TOPIC:

Further to some dialogue regarding fuel-tank coatings: After recently discovering several idle-jets plugged with "varnish" I started doing some searching on the topic. In doing so I learned that some tank sealing products are NOT compatible with today's fuels. I submitted a reference to this based on several aviation sites reports and the known associated problems as they affect aircraft engines/turbines. As it turns out there is an unlimited number of "coating" concerns and warnings on many various forums. Serious stuff !

Having coated my tank 34 yrs ago prior to the prolific blending of fuels and today's additives I immediately became suspect of my coating. This morning I opened the tank filler and inspected the coating. It's relatively soft! A finger-nail will leave a depression in it. Otherwise it's still stuck to the inside of the tank and is intact. No chunks or flakes. As strange as this may sound: I have no recollection of the coatings firmness either at the time of coating or since. (if it ain't broke - don't fix it" !)

I removed the tank and drained it. I removed the fuel-valve and the fuel-sending unit. The tank (coating)is now air-drying. The fuel-valve and the sending unit appear clean and as new. No indication of any "coating" from a dissolving tank coating. Additionally; the small fuel-filter (2 yrs old) is clear. I was expecting some flow resistance, but no. My idea now is to let the tank air-dry for several days and determine whether the coating has changed in its firmness in any way. Because it is so close to the end of my riding season, I'll put it all back together and continue to fill with ethanol-free Premium and see what happens.

It should be kept in mind that the idle-jets are strategically placed at the fuel-level in the bowl. A blockage could be exacerbated by the fuel level being low and/or the fuel level dropping due to evaporation if the bike has not been ridden for for some time. The residual fuel in the orifice could then potentially dry - leaving a deposit of "whatever" which cumulatively over time could eventually block or plug it.

It's quite disconcerting to install a freshly rebuilt (squeaky-clean) set of carbs only to see heavy discoloration in the throttle bore downstream of the idle ports after only two tanks of fuel !

Just some thoughts and ideas to promote and provoke !

I wonder what the manufacturer of the coating might have to say about this.

From what I can gather in reading material on various product sites it seems that most sealant manufacturer's are acknowledging this issue by stating which of their products are "alcohol" compatible and which ones are not. In some cases the manufacturer is stating specifically which of their products should not be used in aviation fuel tank applications due to the liability, I am assuming. The same will apply to any fuel-tank, aviation or otherwise.
What we must keep in mind is: How far back did we seal our tanks and in some instances it seems apparent that they worked with the available fuels at the time, but not necessarily now.

The fact that my sending unit, fuel-valve and filter are so clean simply adds to the mystery. Theoretically it could be that they are all exposed to liquid (and vapour) continuously. One would think the idle jets would be as well unless as suggested before - they are exposed do to a low level in the bowl in which case it could be argued that the dissolved coating that makes it to the jets, oxidizes and dries in the tiny orifice. The devil's advocate would reply with; "But the jets are still exposed to fuel vapor at the very least." No argument there but "something" is plugging these tiny buggers and we need to no what that is and how to remedy it. What is very irritating is the inability of "fuel-cleaning" products to remove it not to mention the inability of the blockage to re-hydrate with fuel and dissolve the crud during normal operation.

Hypothetically speaking: The issue could possibly be eliminated if the idle-jet orifices weren't so damned small. One could rationalize that larger idle-jets would (perhaps) not plug-up. The concern I would have in going "bigger" is that I believe the idle jet is critically sized for the "transition" ports. The main idle port can be adjusted with the idle-screw. There is no such adjustment for the "transition" jetting so the idle-jet itself is the governing restriction and "going bigger" would likely mess-up the throttle transition not to mention a required new setting for the idle-screw.

In a couple of days I'll put it all back together, run it on "premium" and see what transpires over the reminder of the season.

Tank coatings are almost always epoxy based. Comprised of a liquid polymer base and hardener that when mixed together starts to cross-link the molecules to form solid rubber like materials. Depending on the type (most of them are polyurethanes) the epoxy can be soft and sticky to hard and brittle. Most tank liners I have seen are non-hardening types of epoxies that stay pliable throughout their life span. A good liner product should not harden, it would be prone to cracking and chipping off from the metal tank wall.

Most of good quality products are this way, RedKote, POR-15, and others like them remain soft, like a very viscous fluids after they cure. Polyurethanes are very resistant to petrochemicals, and acids. They are usually not tolerant of basic solutions (like caustic soada) and chlorinated solvents (like methylene chloride). Polar solvents such as MEK and Acetone can soften some types of epoxies. Depending on the type ethanol could be a problem, but not for most urethanes.

More often than not the discoloration you get in your fuel is from the dye used not the polymer. But if the tank did not cure properly for whatever reason you could have a problem even years down the road. I recently removed an epoxy liner from the tank on my 1300 project and it was a real nasty messy nightmare of a job... almost easier to replace the tank ( I'm not kidding).