1986 merc 200hp blackmax throttle 'backing off' and other questions

[JerseyJim]

I have an 86 200hp blackmax that runs real well. However, I have some nagging issues with the throttle controls. I think they are ultimately related. I have the 'commander' series of controls (remote choke and up tilt, also up and down tilt on the throttle lever. Fast idle is achieved by pressing the button at the base of the throttle.)<br /><br />1) Idle speed in gear is about 500rpm. This SHOULD be about 700, but no more than 750, right?<br /><br />2) At mid to high rpm, the throttle will 'back off' by itself (ie, if i set the throttle at 3500rpm for a comfortable cruise at about 20kts, the throttle will back off to 3200 by itself if I dont hold it. This also applies for high rpms, where i push the throttle down to say 4500rpm, if i lift my hand off the throttle it will back down to 3200 all by itself. Where can i fix this, is it at the motor, or in the control box itself?<br /><br />3) There is a lot of 'slack' in the throttle before you actually get into an area where the rpms go up.. The throttle lever is almost at 3/4 before I just start increasing the throttle off of idle. <br /><br />4) WOT is about 4800rpm and about 31kts. At least thats the throttle pushed to the stop. Could that slack be keeping my from hitting true WOT, pushing up to 5500 rpm? The previous owner said he had the boat into the 50mph range. Granted this could be prop related, but i should probably fix the throttle problems before i start throwing $400 propellers at it.

 

[Maximerc]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

Jim... I have a 1984 150 black mac that does the same thing . I have a quicksilver control box. I am pretty sure that the darn things are not suppose to "backoff" however I do believe that the throttle not engaging till about 2/3 of the way forward is normal. If it engaged too early it would make the throttle too sensitive and it would make adjusting the "fast idle" very difficult.. Pull the engine cover and with the engine off pull the carb cover.. look in for that nice wide open carb. I do that with all my engines .. Like to know that I am goin WIDE OPEN !!

 

[Kenny Bush]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

The throttle backing off is strictly a shifter issue. Pull the shifter base cover off and there will be a "Tension adjustment screw". Just tighten this screw a little bit and test. Repeat if necessary. As for the idle.... If you can idle at 500 OK, then I would leave it alone. I know the book says 650 to 750 but if the engine is totally balanced(Equal compression in each cylinder), I have seen them go to 450 or so. Don't forget that your timing, and throttle go hand in hand with each other. As you give it more gas, the timing also advances until you hit the "Max advance screw". In your shop manual, this will be listed under "Timing and Synchronization". You say you cannot reach wide open throttle. With the engine and key off, move the shifter to wide open throttle...As much as you can give it. Then go to the engine and see if the carburator linkage can be opened up more by hand. If the linkage is not bottomed out, you need to adjust the throttle linkage accordingly. If everything is adjusted correctly, you should be able to move the throttle up and down good response. If the adjustment will not hold on either end, then your cable may be stretched.

 

[JerseyJim]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

maximerc: well, it shifts out of neutral as it should, but having to take up about an inch of 'slack' after it shifts does not seem normal. I had a similar shiftbox on my '91 walkaround with a mercruiser i/o. The throttle went up right after forward engaged, no slack at all.

 

[JerseyJim]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

i only wondered about the idle being low, because it idles fine, but the engine shakes like a sonnova gun at 500rpm, and seems to run smoother at 6-700.

 

[Kenny Bush]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

JerseyJim, not to change the subject, but what kind of speed are you getting with your Aquasport with the 200. And also do you have an electronic box on your T-top? I am only getting 43 mph max with a 19 pitch prop on a 21' CC. The wind resistance is killing me... Especially in a crosswind. And I even have trim tabs. A 21 pitch prop gives me the same speed but less RPM's. My "Sweetspot" is about 32 MPH or 4100 rpm's. Anyway, just sizing you up....

 

[JerseyJim]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

i do have an electronics box, and a windscreen that goes right up to the electronics box. The GPS says 30/31kts at 4800rpm, around 20kts at 3500rpm ... My comfortable cruise seems to be about 20kts at 3500. Often I have found that the boat rides better at higher speeds, to take advantage of the length of the boat from wave to wave. I was chopping through 3 footers this weekend at 30kts with no spray and no pounding. <br /><br /> I'm not sure what pitch prop i'm running, i keep forgetting to pull the numbers off it.

 

[Rangerbilt]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

Hi, I just want to know if you guys came out with the fix on the throttle backing out during mid to high speed. I have the same problem with mine. I have a 1983 150HP blackmax. I have to hold the throttle control to keep it at wot. If I let it go it slowly backs out.

 

[JerseyJim]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

ranger: i'm going to try the set screw this weekend...i'll post my results here...

 

[Rangerbilt]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

Thanks Jersey Jim.

 

[Maximerc]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

Ranger I have not torn into my throttle problem yet have You??

 

[KCLOST]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

Yep, there is an adjustment screw that you need to mess with to get the throttle lever to stay in place. I'll get my manual out tonight and post the directions....<br /><br />Mine does the same thing, but doesn't seem to bother me..<br /><br />Idle 650 rpms, Jersey..<br /><br />One thing I'd like to ask you is if your upper exhaust ports are not submerged below the surface of the water... If so try trimming the motor out to raise them above the surface and see if that increases your rpms 100-150+ at idle.

 

[JerseyJim]

Re: 1986 merc 200hp blackmax throttle 'backing off' and other questions

I havent torn into this either...I recently had the fuel pump rebuilt and the intake manifold gasket replaced, and the merc tech that worked on it - a VERY VERY fair shop mind you - told me not to bother with it, as it is a nylon set screw, and it was a known problem. Tightening the nylon screw may help, but it will happen again.