Lots of shotgun here. When you refer to "gunning it" I assume this is in neutral. This is a great way to destroy the engine. The RPM range you describe almost indicates it's going into rev-limit. On the '87, this can be caused by a temp sender, a water-flow sender, or the oil filter. You should have a multimeter on your console that will give you a rev-limit indication. Even if you don't have the gauge, the engine will protect itself if a sensor indicates a problem. Now, let's start with basics. Run the engine at idle with backpressure, ie, in the water. Using plug-boot removal pliers, remove 1 plug boot at a time and reinstall it until you positively identify the offending cylinder because the RPM won't drop. At this point you know you have 120# compression, so you need spark and fuel. Spray carb cleaner directly into the carb throat for that cylinder. If the engine picks up RPM, the problem is not enough fuel. R&R the carb and clean it properly. Many times the problem at idle is the air meteriing jet on top of the carb. As far as checking float level, don't turn the carb upside down. Turn it so the float pin is up and the float hanging down and the float lightly touching the needle. In this position, maske the adjustment that makes the float parallel to the body. If you have fuel, the last thing is spark. Again, pull the plug boot away from the plug and listen for spark jumping. If you can't hear it, there isn't any, that simple. You've tried swapping coils and thought that was the problem, but replacing the coil wasn't the answer. I've been servicing Suzukis since 79 and have quite a bit of experience and tech schooling on them, including working for Suzuki. All you need to do with these engines, as with any brand, is take a systematic approach each time you work on it. Haphazard repairs just compound the problem. If your service manual refers to a V4 and you have the I-4 (which you do, as Suzuki didn't make a V4, only a 90 and 100), only the theory of operation is the same. The carbs are not, including idle adustment and synchronization of linkage. Back up, take a deep breath, slow down and try it my way.
