73Johnson135dies@idle@#4ComprStroke

[SCO]

My motor almost failed while on the water this weekend, 1st time it has done this. I couldn't shift into gear withoutit dying(low throttle). Later, on the trailer on the water muffs, it died at low throttle consistently after some 15 or 20 seconds or shorter, again for the 1st time. I put in new plugs with no change. 7 times in a row it died on the compression stroke for the #4 cylinder. I deduce it misses on #3 to stop on #4 compression stroke. A couple of times it just had enough inertia to pass #4 and stop on the #1 compression stroke without firing on #4 or #3. It never stopped anywhere else. Tested compresions...good as listed below. Sometimes it would hesitate like a miss but continue running but I could tell it was the same problem that caused it to stop at other times. Is this probably a power pack problem? Grounding plug wire or coil breakdown? plugged carb jet? Do bad stators cause powerpack failure? Does checking compression without grounding plug wires breakdown a powerpack or coils or stator? Hope yall will help me to understand this. Thanks in advance <br /><br />8/19/01 1 140 3 138 2 137 4 140 FYI cyl 1 is top right, 2 top L, 3 bottom R, 4 bottom L. firing order 1234, This engine is cross flow w 2 carbs, '73johnson135V4.

 

[JB]

Re: 73Johnson135dies@idle@#4ComprStroke

Howdy SCO. You are running on 2 or 3 cylinders. To identify the dead cylinders, start her up an remove plug wires, in turn. If no change occurs, that is a dead cylinder. If engine dies or slows, that is a good cylinder.<br /><br />When you have ID-ed the dead one(s), hold plug wire near block and see if you can get a 1/2" arc.<br /><br />If 1&3 or 2&4 are dead, suspect your ignition, if 1&2 or 3&4, suspect fuel starvation.<br /><br />Let us know what you find.<br /><br />Standing by.<br />JB

 

[SCO]

Re: 73Johnson135dies@idle@#4ComprStroke

At lunch, I tested and sure enough the #4 cylinder doesn't fire. All others do as proven by a smooth run when I disconnected #2 or #2 and #4 simultaneously. In that case 1 or 3 fired every other stroke for even operation. I also disconnected each one individually to confirm. I'll test spark tonight and report back this eve or next morning. Thanks and I hope u will stay with me to continue the trouble shoot.

 

[SCO]

Re: 73Johnson135dies@idle@#4ComprStroke

I took the #4 plug out and with it loose and motor running I could clearly in daylight see the spark plug appearing to function properly. Was a little nervous about igniting any fuel mist coming out of the cylinder so I didn't walk up real close to hold it exactly 1/2 inch away, but the spark looked like it should ignite anything ... like one of those lightening lamps popular 10 years ago. Later I had the plug in and pulled the wire, with the engine running. Putting the plug wire back on caused the engine to briefly rev( approx 1/2 sec). The plug is wet on inspection. I'm thinking this is a fuel problem and somehow enough builds up to cause the rev when I disconnect and reconnect the plug wire though I would think the exhaust stroke would purge any leftover. This engine runs normally at speed. Previous plug showed combustion.

 

[JB]

Re: 73Johnson135dies@idle@#4ComprStroke

Ahoy, SCO. #4 is a dead cylinder. It seems to be so for fuel reasons. Because it shares carb with #2, I would suspect reed valve problems. Double check that #4 can produce a 1/2" spark.<br /><br />Copmpression check and reed valve inspection are in order.<br /><br />Red sky at night. . . <br />JB

 

[SCO]

Re: 73Johnson135dies@idle@#4ComprStroke

Reed valve makes sense. Although that compression tested good(1st post) I recall that cyl was some 15psi down the time I checked it before. I thought it was a reseated ring that brought the pressure back up cause I have run it regularly this summer. Maybe I got a false reading this time. I'll recheck. Is a reed job a big job? Can you service it by removing the carbs or do you have to dissassemble the powerhead? Will a bad reed be obvious in comparison with the others?

 

[SCO]

Re: 73Johnson135dies@idle@#4ComprStroke

I'm going post w updates to keep the thread alive. I looked carefully for spitting at the carb and see none. I'm going to take off the carbs and look at the reeds this weekend. I have found that even though a single carb supplies cyls 2 and 4, a single barrel of that carb is dedicated to cyl 4 so a problem in that barrel of the carb could cause the problem. I see three possibilities for my idle fuel supply problem carb, reed, or crankshaft seal. I rechecked and that cylinder has good compression and good spark, though I will also put a timing light on that plug and check that the #4 plug fires regularly. Comments invited. For example, do crankshaft seals between cylinders frequently go bad, or is that a one in a million?

 

[SCO]

Re: 73Johnson135dies@idle@#4ComprStroke

Just had the bright idea, since this engine has 2 carbs, to switch the carbs and see if #4 starts firing.

 

[SCO]

Re: 73Johnson135dies@idle@#4ComprStroke

This is the wrap up post. Problem solved. #4 now fires and the engine doesn't die at idle. I didn't switch the carbs to test, just took off the lower carb and cleaned it carefully paying careful attention to some small idle fuel jets that entered the air of the venturi just past the throttle baffle. It was clean and I saw no obvious problem but I recleaned it anyway and made sure all fuel passages were clear. I also readjusted the float to clymers recommendation. It was mis adjusted such that the bowl did not fill as much as it should have. <br /><br />Corrections: in the past posts I thought it significant that the engine raced when I pulled a plug on #4 and put it back on again(with a wooden tong). I foung all cylinders will do that if you pull a plug on and off. Also, I've gotten conflicting info on which barrel of which carb goes to #4cyl in this cross flow engine. My best info and possibly incorrect is that the bottom carb does supply 3 and 4, the left barrel goes to the right cyl(#3), and the R barrel goes to the L cyl(#4).