Trouble shooting Merc 200hp

[steve forsythe]

Re: Trouble shooting Merc 200hp

Marlin....I know mine has always given me trouble in the mid throttle location. If i have run it a little, then come down off plane, putt around a little, and then attempt to slowly throttle back up, she boggs down around 2000-2500 rpm's. If you gun it, it will fire right up and go, but if you stay right there, it will conk out. I have been told it could be timing, linkage, dirty carbs, fouled plugs, and 100 other things. I am wondering if it relates to my powerhead problems? Anyone have an idea if the two are related or how to correct? <br />Thanks.

 

[gss036]

Re: Trouble shooting Merc 200hp

I have been running a 1989 Merc 200 w/carbs, since new, ( in saltwater) put a rod through the block at 140 hours, put on a new powerhead and has run great since. I use NGK surface gap plugs, changed about 350-400 hours.<br />I have the head gaskets changed every 2-3 years depending on the hours. I decarb about every 100 hours.<br />I have never run my carbs dry, sometimes, like now, has set for almost 3 months in the barn, I think it will fire right up and run. If I get a little surging after the first trip I will change the fuel/water filter because of condisation(?) build up in the 115 gal alumiumn tank. I do leave the fuel cap off of the tank inside the barn, stick a paper towel in the inlet, since starting this, I haven't had the problem though.<br />I get a little surge at 3500 rpm, I was told that was because of the fixed jets on the carbs, going from low speed to high speed,??.<br />It sounds like you are doing things right, just a run of bad luck. The 5800 RPM is way too high, should not be over 5500. I know a lot of guys say to run that high, but the book calls for 5000/5500. If the timing is advanced too far, you create a hot spark and could hole a piston or scoring. Holing a piston is pretty common on 2 stroke bikes running at high RPM for too long. I've done that on both 175 and 400 Yamaha enduro's/motocross bikes. Just my 2 cents and thoughts. Gary

 

[kshatzer]

Re: Trouble shooting Merc 200hp

Just wondering if anyone else has any ideas on this topic

 

[steve forsythe]

Re: Trouble shooting Merc 200hp

I really sound like an amature here, but is it easy to decarb? Should i do it myself? Should i spray anything into the carbs to clean them? Should i run one bottle of fuel stabilizer at high concentrations like the bottle says (1 bottle per 2 gallons), to clean out all the gum and varnish?

 

[TopNotch]

Re: Trouble shooting Merc 200hp

My brother had the same engine on his 20' Aquasport. <br /><br />With the same exact problem that you are having. He blew his engine twice, until his mechanic finally got it fixed.<br /><br />There was not enough fuel pressure going to his engine, an aftermarket fuel pump was added inline before the engine. Problem solved. The lack of fuel and lubrication had overheated the cylinder and blew it. I cant remeber which cylinders they were but as soon as he got the fuel pump in there, that was it. Fixed the problem.<br /><br />He was too scared to run the engine anymore so after a year more with the engine he decided he cant gain trust in it, and went back to OMC.

 

[steve forsythe]

Re: Trouble shooting Merc 200hp

Is that a pump that goes under the cowling? Or back by the primer bulb? Is it in addition to the stock fuel pump, or do you have to take that one out? Do you know what kind af aftermarket pump he got?<br />Thanks.

 

[kshatzer]

Re: Trouble shooting Merc 200hp

I sure wish I had seen this a week and a half ago!!! Not a good indication of things to come. I've always had OMC prior and guess I should have tried to stay with them except the boat dealer was a Merc dealer.

 

[TopNotch]

Re: Trouble shooting Merc 200hp

Hey Purse...<br /><br />My brother is offshore fishin for the next couple days, I will ask him when he gets back. But the pump was installed behind the primer, (actually i think the primer was removed-makes sense)<br /><br />oh and pretty sure he left the stock pump in...but again i will ask about the peticulars

 

[gss036]

Re: Trouble shooting Merc 200hp

I would think that he would have to install some type of electric fuel pump in order to put it in the fuel line. Never heard of that. I know all the new cars, etc., have electric fuel pumps in the tanks or inline. I don't see why it would not work for a outboard since the fuel is sucked in by a diaphram type pump.<br />I have a set of fuel line connections that I use to siphon out my old fuel for the lawnmower and it once you get it flowing with the primer bulb, it flows slowly until disconnected. Just pulled out 15 gal. yesterday, getting ready for the July 1st opening in our areas for Salmon, yeah!!!!!!!

 

[Hooty]

Re: Trouble shooting Merc 200hp

Bosch, Carter and Holley all make electric fuel pumps that are good. I personally like the Carter red pump. There are some ramifications you need to consider when using a electric fuel pump like emergency shut-off and wiring with or without a relay.<br /><br />c/6<br /><br />Hooty

 

[TopNotch]

Re: Trouble shooting Merc 200hp

I would wait until i talk to my bro (or talk to a outboard mechanic that has done this) cause i know there was a specific fuel psi shut-off that may be important to know.

 

[KennyKenCan]

Re: Trouble shooting Merc 200hp

One place that you may have overlooked...<br /><br />Check the reed assembly, it may have a cracked or stuck reed which could cause the problems you are experiencing.<br /><br />Just a thought.<br /><br />I have never heard of any Merc engine needing an electric fuel pump unless the fuel tank was more than 25 feet away from the motor.<br /><br />Not too sure I would go that route, as the fuel pumps on these engines are very reliable and 98% of the time are more than enough to supply the motor with fuel.<br /><br />Kenny

 

[Kenny Bush]

Re: Trouble shooting Merc 200hp

I do agree with Kenny K C that the reeds if broke or stuck open would present problems in oiling that cylinder..... Basically with a open reed, your engine will not generate enough vacuum to suck in the fuel/oil into the chamber.

 

[steve forsythe]

Re: Trouble shooting Merc 200hp

probably another dumb question, but, can i check for that problem without a lot of difficulty? Or is it an operation that an amature should not perform? How expensive is a broken reed fix?<br />Thanks

 

[KennyKenCan]

Re: Trouble shooting Merc 200hp

To check the reed assembly is not difficult, but it is labor intensive.<br /><br />You will need to remove the intake mainfold to get to it.<br /><br />You can leave the carbs on, but you will need to disconnect everything that goes to them.<br /><br />The reed assembly is on the back of the manifold.<br /><br />You will need gaskets and sealers to reassemble.<br /><br />Kenny

 

[gss036]

Re: Trouble shooting Merc 200hp

I got to thinking about the last time I had trouble with my motor dying, early last spring, I would fish down drift with my kicker motor, fire up the 200 Merc, throttle up, it would start to get up on plane and sputter out, pump the primer ball and retry again and away I would go, it did this like 3 times on me, yet when I fired up after the last drift to head back across Georgia Straight it ran great. I pulled the fuel filter, it looked ok, a little water but not much, changed the filter and it has never done it again.<br />Maybe a bad filter or seal and it was sucking a little air??<br /><br /> I asked my mechanic about rough idle and he says it is because I use regular gas, said to take a tank of High Test and run at idle and I would see a differnce and it would smooth out, although I never did try it, too much of a hassle I guess.<br />Just something else to ponder on!!!!!

 

[steve forsythe]

Re: Trouble shooting Merc 200hp

Thanks GSS for the info. I have replaced the fuel filter, and run a water separator. I am using gas stabilizer now also. I am wondering if i should de-carb or run some ring free through? I also heard you shouldnt use high octain fuel....? Any one have a thought on high..er octain fuel. I use 87 from the local gas station.

 

[Hooty]

Re: Trouble shooting Merc 200hp

The 87 proof should work fine. <br /><br />I'm still thinking about a busted or even a missing reed. How would that keep one cylinder from oiling? Usually if ya got a busted reed and it didn't trash a piston and/or cylinder when it went through, it just blows fuel back out the carburetor. It wouldn't cause any less vacuum because the reed opens on the down stroke anyway. Am I missin' something?<br /><br />c/6<br /><br />Hooty

 

[Kenny Bush]

Re: Trouble shooting Merc 200hp

Hooty, when the reeds are open or broke, you get inefficient fuel flow. Basically you cannot generate enough vacuum to pull the gas/oil into the cylinder completly(on some models). Some engine designs have smaller chambers, and the reed blocks flow oil down by gravity in this situation. Also, open/busted reeds can affect your compression readings also (On some designs). I wish we were at the blackboard, so I could draw you a diagram...with a few beers of course.

 

[clanton]

Re: Trouble shooting Merc 200hp

After you do all of the above post, have you checked the jets in the carbs to verify the correct jets are install the carbs, all carbs may not have the same jet size. Verify max timing at full throttle for all cylinders, while engine is under load.