1963 Merc 100hp won't accelerate

[waymilky]

The engine starts easily,idles smoothly,and runs smoothly at low (<10mph) speed. When I try to accelerate it picks up speed to about 20mph then it slows down without moving the throttle. It sounds like it is going to die, but doesn't as I pull the throttle back. At other times I can get it to run with the throttle pushed forward but the speed varies between 10mph and 23mph with the throttle in the same positin. It never runs wide open.<br /><br />Waymilky

 

[Elmer Fudge]

Re: 1963 Merc 100hp won't accelerate

Hi waymilky, welcome to the forum <br />It seems that your problem might be fuel starvation.<br />1.check that there are no air leaks in your fuel line.<br />2.check that the fuel tank is venting ok<br />3. replace the diaphrams in the fuel pump<br /><br />If the problem persists lets us know and we will move on to the carbs.

 

[waymilky]

Re: 1963 Merc 100hp won't accelerate

It appears I have two fuel pumps, the top one I removed and the diaphragm is intact. Is the diaphragm supposed to be taunt or is it okay to have a little slack in it? The bottom fuel pump I have not removed as I can't get to the bottom screw. Is there a trick to get to this screw as it is down below the level of the engine casing and there is only about an inch and a half between the casing and the screw. In addition, it is under the fuel pump so I need to go around the pump. There must be a trick or tool to use. Advice please.<br /><br />Waymilky

 

[Elmer Fudge]

Re: 1963 Merc 100hp won't accelerate

Does the primer bulb get soft when the motor cuts out?<br />Has this motor been laid idle for long period, say like over 3 or 4 months?<br /><br />Go ahead and rebuild the fuel pump anyway, diaphrams can sometimes develop leakage areas that are smaller than a pinhole, causing a loss of vacumm pressure.

 

[gwmark78]

Re: 1963 Merc 100hp won't accelerate

You should have an access hole in the bottom cowl for the lower pump

 

[waymilky]

Re: 1963 Merc 100hp won't accelerate

Yes, the boat has sat idle for a prolonged period. I think it has only seen water twice in two years, once twelve months ago and again yesterday. When I used the boat last year it did not run properly then either, as I recall it would only run slowly. Yesterday I did notice that after pumping the bulb firm that it would be softer when I went back to recheck it. It would not be as soft as prior to the initial pumping, but it would not be as firm as after I pumped. Would you suggest that I go ahead and replace the bulb and fuel line?<br /><br />GWMark78,I found the access hole. I didn't see your note till after a local dealer told me I had to lower the engine cowling. I loosened all kinds of bolts trying to lower that cowling. Finally in frustration I stopped and came in and found your reply. I just couldn't believe I missed that access hole. Thanks for your help.<br /><br />Waymilky

 

[Clams Canino]

Re: 1963 Merc 100hp won't accelerate

You may have to clean the carbs too. This can be done with them still on the block - though it gets "creative".<br /><br />-W

 

[Elmer Fudge]

Re: 1963 Merc 100hp won't accelerate

It is not necessary to replace the primer bulb unless it is faulty, as of yet that has'nt been determined, has it?<br />As Clams Canino mentioned you may have to clean the carbs, i suspect that a fair bit of varnishing has taken place since the motor sat idled.<br />If you are going to attempt to do this your self, you should first get a service manual for your engine's make and model year, if you don't have one you can order one at the bottom left of the page.

 

[trackerdave]

Re: 1963 Merc 100hp won't accelerate

Clams, how would you clean them on the block?

 

[mikekreft1]

Re: 1963 Merc 100hp won't accelerate

I have a sea ray with a merc 150, I had the exact same problem with my boat idles good, at 15-20 I get a loss of power. I took it to my mechanic and 2 out of 3 of my carbs need rebuilt. He is charging me $96 per carb plus parts. I get it back next week so I am not yet sure if that will fix it but the mechanic is 100% sure it will.

 

[Laotzu]

Re: 1963 Merc 100hp won't accelerate

Waymilky,same problem I had. My motor sat for 4 years before I bought it and it had developed some varnish in one of the carbs bowls.. Starved #1 and was running on 2 cylinders. I removed mine to clean(50hp) and wasn't too difficult. Just be careful when you remove the bowls, nothing screwed down inside there.<br /><br />Jerry

 

[waymilky]

Re: 1963 Merc 100hp won't accelerate

So far I have replaced the fuel pump diaphragms and ran some carburetor cleaner through the carbs. I don't know yet the results as I haven't been back to the lake and won't make it this weekend. Maybe this week I'll make it out and either be back to thank everybody for success or to ask for more suggestions. Thanks for now.<br /><br />Waymilky

 

[waymilky]

Re: 1963 Merc 100hp won't accelerate

I finally had a chance to get to the lake and unfortuneately no change in the engine. I'm guessing from the previous posts that I should look at the carburetors next. Is this something I can do, or should I take it to the shop. I kind of like messing with(up) things so if it doesn't take specialized tools I wouldn't mind taking a whack at it. Do I need to buy a carburetor kit or just disassemble and clean? Is there any place I can get step by step instructions? How about a diagram? <br /><br />Thanks in advance,<br /><br />Waymilky

 

[Clams Canino]

Re: 1963 Merc 100hp won't accelerate

If you can pull the brass main yet cover at the bottom, remove all 3 float covers (as a unit) and pull the 3 idle screws you can spray just about every orifice with the little red hose on the carb cleaner. USE a wet-vac and a straw to suck out the float bowls as needed.<br /><br />But 1st try running it with someone squeezing the ball. Also..... make SURE you know the motor is not overpropped for the hull it's on. that's like trying to take a car off in 5th gear... won;t happen.<br /><br />-W

 

[AMD Rules]

Re: 1963 Merc 100hp won't accelerate

Use <caution> when vacuuming flammable liquids. Most wet-vacs do not include an explosion proof motor.

 

[Clams Canino]

Re: 1963 Merc 100hp won't accelerate

Agreed.... the float bowls mostly drain out the main jets. Vac is just for very bottom.<br /><br />-W

 

[waymilky]

Re: 1963 Merc 100hp won't accelerate

Improvement, but still not quite right. When I first opened this blog the engine would bog down before it got to between 15-20 mph. It now runs faster, but still not constant and still running at WOT causes it to bog down. In years past,at WOT the boat would run 32-34 mph. Now it will run at 28 mph, but when I open the throttle for that last little bit it bogs down. While running in the lower speeds below 10 mph the engine runs smoothly with no speeding up / slowing down cycles. However when trying to maintain a constant speed over 20 mph the engine surges then lets off repeatedly.<br /><br />Suggestions?<br /><br />Waymilky