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The MT-07 Forum

Carburetor vs Fuel Injection


bornagainbiker

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I like the fuel injection on my MT-07 very much.  I love the way cold starts are quick and smooth, and the way that after the cold start it runs smoothly as if it's already warm.  I appreciate not having to choke it and remember to un-choke it as it warms up.  I love the 60-65 mpg I get (verified by recording pump gallons and GPS miles).  I will continue to like it until something goes wrong with it when I'm away from home and can't fix it on the side of the road.

In all fairness though, I've never had a car with fuel injection leave me stranded with a fuel system problem, and I don't expect the motorcycle to be any different.  I did have one car develop a fuel pump problem that made me stop to let the pump cool off for 15 minutes, every few miles, so getting home took a long time, but fuel pump problems aren't limited to fuel injected vehicles.

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I had a Zuma 125 scooter with fuel pump issues, like Triple Jim had.  If the scooter was warm, pulled up parked for a short time, the engine wouldn't start.  It would have to sit for around 2 hours to cool before starting again.   It seemed to be related to heat in the fuel in the tank affecting the fuel pump.  Nearly $300 for the pump, which I installed. - big negative for EFI in my book.   I'd take a carb over EFI on a single cylinder bike any day.  Once jetted in and with a Dial-A-Jet installed to compensate for leanness it is good to go.

You see, the only problem I've ever had with carburetors is if the bike is parked for a length of time long enough for the fuel in the float bowls to break down.   With a single it is easy to turn off the gas and drain the float bowl.   With my KLX650 the fuel would go bad within around 7 days, so I'd simply drain the float bowl and all was good.   Now with my Zephyr 550 it was a pain in the butt to drain the four carbs, so I like the idea of EFI on the road bikes.  After all, should they break down I'm on a public road, no problem with getting towed.   On the trails a carb might be fixable, but the thing is when jetted in they just really don't have anything go bad, having no electronics.   

One other nice possibility is exemplified with my KLX250.  I am going to a big bore 299 kit along with a less restrictive exhaust - plus a Mikuni TM36-68 pumper carb.  Jetting is fairly established for that set up with maybe a little fine jetting, but it's all pretty much plug and play with the cost being the hard parts if one does the work.   Total cost in my case with a used exhaust and a good buy on a used carb, will be around $450.   You can't do that as easily with EFI.  So with my dual sport single I prefer the carb set up.   Not so with the street bike multi-cylinder, I like the EFI on it since I'm not doing any engine hop ups that would call for a reflash, plus no need to drain any float bowl if the bike sits for a while.   

These are my thoughts and opinions on the EFI vs Carb thing.  Might be different if I had experience with EFI programming.  Look forward to reading others' thoughts and experiences.  

Edited by klx678
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M. Hausknecht

I miss carburetors. Once you figure out what the jets and needles do and how they contribute to the air/fuel ratio at various engine speeds and throttle openings, you can make significant changes to your motor and get the mixture where you want it reliably, and without an after-market ECU, laptop and software, and expensive dyno time. For a stock or nearly stock motor, FI seems to work well and its nearly idiot-proof as long as you have adequate fuel pressure and your injectors haven't gotten too dirty.  But once you head down the road of improving volumetric efficiency, the stock ECU, with its emphasis on controlling emissions and fuel  economy, becomes a hindrance. If you add a pipe and better intake, a reflash from 2WDW or Hordpower, as good examples, seems to be essential to get any additional power from your mods. But more than that, you need a new ECU  and the expertise and equipment to create your fuel maps. To be fair, if your carbed bike came with CV carbs, and it probably did, if you're looking to maximize power you'd want to go with flat slide carbs and they aren't cheap either but you can tune them yourself.

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The flat slide pumper for my KLX listed at $179, but I got one lightly used for $150.  Not too bad.   If I had some guts and could afford a possible mistake I would have tried the regular TM36 flat slide without the accelerator pump.  After all, the SR500 ran a VM36 round slide no accelerator pump, which was the norm in the 80s for it.   Regular flat slide is only around $100 new.  I guess another time...

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I put a TM36 on a XR400 primarily to add an accel pump. The bike didn't come with one and they were notorious for off idle bogs. The pump shot on the Mikuni was so strong that the bike couldn't handle it, but the throttle response different compared to the round slide was noticeable. That Mikuni was just fussy in general. Ended up moving to a RFS KTM with a Keihin FCR in it.... oh my, that carb is magic. I thought I loved fuel injection for it's instant throttle response, but the FCR carbs changed my mind back. They're perfect everywhere. 

At last count, I've got over a million miles logged on carbs- bikes, cars, trucks, mowers, weed eaters, chainsaws, tractors... whatever. Zero failures. I've got about 300,000 miles logged on fuel injected vehicles. Never had a fuel related failure with them, but have had to fight with some sensors here and there. I'll take either one. They're both perfectly reliable. I prefer FI on the street bikes nowadays because my riding gear no longer stinks when I get home and hang it in the bedroom.

 

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M. Hausknecht

I had a quartet of 33mm FCRs on a very stout FZR400. Loved them. Easy to tune, great throttle response and peak flow.

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Like I said, about the only negative is the float bowl fuel going bad over time if not ridden or drained.   The only other issue is if one is going up significantly in elevation, making the carbs run rich.

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Well I always swore I would never get a fuel injected bike, but after years of driving fuel injected cars without a single problem I relented.  carbs aren`t that easy to tune unless you have years of experience. One problem I found is that since the advent of unleaded fuel you cannot rely on plug colour to tell if it`s running rich or lean. since derestricting my airbox and fitting the Acrapovic system my bike still runs fine. The O2 sensor and the computer were able to make whatever changes were necessary. If the bike had carbs I would probably have had to rejet it. 

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Talk of fuel pump problems, I remember having to ride in the boot (trunk) of my father's car so it could receive a tap from me to keep it going.  Just btw.

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Just do it! 

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1 hour ago, robbo10 said:

Talk of fuel pump problems, I remember having to ride in the boot (trunk) of my father's car so it could receive a tap from me to keep it going.  Just btw.

Sometime in the 1930s my uncle's Model A had a carb problem in Washington, DC.  My father stood on the running board, hood open, holding a tin can with a hole punched in the bottom and his finger over it, metering gasoline into the carb.  They got it home.

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My grandfather had a 30's Ford pickup  that was his tow truck for the service station he ran. It started knocking while he was hauling a car in. He was the only tow truck in town, so it had to be fixed to get back. He trimmed a piece of leather from his belt and put it in place of the bearing that'd hammered out. Not only did it make it back to the shop, but he had to use the truck that way for a few weeks til he had the time to fix it. 

 

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On the subject of belts, my great grandfather had a Benz in 1896. The drive belt was leather and needed constant repair on the go... so before chains.  Now, back to fuelling....

Just do it! 

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