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1979 50 hp mercury thunderbolt issues

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p2v

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"Hi, I have the engine listed

"Hi, I have the engine listed above that is a having speed issues, the engine used to do 30mph now it barely does 10mph. I changed the spark plugs, someone told me it could be the old battery. I dont want to get rid of the engine because it is very reliable, but I am not a mech., and dont have a clue what it could be? Can someone help please?"
 
Spark? compression? If you are

Spark? compression? If you are not a mech. than the only things I can tell you are to spray somthing into the carb throat to see if it picks up. (Ether ect.) (Fuel) Get a pliers and tape the jaws and handles to avoid a shock and pull the plug wires off one at a time with it running to see which cylinders are not making power. If the plug wire does not appear to be live than the electronic ign is the problem.
 
"Okay I guess I can do that wh

"Okay I guess I can do that what type of plugs should this engine have? It had NGK and I replaced them with NGK, is that the right plug for this engine?"
 
"clean the carbs, if you have

"clean the carbs, if you have a clogged jet 1/2 that engine is not getting fuel or oil"
 
"Dirty carbs could be the prob

"Dirty carbs could be the problem .I been reading alot of posts, Great Web Site !!! I've been cleaning the plugs alot lately. After I clean the carbs, should I replace my prop? It has a crack in it. Could that part of the problem also? I have two props that came with the boat when I bought it. I don't know which 1 is the right one for this engine. Anybody knows what is the right size and pitch for this motor? Thanks in advance"
 
"The prop has to be "fitte

"The prop has to be "fitted" to the rig you are hangin' the motor on and has little to do with what some paper chart says or what may have been on the motor when purchased.

Makes sense if you think about it. If you are using your 50 to push along say a 14 foot aluminum with only 1 passenger normally, you can use significantly more pitch than if you have it on a 16 foot fiberglass with 3 passengers - the degree to which the motor has to "work" determines the prop pitch - there is no "one size fits all" prop, in fact most new motors do not come with a prop or it is "fitted" when purchased according to "your" requirements.

What do you have this hangin' on? I can run some numbers for you and see what the calculator spits out..."
 
"10.5x 14 or 15pitch for a lig

"10.5x 14 or 15pitch for a light boat. If this engine is new to you and its been put up for a while, stop and clean the carbs, change the water pump now before the pieces go up the block. Do the compression test before spending money on a bad motor."
 
"Thanks guys all great idea&#3

"Thanks guys all great idea's, I will put them to work this weekend. I am also going to buy a online manual from this site, to help get this motor back to tip top shape. Should I get the online version or the paper version? Any recommendations would be great. Thanks All
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"Hey Graham and JB, I right no

"Hey Graham and JB, I right now have a 10 x 12p and for a spare I have a 10.38 x 13 p. Both have nicks and cracks. My friend did the compression test and the #'s are 106,110,109,& 108. I believe thats okay, well he said it was. This weekend, like I said in the earlier post I will clean or rebuild the carbs depending on the price, I'm buying a new prop changing the spark plugs wires after I do that test that Bandit stated. But I don't think it's the ign., because wouldn't thats cause the motor not start. The motor starts just fine. Well thanks guys.<font face=""symbol""></font>}"
 
"you can get your props repair

"you can get your props repaired for $40 each, they can even be re-pitched, up 1p if needed."
 
"Hey guys, I never knew that y

"Hey guys, I never knew that you could repair props, I got both carbs rebuilt, for 50 bucks. I will reinstalling them tomorrow & let you know how it turns out."
 
It would be a good idea to rep

It would be a good idea to replace all the fuel lines before completing your assembly. I just had to tear down and clean freshly rebuilt carbs due to a split fuel line that plugged up my carbs. It is cheap and easy and well worth it to ensure you will not be sucking any air into your fuel lines.
 
"Hi guys,

I installed the

"Hi guys,

I installed the carbs and started the motor it started fine as always, but it turns off. It was starving for fuel. I was pumping gas into it through the ball just pumping the ball and it stayed on. As soon as I stopped feeding it gas the motor died. Does this motor have a fuel pump that could be bad or a clogged filter somewhere? Any info would be great thanks."
 
"Good morning, i have a 17 ft

"Good morning, i have a 17 ft pro style bass boat with a 115 merc (late 80s) i have a prop with 19 pitch, it runs out great with 2 people, but with three people its a little sluggish getting on plane, is this a prop issue?"
 
"need to know max rpm of engin

"need to know max rpm of engine without a load. There is no 1 prop for all different loads, sometimes you have to sacrifice low end for high end, or vise versa"
 
"I installed the carbs and sta

"I installed the carbs and started the motor it started fine as always, but it turns off. It was starving for fuel. I was pumping gas into it through the ball just pumping the ball and it stayed on. As soon as I stopped feeding it gas the motor died. Does this motor have a fuel pump that could be bad or a clogged filter somewhere? Any info would be great thanks."
 
"Hi guys I figured out my prob

"Hi guys I figured out my problem with the carbs. It don't have a fuel pump or fuel filter. It was a dumb mistake by me a do it yourselfer, when I reinstalled the carbs, I made my own gaskets, the gaskets had a tiny hole that I forgot to make. I didn't realized that it was there or important for that matter.

I realized when I took the carbs off, & ready to take them back to they guy who rebuild them. I found the old gaskets and noticed it. Now the motor sounds great again. I have to finish putting everything back together and take it for a test drive.

I just wanted to THANKS ALL YOU GUYS THAT HELPED ME OUT !!!"
 
"Hey all. I have a late 70s M

"Hey all. I have a late 70s Merc 700 (70hp) outboard that needs throttle adjustment. I found the following on the Great Lakes Fisherman forum. Can anyone confirm that this procedure will work for my year/model Merc? -

Engine Idle Speed Adjustment(Boat-In-The-Water) Mercury I/O
Warning

DO NOT leave helm unattended while performing idle speed adjustment. Boat MUST BE moving forward (not tied to the dock) when setting idle speed.

Engine should idle at 650-700 RPM with boat in the water, drive unit in forward gear and engine at normal operating temperature. If idle speed is incorrect, proceed as follows:

1. Disconnect throttle cable from carburetor. Be careful not to lose spacer on anchor stud and spacer and bushing on throttle lever screw.

2. Start engine and place remote control lever(s) in forward gear, idle position. Adjust idle speed adjustment screw to obtain recommended RPM.

Caution

Throttle cable brass barrel MUST BE adjusted properly (in next step). Over-adjusting barrel in the other direction will exert excessive pressure on throttle lever, which could cause damage to carburetor linkages.

3. Stop engine. Readjust cable brass barrel (to compensate for throttle lever movement) and reinstall throttle cable. Be sure to tighten attaching nuts."
 
Clarification to the post abov

Clarification to the post above...

The issue I am having is as follows.

The engine won't stay running until I move the control box lever about 3/4 of the way forward (or backwards). The gears seem to shift fine but the engine will die unless I move the lever quickly to get up and moving at a decent pace.

Is there a simple way to just adjust the cable while the boat is on my trailer?
 
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