1978 Mercury 700 series Mercontrol questions...

[austin_colby]

We just recently purchased a Starcradt 15' runabout with a 70hp outboard 700 series Merc. The engine runs strong but possibly not at its full potential. There is a RPM guage to the left of the steering wheel which indicates the motor runs at about 3800-4000 during full throttle on the mercontrol and about 1000 rpm at idle. When you engage the lever on the mercontrol, the prop starts spinning but there is no throttle until about 3/4's of the way through. I verified this by removing the motor cover and watching the component that the throttle cable is hooked up to only start to move at about the same point. My question is, is there an adjustment for the throttle cable? I saw the one on the motor that actually anchors the cable but that doesn't seem to effect where the throttle engages. It is almost like the throttle cable is stretched but I didn't want to rip everything apart if there is a simple adjustment that I am missing. Thanks for the help in adance.

 

[Chris1956]

Re: 1978 Mercury 700 series Mercontrol questions...

Austin, As far as I know there is no adjustment on the Merc control. You need to place the throttle wide open (motor not running) and see if the carbs are all the way open. If so, the cable adjustment is correct.


If the cable adjustment is correct, do a compression check and then a link and sync, to assure your WOT timing is correct. If both are good, maybe the pitch of the prop is too high. What is it?

 

[Scaaty]

Re: 1978 Mercury 700 series Mercontrol questions...

The distributer does a lot of movement before the throttle opens. I think your fine. If it idles fine, the throttle cable is correct. There is no way that inner cable would stretch in my opinion. If the moment of moving the throttle forward, it comes off the idle stop..thats correct. Theres a lot of things that will slow a boat down besides what you mention.
Read this..
http://forums.iboats.com/showthread.php?t=168855

 

[austin_colby]

Re: 1978 Mercury 700 series Mercontrol questions...

I've played around with the boat for about a month now and have had no problems but just curious about a couple things...

1. Does 29 mph seem like the right top speed for a 1978 Starcraft with this motor. I have talked to a few people and they seem to think that the motor should have a little more power but unfortunately I have yet to check the prop pitch. Someone said to make sure that it is between 15-17 I think so I will check when I get home.

2. I checked the carburetors and watched the throttle control. The carbs are at WOT at the end of the throttle control but it really seems weird that I don't have throttle until about 2/3rds of the way through. I am not too familiar with the primary/secondary pickup system but didn't want to change anything in fear of completely screwing up the motor.

A couple of local service shops told me that the motor is junk and they would not touch it. One guy said that the top piston compression is most likely lacking so I am going to have to check that. (That was the answer as to why the motor only reached 4000rpm instead of 6000) Also they said that most the parts for the overhaul are no longer available so I am stuck on what to do.

 

[redjmp]

Re: 1978 Mercury 700 series Mercontrol questions...

That seems a little slow. I had a 65 hp on a 15' ski boat that did 34mph with a 15p. I stuck a 17p and lost a lot of holeshot and cut it down to 31mph.
It only had 105 on the top and 125 on the rest so I sold it.
It was a '65 and pistons for that one were no longer available. I'm sure I could have found some good used ones but the motor had steel drive and crank shafts that had rusted and even with new seal kits it would have kept leaking from the bottom end because of the grooves that had worn into the shafts.
I'm sure you can find new pistons and rings for your '78.
Why don't you do a compression test and report back your readings.

 

[austin_colby]

Re: 1978 Mercury 700 series Mercontrol questions...

Just a little info about the prop... I don't know if this is the right size or pitch for the boat but I bought it with:

Quicksilver 48 76280 A5 14p 10 1/8" stainless steel prop

Does that seem to be the right prop for this type of application?

 

[redjmp]

Re: 1978 Mercury 700 series Mercontrol questions...

Are you sure its only 10"? That awefully small for a 70 hp. Like that it should redline at 5500 easily.
should be more like a 13 x 17

 

[austin_colby]

Re: 1978 Mercury 700 series Mercontrol questions...

It is definately no more than 10" so perhaps that is the problem. Also I think that there is a chance that the tach could be incorrect.

Another quick question, the current plug set does not have a ground electrode over the center electrode. Is this a standard marine plug or perhaps a hybrid that was used? Thanks for all the help btw.

 

[redjmp]

Re: 1978 Mercury 700 series Mercontrol questions...

Those are normal plugs for an outboard.

 

[Chris1956]

Re: 1978 Mercury 700 series Mercontrol questions...

Austin, First of all, rebuild parts for that motor should be commonplace in both the Merc Dealer and aftermarket. There are some discontinued parts, but they are not usually normal rebuild parts, and usually can be had from used sources, if necessary. You need to check the compression. the cylinders should be close in compression. if not and it still runs OK and has enough power, why worry.

As for the prop, you should match up your part number using a merc prop list, or crossover to a Michigan Prop, to see what you have. I agree that 14-17 " pitch is likely in the ball park as the correct pitch for your application.

 

[charliegiggles]

Re: 1978 Mercury 700 series Mercontrol questions...

I have a 79' 70HP with a turning point 10 1/2 x 13 pitch propeller on an aluminum Starcraft 16.7' boat.

Your controls and cable sounds the same as mine in that nothing too much happens until you are about 60% forward in gear. It sounds like your cable is properly adjusted as the carbs fully open at WOT.

I bought the motor used and have found all necessary parts so far without too much trouble.

Your RPM's sound low to me as the proper operating range as per the manual for my motor is between 5000-5500 rpm. I suggest you purchase a manual for your motor.

My motor currently runs at 5000 rpm at WOT which is a bit low but within the range. I will be testing a 12 pitch prop to see if I can bring the rpm's up a bit closer to the 5200 to 5300 range.

You definately don't want to go above 5500 rpm. Hope this helps. It sounds like your prop has too much pitch to me however I'm no expert and many people on this forum have provided very valuable advice.

 

[austin_colby]

Re: 1978 Mercury 700 series Mercontrol questions...

Compression test results are in and each cylinder has 120lbs exactly. Does that mean that there is something set incorrectly with the carburetors or perhaps another problem that could have been overlooked? I really do not have a way to take the boat to the river and do the adjustments like in the faq posted above because of the distance. Is there a way to recalibrate it using the muffs?

 

[ricksrster]

Re: 1978 Mercury 700 series Mercontrol questions...

Do you have a tach? What are your RPM at WOT?

 

[ragu]

Re: 1978 Mercury 700 series Mercontrol questions...

I am having the same exact problem with mine also a 115 mercury 1970 i just took it to the boat mechanic. He said i need new cables said they look to be the origional ones and that they are very stiff. Does your idle lever lift up when you advance the throttle? I dont think it has anything to do with your prop!! I tried 2 others and they had no impact on the controls i think it is your cables !!

 

[austin_colby]

Re: 1978 Mercury 700 series Mercontrol questions...

I think that it might have something to do with the prop... I can run the engine at WOT out of the water with the muffs at about 6000 rpm but with one person in the boat in the water it will only get up to about 4100. Top speed yesterday was about 30 mph. I believe the prop is limiting the RPMs and the speed but I do not know which way to go. Should I try a higher or lower pitch or just leave it alone? From previous experience with two strokes, it seems that they run better at the higher rpms and usually have a decent powerband up there also.

 

[ragu]

Re: 1978 Mercury 700 series Mercontrol questions...

back to the beginning of your question you wanted to know why the shifter moves quiet aways till something happens. So does alot of other people on here from what i found in the search. Seems like alot of people are having the same problem with a mercontroller. Why would it travel so far if the cables are adjusted properly? Could it be a worn roller inside the controller? Does anyone know ?

 

[austin_colby]

Re: 1978 Mercury 700 series Mercontrol questions...

I still would like to know the answer to that question but don't want to rip the mercontrol apart to see if there is an adjustment. Here is my theory though... Since there is a certain amount of travel that the transmission cable needs to engage the drive, the throttle cable also must have the same amount of play. If it was adjusted so that the throttle cable started revving the engine immediately after the shift out of neutral then it might damage the gearbox if the transmission wasn't fully engaged. It really is no big deal since the control opens the carburetor to WOT. If it doesn't then there might be room for concern. Now only to figure out this prop pitch problem...

 

[ricksrster]

Re: 1978 Mercury 700 series Mercontrol questions...

First:
6000 RPM out of the water is not good for the motor.
Next:
You are correct. 4100 RPM is too slow. You might want a lower pitch prop. How much lower I do not know. Before you do that, you could try adjusting the trim up or down a notch to get a better angle.

 

[Chris1956]

Re: 1978 Mercury 700 series Mercontrol questions...

Austin, There is no adjustment inside the MerControl. All adjustments are at the motor end of the cables. As long as your controls allow the carbs to open all the way, they are adjusted properly. The MerControls have quite a bit more travel than the motor's throttle.