76 cb360 idles high

I am relatively new to motorcycles, I picked up a cb360 last summer, I recently brought it in to the shop for a tune up since I am not very knowledgeable able. I noticed it idled higher when I got it back (between 2-3000 rpms). After riding for awhile when I am at stop lights and such it idles around 4000 rpms. I have tried turning the idle lock screw as it says in the service manual but no mater how much I turn it there is no effect. Any advice?


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I had the same problem recently. Could be your carbs out of sync or an air leak at the intake manifolds.

Start it up and spray some WD-40 around the entire joint of the carb boot to the head, and the carb boot to the carb, on both sides. If your idle surges, you have an air leak.

If not, that points to carbs. You will need a manometer and the carb sync tool to accurately sync the carbs. I use this kit and it works quite well http://www.common-motor.com/honda-360-carburetor-synchronization

You can also pull the carbs off and "bench sync" them. The sync screw is between the two carbs. It has a flathead slotted head on it, with an 8mm (i think) nut on it. This screw controls the difference between how open your throttle plates are at 'closed' position. To bench sync, open the idle speed screw (big screw on the side with ridges for your fingers) until you can get a straightened paperclip slid underneath the throttle plate on one side. Then, use sync screw to make them match. The sync screw only changes one side, so make note of which side that is, and do the other one first. The paperclip should feel exactly the same coming in and out of underneath the plates. It should just barely drag, so as not to damage the plates or carb body. When they are close as you can get them, back the idle speed screw all the way out so the plates are just about closed. There is a stop screw that moves when you twist the idle speed screw, make sure it is just barely touching and not opening the throttle plates at all. Put the carbs back on, and it should idle better. Clear as mud?

A lot of shops don't know what the hell they are doing when it comes to older motorcycles, so beware. The 360 should idle at 1200 RPM. You shouldn't be riding it when its idling at 3-4k.

Thanks, would an air leak or out of sync carbs cause the idle speed screw to have no effect when turning it? I will check for an air leak when I get home.


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Yeah. Backing the screw out as much as you can only closes the throttle plates, so if you have too much air coming from somewhere after the throttle plates (i.e. intake manifold) you can close them as much as you can and you will still have a bad mix. If you look closely at the linkage for the screw you will see that there is a tiny threaded and that goes in and out as you turn the screw. All it does is essentially open your throttle plates a very slight amount to allow for more mix to reach the cylinders.

On the other hand, if you screw that screw in to the point where it contacts the throttle plate and starts opening it, regardless of an air leak, your idle will raise.

Cam chain. Not fully versed on the 360 but all other Hondas i have worked on also needed accurate cam chain tension. get a manual or download one. Don;t piss with cabs until you know the Cam is set right.

Sounds like a throttle cable binding somewhere or not sitting right. Check where the cable mounts on the carbs. See if both carbs are closed evenly while on the bike before you pull them out and bench synch them. Bench synch is a must, but also make sure the cables are ok. This has happened to me before after working on something else and then the bike was raving higher as soon as I started the bike. Turned out one of the cables had pulled out of the ferrules and caused it to pull on the throttle .


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TheCoffeeGuy said:

Cam chain. Not fully versed on the 360 but all other Hondas i have worked on also needed accurate cam chain tension. get a manual or download one. Don;t piss with cabs until you know the Cam is set right.

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Yeah, You should really set your cam chain tension, adjust your tappet clearances and set the timing too. Then move on to carbs.

+1 on the manual, don't use a haynes or clymer there are plenty of links around for the factory service manual for the 360

Thanks everyone for your advice! I will begin checking things off the list today


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Update. Just recently had a chance to take the carbs apart and clean the jets. Ordered new intake manifolds and carb bowl gaskets. Hopefully I'll have it together this weekend and we will see if the problem is fixed. Just noticed one of my valve caps has a pretty wide crack, would that cause an air leak?


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I was struggling with high idle back when I got my CB360. My problem was the leak in the intake boot area and it solved with new boots. As mentioned before, do the entire cam chain-tappets-points-timing dance as outlined in the manual while your working on your bike.

dantyler92 said:

Update. Just recently had a chance to take the carbs apart and clean the jets. Ordered new intake manifolds and carb bowl gaskets. Hopefully I'll have it together this weekend and we will see if the problem is fixed. Just noticed one of my valve caps has a pretty wide crack, would that cause an air leak?

Click to expand...

No, high idle condition would be caused by too much air entering the combustion chamber. The rocker box is isolated from the combustion chamber so it wouldn't affect it.

The idle issue is fixed! Cleaned the carb and did a bench sync, as well as new intake manifolds. Not sure what did the trick but it works.

Except now it's pissing out oil from under the crank case and now I'm stranded on the side of the road


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Swap out your intake boots next time you have the carbs off. If it still idles fine you can sell one set. It's probably not the manifolds tbh they have to be pretty chewed up or noticeably brittle and cracked to leak air.

Did you remember to tighten up your drain plug man?!

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I was thinking I would try doing that in the next week or so.
Haha yep the drain plug is tight! Had to double check because that's a mistake I would make


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First thing I would have done is get back to the shop and complain. (well, actually I wouldn't, I haven't had a bike in a dealers workshop since 1977)
A few (3~4) years later I ran workshop and did all my own stuff 'after hours' 8)
They screwed something up, maybe adjusted throttle cables too tight, didn't do carb sync properly (probable because Honda haven't made sync adapters for ??years) Could have left a vacuum plug out of carbs, throttle shaft plugs could be missing plus of course, everything else that's been mentioned.
The intake manifolds can be hard enough not to seal and cause air leak. They can also have a broken gasket or 'O' ring
Remove the sprocket cover on left side, check gearchange shaft and clutch pushrod oil seal, if you have blocked or trapped/crushed engine breather hose the crankcase pressure can push seals out of case