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1983 Johnson 90HP: runs if I increase the throttle on start, but dies in idle

P

paranoiccritic

Member
Hi All,

I realize this is a question that has been asked a million times, but I think I've covered a number of the standard bases.

My 1983 Johnson 90hp has newly cleaned/rebuilt carbs, new fuel lines, a new Johnson OEM fuel pump, spark, and it pisses well. I just replaced the fuel pump, and now the motor won't keep running. It'll start right up, run for a few seconds, and then die. I engage the warm-up lever every time I try to start it. After quite a few attempts with normal startup procedure, I engaged the warm-up lever, took the hood off of the motor, pulled the throttle lever back to give it more fuel, and then re-started ... and it roared and kept roaring. And ran and ran (with high throttle and high RPM, in neutral). When I disengage the warm-up lever, it died again (e.g. seems like it won't idle). I would consider manually setting the throttle high to get it started and then get underway, but I can't start it in gear, and I can't put it in gear until the warm-up lever is disengaged - plus, I understand that starting in gear is a baaaad idea, just trying to figure out what to do to get the damned thing running. I've advanced the idle set screw to increase idle speed (no Tach, so I can't tell you what the speed is), but this hasn't solved the problem. any ideas on what to do next?

Best,

Fred
 
paranoiccritic said:
Last I ran one was a couple weeks ago. 120, 119, 121, 120 - should I run one again?
Click to expand...

If the engine was acting up "before" you took that compression test, then NO..... BUT if all was well at that time and the engine started acting up "after" you checked the compression, then obviously YES. Actually it would be a good idea to double check the compression anyway.

Also, with "all" spark plugs removed, check to see if the spark will jump a 7/16" air gap with a strong blue lightning like flame... a real SNAP!
********************
(Spark Tester - Home Made)
(J. Reeves)

You can use a medium size philips screwdriver (#2 I believe) inserted into the spark plug boot spring connector, then hold the screwdriver shank approximately 7/16" away from the block to check the spark or build the following:

A spark tester can be made with a piece of 1x4 or 1x6, drive a few finishing nails through it, then bend the pointed ends at a right angle. You can then adjust the gap by simply twisting the nail(s). Solder a spark plug wire to one which you can connect to the spark plug boots, and a ground wire of some kind to the other to connect to the powerhead somewhere. Use small alligator clips on the other end of the wires to connect to ground and to the spark plug connector that exists inside of the rubber plug boot.

Using the above, one could easily build a spark tester whereas they could connect 2, 4, 6, or 8 cylinders all at one time. The ground nail being straight up, the others being bent, aimed at the ground nail. A typical 4 cylinder tester follows:

..........X1..........X2

.................X..(grd)

..........X3..........X4

This can obviously be modified to a 6 or 8 cylinder setup tester.
********************
 
I had rebuilt the carbs a few weeks ago. At a friend's suggestion, I took the carbs back off to inspect them to make sure the idle/low speed jets were still clear. Every jet and orifice in both carbs was squeakly clean, free and clear, but the gasket between the carb and the bowl was strangely warped. I got the rebuilt kits online, and I remember remarking when I was rebuilding that this gasket from the kit didn't look exactly like the gasket that I was taking off. I should have known better, but I thought they looked close enough. Now after having run the motor, and looking at the gasket, it looks like the new warped gaskets are blocking the orifices on the port and starboard sides of the bowl, in what would be amidships on the bowl (next to the posts that feed the high-speed jets). No matter what, I'm going to find the correct gasket and replace these, but I'm thinking that blocking these orifices could cause the problems I'm seeing. Please let me know if this makes any sense and if it seems like it's in the ballpark of a good idea to replace these gaskets. Will let you know how it goes. Thank you for the recommendations so far.

Tried to post pictures, was able to select then and click the 'upload picture' button, but they simply don't seem to appear anywhere.

Cheers,

Fred
 
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