Dies after giving throttle

[trey]

Im new at this so work with me guys..I bought a my boat early spring and never had any problems with it until this recent November. My motor is an 77 Mercury 850 thunderbolt, my problem is that when i give throttle it dies, but if i tap on the throttle very slowly and work my way up to speed it goes forward just fine. This doesnt happen at all when im in the garage and i have a muff on it, i can go forward a reverse without any problem. Im thinking maybe dirty carbs? or dirty fuel filter? How can i fix this before fishing season arrives, thanks in advance

 

[Don S]

Re: Dies after giving throttle

When on muffs, you don't have a load, that's why it works ok.
Probably a carb rebuild will cure your problems, along with a sync & link, a dose of powertuner, new plugs, and filters and you should be good to go.
What about the gear lube and water pump impeller? Have they been serviced in the last few years?

 

[trey]

Re: Dies after giving throttle

well don, i bought this boat from a boat dealer so i would have assume he replace all the gear lube and water pump impeller. i like every thing works fine beside the stalling after going forward..

 

[trey]

Re: Dies after giving throttle

Don, how much does it cost to rebuild your carberator? and is there a cleaning fluid i can buy to clean it instead?

 

[jeff_smith_0423]

Re: Dies after giving throttle

I have this exact same motor - haven't had it in the water yet as i just got it in early december. I rebuilt the fuel pump, both carbs, and replaced all the fuel lines for about $30 in parts. I've never tackled such a project and found it to be pretty easy. I made due with a Seloc manual, but the old salts here will rightfully suggest getting a factory manual.

unless you have a fuel filter inline with your tank, the only "filters" are a screen at the fuel pump (very easy to clean, one screw to remove) and two screens at the fuel inlets on the carbs. The seloc manual says that mercury reccommends removing and discarding both of these screens, and not replacing. My upper carb fuel inlet was completely blocked with varnish and crud.

This forum is excellent for assistance. If you're willing to do your homework and follow the suggestions of the old schooler's like Laddies, you'll be on the water in no time.

What sort of boat do you have this motor on? I have it on a 15'' fiberglass trihull. Interested in what kind of speeds you're seeing and what kind of fuel economy you're getting. I'm VERY anxious to get out on the water!

 

[trey]

Re: Dies after giving throttle

jeff,its hooked up on a 16' skeeter hawk, my top speed is about 40-45mph. Fuel wise im not sure, i have a 10 gallon tank hooked up to it and when its full it would last me about 4 hours on the lake. So after cleaning your carbs and replacing your fuel line, and fuel pump. Did your motor run any better with a load?

 

[jeff_smith_0423]

Re: Dies after giving throttle

I'm currently searching out a suitable tank so i can put a load on it. I've never had the boat in the water. I had to rebuild the fuel pump and carbs just to get it running, as it sat for about four years with bad gas in it.

 

[achris]

Re: Dies after giving throttle

The easiest thing to try before going to all the trouble of removing and stripping carbs and the pump is to richen the mixtures slightly. Just turn the idle mixture screws about 1/8 to 1/4 of a turn counter clockwise. The engine would probably benefit from having the carbs cleaned, but if the only problem is that it's too lean, this is the fix.

Chris...........

 

[toughinboots]

Re: Dies after giving throttle

I am having the exact same problem. I was told it could be a timing issue. Let me know what you find out on yours!
Justin

 

[b0b88]

Re: Dies after giving throttle

lol im having the same problem on the same engine?? I'm wondering what the problem is as well, please keep us informed!

 

[tredragon]

Re: Dies after giving throttle

The easiest thing to try before going to all the trouble of removing and stripping carbs and the pump is to richen the mixtures slightly. Just turn the idle mixture screws about 1/8 to 1/4 of a turn counter clockwise. The engine would probably benefit from having the carbs cleaned, but if the only problem is that it's too lean, this is the fix.

Chris...........

try this (above) first all. take off the wraparound cover. get on mercruiserparts.com or get a manual of some sort. find idle mix adjustment screws (on my 69 thundeerbolt it's top right corner of air intake of each carb). Turn each about 1/4 CCW. If you have rougher idle after this, look near the distributor for the idle speed screw.

 

[raporter]

Re: Dies after giving throttle

I am having this same problem with my 1988 60 HP Mariner. I have tried setting the carbs richer but that didn't help. I can fish all day and seems like everything is OK. I'm not really running that fast but when I go to put the boat on the trailer and power up the last couple of feet it just bogs down and dies. I was thinking of doing a carb rebuild after fishing season is over. Seems to be a pretty common problem.

 

[72 Roody]

Re: Dies after giving throttle

Have the same issue on a 73 650 65hp. Took it to the mechanic, had the carbs rebuilt, a tune up and the same issue. If I tilt mine up a bit, git'r wound up and slowly tilt'r down she runs like a champ. Planes real nice, just the initial go is rough? So............

 

[achris]

Re: Dies after giving throttle

I am having this same problem with my 1988 60 HP Mariner. I have tried setting the carbs richer but that didn't help. I can fish all day and seems like everything is OK. I'm not really running that fast but when I go to put the boat on the trailer and power up the last couple of feet it just bogs down and dies. I was thinking of doing a carb rebuild after fishing season is over. Seems to be a pretty common problem.

The reason you're bogging down is that this method of trailering a boat puts HUGE load on the engine. I would be suspicious if it didn't load up.

Chris.............

 

[tredragon]

Re: Dies after giving throttle

I am having this same problem with my 1988 60 HP Mariner. I have tried setting the carbs richer but that didn't help. I can fish all day and seems like everything is OK. I'm not really running that fast but when I go to put the boat on the trailer and power up the last couple of feet it just bogs down and dies. I was thinking of doing a carb rebuild after fishing season is over. Seems to be a pretty common problem.

It seems to me that the balance between idle speed and idle mix is crucial. You're tuning for the best of both worlds, something in the middle. As was stated, driving onto the trailer puts more load on the engine since now it has more than just the friction of the water pushing against it, it has the friction of the trailer to deal with. If you're lower RPM's are more "boggy" you might be too rich? Just a shot in the dark.

 

[tredragon]

Re: Dies after giving throttle

Have the same issue on a 73 650 65hp. Took it to the mechanic, had the carbs rebuilt, a tune up and the same issue. If I tilt mine up a bit, git'r wound up and slowly tilt'r down she runs like a champ. Planes real nice, just the initial go is rough? So............

When tilted up there is less load. Once you get it going, you have some momentum. Have you tuned the carbs on the water, trimmed down, warmed up? Bring a long flathead screwdriver and keep the wraparound cover off... should have it tuned in a matter of a few hole shots... maybe 10 minutes. You're looking for about 1/4 turn CCW (rich)... you can do one carb at a time too and adjust to whatever makes the motor happiest in both low and higher rpm's.

 

[raporter]

Re: Dies after giving throttle

It seems to me that the balance between idle speed and idle mix is crucial. You're tuning for the best of both worlds, something in the middle. As was stated, driving onto the trailer puts more load on the engine since now it has more than just the friction of the water pushing against it, it has the friction of the trailer to deal with. If you're lower RPM's are more "boggy" you might be too rich? Just a shot in the dark.

It is more than "bogging" it just dies like it is running out of gas. I adjusted the carbs like the manual said to do. I have always loaded on the trailer this way and didn't get this reaction.

 

[tredragon]

Re: Dies after giving throttle

It is more than "bogging" it just dies like it is running out of gas. I adjusted the carbs like the manual said to do. I have always loaded on the trailer this way and didn't get this reaction.

I guess what I was saying was based on personal experience. I had a great idle, and if I just bumped the throttle a tiny bit, she'd run... but any more than that... bog and die. When i richened up the mix (more than the manual, just tune it on the water based on actual results you get)... I got a lopey idle, so I adjusted idle speed. That same day I had to richen even more and adjust idle speed because I was only getting 13MPH at WOT. So far I've been averaging around 22 or 23MPH... so I went another 1/2 turn this time (being ambitious) and wa-la... back to 23mph.

 

[72 Roody]

Re: Dies after giving throttle

Tred

I haven't tuned it that way. I know that's what I needed to do, but when I got'r to the lake, ran into some starting issues, choke wouldn't acuate, starter started the click, and battery not charging. Gotta love those old motors!