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Discussion Starter · #1 ·
Just finished rebuilding and tuning my 1997 MXZ 670. Today for the second time it died under hard acceleration. It quits after about 7 or so seconds at WOT, otherwise it runs absolutely fine. It takes a good hour of cool down and then it slowly starts to fire and run. It’ll run after that….like a sewing machine. I can’t figure out what’s going on, it has good spark and all kinds of fuel. It will not fire till it cools right down. Ideas? I’m lost.
 

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Discussion Starter · #2 ·
It was on a 40 mile round trip and it was rough riding. A friend and myself finally found a nice smooth open stubble field to open our sleds up and……blaaaaah to a dead stop. 😂😂. It’s like someone reached over and shut the key off a 8k rpm. We pulled and pulled on the rope, musta had the plugs in and out 10 times. We even squirted fuel directly into the plug holes with the primer and no bang, not even kinda.
 

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Discussion Starter · #5 ·
Yeah, excellent points. I’m going to run it hard again close to home and try and mimic the problem again. Tow it home and drop the main jet access plug to see if the carbs run dry. It could be one of those deals where it’s an absolute pig to start when it’s that hot. Sure, there is plenty of fuel from the primer, but doesn’t mean it’s getting supply through the inline filters. I put some large inline after market filters in last year, they look ok but doesn’t mean they’re not restricted. In fact, I’ll just put new ones in and try it. I hate it when it quits like that.
 

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Discussion Starter · #8 ·
So far so good. I went back to square one and started rechecking things. Was getting my new set of plugs ready for this pull and realized the old set wasn’t gapped! They were close to .030. 😬😬. My bad, I told my son to put the plugs in when we were putting the engine together and I totally forgot to mention to gap them.
 

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gap wouldn't cause loss of total power though.

My bet would be the CDI sitting just behind the exhaust pipe and getting to hot. Pretty common issue. My Summit had the same issue. I made a heat-shield to block the heat from the pipe from hitting the CDI.
 

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Mine did same thing… all day long at any rpm’s except wot 8k. Do the 8k for few seconds and it would cut out. Roll to a stop pull the rip cord go again till I hit wot…. Stator. Won’t be able to ohm it cause it seem fine. Only creates a broken wire when hot or vibration. Electrical wizardry. Only way is to swap a good known stator. Or get a new stator or rebuilt one.
 
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