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1979 70hp merc when put power on cuts outsome one help

J

jacko1

New member
"Hi i a have a 1979 70hp mercu

"Hi i a have a 1979 70hp mercury,the motor runs like a dream at idol and starts stait away every time, it has heps of spark and seems like good fule presher(pumps heaps)but when u put it in gear and go to put the throtell on it just dies, does eney one no what the problem could be.Thanks jack."
 
"Here's a partial list:

"Here's a partial list:

1. Bad fuel

2.Need to clean carbs

3. Linkage mis-adjusted, meanin the carbs are opening before enough spark comes in (which is easy to have happening with that Mickey Mouse linkage), or

4. If you're really lucky, the idle adjustments are set too lean.

Jeff"
 
"Thanks jeff, i have had the c

"Thanks jeff, i have had the carbys cleand, new fule @ 100ml to every 5 Ltr, and turnd idle ajust out 1/2 a turn. I have not yet touched eney of the linkage adjustments yet as i dont no wot to touch.I also forgot to mention that it revs fine out of water, only dose it in water under load."
 
Gotta be the carbs are opening

Gotta be the carbs are opening too soon. The spark MUST advance all the way before the carbs open more than 1/4 of the way.

Jeff
 
"the top timing (advance&#

"the top timing (advance)i think, should it flop around or should it be solid, also is there a easy way to set linkage ajustments thanks.jack"
 
"Whoa! Do you have a rotating

"Whoa! Do you have a rotating distributor on yours? Or is it all electronic ignition? If the later, ignore everything I said (like my wife always does!)


Jeff"
 
"na mate it dose not have a di

"na mate it dose not have a dizzy,all electronic its driving me crazy now, dont wont to go to marine shop and pay $1000 for some think i recon is a esy fix. ( I HOPE )"
 
Sorry--forgot that year was al

Sorry--forgot that year was all electronic. I'd get the carbs rebuilt.

Jeff
 
"water in the fuel?
dirty ca

"water in the fuel?
dirty carbs or the trigger is bad (it's in with the stator) Have you put a timing light on it? checked the spark at those RPMS with a timing light and a buddy watching the light to check for spark misses? whats the compression.

Grab a spray bottle, put some gas mix in it, take the cover of the carbs off, run the boat, have a buddy drive(or leave the boat on the trailer, back it down the ramp just engouh to cover the lower half of the mid-section, run the engine in gear and then you spray 1 or 2 squirts into 1 carb at a time, when then engine increases in power you'll know which carb isn't working. Rebuild that one. If the idle mixtures are lean they won't let the engine transition good to the high speed but if one of the carbs high speeds is dirty it wont go or stay at higher RPMS under load."
 
"think mite of solved it(i

"think mite of solved it(i hope).I took the boat to shop two days ago, thay said that it was all out of tune, called me and i picked it up two hours later.
Went strait to ramp and it was the same(run fine die in gear)took it back to shop and they rang me next mornig saying that thay change the power pack and every thing tested fine.Strait back to ramp, put it in and it took of like a 70hp merc should, after 10 min it died again doing the same thing.I took the cover off and played around and found if i took number 1 lead off moter wood not start,take number 3 off same thing,when i take 2 off runs the same.Maybe number 2 coil braking down. (Can this happen)"
 
"Your right, you can test this

"Your right, you can test this by swapping the coil from 2 to 1 or 3 before purchasing, could be bad lead to the coil, swapping is cheaper, good luck"
 
"I have an 84 model doing same

"I have an 84 model doing same thing, mine is on the #1. Had coil replaced 2 years ago started doing same as before and as yous no will not run under strain, but like a charm out of water. I am going to change #1 again because when pulled #1 plug wire cranked and ran as nothing sounded like was wrong. Unhooked wires fom coil coming from swich box and nothing changed, so I am going to start with replacing that coil again. I think and hope that is or could be part of our problem. Will let you know in a few days!"
 
"still no go, have changed coi

"still no go, have changed coils and still the same. i am geting a bad gray carben build up on no.1 eny sugest,"
 
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