Cleaning carburettors

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Cleaning carburettors

Postby Freddy » 28 May 2018, 02:15

As a constant recurring theme is blocked up carburetors thought it worth sticking down a few thoughts on the subject.

On infrequently used bikes, or bikes that will not be used for a period of time, the carburetors should be drained before putting the bike away. It is the fuel evaporating out of the bowls as the engine sits idle that is the main cause of the problem. The fuel evaporates away leaving behind residues which set rock hard. This buildup continues each time till it completely blocks fine jets, sticks float valves etc. Ways to drain the carbies ....
1. Open the drain screws in the bottom of the four float bowls to drain them,
2. Disconnect the vacuum pipe at the back of the fuel tap and let the engine idle till it stops from running out of fuel (remember to turn off the ignition switch)
3. Fit a manual fuel tap, turn it to off, and let the engine idle till it stops.

Draining the carbies won't 100% eliminate the problem, but it will extend the interval between potential problems by a massive amount.

Cleaning carby jets. This buildup sets so hard that there is no guarantee that chemical or ultra sonic cleaners will remove it from inside the jets. Mechanical removal is the only sure way. That is easily done with main jets as they are large enough to run a piece of fine nylon fishing line through to scrape this crap off the internal walls of the jet. But the #35 pilot jets are so small that even the smallest diameter fishing line is near impossible to thread through. Just because you can see light through the jet if held up to the sun is no guarantee there is not buildup on the walls making the jet effectively a smaller size. So really replacement with new genuine Keihin pilot jets, easily obtained at about $5 each is the best solution.
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Re: Cleaning carburettors

Postby shaunf » 16 Aug 2018, 09:12

Thanks for the advice Freddy, mine could be due a clean, I take it we cant use the stock fuel tap?
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Re: Cleaning carburettors

Postby Freddy » 16 Aug 2018, 10:59

shaunf wrote:Thanks for the advice Freddy, mine could be due a clean, I take it we cant use the stock fuel tap?


You can if your prepared to manually drain all 4 carbies using the difficult to reach drain screws in the bottom of carbies. If I was going to do that I'd make up or source a long thin T handle with the appropriate size Allan key head so you can easily get at all 4 from one side (this is a 750 I'm talking about).

Alternatively replace the vacuum operated tap with a manual off one, and just run the carbies dry with the engine. I own a little XT250 that is sometimes infrequently used so I always drain the carby this way. I know how far to turn the fuel off from home to get me there, and by the time I've taken my helmet and gloves off (with the bike idling in neutral) it cuts out.
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Re: Cleaning carburettors

Postby David Richard » 16 Aug 2018, 19:37

hi shaunf ,here is what I do sometimes with mine if I know it wont be used for a while ,im able to park about quarter of a mile away from home I pull off the vacuum pipe off the back of the tap ,shoot down the road which is dead straight into my road then it runs out ,you need to see how far you will need its not easy ,but doable ,its a faf putting the pipe on ,im sure you could extend the vacuum pipe and devise and put a small valve in under the tank to make it easier ,good luck david
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Re: Cleaning carburettors

Postby Swampy » 17 Aug 2018, 09:11

I drain the tank and carbs each year when I put the bike away into its VacBag. A small length of hose with a bolt & jubilee clip to cap one end of the pipe off, the other end onto the petcock, run the engine until it runs dry, then a long screwdriver with the correct size hex head to drain the carbs, I have never had a problem with reaching any of the drain screws at all.
But what I have noticed is when I recommission the bike in the spring, I sometimes get a fuel leakage from the carbs, so far every time its stopped after 5mins or so, chatting about this at Reading in July with eddie I think it was, apparently its the rubbers that dry out.
Cant win either way really :o
Swamps :)
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Re: Cleaning carburettors

Postby Ivor » 04 Sep 2018, 13:25

just took my carb bowls off they were full of gunk , all clean now :)
i hate being bipolar its awesome :/
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