Sticky Carb

After a 2 years of time off I got my 1970 750 Commando S running. I installed a new Mikuni single carb. After less than 100 miles of running the carb started to stick. First it was slow to return to idle then it become hard to open the throttle. Last night I took it off and opened it up. The slide was covered in a brown sticky goo as was the inside of the carb and the intake manifold. I cleaned it up and it ran fine with good throttle response. Also the left cylinder smokes on start up for about a 1/2 minute. I looked at the Amals that came off and they are clean as was the intakes. My guess is the left intake valve guide seal is shot probably from sitting. Valve gaps are correct. I am going to take my compression tester home tonight and check that. Looks like the head is coming off for some service. Any other thoughts out there would be welcome.

Goo is probably as the gas is eating your fiberglass tank.

I would think goo in the carb would be from fuel.

maylar said:

I would think goo in the carb would be from fuel.

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No, goop is from fuel, goo is from gas eating the fibreglass. :wink:

Sorry to hear that,but is probably the fuel ( ethonol ) eating the resin.I had it happen to two tanks in the last year. Almost lost an engine.It gums the slides first,then the valve guides stick.The bike will run lean and the pipes probably discolour on you if you keep riding it. I used caswell tank lining on mine.
Bruce

Thanks for the replys and advice.
The tank liner is on order. Once I have the tank done and put in fresh fuel and some cleaner like Sea Foam do you think the smoking will clear up or should I pull the head to clean the valves and guides before I run it?

I took off the carbs on one bike,brought the piston up to close the valves on that side.I then used spray nine,or any other good cleaner and sprayed it into the intake port and let soak.I used small rags and wiped out the port as clean as I could. Came out spotless. I then did the same on the other side.You can see if there is any buildup on the guide before you start.I took the head off the first bike because I had just done the engine before the problem started.It had 100 miles on it before it started acting up.I took out the valves to check ,but everything was ok. I would suggest if it just started to do the cleaning only. It of coarse is your decision.When you get the caswell liner let me know and I will walk you through it.We have done a couple of them now.The first bike belonged to a friend and he opted not to remove the head,but to try the cleaning.It worked and he has put 800 miles on since.
Bruce Chessell

Just a quick note. If you suspect the valve seals take the head off to be sure. Winter is almost here anyway.The 2 bikes I was talking about had little mileage since rebuilds,so we knew the valve seals were ok,besides I had just done the complete engine rebuild on the one and it was too risky.If it were me I would strip it according to your earlier post.
Bruce

I am tempted to try the clean it route as the goo in the carb came off easy with carb cleaner. What is spray nine? Another friend recomended butyl cellulose injector cleaner.

Hi Boz:
It is just a cleaner we have here in Canada.Walmart has it.I use it to clean the head on my bike everytime I wash it.It lifts the oil right out of aluminum. It must be used cold.Gunk or any other good auto cleaning spray should lift it.My ports were plugged with the brown goo also.It must be the resin mixed with the fuel.That is what leans the carb out.Be sure to let me know when you get the caswell .It is the only thing that works.
Bruce

bchessell said:

Hi Boz:
It is just a cleaner we have here in Canada.Walmart has it.I use it to clean the head on my bike everytime I wash it.It lifts the oil right out of aluminum. It must be used cold.Gunk or any other good auto cleaning spray should lift it.My ports were plugged with the brown goo also.It must be the resin mixed with the fuel.That is what leans the carb out.Be sure to let me know when you get the caswell .It is the only thing that works.
Bruce

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Spray 9 is great stuff. It's like Windex on steroids.

If your left cylinder is smoking at idle, are you idling on the center stand or on the side stand?

If you let the bike run on its side stand, oil pools up around the exhaust valve, as the drain is in the middle of the head. The oil level will actually fill past the top of the valve guide before it reaches the drain hole, and you have instant smoking cylinder.