78 johnson 15HP-lead shot in carburator??

[gdc0581]

I am re-building the subject motor. It has good even compression of 120 PSI in both cylinders and good spark. I've put in a carb kit, new water pump, and thermostat. The problem I'm having is strange behavior at idle. With the engine warm, it idles OK at first, but slows down and stops over about a 30 second period. I've re-built lots of carburators, but have never removed the core plugs. I've been reluctant to remove this one because the BRP parts diagram shows 3 lead shot that look like they would be under the core plug (item number 2 in the diagram). I figured I'd probably loose one or more of them.

After reading every post in this forum about core plugs, I decided to remove it and found no lead shot. It is possible that they were lost/removed by a previous owner/mechanic. The problem is I can't figure out what function they would perform if they were there. They would just rattle around like the preverbial BB in a boxcar. I'm also confused by calling for three shot. Newer motors, 1985 for example, use the same part number, but only one. I have lots of lead shot, but don't know what size I would need. When I applied compressed air at the core plug hole, I dislodged a piece of rubber from the low speed jet hole on the front of the carb, so it is possible that I have fixed my problem. I just don't want to install the new core plug without the shot if it is supposed to be there.

Does anyone know if the shot should be there and what function it performs. If the shot should be there, the size (diameter or shot size number) would be very helpful. Unfortunately, I'm a ferry ride and a two hour drive from the nearest dealer so I don't want to go there and pay $3.51 per shot if I don't have to.

 

[waynehol]

Re: 78 johnson 15HP-lead shot in carburator??

The lead shot are used to seal openings and typically do not need to be replaced. That shot does not rattle around loose.
Chances are real good the rubber you blew out with compressed air was the source of your problem. You might me having some ethanol issues with it eating up fuel lines and depositing gunk in the carbs

Good luck!

 

[gdc0581]

Re: 78 johnson 15HP-lead shot in carburator??

The rubber I blew out looked like it was probably part of the seal used around the low speed jet. It could have been from 3 carb rebuilds ago. I recently bought the motor so don't have any of the history. I've replaced all of the fuel lines and didn't really see any signs of alcohol related deposits in the carb. I'll put the core plug back in and report the results.

 

[R.Johnson]

Re: 78 johnson 15HP-lead shot in carburator??

The lead shot is used to seal a drilled hole after manufacture. the manufacture of the carb body will require drilled passage's which will often end in a blind hole. The entranse of this hole most time's will need to be sealed. Lead shot is an easy way to do this. Most time's, they need not be removed. To replace a soft plug, use a punch with a face about the size of the plug. Hold punch in place, and strike with a hammer. This will expand the plug into it's seat.

 

[AlTn]

Re: 78 johnson 15HP-lead shot in carburator??

the lead shot does not go under the core plug...just clean those three tiny holes for the idle circuits which you'll see enter the carb throat behind the throttle plate....each should have the same spray pattern when you shoot spray carb cleaner in them

 

[gdc0581]

Re: 78 johnson 15HP-lead shot in carburator??

It looks like that fixed it. It will now idle indefinitely as long as I don't try to go too slow. It still seems to miss occasionally so I'll need to get my spark checker and look at the ignition.

Now that you mentioned what the lead shot does, I found the three on my carb being used to close individual drill holes. The confusion came from where they're shown on the parts diagram.