It's the 790,no airbox,unifilters and properly jetted. It's ran great for years but it just set for almost 2 years with no time to run it. New plugs,new fuel line,tank has been drained of fuel twice through petcock and petcock pulled and check for operation and cleanliness. I drained the float bowls before I put the bike up every winter. I've run almost a full tank of quality fuel with seafoam additive. I ran seafoam through the carbs intame while running bike. It runs great at idle,it cruis essential well at anything below 4k and never stalls. Get it up around 5 to 6 k and it will stall in just a minute or two. The bike sets in a garage,doesn't get wet. I checked for tightness the plug wires to coil and to plugs. All vac caps are in good condition and present. The tip over line from tank to under the frame is clear. The vent through the gas cap has been torn apart and cleaned and checked. The battery is old but fine and is actually a bit bigger then stock as its a ytz14s. Any ideas?
Preliminary thought......you changed the fuel line. Does it run straight to the carbs? Size? Any kinks/restrictions? It sounds like fuel starvation much as when you switch from main to reserve. Are you getting to the point at which flow is insufficient to meet demand and draining the bowls? Inline filter clean?
Does the engine pick back up when you back off the throttle for a few seconds ? If so sounds like a fuel flow problem. Check the inline fuel filter, remove jets and clean out passages, could be internal part blockage. When you remove the bowls put a container under the carbs, open the petcock, momentarily, and see if both carbs flow fuel well and equally.
The new fuel line was done after symptoms as an attempt to rule it out. Fuel line feeds both carbs. In line filter has beenough removed long time ago. I havnt gotten to digging into the carbs yet,trying to rule out all things before I do that. I have never had good luck messing with carb cleaning, if it needs that it's going to my local shop and I'll pay to play! I am also trying to find any info or knowledge that would point toward an electrical fAult common or obscure.
Is it a stumbling stall like fuel starvation or sudden total cut off?
My own experience of cleaning carbs is that for less than $100 you can buy 3litre ultrasonic bath that will take a pair of carbs and 101 other intricate objects for cleaning. Compare that to the bill from your local shop - and afterwards you have still got the ultrasonic cleaner.
Works best for carbs with float bowls and slides removed but in the bath too. That way all the galleries get flooded and de-varnished.
It's an abrupt cUT off,like a kill switch gets thrown. Start up can be done usually within 10 seconds or less just by pulling clutch switch and pressing play. Everytime is the same. At first I thought kickstand switch or short in kill switch but nothing ever has to be done other then just clutch and hit start. I have experience with ultrasonic cleaners,we have one at work but to do it right you still need to take stuff apart down to the jeTS and all because the solution doesn't dissolve any big stuff stuck behind things,it just breaks it loose.
Taking the float bowls off and slides out provides good access to the jets from all sides but a sharp cut off sounds more electrical like a coil going open circuit.......but you have two ignition coils......which points towards pick up or an igniter issue.
I'm betting on the igniter on this one--especially if you still have the original one. The 790 (270 degree) engines have a history of this type of problem.
I let my independent shop have it for awhile and they did all the sake stuff I already tried with the exception of using good clean racing fuel (they are an MX shop ) . They said they couldn't replicate the shut down so I took it back. I've ridden it about 30 miles since then and it hasn't done it since.
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