Surging

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fischer550

Member
Mar 24, 2014
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Fort Collins, CO
So I was riding my new bike today, and out of nowhere it started surging at random times, and would then correct itself but then start again and so on. I took the carb apart, looked fine cleaned out the main jet put everything back together and same thing again :( I have fred's boost intake and the carb sits at a pretty extreme angle, could this be the problem? Thanks.
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
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Central Area of Texas
Check to make sure you're getting a steady flow of fuel from tank

That is what I would check first and ifyouhave an inline fuel filter make sure it isn't partially stopped up.

Map
 
crassius

crassius

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Sep 30, 2012
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USA
at extreme angles, the float can stick against the side of the bowl - I'd get a piece of rubber hose in there to level the carb
 
KCvale

KCvale

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Feb 28, 2010
3,966
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Phoenix,AZ
Pictures help but 'surging' is usually caused by either the throttle cable binding and adjusting the throttle, or a low fuel condition, if you have left your 2-stroke idling with the fuel turned off it revs up before it dies.
 
crassius

crassius

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Sep 30, 2012
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get a piece of pipe that fits into the carb (I have an old metal mop handle that fits nicely & I keep cutting lengths off it) then put a piece of hose where the carb is now, then put the pipe in the hose and the carb on the pipe

bend the hose till carb is level and put hose clamps on the ends of the hose

if needed, make a hanger to hold carb steady against frame or other support
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
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Central Area of Texas
I have had carbs mounted at pretty extreme angles and they work just fine as long as the float level is set correctly, honestly no need to make a hose for changing carb angle, and from what I've seen in the pics of your bike fischer550, your cab is setting in excellent position, very little forward lean and will work perfectly without doing any mods to intake tube or using rubber hose.

Sorry crassius but that mod is just not needed and I dont want to see fischer550 mess with something that I know for a fact isnt an issue with his bike, not meaning to shoot you down here at all, but his carb is setting at a good angle and adding rubber hose and a brace to pull against carb to level it is just not a good way to go.

Map
.wee.
 
S

scribling

New Member
Mar 31, 2014
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Simi Valley
I had the same surging problem when I tried to add a boost bottle intake. The intake for the boost doesn't have the same bend that the original does so the carb sat at a slight angle. The engine would race then quiet, race again and again without me touching the throttle; and that was with the boost nipple plugged. As soon as I put the stock intake back on the racing stopped. The change in angle of the carb was only a few degrees but it made a huge difference.
 
mapbike

mapbike

Well-Known Member
Mar 14, 2010
5,502
109
63
Central Area of Texas
Normally when the engine is racing like you described it's because it has an air leak.

if all is correct and there are no air leaks it should not surge, even with a "Boost Bottle"

and as far as carb angle is concerned I have had my little NT carbs at some pretty good angles and never caused any problems, but then again there's only so much angle they can stand.

Map
 
Last edited:
KCvale

KCvale

Well-Known Member
Feb 28, 2010
3,966
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Phoenix,AZ
mapbike said:
Normally when the engine is racing like you described it is because it has an air leak.

if all is correct and there are no air leaks it should not surge, even with a "Boost Bottle"

and as far as carb angle is concerned I have had my little NT carbs at some pretty good angles and never caused an problems, but then again there is only so much angle they can stand.
Map
Click to expand...
Well, ya, when a float bowl start running empty it sucks air leading to high high lean mix issues.
 
SuperDave

SuperDave

Member
Sep 24, 2011
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Panama City Beach, Fl. USA
Carbs can run at an angle properly if the float is set right, if it was okay running level but not at an angle, maybe the float is riding too low and allowing the emulsion tube to suck vapor or bubbles instead of liquid fuel? That would result in a lean condition(too much air, not enough gas), like an intake leak does, then when the float drops even further, then more fuel rushes into the bowl, temporarily covering the emulsion tube with liquid gas, restoring proper operation. Then the cycle begins again, resulting in a surging condition.
 
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