Home › Forum › Ask A Member › 1978 Johnson 75 hp Stinger stalls when throttled up
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fleetwin.
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August 22, 2015 at 12:17 pm #22484
Yeah, I wouldn’t attempt to remove the jets without having the proper tool, that is probably how one of the jets got damaged. In any event, did you remove the jets? If not, I would just use a little cloth pipe cleaner to clean the jets while they are still installed in the carbs. Simply drain the carbs, now spray engine tuner/carb cleaner on the pipe cleaner and run it into the bowl drains and through the high speed jets. Once removed from the jets, a brown/green staining on the pipe cleaner indicates dirty jets. Before reinstalling the carb drain plugs, reconnect the fuel line and pump fuel through the carb bowls in an attempt to wash out any debris dislodged while cleaning the jets. Yes, not the most effective way of cleaning up the carbs, but this might solve the problem for now. Keep in mind that jets that are loose in the bowls can create a fuel restriction as well.
Perhaps the fuel pump is weak, or there is an air leak/restriction in the fuel system causing the engine to starve at high speeds.
Have an assistant pump the fuel bulb constantly while you accelerate the engine to see if that helps. Any signs of water in the fuel?
Be sure to heed everyone’s advice about propping this engine, it is really meant for a light/high speed hull, and has little mid range power for pulling skiiers or planning difficult hulls.
But, it seems like I have jumped ahead as well. Listen to Frank, the sync/linkage specs have to be right or the engine will stumble/stall when accelerated.August 22, 2015 at 10:37 pm #22495To answer the one question, what are nozzle gaskets: (well, that’s what I call them)There is, of course, the main bowl gasket around the outside of the bowl. Then there is a small ring gasket that goes in the center of the bowl, on the same plane as the outer bowl gasket. That’s the nozzle gasket.
Long live American manufacturing!
August 22, 2015 at 11:19 pm #22497So…..We are still diagnosing an "engine problem" when there has been zero information on what boat and what propeller you are running even though the question has been asked early on.
August 22, 2015 at 11:43 pm #22499quote Pappy:So…..We are still diagnosing an "engine problem" when there has been zero information on what boat and what propeller you are running even though the question has been asked early on.
Easy now, am thoroughly agreeing with you. Just offering some simple things to look at while waiting for boat/prop/RPM data.
August 23, 2015 at 4:02 am #22506The boat is a 16′ Thundercraft, running a 13 1/2 x 15 pitch prop, but I think the boat data is irrevelant at this point. The motor will start and idle well, it revs up in neutral but the moment it goes in gear it stalls. It stalls when put into forward or reverse. The other day I got it to stay going at 3 mph but if I increase the throttle it stalled. I sprayed some deep creep into the carbs and it ran a little faster so I figured it could be the carbs. I took them apart and cleaned them but it’s worse again. Now it stalls as soon as I put it in gear.
August 23, 2015 at 12:49 pm #22516OK, well the best place to start is with checking sync/link. If one of those throttle butterflies is opened, even just slightly, the engine will behave this way. Make sure the throttle roller is not touching the cam at idle. Do you have a manual with the sync/link procedures? Have you done a compression test? These engines don’t do the usual OMC sneeze/cough thing when lean, they just kinda fade out and stall.
Have you done a spark test/replaced plugs? These engines will idle pretty well in neutral on two cylinders, but will die quick under load. Checked fuel filter/restrictions/air leaks/fuel quality/water? Having an assistant pump the fuel bulb might while the engine is running might help pinpoint pump problems/air leaks/restrictions as well.
PS- The 15" prop seems right for that rig, is it a cupped prop? Did you remove and physically clean the low and high speed jets on the carbs when you cleaned them? Were the carbs dirty, or did everything seem relatively clean? Is it possible that one float is stuck closed starving a cylinder? Remove the top bowl drain plug and pump the fuel bulb to make sure fuel is flowing into the carb, repeat with the other two carbs.August 23, 2015 at 6:36 pm #22526Thanks for the advice all, I followed the script that Fleetwin gave m in that last post and I found a problem. I should have checked this a while ago but here is what I found: I checked the plugs and noticed some water in the bottom plug. I ran a compression test and got top 125, middle 125 and bottom was 0 but the tester had water in it. So I pulled the head off the tester and when I turn the motor over water shoots out. So cooling water is leaking into the bottom cyl. I had this same problem on a 1975 Hustler and I changed the exhaust cover gaskets and head gasket and it fixed the problem. But would the water in the cyl affect the compression test. I did the test a second time and got it up to 30 psi before it started leaking again. Where should I go from here?
August 23, 2015 at 8:03 pm #22531Well, the first thing to do is get that cylinder/crankcase dried out before rust occurs. I would remove the gearcase and start the engine without it/water. Let the engine get good and warm, then pump those cylinders full of oil through the carb throats while it is running. Hopefully the lack of water and high heat will evaporate any residual water in the cylinder/crankcase.
Once the internals have been protected we can get back to the compression/water problem. Unfortunately, leaky exhaust cover gaskets wouldn’t really affect compression, so I would pull the head, hopefully you will find a blown head gasket. Plan on pulling the powerhead if the exhaust cover gaskets need to be replaced.
Will cross my fingers for the blown head gasket!August 23, 2015 at 8:10 pm #22533How will I know if the head gasket is blown?
August 23, 2015 at 8:37 pm #22536The metal fire ring is usually distorted/head gasket material burned in the area of failure. Look for corroded/damaged sealing surfaces on the head and block where the failure occurred as well.
Feel free to post pictures if that will help.
For now, I am more worried about protected the internal parts of the engine, so pull the gearcase off, fire her up, and pump those carbs full of oil! -
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