Mikuni VM33 carbs have oil dripping

[blackhawk]

I have a 1981 GS1100EX. It has a set of VM33 Smoothbore carbs that have been on the bike for almost 20 years. I ride the bike regularly but not a lot, mostly short trips. The carbs have pods.

On the two carbs on the left, I keep finding oil on the bottom of the bowl on the drain plug. It will drip a single drop every 4 or 5 days. The oil is coming from the air intake side. If you take off the pods, there will be a little oil in the rubber where it slides on to the carb. You can also see a little oil at the end of the carb where the air jets are, which set right next to the pod.

I cannot figure out why this oil is collecting here. I am not 100% sure if it is motor oil or the air filter oil. I really don't see how motor oil could be leaking back through the carbs. The inside of the carb throttle body and intake manifold are spotless with no signs of motor oil. My best theory is that gas vapor is somehow causing the filter oil to dissolve and collect at the inlet.

I can wipe this oil off the carbs, not drive the bike and still find the oil collecting on the drain plug. So, it happens when the bike is not even running. The engine was completely rebuilt less than 400 miles ago. New valves, seat grinding, new valve springs, ported head, bored cylinders, with new pistons/rings.

Any ideas?

 

[Agemax]

hi, it sounds like you are/have over oiled your pod filters. remove them clean them and TEMPORARILY fit them back on dry. ride for a while and see if the drips stop.

if it does then re oil the filters again very lightly.

 

[Crazy_Russian]

where is your breather located?

 

[blackhawk]

Agemax = It has been about 1-1/2 years since I oiled my filters. I don't think that they are over oiled. I just feel like something is going on with my carbs that is letting gas or gas vapors dissolve even the normal amount of filter oil. My pods don't even look oiled at the top any longer. All the filter oil is at the bottom half.

Crazy_Russian - The vent hose from the breather on top of the valve cover is routed down below the carbs. It exits even below the swingarm.

 

[loud et]

Maybe the two carb bowl drainplugs are weeping just the slighest amount of gas and the gas is becoming discoulored by road dirt, dust or your bikes emssions somehow?
Just a thought.

 

[Agemax]

but you say it is the 2 carbs on the left, which will always be lowest when bike is on the kickstand. you also state that "all the oil" is at the bottom of the filters, that is gravity.

i still suggest you take them off and wash them out

 

[blackhawk]

Agemax - I will take them off and let the bike set a while without the pods and see if the oil drips go away. I still don't think over oiling is the root cause though. I have been using these carbs for about 20 years and never seen this problem before. Something is causing the oil to collect via gravity at the bottom of the pods. I am still not ruling out motor oil, but that just seems very, very unlikely.

Here is a little more history on the subject:
Before the engine rebuild, I started seeing pure gas leaking from the bottom of the pods on the #1 (left) side. I adjusted the floats and got the majority of the gas stopped. At this time, I started my engine rebuild. When I put the carbs back on then, I adjusted the floats a second time to the lowest possible specification and got the gas leak to stop completely. But a few weeks after that is when I started to notice the oil collecting on the drain plug. I was running rich, so I took the main and pilot jets down a notch and also adjusted the needle one notch to the lean side. The bike runs well, but in the past month the #1 spark plug has fouled out twice. This just happens when the bike is first cranked. I have owned this bike so long that I can tell right away when one cylinder isn't firing. So, I just think something is going on with this #1 carb especially.

 

[Agemax]

ok then, is it popping or spitting back through the carb(s)? have you rechecked the valve clearances since the rebuild?

 

[blackhawk]

No, there is no spitting or popping. When you are out on the highway the bike runs great.

I adjust the valves after about 300 miles on the new engine. I saw the oil problem before and after the valve adjustment. I only had to adjust about 5 or 6 valves and they were only out by .001 inches.

I will try and post a picture of what the drip looks like this evening.

 

[Agemax]

does the pet cock leak when the engine is off? or do you leave it on prime?

 

[blackhawk]

Petcock does not leak and I never set it on prime.

 

[blackhawk]

I removed the pods, cleaned the oil, and haven't ran my bike. It has been sitting in the garage like this for 36 hours. I checked it tonight and it still has oil that is collecting. See attached picture. I cannot find where it is coming from.

 

[blackhawk]

Here is another pic showing the different places that I find the oil collecting.

 

[GateKeeper]

try this....

clean up all the oil you can see and find, then get some talc powder or baby powder and apply it in the areas you think it's coming from or just all over...and you should see where it's starting from hopefully...

.

 

[koolaid_kid]

Have you examined your cam chain tensionser? It is the most likely source of oil at the back of the engine in the carb area.