Sticky Carburator

I had used a 36mm Mikuni on my MK111 for two years without any issue until last year. My problem now is a sticky residue being left on the forward face of the slide and carb body causing the slide to stick . If you look in the carb manifold you will notice the sticky brownish substance . The only change from the previous years was a fibreglass Interstate tank which i had refurbished using POR 15. The POR had cured for over 3 weeks before any gas was added to the tank .

Looking for ideas . Thanks in advance.

Try changing gas brands, they are not all equal. My own fiberglass tank was eaten by gas from Petro Canada but was fine using Esso. I had not coated it so it was vulnerable to the additives in modern fuels.

I plan on using POR15 on the fiberglass tank on my project, I just hope it goes well. I received good feedback on POR15 from others with the same problem, could it be some spots were missed during the treatment of your tank?

Jean

I posted the same question 6 months back mine would just stick in the wet. The replies that come back suggested that the modern gases were dissolving the fiberglass,with the ethanol blends being very harsh, or it could just be fuel residue from lack of use.

That residue is the result of the ethanol in the gas dissolving some of the resin from the fiberglass. It ends up leaving deposits on the carb slides, intake runners and valves. These deposits are usually dark brown to black, looking almost like burnt sugar, and don't readily dissolve in carb cleaner. Soaking in denatured alcohol or MEK seems to loosen it up enough to clean.

I've seen this on a couple of bikes, and I replaced my 'glass tank with a pakistani steel tank, because the Caswell sealer didn't work.

US Congress mandated 10% ethanol last year, in an effort to reduce US dependence on imported oil. Talk about poorly thought out and shortsighted...

If you are in a market where non-ethanol containing fuel is available, use it. If not, plan on spending money to alcohol-proof your classic bike.

Just a thought here, I've run into the same thing here with my single Mikuni and I'm running a steel tank. I also use clear plastic gas lines because they give me a bit of a heads up when I'm running low on fuel. I have to change them regularly as the gas degrades them and it occurred to me that possibly material is leeching out of the plastic and causing my slide to stick.

It could also be crud in the tank being dissolved by ethanol and making it's way in the carb.

Jean

sticky slide

Hi to let you know I have a 34mm mukuni which when bought new slide was sticking after 600 miles found same sticky like varnish in carb mouth and slide. Cleaned carb of course very well but slide still sticking wee bit around 2000-2500 rpm changed gas from high test, to low test, mid grade still found that sticky varnish like substance on carb mouth and slide. What I did do while I was complaining to supplier about carb was add a second spring to carb one actually from my old amal and this corrected problem. This I did with only 600 miles on new carb. My supplier did send me new carb about 10 days later I put new carb on and now have 3500 miles on new carb with no sticky slide issues. Was the problem in the fuel or was it mechanical I would have to say you tell me. I think that when you drive an 8 cyl car you probably won't notice a tank of bad gas {some water} but in a 2cyl it will cough and sputter here and there you know gas is not so good stay away from that garage. I think sometimes with the price of gas today stations don't sell as much high test as they do the cheaper stuff and the longer the gas stays in the tank the more chance the tank sweats the more water. The cheaper gas sells faster and therefore is fresher if that makes any sense. I burn more regular once an a while I throw in a tank of high test.

Would a bit of acetone or MEK in the gas help with this?

BrianK said:

Would a bit of acetone or MEK in the gas help with this?

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I wouldn't put either in a fiberglass tank.

I don't know about your areas but here in CA the gas evaporates quickly and leaves brown residue. I noticed this on one of my bike carbs after only parking it for a few weeks.
On Hondas it plugs up the tiny fuel passages. The remedy is to run a bit of Stabil all the time on bikes you don't run every day. The Stabil prevents the fuel from turning into goop for a much longer time.
On steel tanks some folks also add Marvel Mystery Oil to prevent rusting.
A number of other things happen from the alcohol, such as tank melting on plastic and certain rubber carb parts turn into jelly. The real remedy for this on O rings and such is to use alcohol resistant O rings.
The only remedy I've heard for glass tanks is sealing.
My little brother uses aviation fuel (expensive) to prevent this problem.

I had a fiberglass Interstate tank on a MKIII, and had the same issue, sticky slides about every 1000 miles, Replaced it with a steel roadster tank, about 3500 miles now and no issues. BMW, Ducati, & Motoguzzi have had probblems with Acerbis made fuel tanks, with expansion & paint bubbling caused by the ethenol in US. gas. It's not just the old relics with fiberglass tanks that are having probblems.

Ken G.