Modern fuels: carbs versus fuel injection

[JadeRider]

Hello everybody, I am contemplating replacing my bike and I am curious as to whether modern fuels have a bad impact on carbureted engines or if carburators are actually better today


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[poser]

The ethanol in fuel will gum up a carb in just two or three weeks. Of my dirt bike sits for just a few weeks, I've got the pull the jets and clean them.
FI doesn't seem to be bothered by it as much.

[KenH]

An older bike may suffer damage to rubber and plastic fuel system parts from ethanol. Sometimes it is a simople matter to replace o-rings, fuel lines, and such with parts made from ethanol resistant materials.

Always turn the fuel off and run the carb bowl dry and you'll not have a problem with gummed up carbs.

E10 tends to run a little leaner than E0. Most carbed bikes are jetted quite lean to appease the EPA. Most carbed bikes will benefit from 2 or 3 sizes bigger main jet, raising the needle, and opening the idle mixture screw a turn or so.

It is not uncommon for ethanol content to vary a few % (0% to 20%) due to inconsistent mixing in retail tanks. This common inconsistency will result in varying air/fuel mixtures.

It is unwise to let E10 sit for more than a couple weeks. Eventually the ethanol will separate from the gasoline and form a layer at the bottom of the tank. Turn the fuel on, and the carb will fill with low-octane E0 will the octane-boosting ethanol sits at the bottom of the tank. Running an engine on insufficient octane can cause damage. Flip the fuel petcock to reserve, and the carb is filled with pure ethanol, which will run extremely lean and potentially damage the engine.

Carbs do not automatically adjust air/fuel mixtures for varying fuel qualities and properties. Modern EFI adjusts itself automatically. EFI engines usually consistently make more power and perform more efficiently than carbed engines in the real world of intentionally contaminated fuels. Later model EFIs adjust themselves better than earlier EFIs.

[poser]

Originally Posted by KenH

Always turn the fuel off and run the carb bowl dry and you'll not have a problem with gummed up carbs.

this is what I do if I know I'm not going to be riding within the next week. If something comes up and I don't ride when I though, I'll pull the bike out and drain the carb.

[JadeRider]

Wow, pretty awesome stuff. Thanks y'all. In this case I am considering a KTM 950, which is being offered here. I am guessing is a bit more modern.

[Dave in Houston]

Originally Posted by KenH

It is unwise to let E10 sit for more than a couple weeks. Eventually the ethanol will separate from the gasoline and form a layer at the bottom of the tank. Turn the fuel on, and the carb will fill with low-octane E0 will the octane-boosting ethanol sits at the bottom of the tank. Running an engine on insufficient octane can cause damage. Flip the fuel petcock to reserve, and the carb is filled with pure ethanol, which will run extremely lean and potentially damage the engine.

I think it's even worse than what Ken describes here.

Gasoline containing ethanol absorbs water very easily. My understanding is that the phase that separates from the gasoline is actually ethanol with absorbed water, and that stuff won't burn at all.

[dukey33]

My 98 Shadow sat for 6 weeks waiting for me to get off the sofa and replace the stator. When I got done, I threw two capfuls of Seafoam in the tank and the bike started with no problems after the carbs refilled.

I did not run the carbs dry before parking it and the bike has been running fine since I put it back on the road. YMMV.

[focus frenzy]

The ethanol absorbs the water that naturally builds up in the fuel tank. Way back before the government made them put it in gas people put it in their tanks deliberately to remove water from the system.


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[focus frenzy]

Fuel injection is so much better.
Tuning involves clicks of a computer mouse, no more pulling carbs off and on trying different combinations.


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[Dave in Houston]

Originally Posted by focus frenzy

The ethanol absorbs the water that naturally builds up in the fuel tank. Way back before the government made them put it in gas people put it in their tanks deliberately to remove water from the system.

This is true. However, back then, fuel tanks only had alcohol in them when someone added it (usually methanol or isopropanol, by the way) in the form of a fuel tank drying product.

Now that gasoline always has alcohol (ethanol) in it, the gasoline much more easily absorbs water from the atmosphere or through rain or other contamination. When the water content of the overall mix gets to a certain level (0.2 to 0.5% or so, depending on the temperature) a separate ethanol/water phase will form. That can cause problems.

See (for example) http://www.wellworthproducts.com/art...separation.asp

[TwoSmokeDS]

I thought the solution is Stabil.

[TwoSmokeDS]

At recent SETEX 450. Out of 40 bikes, two bikes had engine problem and DNF. Both were EFI.

[hizzo3]

Originally Posted by focus frenzy

Fuel injection is so much better.
Tuning involves clicks of a computer mouse, no more pulling carbs off and on trying different combinations.


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This is my love of FI. Put new pipes on my bike, upload map and done. My car was running hotter than my liking. Plugged it in, changed the fan speed map. My brother upped his intercooler, uploaded several maps.

Sure beats wrenching just to find you have the wrong jets or timing needs to be changed on a flywheel and such. Yes there is more to go wrong on FI, but it can give you more performance than what you could achieve all things equal with a carb'ed engine.

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[RollingJ]

If I have fueling problems on the trail I can loosen two screws, swing the carb bowl to the left, pull the bowl plug (or the whole bowl) and fix whatever ails me with a can of brake cleaner and a few screwdrivers.

There is something to be said for a gravity/venturi-fed system.

[SilverBullet]

Originally Posted by TwoSmokeDS

At recent SETEX 450. Out of 40 bikes, two bikes had engine problem and DNF. Both were EFI.

Plenty of bikes didn't finish that ride. Were the problems with those two EFI bikes related to EFI? Also saw many EFI bikes out there without any problems.

I do acknowledge though that many EFI related problems can be near impossible to repair on the trail. Fuel pump, injector, sensor, etc. But then stop and think that 98% of the cars on the road are EFI so you know where things are headed.

_

[poser]

Originally Posted by SilverBullet

I do acknowledge though that many EFI related problems can be near impossible to repair on the trail. Fuel pump, injector, sensor, etc. But then stop and think that 98% of the cars on the road are EFI so you know where things are headed.

_

I think all of the 4stroke MX bikes have gone EFI, even the 250s, and a lot of the trail bikes are there too

[TwoSmokeDS]

I am aware of 4 failures.

2 failures possible related to EFI: (1) Lee's bike couldn't idle (2) Electrified's

2 failures not EFI related: (1) SB's clutch and (2) Wedge's disk brake.

[Meriden]

I guess I'm not afraid of ethanol in fuel and routinely leave small gasoline engines, and lately a car, to sit for months at a time without fuel related problems. In fact I'm always surprised when a generator that I've let sit for two years fires right up on the fuel left in it's tank. Sure there are problem with varnish and corrosion in some cases, especially antique bikes stored for years, but I think that there is a hysteria surrounding fuel as well. I believe it was OU that did a study of long term storage of gasoline and E10 and determined that as long as the engine had the proper sealants and gaskets not much prep was needed. I posted the link on ADV about a year ago, if I can find it I'll post it here.


I am a complete convert to fuel injection and consider it far less troublesome than carbs. For example when I changed exhaust and didn't have to re-jet. No work is needed to go riding in higher elevations. Fuel efficiency is better. Cold start is simpler and faster. I'm not saying EFI is perfect, but I'd much rather clean a throttle position sensor plug than chase those tiny jets around a workbench.

m

[hizzo3]

Originally Posted by TwoSmokeDS

At recent SETEX 450. Out of 40 bikes, two bikes had engine problem and DNF. Both were EFI.

I am curious how many of these were stock vs 'race' efi's. Also curious on placement of efi vs carb'ed

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[Meriden]

Originally Posted by hizzo3

I am curious how many of these were stock vs 'race' efi's. Also curious on placement of efi vs carb'ed

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How do you mean "placement?" Where is it located on the bike? The BMW EFI is buried under the seat between the frame rails, the gas tank and the motor.