Idle/start problems '73 Johnson 135 v4

[SCO]

I have been plagued by poor idle start problems with this engine.<br /><br />It runs great everywhere else, and I thought with some running time it might begin to idle better. rpms are 700 at idle immersed, and 1000 on the muffs. I have triple checked spark, with a spark tester and get good, regular, strong 7/16(edited, I tested for 7/16, not 5/8) jump. <br />compression is 120 plus all around, with little deviation.<br /> <br />Takes too long to start, and multiple tries even after the choke has pulled fuel to the engine. Once it starts and runs a while it idles ok on muffs and in the water, but will sometimes die when putting it into gear. It is much harder to start in the water. I am alweys envious of the idle and start of other 2 strokes and sometimes wonder if the newer ones just start and idle better inherently, and that maybe in '73 they hadn't figured out how to make the engine idle properly yet. <br /><br />This weekend for example I had run at 3700 for some 15 minutes, then idled into the boat ramp area for some 5 minutes, and when powering onto the trailer it bogged and died. Restarting and running at some 2500 or so for a few seconds allowed me to power up to near wot with no bog. I cant tell if it is fuel starved or loading up with too much fuel at idle. <br /><br />Joe, if you are reading, you gave me the idle jet info for this engine, that some were too small, and can be drilled just to size(.031 inch diameter), or they could be clogged some). I will check for this. Could these symptoms be caused by misfitting reeds or leaky choke butterfly flapper? Is there a way to check idle suction or airflow. If internal seals are leaky I guess the problem is very difficult to correct requiring overhaul.<br /><br />The plan:<br />1) carb kits and immerse carbs overnight in a cleaner. Drill idle jets if necessary. Any recommendations for a cleaner?<br /><br />2) rework butterfly linkages and carefully check fit.<br /><br />3) Replace reeds. <br /><br />Sorry for the long post. Resummary of questions:<br /><br />Is the motor loading up with too much fuel at idle, or starving in your opinion('s).<br /><br />Do these '73 v4s inherently start and idle poorly?<br /><br />Are reeds/ internal seals a likely culprit for poor idle/start?<br /><br />Is there a way to check idle suction or airflow?

 

[Joe Reeves]

Re: Idle/start problems '73 Johnson 135 v4

SCO.... In reply to your questions:<br /><br />1) Dismantle the carbs completely before immersing in carb cleaner. Be sure to remove any nylon/plastic components. Use regular automotive carb cleaner which is usually available in a one gallon container, equipped with a small basket.<br /><br />2) Rework the butterfly linkages via the external linkage rod setup so that they open and close at the same time.<br /><br />3) I would not replace any of the reeds unless they were broken. <br /><br />4) You can easily check whether the engine is starving by simply having it running with the carburetor face plate off, then one throat at a time, stick two (2) fingers in the carb throat. If the engine slows down, consider the mixture okay. If the engine rpms increase, consider that cylinder running lean (starving).<br /><br />4a) With the engine not running, pump the fuel primer bulb. If fuel flows out any of the carb throats, it would be loading up. It would also load up if someone installed the wrong jets in the carburetors in some vain attempt to increase horsepower.<br /><br />5) The 1973 V/4 engines only start and idle poorly if something is wrong. They're a good design and normally start and run just fine.<br /><br />6) Reeds/internal seals are not a likely culprit for a poor idle/start condition. That would be quite unusual.<br /><br />7) Sticking your fingers in the carburetor throats as mention above would be a fairly good indicator of checking the idle suction or airflow?<br /><br />If that engine has compression in the range of 100+ psi and even on all cylinders, has spark (w/plugs removed) that will jump a 7/16" gap with a strong blue flame on all cylinders, the carburetor passageways are clear and proper, and the choke operates as it should, it should start within four or 5 revolutions.<br /><br />I'm assuming that you pump the fuel primer bulb up hard first, and that you do increase the throttle setting before attempting to start the engine (not attempting to start at a dead idle). Let us know what you find.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Thanks Joe. I will do all this weekend if I can get the carb kits. Right now, when cold on the muffs, at best it takes a full 6 to 8 seconds of full choke good battery cranking before it shows any life then takes another 3 to 5 seconds to catch. I always pump up the bulb, and it doesn't leak out the carbs. Since it should start in 4-5 revs or so and only sputters slowly to life, I'm now suspecting starvation/jet clog/insufficient diameter. I'll do the finger tests, recheck compressions and spark, check jet sizes, inspect reeds, rebuild carbs, test and report back. Thanks again.

 

[Dhadley]

Re: Idle/start problems '73 Johnson 135 v4

The 73 135's did idle funny. We used to put 115 heads on them and it seemed to help a lot. The sensor air gap was critical too. <br /><br />Keep us informed after you get the carbs cleaned.<br /><br />Good luck!

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

what sensor, the flywheel magnet sensor(s)?

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Update. I pulled the carbs today, and they were clean. I had a wire gage tester, and found a copper wire that fit into the .035 hole with a fair amount of slop so was clearly less than .031 diameter. This wire was larger than any of the 4 idle jets. I couldnt find a drill that size anywhere, so I have to leave it. I also was afraid to unscrew the jet without the omc tool for that purpose. What do you all recommend, getting the omc jet unscrew tool and 4 new jets(what diameter), or just drill them out to .031? Is .031 the ideal diameter or is there a jet I should buy?

 

[johnm]

Re: Idle/start problems '73 Johnson 135 v4

Hi SCO,<br /><br />I too have a similar problem, but my motor is a 55HP 79 Envinrude. Engine is fine until it warms up and then sits for 10 minutes. I have tried a lot of things with the help of this forum. Unfortunatley though, I still have the problem but have learnt heaps in the process for which I am grateful. You may want to do a search for "JohnM" or "Carbs didn't look dirty. Is this normal". There is a plethora of info that may solve your problem in this thread. <br /><br />I have ordered new carb kits(again) and new jets for my carbs. I am hoping this fixes the problems I am having.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Update: I checked with the local dealer and found the recommended jet size is .030, but not to contradict Joe, there is no american drill size at .030. Drill sizes go from .292 to .031. I purchased these 2 drills and found that the jets are just larger than .292, and probably the omc part diameter of .030. I'm thinking the jet sizes are ok, but I ordered new jets, and will drill the existing ones to .031 to test.

 

[nickscarpinato]

Re: Idle/start problems '73 Johnson 135 v4

Hello SCO: I removed the heads from my 115. You asked about the torque to get them off so I used a Torque wrench to see, none took more then 30 flbs.I hope you don't find what I did, one cylinder scored very badly. I'm sure the person I bought this from had this apart seen the problem and put it bad together just to sell. About your idleing problem, to get an idea if the carb is lean, let it idle and slowly close the choke plate by hand and see if you get a better idle. If you do then the idle needs a richer mixture ie: larger jets. The next thing to try is each venturi separtely. Take a pencil and while it's running block off the hole in the throttle plate one at a time. If it does not change for the better, the carb may be too rich or it is ok and your problem is elsewhere. Have you checked the Timing? What about the timing pointer position? Nscarpi

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Thanks for the info Nascarpi. The idle problem is longstanding, and early on a mechanic checked the timing and found the pointer off and reset it. I think just to be safe I should check it too. I've also been thinking of mounting a timing light and videocam on a tripod, and running wot just after sundown to check timing. The one lower cyl(still has 120 psi) worries me to suspect a bad gasket, ring, or score. I am going to try these suggestions this weekend. Ill recheck pressures all around too and report back. The ease of bolt removal does lend to the idea that the seller of your engine did in fact take those bolts off. The question now is this: What torque does it take to start yield of the head bolt? I could buy a new one and test this.

 

[sparkroost]

Re: Idle/start problems '73 Johnson 135 v4

the 1973 115/135 used high compression pistons/heads. If your fuel was not up to snuff wouldn't this cause bad idle? Back in 73 they had the good stuff! regular lead fuel.<br /><br />Just for curiosity sakes... couldn't you drill a small hole in each cavity on the intake manifold(4 of them) and put a vaccum gauge on it? I know this is how it's done on a 4 stroke, but 2 stroke I am not sure if this will work.<br /><br />Also I was told to set the timing at 20 deg full advance?(maybe 18, can't remember) for these old motors because of the high compression heads/pistons.<br /><br />something else to remember. Visually synking the carb plates is not close enough. disconnect the linkage and try and start the motor. It needs to be warm to do this otherwise it won't start. But when it does start look to see that it's trying to run. I could not get my engine to run at 800 rpm.. disconnected the linkage and it was idling at about 500!! So why not 800... hmmm.... the linkage was off between the two and they were fighting each other. Sometimes the shafts get worn(actually it's the brass bushings that get worn) and the shaft will "tilt" as they are actuated. This translates into "slop" and will throw off the carb synk. Cylinder compression is crutial in these motors cause the carbs can't be adjusted pr. cylinder.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Good points Spark. Does anyone know if the old leaded gas engines should be jetted to a special size, or is that built in to the OMC recommended jets? Same question for timing, should it be retarded? I use midgrade gas. Have heard premium can have gasahol and low grade is junk.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

On third thought, best for now to test each carb throat and look for a lean condition. I could even get undersize jets and drill and test till I find the right size

 

[sparkroost]

Re: Idle/start problems '73 Johnson 135 v4

You cannot adjust the jets for high compression! You can only reduce timing, change head gasket thickness(with this you will need to change jetting also). Only problem changing the head gasket thickness would be loss of power. If you have a 115 for instance, you would drop it down to say 85hp with lower compression gaskets.<br /><br />Might be a fuel additive you could use to get the octane up. You could always fill up at the boat docks pumps as they usually have the good 103 racing fuel.. But... $$$$$<br /><br />If you have good compression you should be able to get it going like it is.<br /><br />As for drilling the orafices... those holes are a specific size as you know. Drilling them out can only create more problems for you. You would have to drill it out perfectly straight, otherwise you are gonna "wallow" out the hole. From your description you are loading up. If you load up on only 1 cylinder it's going to knock off the overall running of the motor. Would be very similar operation to uneven carb synk in the low speed range. <br />Just keep it in mind. What makes an engine run is compression, air/fuel ratio and a clear path for exhaust to get away from the cylinders. Also, to idle good you need to have good exhaust bypass. The majority of exhaust exits from the lower unit. There is a bypass hole in the upper end to release exhaust out the holes in the leg.<br /><br />I am not a professional by any means. But I have been around a few blocks. Just trying to help when I can. Please correct me if I have stepped out of bounds. I am always trying to learn.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

I appreciate your input spark. Ive thought the cylinders to be fighting as it will often start enough to override the starter but not enough to sustain idle. fire die fire die etc. The compressions were all identical but one cyl deviated but as I recall that one was within limits. I like Joe Reeves approach, which is to take care of the basics first, the move on to the weird stuff. When I look at it this weekend though, I'll be glad to have other theories to consider.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Is it a tough job to check/clear any exhaust build up that could be causing excessive back pressure?( I realize this is the most unlikely cause of the problem.)

 

[Joe Reeves]

Re: Idle/start problems '73 Johnson 135 v4

SCO.... If you have compression and the proper ignition, The problem is usually found in the carburetion department as mentioned previously.<br /><br />One thing I neglected to mention... On a flushette, a 20" shaft length engine (height of transom at center) should have its idle set at 1000 rpm. A 25" shaft engine should be set at 1200 rpm. Perhaps yours is set too low?<br /><br />NOTE... Again, the above idle rpms pertain to being set while running on a flushette, not in the water.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Wouldn't that be something. I am reading 1000 rpm on the flushette. I'll check the lu. Should the 20 inches be from the top of transom to the cavitation plate?

 

[Joe Reeves]

Re: Idle/start problems '73 Johnson 135 v4

Measurement would be from center top of transom to keel/bottom of boat. Cavitation plate would be approximately 3/4" below bottom of boat.

 

[SCO]

Re: Idle/start problems '73 Johnson 135 v4

Update. Problem still exists. I went through the carbs and replaced low speed jets with new .030, cleaned passages with omc engine tuner, and replaced all fuel line w new. The holes to the carb barrel are clear also. I'm reasonably sure that the carbs are not restricted in any way. All flappers and throttles appear to be syncronized, undistorted , and precise and operating correctly. The linkages are good and hooked up correctly. The start up was as before, pump fuel, full choke, neutral tHrottle up. 6 seconds crank till sign of life, then intermittent starts and stops as starter overcome, fially periods of runing for 2 or 3 seconds with abrupt halts. Then finally sustained running to a pretty good idle. Once running , can stop and start with no problem . I got one extra clue. On one of the first sustained runs where the motor wouild have continued running, I lowered the throttle to idle, and the engine slowly lost momentum then finally died, so was fuel starved. When warm, the engine has no problem in the idle throttle position. Will check compression again next, and try some shots of premix in the throats. Any comments welcome.