200 Rude missing @ mid RPMs

[mikec]

This board has been great help, hopefully it can be again. My 92 XP engine starts and idles great, compression good, runs 54mph @ 5400 RPMs ;-), when goosing it from idle to WOT she gets out of the hole fab, but at mid RPMS under load, from 1500 to 3000 it seems to miss at times. Sometimes I can find that RPM when it purrs, but not often. Maybe I just dont hear it miss at WOT. It's been decarbonized, and gas/oil is good, no exessive smoke. Items recently replaced: stator, regulator, plugs... Any ideas? It's not reeds or anything like that is it? Maybe needs a carb rebuild, or has a vacuum leak? Seems like just one plug not making it. TIA - mikec

 

[alpineswampman]

Re: 200 Rude missing @ mid RPMs

I just went through this with my Evinrude 120. Does it keep running if you pump the primer ball at these rpms? First check to see that you don't have a blocked fuel hose or a loose fuel line connection. Then put a fuel pressure guage between the fuel pump and the carbs. You will need a fuel pressure guage, a 3\8" or 5\16" brass tee and some pieces of the appropriate fuel hose and clamps. I don't know what the pressures should be for your HP but the 120 should have a minimum of 3psi at 800rpm. I would assume that you're probably somewhere in that neighborhood too. Basically fuel pressure should increase with engine rpms.<br /><br />Did your boat sit up for a long time? It could be trash in carbs. Also, i've been told that if your fuel pump is over 2 years old it isn't compatible with the fuel that is in production right now. Evidently the fuel that we have now eats up the diaphrams in the pumps. <br /><br />Mine ran at WOT and idled fine. The fuel pump put out less than 1psi from idle to 3000 rpms. I disconnected the fuel hose from the presssure guage, put it into an empty gas can and nothing came out which meant that my pump was totally dead! I put a new fuel pump on and now it works like new.<br /><br />Good luck,<br />Brett<br /><br />DONT SPEND MONEY ON A FUEL PUMP UNTIL YOU KNOW FOR SURE THAT THAT IS YOUR PROBLEM!! TEST IT FIRST!! THIS IS ONLY ADVICE AND I GIVE NO GUARANTEE OF ITS ACCURACY AND AM NOT LIABLE IN ANY WAY!

 

[JB]

Re: 200 Rude missing @ mid RPMs

Hi, Mike. I think the swampguy is onto something. The 200 exhaust system resonates in the 3500-4500rpm range. Crankcase pressure waves drop as scavenging improves and thus, fuel pump efficiency drops. As the pump diaphrams weaken, mid range is the first place a sensitive ear will detect a change. Try overhauling your fuel pump. It may not change anything, but then again. . . .<br /><br />Red sky....<br />JB

 

[mikec]

Re: 200 Rude missing @ mid RPMs

Thanks guys. I will definitly look into the fuel system and test the fuel pump. This is a "new" engine for this boat, so Im pretty sure the inboard tank and connects are OK, as the last engine was fine at those RPMs. Great info, thanks! -mikec