Solvent for 98 Octane Fuel Residue

[Steven_A]

Hi There,

I think I have gummed up the carb on my TRS RR 125 by using 98 fuel.
The bike fouls spark plugs and requires 1 and 1/2 turns on the mixture screw to run properly.

What solvent gets rid of 98 Octane Fuel Residue. My bike mechanic mate says it is a real problem getting rid of it and normal carby cleaner doesn't work.

[David Lahey]

Yes it's a common problem and you can get it with any modern car petrol. It doesn't have to be 98.
The trick to avoiding the gum in bikes that are parked for more than a few days between rides is to drain or at least run the carby out of fuel after each ride.

Here are some things that will work on that gum.

Gasket stripper.
Non-caustic paint stripper - methylene chloride type.
Water soaking - it takes a few days to soften the gum then dry it and brush it off. Hot water works faster than cold water.

[brt650]

I use a product that cleans gum and corrosion really well from carb internals. Its Subaru UPPER ENGINE cleaner. Its about $20 from Subaru. More expensive from ebay. Its intended use is, spray the contents of the can into the engine intake manifold while the engine is running. Keeping up the revs as the engine will die down. If you have OCD about smoke coming out of your exhaust, Id close your eyes while doing it.
For carb cleaning it, needs to be used in a very well ventilated area and I use nitrile gloves while using it. Not that I've had it burn me.
Use the nozzle that comes with it and it foams up, leave it for about 30 minutes. I clean it off with brake cleaner.
Brings alloy and brass up like new. It doesn't affect rubber like some carb cleaners I've used does.
Cheers
Brian

[cota]

In other bikes to ungum carbys, i have used MEK - plumbers priming fluid from Bunnings - but do use in ventilated area and take care as per brt650 post. I will have to look up the Subaru cleaner to see what it contains.

Thinking about the original post, I have had a 2018 Raga Race 125 and for the last couple of years a 2021/2022 TRRS Raga Race 125 and I use 98 octane as per TRS recommendation. I have heard and read about people's concerns with the additives, but I don't think I have had a problem. I have tried 91 and 95 but perhaps by thinking too hard about whether there was benefit or not, I felt that 98 was better. But heck, was it just because 98 is a bigger number and is more expensive and therefore must be better
That aside, I have attached the pic of my current plug (iridium because my current model allows standard plug) but my bpmr6a was similar in the 2018 bike. I have run boyesen reeds in both of my TRRS 125's, optimised my jetting and importantly changed my needle from a jjh to a jjj - slightly leaner in that critical just off idle - 1/8th throttle position that I have found in each TRRS i have ridden, which just has a very slight "burble" - ie slightly rich and is a range perhaps well used puttering in sections. While some of my fellow riders would say "get over it - just twist the throttle more", I do like to understand and optimise my carby to my needs - sealevel to about 400m and the warmer climate here in and I am known for delicate throttle twisting.
May be when someone looks at my spark plug below they will say it is too lean, or too rich on the main or has deposits from additives ??? But my bike runs well, does not foul plugs, starts easy, does not ping and is the same plug for a year or more.
The Boyesen reeds (to me) give better performance (torque and consistency in response) low down and great responsiveness through throttle range. The pic of the sparkplug was after a practice ride at our clubs Trial Park (3ha) and not a plug chop after a full throttle firebreak run.

Spark plug.jpg (726.59 KiB) Viewed 10051 times

[brt650]

Thought I’d post some before and after photos of some carbs I just cleaned using the Subaru cleaner.
I removed all the jets and floats and needles. Also the emulsion tube so I can clean all the passages.

[cota]

Wow! Very nice. Off to the shop I shall go - might be too late for Santa's wish list.

[brt650]

It needs to soak for about an hour. I put all the parts into the float bowl and keep topping up with foam spray. I use a nozzle on the spray button. Sometimes it doesn’t come with the nozzle, so use one off my WD40 tin. Don’t leave in solution overnight as it goes salty looking. I clean it off with brake cleaner. I know, more money. Also use in a well ventilated place.