CB360 stuttering idle left cylinder... or banging my head against the wall.

[PK]

OK... gonna see if anyone has any idea what to try next.

76 CB360
Stock Keihin 754A carbs - soaked, cleaned, reassembled. Floats set to about 17mm. Diaphragms in good shape. Stock Jetting
New Points and condensers - gapped to .330mm Timing set static and checked with timing gun.
Tappets set to spec .002mm intake .003 exaust
Stock Airbox (yes filters are clean)
Petcock fully disassembled and cleaned. Tank cleaned and rust free. New gas. New fuel lines.
Spark Plugs cleaned and gapped to .035in
cables trimmed 1/2" and boots reapplied.
Compression 170 both cylinders
Pipes are emgo shortys (Stock were rusted shells)

Bike starts easy. Surges at start then settles to idle. Right cylinder idles fine. Left side wavers up and down. Bike idles between 1000 and 2200. Sort of pulsates as though vacuum or fuel is pulsating. Checked intake boots (wd40 spray) and no visible leaks and no change in rpms. All seems tight and sealed. Slides move freely in carb. It runs well when hitting the road, accelerates clean and no backfire or stutter. The exhaust on the right is steady and strong, but the left sputters between weak and matching the right. This follows the pulsating idle. I did bench sync the carbs. I have one vacuum gauge and an adapter I made by threading a plastic airhose nozzle with a tap and die set. It fits airtight in the vacuum port. I am using one of those Harbor Freight vacuum gages. Read about 12 on the right and about 10.5-11 on the left. I have tried to sync them (switching the gauge between sides) but the surging idle makes this almost impossible.

Whew!!! OK... the question. Anyone have any idea where I can try next??? I am chasing my tail trying to figure this out. I am sooooo damn close, but just cant get a smooth idle on both cylinders. Tried an inline test light for the spark (between plug and cable) and seem to be getting good even spark on both. Bad coils??? Any suggestions???

 

[mydlyfkryzis]

Float spec is 18.5 MM...Your fuel level may be a little high...that would make it richer...

By another HF vacuum gauge, 2 make it easier...It would be worth it in the long run.

Also, motion pro makes a great screwdriver/wrench combo for syncing...speeds everything up immensely.

http://www.amazon.com/Motion-Pro-08-0022-Carburetor-Adjustable/dp/B000GTVOGY/ref=sr_1_1?ie=UTF8&qid=1367434940&sr=8-1&keywords=motion+pro+carburetor+adjusting+tool

Shorty pipes don't help anything except loudness. The 360 engine likes longer pipes...But setup the carbs right before anything else.

 

[Sonreir]

Try hooking up some jumper cables from another battery to boost the available current. A single cylinder stuttering (especially at low RPM) is a classic sign of imminent battery failure on the Honda 350s and 360.

If the problem goes away, it's time for a new battery.

 

[LWRDRTRCK]

i had this with my cb360 i ended up ripping the diaphragm in the carb, super glued it back together and works to this day

 

[PK]

Float spec is 18.5 MM...Your fuel level may be a little high...that would make it richer...

By another HF vacuum gauge, 2 make it easier...It would be worth it in the long run.

Also, motion pro makes a great screwdriver/wrench combo for syncing...speeds everything up immensely.

http://www.amazon.com/Motion-Pro-08-0022-Carburetor-Adjustable/dp/B000GTVOGY/ref=sr_1_1?ie=UTF8&qid=1367434940&sr=8-1&keywords=motion+pro+carburetor+adjusting+tool

Shorty pipes don't help anything except loudness. The 360 engine likes longer pipes...But setup the carbs right before anything else.

Oh I would love to sync the carbs right... but when the idle is sweeping from 1000 to 2200 its like trying to change a tire on a moving car!!! I will try lowering the floats, but at idle I doubt that's the issue. That tool would definitely make it easier to sync!!

 

[PK]

Try hooking up some jumper cables from another battery to boost the available current. A single cylinder stuttering (especially at low RPM) is a classic sign of imminent battery failure on the Honda 350s and 360.

If the problem goes away, it's time for a new battery.

Thanks!! I'll give it a shot, but the battery is brand spanking new and is holding a charge well.

 

[PK]

Well... put in some new plugs (had them) and no difference there. Figured I'd eliminate them from the equation. When you open it up then come to a stop the rpms do surge a bit and hang before dropping back to idle. When it idles it doesn't as much stutter as it does pulse. Almost like you were slightly giving and releasing throttle. The exhaust on the left is not a smooth even purr though. It isn't popping, but kind of gasping and then good, then gasping again. That seems to follow the pulsing rpms. Do the vacuum slides come in to play at all during idle? The manual seems to make it sound like the idle circuit doesn't really use them and the main circuit kicks in around 3000 rpm. Am I right in this?? Just Trying to narrow down the problem.

Thanks for all the feedback so far. This bike is damn fun to ride when you open it up!!

 

[Sonreir]

Manual is correct. Bike will idle just fine if you pull the slides out completely (assuming no other issues, of course).

Any difference with choke on or off?

Hunting idle (revs going up and down intermittently) is often a sign of an air leak, too.

 

[PK]

With choke on it revs way up. I did try spraying the intake manifold boots really well with wd40 and didn't notice any change. Visual inspection they look good too. Still flexible and not dried out or cracked. It does act like a vacuum problem though, yet it also seems like an electrical issue. Like I said timing is dead on, points are right and are new. Condensers are new. Spark plug tester is showing no problems. Anywhere else they could be getting a vacuum leak or any other testing methods? How about the change in exhaust pressure with the drop in rpms? does that point to anything? I have checked the tappets multiple times but I can always check them again... grrrrrrr

 

[PK]

Getting ready to try some black magic Voodoo on the damn thing... maybe shaking a chicken at it would help. :-\

 

[VonYinzer]

It may do absolutly nothing... But pull your spark plug boots off the wires (they'll screw off). Cut about a 1/2" off of each and screw the caps back on (making sure they are in the "wire" not the insulation. If they're original coils, the ends of thw wire break down and can cause intermittent spark.

 

[PK]

Yup already did that with the plug boots. What impact are the coils gonna have at idle? Could that be a problem? Needs new coils maybe? They seem fine when driving.

 

[born2expire]

Float spec is 18.5 MM...Your fuel level may be a little high...that would make it richer...

By another HF vacuum gauge, 2 make it easier...It would be worth it in the long run.

Also, motion pro makes a great screwdriver/wrench combo for syncing...speeds everything up immensely.


Have you used this tool on a CB360 before? it says on their site it fits an 8mm nut but the one on my carb is a 7mm which isnt a big deal i could make it work or shim it a bit. but i would feel better ordering it knowing it was compatible

http://www.amazon.com/Motion-Pro-08-0022-Carburetor-Adjustable/dp/B000GTVOGY/ref=sr_1_1?ie=UTF8&qid=1367434940&sr=8-1&keywords=motion+pro+carburetor+adjusting+tool

Shorty pipes don't help anything except loudness. The 360 engine likes longer pipes...But setup the carbs right before anything else.

 

[mydlyfkryzis]

Borntoexpire: Are you sure you have a 7mm nut. Mine is definitely 8mm. I have a 1976 CB360 ..see my build

I used it a few days ago to finish syncing my carbs.

If you do have a 7mm, so, try finding an eight MM nut that fits.

The tool makes it easy once you find your sync point to tighten the lock nut without ruining the sync.

It really makes tinkering with the sync much easier.

 

[born2expire]

im almost positive but ill double check today and see. i need that thing up and running. i've had it for 2 years and have been dragging my feet and now with a baby on the way i need to get it done before i really dont have time.