1958 Mark 28 problems

[stubbstheman88]

I recently just got a 1958 mark 28 that is FLAWLESS. it is in perfect condition with very little paint scraches, and shiny and totaly perfect three blade ss prop, and probable 10 hours or less run time. When i got it i replaced the points, cleaned the carb, and greased the lower unit. I also checked the impeller and it seemed to be fine and in no need of replacement. The first time i took it out it seemed to have trouble getting over about 3k RPM. It couldnt get enough speed to get my 10ft jon boat on plane. I figured it was the carbs so i took it home and did some adjustments. When i took it back it was a little better and seemed to get up to make 4k max. This being a 22hp motor i would at least expect a decent speed with this small of boat but it seemed like i had a 10 horse on the back. I did a few more adjustments of the carb while running and couldnt get any more speed. and another weird thing was that if u throttled down a tad, it seemed to get bit more speed then full throttle. I know that while turning the handle, the carb completly opens and the spark advances all the way but i dont know why its not getting up to speed. im thinking it might be the prop? or mybe something with timing? Any ideas are welcomed.

 

[Chris696]

Re: 1958 Mark 28 problems

weird thing was that if u throttled down a tad, it seemed to get bit more speed then full throttle. I know that while turning the handle, the carb completly opens and the spark advances all the way but i dont know why its not getting up to speed. im thinking it might be the prop? or mybe something with timing? Any ideas are welcomed.[/QUOTE]

The going faster at less than full throttle leads me to think fuel problem. It's NOT the prop. Most of the time the prop will match the motor unless it's been messed with, but it sounds like you have an unmolested motor. Also I'd think the timing is fine for the same reason. Stick with fuel. Check the plugs after running to see if they are "wet". You might want to install new plugs in order to observe the change easier. Better to see on white than if plug is darker in color. I wouldn't do anything drastic at this point like changing timing or props. Try running it with the choke on just a bit to see if it changes. I'm not an expert, but strongley feel it's a fuel problem. Plus you said it runs faster after adjusting screws. BTW, my Mark 20 w/ 3 blade bronze prop on a 10 ft. Zodiak fly's. Your boat should be so fast it scares the hell out of you. Make sure the float in carb is working correct. Does it float and is it set correct? Mine is made of cork and can deteriate after 60 years.

 

[bktheking]

Re: 1958 Mark 28 problems

A mark 28 on a 10ft jon, are you trying to kill yourself??? I ran my KH7 on my 14 ft Crestliner and almost flipped it in the summer. Anyways sounds like you are down on a cylinder. Have you checked for spark on both cylinders?

 

[backyard mechanic]

Re: 1958 Mark 28 problems

Without hearing it run it's hard to say what's up with it but I'm going to speculate based on your written story... Here's what you said;

*When you got it you replaced the points, cleaned carbs and greased the LU.
*You said you "messed with" the carb and it got better.
*When you back out of the throttle it seems to go faster.
*It seemed to have trouble getting over about 3k RPM.

So here's what I think;
First of all, do a compression check. All repairs start there. Look for how fast the guage "pumps up" and to what numbers.

Messing with the points is to mess with the timing. Hopefully you replaced the condensers while there. If you didn't use an ohm meter to set your second set of points exactly 180* from when your second set opens, you may be out of sync. Were you careful with setting a 0.20 point gap and what was your crank position when you did? The points have to be set when the piston is in a specific place as noted by mark on the crank locater tool pointing at the marks on the point plate. If you don't have to tool you can put the flywheel on and line up the marks then take it off carefully to set points. When your piston is at TDC, the points should be just opening.

You "messed with" carbs. What exactly did you do to the carbs? Float settings are important. The little spring on top of the float have a lot to do with that setting. If you were setting idle speed adjustments, 1 1/2 turns on the low speed jet and 1 turn on high speed (if there is an adjustment) will get you started. Seems you are past that stage however. "Messing with it" made it better is unclear. How does the engine idle? You didn't mention that.

When you back out of the throttle and it picks up that could mean you aren't burning all the fuel you are giving it or perhaps the FP isn't giving you all the engine needs. It could mean the vent to the tank is closed or it can also mean the timing is not correct.

Running at 3K tells me your carburetors are "OK" but not at an efficient level. I'm assuming they do open all the way. In gear, check that the throttle plates are indeed wide open.

Assuming all is linked, sync'd and everything else is running OK I'm going to guess the timing is off. It's always worth while to do a link and sync and see how much better your engine runs. Good luck...

 

[bktheking]

Re: 1958 Mark 28 problems

To add, are we sure the gap is .020 and not .018?