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Author Topic: CB360 right cylinder cold on idle  (Read 1038 times)

Offline hillset

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Re: CB360 right cylinder cold on idle
« Reply #10 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.
« Last Edit: Nov 29, 2018, 00:25:28 by hillset »

Offline teazer

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Re: CB360 right cylinder cold on idle
« Reply #11 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.



When I suggested checking FUEL level i meant this:



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


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.
« Last Edit: Nov 29, 2018, 00:53:02 by teazer »

Offline irk miller

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Re: CB360 right cylinder cold on idle
« Reply #12 on: Nov 29, 2018, 07:51:57 »
Is it a single or double tap petcock?

Offline hillset

  • Posts: 91
Re: CB360 right cylinder cold on idle
« Reply #13 on: Nov 29, 2018, 08:54:03 »
I believe it’s a double tap (meaning there is one connection to the gas tank and two outflow taps to the carbs).

Offline hillset

  • Posts: 91
Re: CB360 right cylinder cold on idle
« Reply #14 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.



When I suggested checking FUEL level i meant this:



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


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 didn’t 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?  I’ll 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 wasn’t firing as much as the left side.  I just got a new set of plugs so I’ll try those out today.

I’m going to drain the tank today and clean the petcock just to make sure there’s no clog there and eliminate that variable.  I don’t 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 it’s 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.

I’ll 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.

Offline advCo

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Re: CB360 right cylinder cold on idle
« Reply #15 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.

Offline teazer

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Re: CB360 right cylinder cold on idle
« Reply #16 on: Nov 29, 2018, 10:36:15 »
+1 to that last post. 

Offline irk miller

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Re: CB360 right cylinder cold on idle
« Reply #17 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.

Offline hillset

  • Posts: 91
Re: CB360 right cylinder cold on idle
« Reply #18 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!

Offline Sonreir

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Re: CB360 right cylinder cold on idle
« Reply #19 on: Nov 30, 2018, 15:22:33 »
Every time. Those Honda twins are very picky about batteries!
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