Hard starting.. poor mileage.. stumbling - Suzuki Burgman Forum
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post #1 of 15 (permalink) Old 07-07-2016, 04:28 PM Thread Starter
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Hard starting.. poor mileage.. stumbling

I don't know if they're all related, but i've been getting the following symptoms on my newly-purchased 2003 AN400 (fuel-injected):

  • When the engine is cold, it takes 3-5 tries to start it when it's cool outside (50-65 degrees) and 2-3 tries when it's above 65 degrees. It only starts on the first try when it's been ridden the past hour or so.
  • It's gotten 34-38 miles per gallon for the 3 tankfuls that i ridden. I do mostly city riding, but i would expect at least around 45 miles/gallon for the riding i do.
  • When coasting at 5-15 mph with no throttle, it stumbles when i give it a little gas, as if it's going to stall (but doesn't). Other than that, it rides fine.

Things i've tried:

  • Seafoam for the last 2 tankfuls - no improvement.
  • I gave 1 tank of premium gas, 1 mid-grade, and 1 low - no noticeable difference.
  • I checked that the spark plug was tightened properly. Its cap and wire seem fine.

Thanks for any input!

Last edited by MooseMax; 07-07-2016 at 05:13 PM.
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post #2 of 15 (permalink) Old 07-07-2016, 05:47 PM
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It may be in need of a valve adjustment. Or it may need the air cleaner cleaned. Or it may need a new spark plug. Lots of thing it could be.
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post #3 of 15 (permalink) Old 07-07-2016, 05:53 PM
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Is the FI light on? If it is, then reading the code could give you a direction to look. But 34-38 MPG is really crummy- there's something really wrong with your bike. Buffalo's suggestions are a good first step.
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post #4 of 15 (permalink) Old 07-08-2016, 05:35 PM Thread Starter
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The red FI light comes on for 1 second when powering up the bike and then shuts off. I assume that's a normal part of the startup procedure.

I'll check the air cleaner and spark plug this weekend.
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post #5 of 15 (permalink) Old 07-08-2016, 06:15 PM
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Yeah, the FI light for just a second is fine- it will stay on if the computer thinks there's a problem.

While you have the spark plug out, maybe try a compression check. If you have a compression tester. Although it doesn't tell you much, it can indicate whether there are leaky valves or worn rings. The 400 has a compression release integrated in the camshaft which limits the compression when it's starting, and that limit can be anywhere between 80 and 120 PSI so the absolute pressure won't tell you anything. The main thing is whether the compression raises after shooting a squirt of oil in the cylinder- if it does, then you're looking at new rings at least.

Anyway, just turning the crank over with a wrench can tell you if the compression is OK- remove the left leg shield (you need to do that anyway to change the spark plug), take off the variator filter cover (2 8mm bolts) and the variator filter (2 screws). Put a wrench on the variator nut (15/16 or 24 mm) and turn it CCW to turn the crank over by hand. It should have a spot every second rotation that gets hard to turn (compressing) then really easy to turn (past TDC and the compressed air in the cylinder pushes the crank back around). It shouldn't hiss while doing so, and it shouldn't be easy to turn through the whole rotation. Again, if squirting some oil in the spark plug hole fixes it, that's a bad thing- new rings. If it hisses and doesn't have much compression and doesn't raise after a squirt of oil, then it's time to look at the valves. It could just need valve adjustment.

If you've determined there's good enough compression, the next thing to look for is some kind of fuel or electrical problem. If the spark plug looks OK, I'd suspect a fuel problem- maybe a badly adjusted throttle position sensor, dirty throttle body, that sort of thing. But since you say it runs OK otherwise, nothing really gross should be wrong with the fuel system.

Good luck and keep us posted! Let's hope for just a dirty air filter or a worn-out plug; when I got my k4 400, my air filter was caked with 1/4" of greasy dust and it had similar symptoms.
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post #6 of 15 (permalink) Old 07-15-2016, 06:03 PM
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i think it's the same problem as my old B400 that died anyway..
poor compression, oil consumption..bad engine..
did the motor twice, payed 1000$, it stalled on a highway at 100mph..
sold it as it was and get a 650. no problems
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post #7 of 15 (permalink) Old 02-13-2017, 07:41 PM Thread Starter
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Sorry it's been so long, but here's an update:

1 - The stumbling problem at low speed disappeared after replacing a dead headlight bulb! The replacement bulb was the same Philips model # as the old one, which had a dead low-beam since i bought the bike. Not sure how would that cause stumbling..?

2 - I recharged the battery (it died from all the starting attempts) and now the bike starts up on 1 or 2 tries, instead of 3 or 4 like before. I think a new battery would help even more. Or maybe the regulator/rectifier is the problem..?

3 - The poor fuel consumption issue still exists. I haven't tracked it regularly, but the last tank got 30 miles per gallon in city riding.

The air cleaner and spark plug are clean.. The brake pads don't seem to stick. I've never adjusted valves before and the process is a bit intimidating, but i guess i'll have to do it. I don't trust my shop to do it correctly.

By the way, what is this mysterious red button for? Pushing it doesn't seem to do anything.
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post #8 of 15 (permalink) Old 02-14-2017, 08:48 AM
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that's the white house garage door opener, you must be driving Trump crazy when you play with it !
clean spark plug kinda says to me everything inside and happening inside the cylinder is ok, rings failing should show as oil or some nastiness in tailpipe , I'm kinda leaning toward fire in the fire and fuel equation and fire to the plug, not after,

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post #9 of 15 (permalink) Old 02-14-2017, 10:30 AM
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My 2005 400 does not have that red button.
How many miles do you have on your bike? A high mileage bike can have a dirty idle screw and PAIR valve
If you are going to inspect your valves, then go ahead and Clean your idle screw and Clean the PAIR valve.
Replace your spark plug and double check that it is the correct plug. I once had a reputable shop service my bike and the put a plug in that was the wrong heat range and it also wasn't long enough. It was shorter than the correct plug. I never went back to that shop.
Also if your battery is old, have it tested or just replace it.
My bike has always had mileage in the 50's and 60's.
I don't know if Rollers and variators make a difference in mileage, but a previous owner could have changed those and caused the mileage to go down.(Maybe!)

2005 An400
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post #10 of 15 (permalink) Old 02-14-2017, 05:50 PM
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Check the valve clearance.

05 Burgman 400
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