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Blood Sweat Tears and Grease => Engines => Topic started by: hillset on Nov 27, 2018, 12:46:06

Title: CB360 right cylinder cold on idle
Post by: hillset on Nov 27, 2018, 12:46:06
Hi Everyone,
     I have a 74 CL360 with mikuni vm28's and a pamco electronic ignition.  Just had the bike in the shop for a couple of weeks (problems getting the pamco to work and had them install the vm28's for me) and when I got the bike back she was up and running again.  The day after I got the bike back I noticed the idle was set pretty high (bike was idling around 3k rpm) so I adjusted the idle screws on the vm28s to about 4 turns out and got the idle down to about 1.2-1.4k rpm (which I believe is spec).

     The problem I'm having now is that the right cylinder is cold on idle, but warms up when I take the bike out for a ride.  At idle, the right cylinder is blowing clear exhaust but its cold and the exhaust pipes don't heat up like the left cylinder.  After riding for about 5 min, the right exhaust warms up, but the idle speed increases to about 2k.

     I've checked compression on both cylinders (right ~ 140, left ~135 but this was without throttle open), verified the timing is correct for left and right cylinders, changed the plugs, and adjusted the cam chain tension.  I've also made sure fuel is adequately flowing from the tank through the petcock to both carbs.  Does anyone have any ideas on what could be going on on the right cylinder?  I know my compression numbers are out of spec and I'm planning on doing a top end rebuild later this winter, but I feel like if the right cylinder is warming up after riding and the left cylinder is running fine, compression shouldn't be causing one cylinder to be cold at idle, especially if that cylinder has better compression than the one that's firing?  Thanks for your help. 
Title: Re: CB360 right cylinder cold on idle
Post by: advCo on Nov 27, 2018, 13:02:34
That compression is fine. Its not accurate anyways since you didn't have the throttle open. Should be no need for a top end rebuild.

The carbs are most likely just out of sync, on VMs you basically just need to pop the filters off and make sure that the slides are opening the same. There are a few different ways to do it, but that's what it sounds like to me.

I would also check for a vacuum leak around the carb boots (use an unlit propane torch or starting fluid etc around the boots) and listen for a surge in RPMs.
Title: Re: CB360 right cylinder cold on idle
Post by: irk miller on Nov 27, 2018, 13:14:03
You didn't mention your air mix.  Where is your air mix on each side?
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 27, 2018, 13:23:24
Thanks for the quick replies everyone.  I'll check to make sure the slides are opening the same on both sides with the popsickle stick trick later today, and I'll try spraying some starter fluid around the carb boot as well.

I haven't touched the air screws on either carb since I got the bike back.  I'll check that as well and make sure they are the same on both sides.  Thanks again for all of the help.
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 27, 2018, 13:42:58
Ok just checked everything:

-Slides are opening at almost exactly the same time.  Right slide is opening a HAIR earlier than the left, but it's like as soon as I see the right side slide move, if I touch the throttle the left side moves too so they're really close.

-I sprayed the right intake boot with starter fluid and did not see the idle increase or hear the engine rev.

-Air screws were at 1.25 on the left and 1.75 on the right.  I assumed this wasn't on purpose and adjusted the right air screw to 1.25 turns out.  Right cylinder is still cold when I was idling.  Anything else I can check? 

Could it be a difference in the internal jetting of the carbs?  I'm thinking my next step would be taking the carbs apart and making sure there isn't anything loose or gummed up in them?
Title: Re: CB360 right cylinder cold on idle
Post by: advCo on Nov 27, 2018, 14:01:01
Make sure you're getting spark on that side.
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 27, 2018, 14:27:29
Yes I have a nice bright spark on the right.  The plug is blacker than on the left side (left side looks brownish-white), and the right side spark is yellow but bright and visible in the sunlight.
Title: Re: CB360 right cylinder cold on idle
Post by: advCo on Nov 27, 2018, 14:54:22
Yes I have a nice bright spark on the right.  The plug is blacker than on the left side (left side looks brownish-white), and the right side spark is yellow but bright and visible in the sunlight.

Is your battery fully charged? You want a nice fat, blue spark.
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 27, 2018, 15:29:09
Yes the battery is fully charged.  I can try putting in new plugs tonight and see how it does with those.  Could fouled plugs cause a cylinder to not fire at idle but fire when riding?
Title: Re: CB360 right cylinder cold on idle
Post by: teazer on Nov 27, 2018, 19:57:35
Sounds like something is not right on that right carb.  The fact that the mechanic set the air screw to 1.75 turns suggests that he had trouble getting it right. There are many possible causes of a cylinder being dead at idel and it could be ignition or it could be carbs.  Others have addressed some of the ignition possibilities, but seems to me to me more likely at this stage to be related to the carbs.

I would pull the carbs and check fuel level and after that I would throw in a pair of new pilot jets, or at least I would check for flow between the two.  You can do that with a can of carb cleaner or WD40.  Spray through one jet and then the other and compare flow rates.  It's not an accurate comparison but will give you an idea if they are close or very different.

I'd repeat that process on the air passages and fuel passages.  One side then the other.

But start with the FUEL levels.
 
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 29, 2018, 00:23:35
Thanks or the help teazer.  I rode the bike around for about 30 min today and pulled the plugs afterwords.  Noticed I had mistakenly put a B6ES plug on the right side and had a B8ES on the left side, which could have caused some of the problem  :o  After the ride the left plug looked pretty black and sooty, so I'm assuming the left cylinder is running rich.

I noticed when I was riding that after about 20 min or so the idle speed dropped.  The bike was idling at 1.2k rpm for the first 10 min, but after riding another 10 min I noticed the bike would become sluggish and die at stoplights if I didn't keep the throttle open a little.  Not sure about what could be causing the idle speed to drop after riding for a while.

When I pulled the carbs, all 4 float heights were within spec, jets were secured and I didn't see any clogs.  I was running 25 pilots so I pulled those and put in 20s since the left plug looked rich.  I didn't have a chance to do a plug chop afterwords so I'll update the post tomorrow when I have a chance.

I tried switching the fuel lines coming off the petcock, and when I did that I noticed the right exhaust warmed up and the left didn't feel as hot.  I know there is fuel coming out of both petcock valves but I'm wondering if there isn't some partial clog on that valve that can be overcome when the throttle is opened.

One last question I was wondering if anyone could answer:  on the vm28's, is the slide supposed to fully close on the air filter side?  So when I take off the air filter and I'm looking into the carb at the slide, should the slide fully occlude my vision of the inside of the carb?  I ask because my idle screws are about 4.5 turns out and there's still about 1/4-1/2" gap between the bottom of the slide and the carb body.  I lowered the slide adjustment screws as low as they'll go and I'm wondering if maybe my throttle is too short?

Sorry for the long post, as always one question leads to a million others.  Thanks again for everyones help, I really appreciate it.
Title: Re: CB360 right cylinder cold on idle
Post by: teazer on Nov 29, 2018, 00:50:53
Let's try to answer some of those.

B6 runs hotter than a B8 and would tend to burn off fuel and should look leaner (cleaner) than the side with the B8.

Plug chops really don't tell us much at less than full load because at lower revs/load, the plugs run much cooler so they don't self clean properly.  Admittedly for a side to side comparison they show that there's a difference, but that doesn't tell us why one side is colder than the other.  It could be jets, or air leaks or ignition advance etc.

The slide has what's known as cutaway on the filter side, so it will always look open on that side.  What matters is the engine side which should close completely and then be cracked open a poofteenth to start with.

(http://kawtriple.com/mraxl/carb/mikuniflow.jpg)

When I suggested checking FUEL level i meant this:

(http://viragotech.com/newtech/Float%20level%20adjusting%20-%20simplified_files/dscn5018.jpg)

Fuel level is what we are trying to set when we mess with floats and even if we get the float height right, sometimes the fuel level is still wrong. It should be 2-4mm below the gasket surface.

You will need an adapter to fit a clear tube to.  That can be achieved with a snowmobile water drain bottom nut like this one
(https://thunderproducts.com/wp-content/uploads/2015/08/Carb_Drain_Kit-tn.jpg)

The item they are selling is a length of hose with a tap in it.  What it's attached to is the bottom nut and that's what you need if your carbs have that large style nut on the bottom.  If you can't find one, I probably have one you can have.

When you looked at the jets, did you spray some WD40 or carb cleaner through them to see if they are similar?  Sometimes a jet is manufactured incorrectly and on old carbs, who knows what has been jammed into the jets to clean them.

Stalling after it has run for a while could be battery not being charged so it goes flat.  Could also be a blocked fuel filler cap or an electrical item breaking down when hot.

When checking fuel flow to a carb, test one side at a time. For reasons I cannot explain, if both sides are open, only one flows most of the time. I think it's because the open pipe has a greater flow rate that the petcock, so it is unable to flow through both open tubes at the same time.

Swapping fuel pipes from one side to the other suggests a flow blockage in one pipe or in the petcock. Empty teh tank and then strip and clean the fuel tap.
Title: Re: CB360 right cylinder cold on idle
Post by: irk miller on Nov 29, 2018, 07:51:57
Is it a single or double tap petcock?
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 29, 2018, 08:54:03
I believe itís a double tap (meaning there is one connection to the gas tank and two outflow taps to the carbs).
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 29, 2018, 09:04:58
Let's try to answer some of those.

B6 runs hotter than a B8 and would tend to burn off fuel and should look leaner (cleaner) than the side with the B8.

Plug chops really don't tell us much at less than full load because at lower revs/load, the plugs run much cooler so they don't self clean properly.  Admittedly for a side to side comparison they show that there's a difference, but that doesn't tell us why one side is colder than the other.  It could be jets, or air leaks or ignition advance etc.

The slide has what's known as cutaway on the filter side, so it will always look open on that side.  What matters is the engine side which should close completely and then be cracked open a poofteenth to start with.

(http://kawtriple.com/mraxl/carb/mikuniflow.jpg)

When I suggested checking FUEL level i meant this:

(http://viragotech.com/newtech/Float%20level%20adjusting%20-%20simplified_files/dscn5018.jpg)

Fuel level is what we are trying to set when we mess with floats and even if we get the float height right, sometimes the fuel level is still wrong. It should be 2-4mm below the gasket surface.

You will need an adapter to fit a clear tube to.  That can be achieved with a snowmobile water drain bottom nut like this one
(https://thunderproducts.com/wp-content/uploads/2015/08/Carb_Drain_Kit-tn.jpg)

The item they are selling is a length of hose with a tap in it.  What it's attached to is the bottom nut and that's what you need if your carbs have that large style nut on the bottom.  If you can't find one, I probably have one you can have.

When you looked at the jets, did you spray some WD40 or carb cleaner through them to see if they are similar?  Sometimes a jet is manufactured incorrectly and on old carbs, who knows what has been jammed into the jets to clean them.

Stalling after it has run for a while could be battery not being charged so it goes flat.  Could also be a blocked fuel filler cap or an electrical item breaking down when hot.

When checking fuel flow to a carb, test one side at a time. For reasons I cannot explain, if both sides are open, only one flows most of the time. I think it's because the open pipe has a greater flow rate that the petcock, so it is unable to flow through both open tubes at the same time.

Swapping fuel pipes from one side to the other suggests a flow blockage in one pipe or in the petcock. Empty teh tank and then strip and clean the fuel tap.
.

This is so helpful thank you so much.  I saw people checking the fuel level like that but I didnít think it was possible since I have one of those large nuts on the bottom of my carbs.  Do you know where I can order one of those adapters?  Iíll do a quick google search for it today and try to get one ordered. 

Also that makes total sense about the b6 vs the b8.  The b6 plug actually looked pretty good, nice brown color on it without much black but I assumed that was because it wasnít firing as much as the left side.  I just got a new set of plugs so Iíll try those out today.

Iím going to drain the tank today and clean the petcock just to make sure thereís no clog there and eliminate that variable.  I donít think the battery is the problem since I just put in a new battery and reg/rect from sparck moto last week.  Could the stalling after itís been running for a while be related to the pamco ignition?

And I did spray some wd40 through the jets to make sure they were clean.  They looked fairly equal to me, but admittedly it was difficult to really tell.

Iíll clean the petcock today, check the charge on the battery, try the new spark plugs, and order those plugs for the carbs.  Thanks again everyone for all of your help, I really appreciate it.
Title: Re: CB360 right cylinder cold on idle
Post by: advCo on Nov 29, 2018, 09:39:29
It would be worthwhile (if you haven't already) to check that your battery is in fact charging properly, despite the fact that you installed a new RR. A simple way is to put a multimeter on your battery on 10x V DC, start the bike and check the voltage at idle and then again at ~3k+ RPM. These Honda twins are notorious for poor charging under 3k RPM. You should see somewhere around 13-13.5v at 3k+ RPM.
Title: Re: CB360 right cylinder cold on idle
Post by: teazer on Nov 29, 2018, 10:36:15
+1 to that last post. 
Title: Re: CB360 right cylinder cold on idle
Post by: irk miller on Nov 29, 2018, 11:23:30
And just to add- I have no idea why it is, but these things fire cold on one side when they are not charged.  Though, if your issue moved from one side to the other by just changing the fuel lines then that is a pretty good indicator.
Title: Re: CB360 right cylinder cold on idle
Post by: hillset on Nov 30, 2018, 15:06:59
Hi Everyone,
     Just wanted to drop an update.  I charged the battery last night and this morning when I fired her up she was idling on both cylinders.  I took the bike out for about an hour and I had no problems, idle was consistent and she was revving pretty well through all gears.  I think the issue was the battery wasn't fully charged.  After getting a full charge on the battery tender last night she was idling well on both cylinders this morning and the battery showed ~12.4v at idle up to 13.4v at 3k rpm.

Thanks for everyone's help, I can't tell you guys how much I appreciate everything!
Title: Re: CB360 right cylinder cold on idle
Post by: Sonreir on Nov 30, 2018, 15:22:33
Every time. Those Honda twins are very picky about batteries!
Title: Re: CB360 right cylinder cold on idle
Post by: teazer on Nov 30, 2018, 16:22:44
We all love a happy ending.  At sometime, it would be a good idea to check fuel levels, but if it's running fine, you can always do that when you give it a spring complete service so that you are ready for the summer riding season.