#3 cylinder not getting hot at idle

[Droneh8tr]

83 VR

So I'm idling in the back yard looking for leaks and such.. I hear that the engine doesn't quite sound right. I feel the exhaust pipes and find that #3 isn't hot... at all.

 

Compression is 160, 160, 168, 160..

Good spark..

I dribbled a little gas into the carb and it clearly ignited.

 

I'm thinking it could be an obstructed jet..

So my question is, do I have to remove the carb. and clean, or is their something simpler I could try? Like maybe remove the diaphragm and blow some air somewhere.

 

I meant to also mention, Seafoam didn't seem to make a difference.

Edited September 25, 2014 by Droneh8tr
Forgot important point

[Neil86]

1. Any evidence of the white sludge that was inside the airbox (in another thread)

being in the air inlet of that carb...there are air bleeds that can plug with something like that.

 

2. Is that carb drawing proper vacuum at idle to allow the idle circuit to operate.

(carb synch).

 

3. Is the YICS system in service or removed? (Possible vacuum leak, leaned out at idle, misfire)

No vacuum leak on synch cap etc?

[Droneh8tr]

1. Any evidence of the white sludge that was inside the airbox (in another thread)

being in the air inlet of that carb...there are air bleeds that can plug with something like that.

 

2. Is that carb drawing proper vacuum at idle to allow the idle circuit to operate.

(carb synch).

 

3. Is the YICS system in service or removed? (Possible vacuum leak, leaned out at idle, misfire)

No vacuum leak on synch cap etc?

 

Wow.. Great questions. I wasn't expecting any of them..

 

1. No whitish sludge evident in the inlet of that carb.

2. I did carb sync the carbs 1 month ago. But, didn't do it upon this issue.

3. The YICS is removed. The plugs are all still in good shape.

[Karaboo]

Try the drain screw to see if the float is filling the bowl. Needle and seat may be stuck.

[Venturous Randy]

When you did the carb sync, did you first check to make sure there were no vacuum leaks associated with this carb. With a bad vacuum leak, you can still be way off on your carb sync and still get good numbers.

RandyA

[flyday58]

You said gas dribbled in the carb "clearly" ignited but I'd remove the plug and make sure it's firing anyway. Also I'd make sure I had a good charge on the battery, as idling could take it down to the point that plugs quit firing.

[rbig1]

The fuel adjustment screw was jammed into the seat on mine would pick up cylinder around 2400. Look in adjustment hole make sure the needle is not destroyed should be straight screwdriver slot.

[Droneh8tr]

Try the drain screw to see if the float is filling the bowl. Needle and seat may be stuck.

Oh yeah, definitely fuel in the bowl. I drained it then refilled.

 

When you did the carb sync, did you first check to make sure there were no vacuum leaks associated with this carb. With a bad vacuum leak, you can still be way off on your carb sync and still get good numbers.

RandyA

RandyA, how do I check to see if THIS carb has a vacuum leak other than doing a carb sync.?

 

 

NOTE TO ALL

I may have found the problem. The YICS plug has a tear on top.. Its a single tear across the top like a knife was drug across it.. I'll replace it tomorrow morning and see if the exhaust starts heating up at idle. I found it with a Ryobi inspection camera. I couldnt see it with my flashlight and mirror.

[BlueSky]

Put some Gumout for high mileage engines in the gas and see what that does. It's much more powerful than Seafoam. Available at Walmart. Chevron Techron is the same stuff. When I first bought my Kawa ZN700, it had been sitting many years with only 1k miles on it. This was 5 yrs ago. It was running ragged on 3 cylinders when I fist got it. I put a full bottle of Valvoline Complete Fuel System Cleaner in a 3.5 gallon tank and ran it through. Afterwards it ran great on 3 cylinders. Changing the plugs got the 4th cylinder running. It's been running great ever since! The Valvoline stuff disappeared from the shelves but the active ingredient in it was the same as Gumout and Techron to the best of my knowledge.

[Neil86]

After replacing plug, check vacuum and resynch of course...

[Venturous Randy]

 

RandyA, how do I check to see if THIS carb has a vacuum leak other than doing a carb sync.?

 

 

NOTE TO ALL

I may have found the problem. The YICS plug has a tear on top.. Its a single tear across the top like a knife was drug across it.. I'll replace it tomorrow morning and see if the exhaust starts heating up at idle. I found it with a Ryobi inspection camera. I couldnt see it with my flashlight and mirror.

 

Yep, the YICS being open will definitely do what you are describing. To check for a vacuum leak, get a can of starter fluid and spray it around the carbs and manifolds while bike is running. If you have a leak, you will know it as the engine will rev some or die.

Here is you a good fix on plugging these ports:

http://www.venturerider.org/forum/showthread.php?t=86100&highlight=Plugging+YICS+ports

RandyA