1200 rpm loss

[MTOLLEY]

hey guys. hope some of you gurus can help me out, this ones got me puzzled. back in january i took a little trip with the boat and ran fine all day(6200 rpm) switched it off for a few hours. when i fired it up again i could only get 5000 r's outa her.by the way this is a 1976 200hp evinrude. been turning 6200 forever and never a problem. checked everything found the timer base bad on #5 cylinder and replaced it. put in a new set of plugs(ql77jc4)gapped at .035 at went to the lake. still only 5000 r's and sometimes would jump to 5200. today i rebuilt carbs(found a SMALL amount of trash in the bottom carb) a new set of plugs and off to the lake. well low and behold i picked 500 rpm up so i now im at 5500. the only thing i havent checked or replace is the fuel line and bulb form the tank to the engine. any takers on this one? sorry for the long post just trying to give as much info as i can. mike t

[MTOLLEY]

anyone got any ideas of this problem? sorry to ressurect an old post but i still cant find the problem. thanks! mt

[H2OPERF]

Give us some more information,have you checked the compression? does it have good spark on all six?Did you check the WOT timing after you changed the timer base? What hull is it on and what prop pitch? is it stock or modified? 6200 sounds high if its a stock 200, maybe your tach is acting up.Dave

[MTOLLEY]

im going to list everything ive tested and tried to this point to solve my rpm loss. as originally stated ive lost @1200 rpm only to gain back around 500rpm. ive tested coils, stators, and everything electrical under the cowling to find that all was good.ive replaced both fuel pumps,all lines and primer bulb all the way back to the tank. no clogged vent or anything else found in the fuel system. the ONLY thing that i havent done is eliminate the key switch, which im headed to the shop now to try. carbs are clean, spark will jump a 1/2" gap with a bright blue flame , compression is even at 135lbs across all six and gets decarb every 6 months. i have run this engine at 6200 rpm as long as ived owned it and to just drop back to 5000 only to recover to 54-5500 rpm is stumping me. thanks for the help. engine is mounted to a stratos 266 f/s,6"manual jackplate running a 25" trophy plus. prop shaft is set at 3" under boat and im able to maintain 12 psi water pressure. the only mods to this engine are a .030" overbore and wiseco pistons. plug color is good and max timing is set at 30 degrees. i have noticed also that when lifting the fast idle lever on the control box that engine doesnt want to rev quickly but slowly climb in rpm. ive tried 4-5 diferent tachs with the same result. they cant all be wrong.

[H2OPERF]

If your key switch has resistance to ground it will usually have weak spark at cranking speeds.Have the coils been upgraded? those old ones with open irons crack with age.You might want to crank it up at night and look for leaks at the coils,You possibly have one bleeding to ground after you get up to rpm and your losing a cyl.This will not show up when checking the coils for resistance only.Did your idle rpm change at all,Im not doubting your tach reading is off now but they have settings on the back for different engines the originl may have moved by vibration.I just read back 30 deg and 135psi thats alot of timing for that compression hope your running premium i would drop that back a few degrees.Dave

[MTOLLEY]

all six coils are new as of 2 weeks ago as well as both power packs.(old screw packs) the stator is @ year old and timer base is @ month old.(good luck to those who need one)

[thumper]

Just a question.
What happens at WOT when you hit the choke?
This needs to be a process of elimination, not willy nilly all over the place.
Pick one thing and pursue it till you can go no farther.
Fuel is usually the easiest. Give us the results of the choke @ WOT.
BTW, check synch and link for the carbs. Reason I ask is that can fail between startups. It's mechanical. If you're unfamiliar with the term, make sure all carb butterflies are moving together and they are all open @ 90 degrees @ WOT
Let us know !!

[Rickracer]

...do it while the motor is warm and dropping rpms. I had a stator causing random misfire, and checked it 3 times before I finally took my meter with me to the lake and checked it hot when it started dropping cylinders. It checked bad hot. :cool:

[EMDSAPMGR]

If you replaced the power packs with new from Bombardier, they have built in rev limiters in them now. Your old ones had no limiters. New ones come with a 5800 limit. The original ones for your engine are NLA from Bombardier. Put your old ones back on. Whenever you put a new timer base on, it upsets the timing and sync and link, as previously mentioned. If that proper linkage relationship if off, it can cause the problems you describe. Be sure the link arm did not come detached. You need to retime (on both #1 and #2 cylinders) and then reset the sync and link. When running that much advance, you must be dead on for timing. Most plugs from OMC are sold pre-gapped at .030 today.

[MTOLLEY]

thanks for the responses guys! the power packs are new from cdi.the packs i took off were @1 old and were also new from cdi. didnt make any difference. replacing stator didnt make any difference either. when i hit the choke at wot the engine loses rpm, im guessing that means its flooding. i would think if it picked up rpm than i would have a fuel restriction somewhere. im not dropping cylinders during a run anymore. it just wont turn more than 54-5500 rpm regardless of jackplate height. ive tried jacking to 2" under pad and still cant get anymore rpm. do cdi packs have a limiter? it sure would be strange for it(the limiter) to start working after a year of running.
yesterday evening i started checking the kill circuit from the engine to the control box. i disconected everything from both packs and connected the red lead from my dmm(fluke 77) to the kill wire and the black lead to engine ground. with the key switced off it shows .5 ohm, which to me indicates that the kill circuit is working. turn the key on and meter shows "open line" which indicates that kill circuit is inoperable therfore engine will run. the strange thing is that if you reverse the leads you should still get the same reading but i dont. with the leads reversed(red to ground -black to kill wire) i get the same reding with the key off but when you turn the key on i show a small amount of continuity in the kill circuit. so today im pulling the control box apart and start tracing wires from control box to engine in search of something. keep the ideas coming guys i need all the help i can get!

[staylor]

on a 175 cross flow. Sometimes I'd lose 500rpm, sometimes 1000, and it was totally random. Turned out that the key switch was worn badly inside and would jiggle around when running till it would drop a cylinder or two. An OMC V-6 doesn't run all that bad on 5 cylinders at higher speeds, so all you'd really notice was the rpm loss. When she'd drop 1000 rpm it was 2 cylinders going, and this you'd notice. Had the kill circuit do the same thing on a merc many years ago and this gave the strange start up behavior you describe. Trouble with intermittant electrical problems is that you're usually reduced to "poking and hoping". One other possibility is a second kill switch that I know is on loopers but may or may not be on your engine. This one is in the shift and throttle mechanism and is a little on-off contact switch engaged by shifting. It's supposed to kill half the cylinders at the instant you shift to reduce lower unit loads. I had one go bad and it would kill 1-2-3 cylinders randomly, depending on it's mood that day. On a looper this is way down at the very lowest part of the throttle- shift linkage, almost down to the lower cowl base. The wire to mine was pinched by the cowl and had worn the connections loose inside.

[Redbullet]

I just replaced and Ingition switch that was only 2 years old. It was putting some resistance to the kill wires to the switch boxes and causing me all kinds of grief. Motor lost over a 1000 rpm at wot and would not idle worth a hoot.

[B.Mac]

I pulled my hair out for two weeks looking for an electrical problem on my Looper that cost me 1200+ RPM and B.Leonard found it in an hour. I had hose rubber in my float bowls on two cylinders causing my needle valves to hang up and run rich on two cylinders. May wanna look them carbs over.
What does your exhaust outlet look like?
Is it blacker than usual?
Got EGT's to read temp diff's on banks?
B.MAC:D

[RRRevinrude]

the anti-siphon valve at the gas tank???have you run it off a separate tank???throw a 6 gallon in there once and try it....greg

[Forkin' Crazy]

To test the key switch/ boat wiring harness, can't you just fire the motor and unplug the large cannon plug just to test run it?

What do the rpms do when you pull it back just off of WOT?

[Markus]

1200 rpm is about what you lose when you completely lose a cylinder on a V6. Have you made a WOT plug chop and made sure that there is action in all six holes?

[MTOLLEY]

ill try to answer in order:
markus:1200 rpm is what i originally lost. traced problem (or part of it) back to a faulty timer base. replaced timer and coil on bad cylinder at same time. also at that time i pulled the carbs and THOROULLY(spelling) cleaned them. found one itty biity piece of trash in the bottom carb. this is when i picked up 4- 500 rpm. all six holes are hot and plug color is fantastic, just short on rpm's.

forkin crazy: that was my intention today but my buddy and i decided to take the cougar mtr out instead and air those twin MERC 260's.( had it to 110 on the gps today just too much boat traffic) ill try that tommorrow when i get home from work.

rrrevinrude: this was one of the first things i did. originally just knocked the guts out of the valve with no change in performance. have since replaced with a new valve. still no change.

b mac: when i lost the orig. 1200 it would blacken the prop. now all is sprkling clean.

red bullet: ive got the rpm loss but the damn thing will idle forever and not foul the plugs.

staylor: my engine is to old to have a kill switch other than the key switch(1976) ive added an emergency kill switch like most newer boat/motors come with(lanyard type) only a complete idiot would run a boat without one! too much bad chit can happen on the water.

guys i really appreciate all of the great replies to this post. ill let you know what i find tommorow night when i get home. this boat is a shoestring budget boat that weve thrown together to play with. between the mirage/300 merc and the 23' mtr/twin 260's ( both are/will be for sale) there is plenty of speed hanging around. just to much boat traffic on our local lake to really let them SCREAM AND FLY! happy 4th to you all! mt

[RRRevinrude]

i would still try it with a puppy tank...it could have a crack in the fuel pick up tube in the main tank...its easy enough to do and will eliminate it being a fuel source problem..and i would do what forkin crazy said-this will eliminate the key and main harness..but remember you won't be able to shut it off.....greg

[MTOLLEY]

well the key switch test shows all is well,even with the red plug unplugged there was no difference. just for ****s and giggles i replaced the stator with a spare i had laying around. the one i removed tested good with a vom but did have some disoloration around the charge coils.the engine seems to throtlle up better with the fast idle lever now. with the fast idle lever is it normal for the engine to jump right up to @3000rpm and creep up a little at a time beyond that? with the old stator it crept up all the time as if the engine were really loaded up with fuel. it will be a while before i get to water test as im leaving on vacation at the end of the week. thanks guys mt