesn't feed one carb or the other sufficiently. Are you using gas filters? The sintered ones are fuel flow blockers....

Hard to diagnose a problem like this remotely. Without really knowing your machine, what kind of work or mods are done...we can only point out problems you can check...we can't narrow it down...We rely on your description. So if you leave out things, we can't guess as well....

As with most things, attention to detail matters. If the carbs are clean and synced, if the timing is spot on with both cylinders, if the voltage is above 12V, and the system is mostly stock, it will run well....We don;t know your skill or observational abilities, so don't be offended if we ask twice..
 

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Discussion Starter #7
The bike is bone stock, other than the transistor ignition. Air filters are stock air boxes (elements are made from a Fram air filter) Petcock is a new factory unit, using the filter screen. Fuel flow to both carbs are free. Carbs are synced using a pair of vacuum gauges that I zero out on one cylinder before each use so that I know they are reading the same. I have synced the carbs nearly every time I go into them because I don't want to leave anything to question. It doesn't have poor throttle response, more along the lines of a surge or slight miss. It isn't running lean or I would expect the good plug to show that. It is in the factory jetting right now. I just went through them again and didn't find any debris (as usual), all passages are clear. All the air jets are in their correct positions. I did swap the slow jet, primary main jet, and main nozzle from the left to the right carb to try and see if the problem switches sides - No Joy.
After that I dropped the floats from 18mm to 20mm went for another ride. Both plugs look better but I picked up an intermittent bog in acceleration from a stop between 4 and 5k rpm ( only happened twice) Maybe it is too lean. I'll probably reset the floats back to stock, recheck the valve gaps, and just ride it. Im not looking for perfect, just better than what it's doing now. When I go out on this bike, it is usually a two tank tour and most of the time I have no idea where I'm at. I want to be sure that it is healthy. If I were running fat or lean on both plugs and it had this running issue, this would be a lot easier. Thanks for all the ideas and I appreciate the help.
 

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4~5K is a problem since E-10 was introduced.
Check throttle shaft plugs are in place
I haven't tried it but I've been told my 'mods for pods' can cure the problem if it's with both carbs.
If it's only one side it may be slight variation in fuel level or an aftermarket carb re-build kit in one side only?
It's why I blueprint the carbs before modifying them, many aftermarket kits have the right numbers stamped on jets but the actual jet sizes are wrong
In my experience the Fram filter repair works incredibly well so that will not be a problem (may cause a slight restriction at 8.5K +)
 

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Discussion Starter #9
Tonight I reset the floats back to 18.5mm and base lined everything again. Mechanically, base engine is set. (Everything from valve gap to the points) to factory as per the manual. Checked the timing static and dynamic. Checked for a possible vacuum leak and came up empty. After that I threw my helmet on and spanked the everlivin' crap out of the old bike and found it erratically does it up through 8K rpm even on acceleration now. I am beginning to think something on the electrical side may be breaking down. I was reallllllllly wishing that with it would just quit so may be it would give me a lead. It appears to be getting worse. It seems to be directly related to one cylinder or the other as one plug gets soot and the other looks good. I guess I'll bring home my Fluke 88 from work and start going after the electrical end. It is charging well and I have an old sears analog ignition meter that I use to set the points up. Eventually, what ever it is, will reach out and poke me in the eye when it gets tire of the game.
 

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Glad your seeing the 'funny' side of playing with 'old' bikes :D
 

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Since much is ruled out so far, I might be suspect of sticky valves on the problem side or the coil secondary wires. (not sure if you ruled those out depending on how you re-wired the coils for testing) I suggest you also try a compression and leak down test if you haven't just as two more pieces of info to add to the bunch.
 

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Discussion Starter #12 (Edited)
I'm going to check through the electrical end to see if I can find the issue. The compression is good -165 on the left, near 170 on the right. ( taken hot) I did do a leak down test on it recently and it passed, although I dont remember the readings. I would think that a sticking valve would stick more as I ride or it would provide more noise, i.e. backfire through the exhaust or intake or at least some sort of sound of escaping gasses through a small opening. I need to take my meter home from work so that I can get more accurate readings, my elcheapo china central meter at home is not that trustworthy. We'll get it yet. Thanks for all the help that everyone in giving.
 

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Discussion Starter #13
Well finally got around to going through the wiring. I traced the entire ignition circuit checking for resistance and doing a voltage drop test. As far as the voltage drop test, I found a dirty connection at the connector at the ignition switch. After pulling the wires and cleaning the connectors themselves, my voltage drop was down to .04v . When I checked for resistance I found that the secondary side of the left coil was at 7Kohms ( after riding it for about 15 miles). As the bike was cooling down I rechecked the coil several times. It finally leveled of at almost 9Kohms. I think I might have found my issue. The coils are the originals ( with the epoxied in wires). With in the last 1000 miles I have put in new points and condenser, replaced the spark plugs and 5K caps, and added a Hondaman transistorized ignition module. I have an old school analog engine analyzer and rechecked the points and timing. I bypassed the new ignition module to run the bike fully on the points. With all this the bike still had the problem. I think the readings from the left coil might indicate I should get new coils.
I keep reading about guys using XS650 coils, are they pretty comparable to what is on the bike and what mods might I have to do to use them ( i.e. lower resistor caps).
 

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No need for lower resistor caps, in fact with 5K caps you should be using resistor plugs.
The mods for XS650 coils are pretty well documented, simple brackets for conversion
 

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Discussion Starter #15
UPDATE!
Finally got back to the 360 on Sunday morning. Checked the points and timing one more time and went for a ride. (we'll call it "going for broke"riding style) After about 20 miles it started missing again. At about 35 miles it started doing it all the way down to an idle. Finally I came to a stop and it was running on one cylinder. This allowed me to go around the bike and check things while it was doing it (a first! )
I pulled a fiver out of my wallet and held it over the tail pipes. Found the left exhaust valve hanging open after the exhaust stroke and most of the way through the intake stroke. Since Sunday, I pulled another one of my engines apart and freshened the valve train on it. Hopefully Saturday I'll get it swapped out and get a look at what is going on with the offending valve. Thanks for all the great input.
I'll let you know how it works out?
 

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Discussion Starter #16
Well, it didn't work out. Problem is still the same. I went through everything again. I have even removed the plugs (on side at a time), put in other plugs, put removed plugs into boots and ran the bike holding them against the top of the installed plugs. The spark looked fine while making the concern happen. The left side always looks fat. I'm pretty confident that I have good reliable spark, timed spark, and good compression. I wonder if I am not getting good atomization on the left side and fuel might be coming out of the main into the airflow as a liquid instead of a mist. How the hell do I figure that one out? The carbs are sync'd and the problem doesn't occur at idle. So I'm guessing maybe I have a main issue. I'll rip into them again.
 

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I know this is super old, but I was having an issue with my bike for a long while where it would start running worse and worse and all it was was the gas cap vent was clogged. I cleaned that and it has run perfect ever since :)
 

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I understand about the charging system and I don't lug the engine. Most of my bikes are under 400cc so I realize nothing is gained at low rpm. Like I said it is at steady cruise with little load. I can get it to happen at 2k, but the time when I experience it the most is usually at speeds where I am cruising along in slower moving traffic at about 45 mph, @ about 4K rpm in 5th or 6th. I am concerned that it is possibly running too rich on the left side.
1 have a 72 cb350, the left side was cutting out, turned out to be trash/rust partially blocking that side of the petcock
 

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Just catching up on this thread. Man I have been babying my CB360 and never going higher than 6k rpms.
 

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Just catching up on this thread. Man I have been babying my CB360 and never going higher than 6k rpms.
this is kind of a revelation for me as well. i’ve been nervous to push it past 4500 even though it sounds great at the higher rpms i have pushed it to. going to try leaning on her a bit harder tomorrow. thanks!
 
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