1977 johnson 70 hp.. driving me nuts!

[diggum smacks]

ok.. i was out fishing one day.. boat ran fine... anchored up... upon moving to a new spot.. boat started this.. backfire type thing... when ever i would rev engine in neutral at the end of the rpm band i would hear a ..." what" style sound... i called a shop.. they said timing.. so i ordered a manual for the motor... in the mean time... since i had 3 carb rebuild kits already and 3 brand new coils.. i went through the motions.. upon finishing i noticed... motor was still givin me what whuut at the end of a rev.. none of these carbs have needle valves or what seems like any adjustements other than float height... i was told i did something wrong... so took the carbs back off.. went over them again.. engine got worse... so went over them one more time.. and again.. no change.. getting a blueish style smoke out the motor.. i dont have timing specs so i cant even put a timing light on it to see if it is indeed out of time or if its just a carb prob... all 3 cylinders have 130 psi so... i have no clue what to do now. ive read other posts and you guys seem to know your stuff... im pleading... help

 

[Bosunsmate]

Re: 1977 johnson 70 hp.. driving me nuts!

Hi
If you run it on muffs you can pull out a sparkplugs ht lead and ground it to try and isolate it down to a particular cylinder/carb.
If you have a timing light, just check that your idle reading is after top dead centre by a few degrees and that it increases as you increase throttle to before top dead centre and further on.
You can also check that the flywheel key hasnt broken by turning the flywheel so that tdc matches the pointer and then check the number one cylinder is at top dead centre then

 

[diggum smacks]

Re: 1977 johnson 70 hp.. driving me nuts!

im guessing #1 cyl... is the top one?

 

[Bosunsmate]

Re: 1977 johnson 70 hp.. driving me nuts!

im guessing #1 cyl... is the top one?

Good guess

 

[diggum smacks]

Re: 1977 johnson 70 hp.. driving me nuts!

ty. ill keep ya posted i appreciate the help.

 

[diggum smacks]

Re: 1977 johnson 70 hp.. driving me nuts!

ok .. timing seems good to go.. havent put a light on it but its not like i know factory specs any way. im not sure what else to do.

 

[racerone]

Re: 1977 johnson 70 hp.. driving me nuts!

Have you confirmed that the flywheel key is not sheared ????---------When carburetors were off all these times did you inspect / look at the reed valves ?-------Can you post a video of the motor running?----Have you confirmed that the fuel pump diaphragm is not ruptured.----Does spark jump a gap of 7/16" on all 3 ----Yes or no.

 

[diggum smacks]

Re: 1977 johnson 70 hp.. driving me nuts!

i turned fly wheel to to check timing... i dont see a reed valve on the exploded view of the carb rebuild kit so i dont know what that is to inspect... checked fuel pump diaphragm a while back... although... ill rebuild that too once shop is open tomorrow ... havent checked the spark jump but i did up load a video.

 

[Bosunsmate]

Re: 1977 johnson 70 hp.. driving me nuts!

Is primer bulb holding firm with engine off?
yes can see that smoke, definitely check spark jump

 

[diggum smacks]

Re: 1977 johnson 70 hp.. driving me nuts!

primer bulb holds true.. i think the diafram may be the issue... when this happened... the vent on the gas tank hadnt released yet... 12 gallon tank was almost half the height... problem hasnt gone away since.. but i checked fuel pump diafram looks good to go. am i checking spark with a plug or open wire? keep in mind all new coils... so if the spark is minimal its prob in the control panel?

 

[Bosunsmate]

Re: 1977 johnson 70 hp.. driving me nuts!

Check with a spark tester- 7/16 gap
Then try a drop test to try and track it down, it seems to improve as engine warms up

 

[Daviet]

Re: 1977 johnson 70 hp.. driving me nuts!

Just a thought.
Almost sounds like a lean spit, try squirting a small amount of fuel mixture into each carb while it is running, when you hit the lean carb, it should sound different.

 

[kodibass]

Re: 1977 johnson 70 hp.. driving me nuts!

A few things I would try, Run motor at night (dark) look for sparks, hold a paper towel in front of the carbs and see if its spitting gas out of the carbs when it does it,(reeds) also a plug firing outside the cylinder does not mean it fires every time in the cylinder (change plugs). Go to the CDI website and look at their trouble shoot section for your make model. good luck.

 

[diggum smacks]

Re: 1977 johnson 70 hp.. driving me nuts!

well as frustrating as it was ... turned out ... it was due to something in my main tank. after switching over to the different tank... motor sputtered and spit for a lil bit... then boom.. no more probs.. thank you all for your help. this was driving me knuckin futs.