mysterious (to me) engine performance

[jeffsaline]

#ygrps-yiv-439257936 .ygrps-yiv-439257936ygrp-photo-title { OVERFLOW:hidden;FONT-SIZE:smaller;HEIGHT:15px;WIDTH:75px;TEXT-ALIGN:center;CLEAR:both;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936ygrp-photo { BORDER-TOP:black 1px solid;HEIGHT:62px;BORDER-RIGHT:black 1px solid;WIDTH:62px;BACKGROUND-REPEAT:no-repeat;BORDER-BOTTOM:black 1px solid;BACKGROUND-POSITION:center 50%;BORDER-LEFT:black 1px solid;BACKGROUND-COLOR:white;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936photo-title A { TEXT-DECORATION:none;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936photo-title A:active { TEXT-DECORATION:none;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936photo-title A:hover { TEXT-DECORATION:none;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936photo-title A:visited { TEXT-DECORATION:none;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936attach-table DIV.ygrps-yiv-439257936attach-row { CLEAR:both;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936attach-table DIV.ygrps-yiv-439257936attach-row DIV { FLOAT:left;} #ygrps-yiv-439257936 P { OVERFLOW:hidden;PADDING-BOTTOM:3px;PADDING-TOP:15px;PADDING-LEFT:0px;CLEAR:both;PADDING-RIGHT:0px;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936ygrp-file { WIDTH:30px;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936attach-table DIV.ygrps-yiv-439257936attach-row DIV DIV A { TEXT-DECORATION:none;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936attach-table DIV.ygrps-yiv-439257936attach-row DIV DIV SPAN { FONT-WEIGHT:normal;} #ygrps-yiv-439257936 DIV.ygrps-yiv-439257936ygrp-file-title { FONT-WEIGHT:bold;} On Sun, 4 Oct 2015 18:56:53 -0400 "tlz4u@... [DSN_KLR650]" DSN_KLR650@yahoogroups.com> writes:   To all:       For the last 3-4 months, my 2002 KLR, (17,500 miles) has been exhibiting some unusual engine performance. When cruising about 35 to 45 mph on the two lane roads in my area, the engine exhibits a very noticeable "flat spot" when I try to gently accelerate. This also occurs as I try to maintain speed as the road climbs a gentle hill. It is usually about 3500 RPM's, and once past it, the bike accelerates suddenly, back to speed. It's almost as though the carburetor slide is sticking at that point for some reason, and would occur about every 30 seconds or so.      Last week end, during intermitant rain storms, the situation got worse, to the point that the bike would slow to 55 mph and then gradually accelerate back to 65-70 mph, my desired cruising speed on the interstate. The bike exhibited no unusual characteristic other than the inability to maintain the chosen speed. When it accelerated back to speed, the acceleration was gradual, not sudden. This also occurred about every 30 to 45 seconds. I'm sure that wind was not a factor.      The throttle slide and/or bore shows no signs of abnormal wear. I'm also sure that wind is/ was not a factor. Any Ideas on what would cause these symptoms?  Robert L. Brewer One of the world's main problems is that "The foolish are full of certainty, while the wise are full of self doubt." <><><><><><> <><><><><><>   Robert,   If I was working this issue I would first inspect the vent tube(s) for the carb and fuel tank.  Maybe an insect crawled inside one and is creating a blockage.   The carb vent tube is on the left side of the carb and in stock configuration on a Gen I KLR it hangs down towards the shock.  This is the vent tube that gets the "T" mod done to it for more reliable running in wet conditions.   The fuel tank vent tube is located at the rear of the fuel tank and the front of the seat just covers it.  If you have two tubes at the rear of the fuel tank it is a CA Emissions tank.  The left nipple/hose is usually marked with a blue dot and is the vent hose.  The right side is marked with a red dot and is for the vapor recovery system.  The hose just hangs down near the rear shock.  With the fuel cap open you should be able to blow air through the hose and tank and it should exit at the small hole in the filler area that the cap covers.  Do not blow compressed air into the hose with the fuel cap closed.  Do not blow compressed air into the vent opening in the fuel cap.  There could also be an issue with the fuel tank cap vent system.  If you want to learn more about it (with pictures) see this thread on another forum.  http://www.klr650.net/forums/showthread.php?t=101547   Next I might inspect the petcock and do a fuel delivery test.  It should provide a gallon of fuel in 3-6 minutes.  A stock petcock must have vacuum provided to open the automatic shutoff feature.  Also inspect the inside of the vacuum hose after riding the bike and doing closed throttle deceleration.  The inside of the vacuum hose should be dry.  If it is wet it suggests a leaking petcock diaphragm.  Also do a very complete inspection of the vacuum hose.  If the ends aren't sealing well and it can't hold vacuum it could restrict fuel flow under low/steady vacuum conditions.   If those systems are in good shape I would remove the carb from the bike and do a complete inspection and cleaning.   Best, Jeff Saline The Beautiful Black Hills of South Dakota 75 R90/6, 03 KLR650 . . . . . . .   ____________________________________________________________ [b]Meet the Graviteers: Ezekiel Victor[/b] http://www.gravity.com/blog/meet-the-graviteers-ezekiel-victor/