Question about Motorcycles
At full throttle engine starves and cuts out. Once revs drop engine runs again. At low rpm no problems.
It sounds like your float in your carb is getting stuck at high rpms. Try taking the bowel off and pushing the float up(make sure to have a bucket for fuel to run into). If it sticks that's the issue an easy fix.
Posted on Dec 11, 2012
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Posted on Jan 02, 2017
are you turning the choke off after its warmed up? most will not run with the choke on and warmed up.
also try running it with the gas cap open to see if you have a vent issue in your tank. if air can't get in, then gas can't flow.
if not a choke or vent issue, then try this. turn the petcock off and then disconnect the fuel lines one at a time going into the carb. start with carb fuel line #1 disconnected (and the rest connected) and in a coffee can, turn petcock on and ignition too. fuel pump should come on momentarily and inject some fuel. see how the quantity looks. reconnect the line to carb #1 and repeat for carbs #2 - #4. your looking for a decrease in fuel to a couple of cylinders.
if all looks fine, i would then focus on the carb floats & jets. have the carbs been off for a good cleaning lately? modern fuel breaks down quickly and could cause a gumming condition in the carbs. spraying the sea foam or carb cleaner into the carbs is bypassing the everything in the carb bowl (but it means the spark plugs are ok) so there could be an obstruction. i would look there first.
if uncomfortable removing the bank of carbs, you can try a quick fix first. with the petcock closed, open the drain screws of each carb and let the gas drain out. go and buy some yamaha carb cleaner (liquid in a black bottle) at a yamaha motorcycle dealer. mix it in a separate container with gas as recommended. close the drain screws on each carb. pour the mixture into each fuel line feeding the carb and let it sit overnight. DO NOT POUR THIS MIXTURE INTO YOUR TANK. its not a fuel additive, but a cleaner that will not harm orings or gaskets, but it will not ignite with a spark plug. open the drain screws the next morning and let the mixture pour out. reconnect the fuel lines to the carbs and test drive it.
if that didn't work, then removing the carbs for a good cleaning is my next step. good luck.
Posted on Jan 28, 2009
There can be multiple reasons for this. Low fuel presure is one cause of this.
If you had dropped the bike the impact can loosen the fuel lines inside the fuel tank. Issues with the fuel pump can cause a low fuel presure. In my case the fuel line was loose but still pushing some fuel into the lines. There is no issue a low rpm cause there just enough fuel to run it at 2000 rpm or lower but not enough pressure to run well at high RPM.
Posted on Aug 10, 2009
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