40hp johnson

[tashasdaddy]

timing usually causes backfire. check the center of you flywheel. there is a groove with a metal key. if this is not perfectly lined up the flywheel had to be pulled (special process) and a new key installed. the proper compressio is not published by the MFG. anything over 100psi and with in 10% of each other is considered runnable.

 

[Silvertip]

Re: 40hp johnson

Is it backfiring or simply "sneezing". Sneezing is sort of a puffing noise and is indicative of a lean condition. It's not caused by low compression. Backfiring is a timing problem caused by incorrect idle and wide and wide open throttle ignition timing adjustment. 90 psi or higher is desireable but the engine will run well with less than that provided both cylinders are within 10% of each other.

 

[DHPMARINE]

Re: 40hp johnson

BIG backfire and no start would be crossed plug wires (grin)

DHP

 

[rickdb1boat]

Re: 40hp johnson

Sounds like it's running lean from a clogged carb.....

 

[itstippy]

Re: 40hp johnson

Clean the gas tank, fuel lines, and fuel filter too. It takes about 2 seconds for a piece of old crud to break loose and clog your carbs jets. If it sat 5 years it's probably got crud in the fuel system that needs flushing out,

 

[tashasdaddy]

Re: 40hp johnson

spark should be blue, and jump atleast 1/2 inch. setting 5 years, you are going to need to service the lower unit, and a new impeller. carb cleaning, with a new carb kit.

 

[rod087]

Re: 40hp johnson

I have changed both coils ,points and condencers,put in a carb kit, it has a new fuel tank, cleaned the lines and the engine runs but still (sneezes) through the carb after it runs for awhile and mostly when i rev it up for a little while like it starts to run lean.Do any of you have any idea what is left that could be wrong?
Thanks
Rod

 

[Walker]

Re: 40hp johnson

Start turning the low speed needle counterclockwise 1/4 turn at a time until it smooths out.

 

[tashasdaddy]

Re: 40hp johnson

since engine faq is down , email me and i'll send you the proper way to set the carbs. please request carb settings. also i'd replace all the fuel lines and clamps there 40 y/o.

tashasdaddy@comcast.net

 

[Paul Moir]

Re: 40hp johnson

Pump the primer bulb and see if it helps or harms the motor. That will rule out sucking air through a leak or fuel pump problems.

Just to be certain, when you rebuilt the carb, you pulled the soft metal plug out of the top of it and cleaned the idle orifaces behind it right?

If none of that checks out, pull the spark plugs and look for differences between the two at the firing end. Could conceivably be a crankcase leak. There would be evidence of oil around the coils, etc, under the flywheel if the top main crank bearing was leaking. Bottom main is harder to tell, but it's usually good.

You'll go nuts trying to get it to idle if you've got a crankcase leak.


EDIT: Slow today! I've been beaten twice. Check out the simple obvious stuff like they say first.

 

[rod087]

Re: 40hp johnson

Hi there Paul , no when i put the carb kit in i didn`t pull that soft metal plug out so i guess i`ll do that.As far as a crane seal the top one seems good there was not any oil leak there but ya the bottom one would be a different story, that looks like alot of work to check that out.
THanks
Rod

 

[Paul Moir]

Re: 40hp johnson

Yeah, I wouldn't bother trying to check the bottom one unless the bottom plug read lean and nothing else seemed wrong.

If you still have the replacement metal plug, go ahead and pull it and check it out.

 

[rod087]

Re: 40hp johnson

Well thats does it anyone want to buy this engine for parts or what ever it runs but still (sneezes
) when i take up the abit abit ,i had carb carb off and checked th reeds and there was a little screw stuck in one when i put it together i thought i had it , it running runnign pretty good so today i rechecked the points because it would kick back a bit when try-ed tryed to start it, and well now it is doing the same sneezingSo sneezing.So if anyone is interested in buying it please let me know.
Thanks
Rod

 

[AlanR]

Re: 40hp johnson

How much do you want for the motor?

 

[rod087]

Re: 40hp johnson

Well the whole unit is for sale it is a 15 foot fibreglass surftamer boat with a yacht club trailer and of course the 40 hp Johnson engine i was asking $700.00 for the unit or if you would just like the engine i would like about $130.00 that is about how much i have in parts in it now.
Let me know if you are interrested in it.
Thanks
Rod

 

[fireman57]

Re: 40hp johnson

Are you sure that it is not overheating? When I had a weak impeller mine started sneezing and then wouldn't restart until it cooled down. Would run fine until operating temperature was reached.