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1990 250 Loss Top Speed. At Full Throttle Engine Slows Down. I Checked Ohm Readings On Pulser And Lighting Coils They Seem Ok
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have you checked compression -
You have three issues to validate. Fuel, Spark, and Air(compression). As the poster above points out, do a compression test first as this is what operates your fuel pumps. If the rest of the power band is operating correctly(idle-mid to upper range) then fuel is the likely place to start. A relatively easy way to eliminate fuel quality and tank/line issues is to hook up an aux tank to the sqeezbulb fitting. Essentially, just get a piece of fuel line, shove it down a pour spout from a 2gallon tank, and you have a make shift aux tank. I use an in line fuel filter to make sure I don't pull any crud from the tank. If you haven't replaced the squeeze bulb recently, get a new one as they are notorious for allowing air into the line at full throttle...Take the intake covers off and make sure all the butterflies on all six carbs are opening completely and in sync with each other. (I had a clamp on one of the port side carbs keeping the port bank of carbs from opening completely. It gave me a mid range issue but caused the engine to bogg down more than I would have thought. I think that since the throttle position sensor was on the port bank, this was causing a knock and the knock sensor was taking the rpms down. ) Go with the simple stuff first, then move on. If the "slow down" you discribe means you lose significant rpms at WOT and when you let off the throttle a little and the rpms go back up, then you might have a situation where the electronics are taking the revs down for some reason. Again, try the aux tank first. More than likely it is fuel related. If this fixes the problem, then remove/clean/replace the check valve in the main tank, change the water separator filter, and if one these doesn't solve it, then replace the fuel pumps (the three pulse pumps) All of this is cheaper than your first hour of check out time at a dealer.Comment
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