1979 Johnson 85hp - carbs

[will62]

Model 85TL79 - uncertain history

Background:
Picked up a 1979 15' Kingfisher bass boat, motor and trailer for $250. At that price, I didn't expect much out of the motor, so I was surprised to find that the motor had good compression numbers (125,133,125,125) and good spark. I had planned to put new kits on the carbs, but it's been about 30 years since I've worked on one, so I decided to get fresh fuel and try to start the motor (in tank) so that I'd have a baseline of how the carbs were doing before the rebuild. Motor turned over several times, then started. Ran it for about 30 seconds, then killed it to check the plugs. All were similar in color and slightly moist. I had good flow from the telltale and it appeared that all cylinders were getting fuel, so I decided to start it again. Slightest bump of the starter, and it started and idled beautifully. I ran into some concerns on the heads that I'll cover in another thread, but in pulling the heads, I found that all 4 cylinders had been rebored to .030 oversize, which may be considered in deciding what to do with the carbs.

I was finalizing my parts order list for thermostats, impeller, gaskets, carb kits... etc, but luckily I held off until I pulled the carbs. I found that the PO had put mismatched carbs on the motor. Although the motor seemed to idle well, am I wrong in assuming that I'll never get an even fuel flow with the current setup?

Upper carb - #324955 (I believe this one is off a 150hp v6)
High speed jet - 48c (spec'd for 85hp)
Low speed jet - 28 (spec'd for 115hp -port side)

Lower carb - #322033 (This one may be original to the 85hp, but I can't find a match on any diagrams)
High speed jet - 48c
Low speed jet - 40

I can put my hands on another #324955. My thought was to replace the lower carb, keep the high speed jets at 48, and the low speed jets at 28. Do you guys think that this is a workable solution, or could you recommend a better one?

Some pics:

 

[SparkieBoat]

Re: 1979 Johnson 85hp - carbs

my only concern would be getting too much air into the cylinders..a higher air mixture would result in a hotter fire and could eventually burn up your pistons. I would think it would be best to get a matched pair of carbs at least from a 85-115..those 150 carbs are probably too big of bore. but I am just guessing. I am not a carb guru.

 

[mekkamaz]

Re: 1979 Johnson 85hp - carbs

Are both 1, 3/16, 1 5/16 or 1 3/8" Bore? For a 85 I'll expect to be a 1 3/16" that?s the one you have?

 

[emdsapmgr]

Re: 1979 Johnson 85hp - carbs

Your short block sounds healthy from the compression. The 125 compression is pretty normal for the stock 85 hp heads from the factory. That's a great sign. Not sure just where you got the carb part number 324955. That may not be the carb number-maybe a casting number or something else. It's unlikely that the upper carb is from a V6, tho possible. The throttle shafts on the V6 engines area different length than the V4 carbs. If someone did change a V6 carb to a V4 carb, they would have had to completely remove the throttle plates, shafts and replace them with the true V4 length shafts. The .030 over pistons are ok with stock jetting. When you bore larger, (.040 and higher) typically you need to go up in main jet size-slightly. Sparkie brings up potentially the biggest problem. You need to be running the same carb throat size on both carbs. The throat size is cast into the face flange of each carb. You need to be sure they are both the same, such as 1 3/16" or 1", etc. If you have two different throat sizes, one will blow more air-and with the same main jet size, you can run those two cylinders lean. Not good. If someone has found a carb from another (maybe older) V4 and installed that, you also need to be careful mixing different year V4 carbs long term. Their internal passageway configurations change from year to year, and require different jetting, even with the same throat size and for the same hp engine. The two stock factory carbs on your 1979 engine were different part numbers. The upper carb has the roller that rubs against the cam, the lower carb does not. So: different part numbers, but same internal configurations. I think you are going the right direction: Best to get two matched carbs from the same year/hp. You will have the least problems if you stay with some 85 hp stock factory carbs from approximately the 1977-79 vintage. 1980 and later carbs don't have the mechanical choke plates like your current carbs-they have a fuel primer system for the choke. Your engine is not setup for that.

 

[will62]

Re: 1979 Johnson 85hp - carbs

Thanks for the input guys. To answer a couple of your questions, both carbs have 1" throats and the part numbers that I gave are stamped on the front of the carbs along with a 1 (indicating throat size). I decided to go ahead and keep the upper that I have and get a matching lower that I found on Ebay. I'll stick with the 48 and 28 jets and post back later with the results.