Carboned Up Throttle Bodies

[acton mike]

my 2016 T100 Bonneville was running just okay; well it could have been running a lot better. A trip to the shop resulted in cleaning of the fuel injectors and cleaning of the throttle bodies and now the bike is running much better ; the erratic idle was gone and the hesitation and stumble off the idle has also gone away along with the slight misfire at road speed. The question I have is this: since the combustion of the air/fuel mixture takes place in the cylinders, and not in the throttle bodies, why does carbon build up in the throttle bodies themselves?
After you all have dried your tears of laughter over this dumb question, perhaps someone could enlighten me as to why this happens.
I know it does happen; I just need an explanation as to why it does.

 

[Greyfell]

I'd like to know, too.

 

[NWGABikerGuy]

Are you certain that it was carbon build-up and not something else gumming-up the works? Fuel injectors and throttle bodies can easily be compromised by contaminated, dirty, or old gasoline, or rust from the fuel tank. Have you checked to see what the fuel filter, tank, and fuel lines look like? Misfires too are often the result of bad fuel, or fouled with oil or too rich a mixture, but actual carbon is not usually the problem. A lot of times "carbon build-up" takes the rap for other fouling issues because it was a bigger problem in years past, and it has become sort of a catch-all phrase for diagnosing the problem. I would ask the shop specifically what they saw, and more importantly, what they used to clean it up. This will give you a better idea of what your problem actually is. I would bet money it is more likely fuel related than carbon. Just my 2 cents worth.

 

[Qship]

Usually a build up of crankcase gases that are deposited on the intake parts(injectors, throttle bodies, valves) when fed back into the engine in the air intake system through the PCV valve.

 

[acton mike]

Are you certain that it was carbon build-up and not something else gumming-up the works? Fuel injectors and throttle bodies can easily be compromised by contaminated, dirty, or old gasoline, or rust from the fuel tank. Have you checked to see what the fuel filter, tank, and fuel lines look like? Misfires too are often the result of bad fuel, or fouled with oil or too rich a mixture, but actual carbon is not usually the problem. A lot of times "carbon build-up" takes the rap for other fouling issues because it was a bigger problem in years past, and it has become sort of a catch-all phrase for diagnosing the problem. I would ask the shop specifically what they saw, and more importantly, what they used to clean it up. This will give you a better idea of what your problem actually is. I would bet money it is more likely fuel related than carbon. Just my 2 cents worth.

I appreciate your comments regarding the problem being fuel related but there was definitely a crud build up in the throttle bodies and injectors. I burn 91 octane fuel from Petro Canada or Shell and so i am pretty sure the gas i purchase is fresh and not contaminated and i put a lot of miles on the bike (45,000 kilometres in the 4 years since the bike was put on the road new). The tank is clean and rust free..

 

[sikatri]

Is the gas you use ethanol free? I know ethanol gas isn’t good for carburetor model motorcycles and I’d guess it still gums up injectors and adds crud to throttle bodies. Part of maintenance to clean things up, with 40k plus kilometers I’d say you were overdue.

 

[NWGABikerGuy]

I appreciate your comments regarding the problem being fuel related but there was definitely a crud build up in the throttle bodies and injectors. I burn 91 octane fuel from Petro Canada or Shell and so i am pretty sure the gas i purchase is fresh and not contaminated and i put a lot of miles on the bike (45,000 kilometres in the 4 years since the bike was put on the road new). The tank is clean and rust free..

I agree with @sikatri that your mileage calls for regular maintenance/cleaning of your fuel system. Actually, all octane ratings contain the same amount of detergents as usually required by law/regulations, although the "top tier" brands are assured to be the best quality. With every oil change, I use Liqui Moly Pro-Line fuel system cleaner, as I have found that it worked best when I used to play with high performance European cars. I do this with cars, trucks, and motorcycles and have never had a carbon build-up problem. I'm guessing that the shop charged you for a "top-end" cleaning, which usually involves them adding a container of similar cleaning product, running your engine up to operating temperature for a few minutes, then charging you for the product plus an hour of labor. If regular treatment doesn't solve your problem, then I would think that something else, probably involving oil and or blow-by gases is causing your problem, and repairs are needed.

 

[NWGABikerGuy]

I agree with @sikatri that your mileage calls for regular maintenance/cleaning of your fuel system. Actually, all octane ratings contain the same amount of detergents as usually required by law/regulations, although the "top tier" brands are assured to be the best quality. With every oil change, I use Liqui Moly Pro-Line fuel system cleaner, as I have found that it worked best when I used to play with high performance European cars. I do this with cars, trucks, and motorcycles and have never had a carbon build-up problem. I'm guessing that the shop charged you for a "top-end" cleaning, which usually involves them adding a container of similar cleaning product, running your engine up to operating temperature for a few minutes, then charging you for the product plus an hour of labor. If regular treatment doesn't solve your problem, then I would think that something else, probably involving oil and or blow-by gases is causing your problem, and repairs are needed.

I just read your question again, and it dawned on me that I completely missed the point of your question (Duh!). I really have no clue as to why it builds up in the throttle bodies unless combustion pressures prevent it from building up where combustion actually occurs and it has to build up somewhere previous to the exhaust? This is, of course, a SWAG (Silly Wild Ass Guess) on my part, so there you go. I am certain that someone else has a better guess, or actually knows why. But this is my best shot. Sorry.

 

[sikatri]

Not sure what kind of recycling (air/fuel) system this particular model has. Depending on how it does this could be a clue (refer to Qship’s earlier post). In the mean time, I would just try to occasionally give it a clean and see if that keeps it running well. I’m always intrigued by the mechanics of machinery, I’d also be interested in a more knowledgeable explanation. I think Qship’s explanation is where my thoughts are on the why. I know I couldn’t expand on it. LoL.

 

[acton mike]

I agree with @sikatri that your mileage calls for regular maintenance/cleaning of your fuel system. Actually, all octane ratings contain the same amount of detergents as usually required by law/regulations, although the "top tier" brands are assured to be the best quality. With every oil change, I use Liqui Moly Pro-Line fuel system cleaner, as I have found that it worked best when I used to play with high performance European cars. I do this with cars, trucks, and motorcycles and have never had a carbon build-up problem. I'm guessing that the shop charged you for a "top-end" cleaning, which usually involves them adding a container of similar cleaning product, running your engine up to operating temperature for a few minutes, then charging you for the product plus an hour of labor. If regular treatment doesn't solve your problem, then I would think that something else, probably involving oil and or blow-by gases is causing your problem, and repairs are needed.

interestingly enough, the Triumph's owners manual, under the heading of the maintenance schedule, refers to "check fuel system" which i suppose is a phrase open to interpretation.. Triumph dealers are thin on the ground around here and there is little to no public transport which between my home and the triumph dealers which is an issue since it aleays seems that one has to leave the bike for service.
I did find an independent shop which has the software to deal with the Triumph EFI system and which i can get to via public transport..
I do the oil/filter and lubrication and light maintenance tasks myself but it did not occur to me to check the throttle bodies and injectors. Anyway, the work has been done and the engine is back on song and I shall start periodically using good quality fuel system cleaner

 

[sikatri]

If you don’t have a shop manual I would buy a Triumph one. Even if you don’t have all the tools you might find you can do some of the service procedures at home even with an EFI system.

 

[Greyfell]

I found a website, for US and Canada, that shows where to buy ethanol-free fuel. I don't know how well it is kept up to date, but it is worth checking whether you have a station near you.

Ethanol-free fuel

 

[Greyfell]

In addition to the above, Lucas Oil has a treatment specifically for ethanol gas: Lucas Oil Fuel Conditioner

 

[brooke]

Things certainly aren’t getting as dirty in there as they used to . Before the ban on lead fuel we would change plugs every fall and points and condenser too , just for good luck . Now a set of plugs last a life time ,often because mechanics are afraid to remove the originals and of course the ignitions are now so powerful that they will fire just about anything. Think Q is right on about soiled throttle plates/ bodies . I always pick up a big bottle of CTC injection cleaner when it’s on sale and throw some in everything I have with irregularity . No idea if it works .

 

[brooke]

I found a website, for US and Canada, that shows where to buy ethanol-free fuel. I don't know how well it is kept up to date, but it is worth checking whether you have a station near you.

Ethanol-free fuel

That’s great info Greyfell . Looks like Shell 91 will get you from coast to coast in Canada .