Identifying carb on a 1978 Johnson 25hp

[Rotti]

Hello,<br />Ive recently bought an old Johnson 25hp. The previous owner said that it ran just fine 1 year ago and might be produced in the beginning of the 80s.... well, after looking up the serialnumber after I came home, I found out that the engine is a 1978 model. After a closer inspection I also found the reason why it didnt fire up at all: the little fuel supply for the choke-injector and the main fuel hose for the carb were swapped and therefore the carb was just flooded each time I squeezed the ballpump! Having learned the hard way again that the former owner was a liar, Im also wondering why the engine has a 20hp cowl. He told me that this was the only one he could get as a replacement for the old one. Yesterday I searched this forum for some help, because although the motor starts up very nicely, I cant get it to idle smoothly, I always have to keep it alive with a little bit of throttle! During this search I learned that the carbs for the 20hp Johnsons have a nylon ring inside which reduces the diameter of the carb and therefore limits the hp to 20- my carb also has such a ring inside!? Do the 25hp have it or not? Right now I come to think that my motor has been put together from scrap from other Johnsons... I don´t mind as long as it runs, but for the start Id like to know what Ive got here! There is a small tin-tag on the carb with a number on it, but I dont know where to look it up? I want to go for the 25hp, so maybe I´d need another carb anyway?<br />If somebody has an idea of what could cure the poor idling of the motor would be great as well!<br /><br />One more thing:<br />When I checked the throttle flap position on closed throttle and WOT, I found out that if I put the motor in forward gear and pull the trottle to WOT, the throttle flap inside the carb doesnt stop in the vertical position (which would give maximum airflow) but sort of flips over to a 45° position which would limit airflow again! Is this correct? Before it flips over i can feel a little bit of resitance in the throttle handle. I´m really puzzled about this..... <br /><br />Thanks to you all!<br /><br />Wolfgang

 

[Rotti]

Re: Identifying carb on a 1978 Johnson 25hp

Some more informations:<br />While checking the OMC parts catalogue online, Ive learned that OMC started using primers instead of a choke first in 1984, so the carb which is on my engine (and definetly hasnt a choke flap at all) must be from a newer motor. What I need to know now is wether the carbs for 25hp had this nylon ring inside or not, because I think that I couldnt get a 25hp engine work together properly with a 20hp carb- or am I wrong in this? I simply dont want to waste time and efforts due to mismatched components, thats why Im asking!<br />Any help would really be great!<br /><br />Wolfgang

 

[Rotti]

Re: Identifying carb on a 1978 Johnson 25hp

Does really nobody know something?! Please......

 

[Scaaty]

Re: Identifying carb on a 1978 Johnson 25hp

I have the exact same monster. Weird! Guy I got it from said is was a 25 ...hood was painted over. Scraped enough to find 20 on the side. Has a rebuilt powerhead, and no numbers...still can't tell the year. Late 80s because of the throttle has cable actuation. I have the same throttle butterfly deal..goes past open throttle. No diff on the water though, just see where its wide open and look at the handle marks. You will know when you open it to far. On idle, I have no idle adjust anywhere on the carb, for idle speed that is. I can't tell ya about the ring in the carb...have to go out and look at it. I just don't worry about it. Mine is a Primer Carb too. Just don't crank it down too much on idle, and if it runs, just use and get used to its quirks.

 

[Rotti]

Re: Identifying carb on a 1978 Johnson 25hp

Thanks Scaaty,<br /><br />nice to hear that somebody else has got the same troubles than I do! I think youre right, I wont f... around with it anymore until I have it in the water. Maybe I just trick the idlespeed by cutting off two turns of the spring underneath the idlespeed adjustment screw and turn that screw a little bit further in! Should have the same effect as if Im constantly janking the throttle to keep it running. Meanwhile Ill go on scanning iboats- maybe I can dig out some more informations in another thread!<br />Thanks for your answer, as soon as I run into some news Ill keep you informed!<br /><br />Wolfgang