The mikuni carb on my 850 becomes sticky in the cold or wet, ie wet greasy cold corner, button off & find out you are still pulling 4k. That makes the ring piece stick to the seat quite well. The other weekend while cruising along aboring streetch of road at 70mph @4000rpm I noticed the bike started to accelerate. It was like the slide was sucked against the carb body and moving up.A quick blip on the throttle and it was back to normal .How come when you put a jap carb on a british bike it behaves british. the slide is brand new. Any suggestion for afix,maybe apiece of front fork spring and the grip &wrists of a gorilla might help.
sticky mikuni
- Thread starter splatt
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splatt said:
i had the same problem - are you over lubing your throttle cable and the excess lub getting into the carb body (i was, and the crap gummed up slide movement )
i ended up using the stock mikuni spring and fit one of the smaller amal carb springs inside of it (so 2 spring on the slide) - makes the throttle pull a bit harder (not to bad through) and i haven't had the problem since then
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Mine has started doing the same thing recently. In my case I'm pretty sure that it's gumming up due to not being used enough. It's sat for periods of up to a month and I think gas residue gums up the slide. It doesn't seem to happen if I use it more often. ( there's a message there.)
I had the same kind of issue when exiting a freeway. The carb stuck open until I "blipped" it. Turns out the whole intake system was gummed up with a brown residue from the fiberglass tank sealer. If you pull the carb and manifold off make sure that you put lock tight on the inner allen head bolts for the manifold. Don't ask how I learned about that! 
:idea:
:idea:mikie3117 said:I had the same kind of issue when exiting a freeway. The carb stuck open until I "blipped" it. Turns out the whole intake system was gummed up with a brown residue from the fiberglass tank sealer. If you pull the carb and manifold off make sure that you put lock tight on the inner allen head bolts for the manifold. Don't ask how I learned about that!
Do you recall what brand of sealer you used?
Interestingly I have had a similar problem but only when it was particularly hot (not in Scotland obviously - while on holiday!) When I stripped the carb there was a sticky residue around the bottom of the slide, possibly from sludge in the second hand tank I had fitted just before leaving. The odd thing is that with the engine off, the slide could clearly be heard snapping shut. Cleaning the slide & body and stretching the spring seemed to cure it. Later the next day, when it was really hot again, the sticking returned. I found that if I left plenty of slack in the cable that it behaved perfectly. At home with the cable adjusted exactly as it had been there is no sticking – I am convinced that the heat was playing some part.
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I was on the same trip with David and experienced similar problems (and a host of others I won't bore you with) The double spring thing (using the old Amal spring on the inside of the Mikuni) is a sound idea, my MK3 Commando has that mod already although stupidly I left for a 4000 mile trip without modding the carb on the Commando I took.
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Gino Rondelli said:I left for a 4000 mile trip without modding the carb on the Commando I took.
4000 miles - wow -now that must be a tale of roadside repairs?
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If you have a fiberglass gas tank that has not been coated with a two part epoxy sealer, the new gas will cause the fiberglass to breakdown and you will get a coating on the slide and inards of the carb that will translate into a sticky throttle. I guess there are some other carb spring related problems but I know for a fact that the fiberglass tank scenario occurs.
I have been following various threads discussing fuel additives attacking fibreglass, but that doesn't seem to be a problem in the UK yet - different method of boosting the Octane rating perhaps. I normally run an untreated fibreglass Roadster tank and there is no sign of any attack. Have any of our European members noticed this problem?
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DavidT said:
the fiberglass eating additive is ethanol - in the majority of the US its 10%- you know us wise Americans - spend a butt load of money to reduce our dependence on foreign oil by the addition of ETOH to our fuel - even though the cost of producing the ethanol is way more expensive ( and polluting) than just using it straight up not to mention the impact on global food/corn cost
more importantly though - i had to buy a new alloy tank :lol:
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mikegray660 said:
Ethanol contains less energy/volume than gasoline and is hydrophilic, too.
This means our mileage goes down a little bit and we get water in our fuel.
The 10% mandate is federal law - we are expected to use at least 9,000,000,000 GALLONS of ethanol this year.
Ethanol is produced in the US primarily from corn, driving up the worldwide cost of cereal grains, and we use more energy to produce this than we get back.
On top of that, we subsidize ethanol production to lower the cost to the refineries, and place tariffs on imported ethanol. Brazil produces ethanol primarily from sugar cane stalks after pressing, and could sell the product to us for less than we produced corn ethanol, but this is considered not in our interests.
Fitted the spring out of an amal and it seemed to fix the problem,although I did notice the elevator stopped short of going all the way to the top.The mikuni spring was coil binding about 4mm short.We are just starting to get ethanol blend fuel here now,when we went unleaded 10 year or so ago the crap they blended dissolved older rubber hoses,we had cortinas & escorts burnihg everywhere.
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