1978 johnson 150 wont go full throttle

[old evin]

sorry about jumping in.im new on iboats. thanks ill try that

 

[old evin]

thanks for help. previous owner disconnected kill switch and had the end taped up. tape came loose and it was grounding out couldn't tell by looking at it but I put a cap on it and re taped it and it fired with key. your diognositics where on the mark

 

[10Rams]

Okay finally took the boat out and it had full power. I rode around for about a minute then let off the throttle and now half power again then my battery was to dead to try again. I have spark on all cylinders. Could the blue purple green and white sensor wires cause this if they were hooked up wrong.

 

[emdsapmgr]

Likely you still have an ignition problem. Weak ignition components tend to fail once the engine heats up to normal operating temps. May run fine when cold, then start to crap out when it warms up. When it's not running well, check for spark. Either a cyl drop test, or use an inductive timing light on each plugwire. My 78 factory manual says you've got the power packs hooked up correctly (even though their sequence may not be the most logical.) Keep in mind that in addition to the power packs, you have additional ignition components, the stator and the timer base. You may want to throw some investigative time their direction. This website has some great troubleshooting tips: cdielectronics.com I esp. like the cranking voltage output tests for the stator and timer base. (you'll need a special Peak-reading voltmeter to read the voltages) Once you qualify them, the back to the powerpacks. Are you running a tach in the boat? Does the tach work? (A battery charging issue is usually the reason that the tach acts up.) This problem is not related to any ignition problems.

 

[10Rams]

Thanks. Whats the chance of the timer base or stator going out? First outboard ive worked on so i dont wanna mess it up. Ima take it out again tomorrow with a fully charged battery and see what happens. And also to answer your question about the tach none of my gauges work they did not work when i bought the boat not sure where as to start on them either.

 

[emdsapmgr]

Since this engine is the first outboard you've worked on, sounds like you need to make a maintenance checklist and start at the top of the list. Some items for the hit list: change the impeller in the lower unit. Change the lower unit gear oil. Compression check the engine. Discard any old fuel-put fresh premix fuel in the tank. Check for spark on all plugs when cranking the engine. Check the choke for proper operation. All/any of the original fuel hoses on the engine are not made to handle today's ethanol fuels. You will want to replace them with new (see the factory parts lists for part numbers.) This will probably include both fuel pumps. Bits of disintegrated fuel hose can migrate down into the carbs, causing possible running problems. Depending on how it runs, you may need to overhaul the carbs. A running tach will help you decide it it's idling correctly and if it performs normally at WOT rpm's. (And if the engine is re-charging the battery.) I recommend a factory service manual for these efforts. See this website: outboardbooks.com

 

[10Rams]

turns out one cylinder has scarring. anyone know about the price to just have that one cylinder replated to oem specs?

 

[emdsapmgr]

Why not just overbore it and go with one oversize piston? The factory makes oversize pistons in three sizes: .020 over p/n 5006709 .030 over p/n 5006669 and .040 over p/n 5006710. These pistons are sold as a "kit". Not sure if it's a "kit" because it comes with the piston pin, or if the kit also includes rings. You'll have to ask. It's also a good idea to understand why the piston failed. Perhaps an autopsy of the carb that feeds that cyl will tell you why that one cyl failed. If you do overhaul it, go with 6 new ringsets.

 

[10Rams]

I thought when you overbored one cylinder you would have to do the other 5? Is that incorrect?

 

[10Rams]

also how hard is it to get the block off....?

 

[emdsapmgr]

You can overbore just one piston. The oversize factory pistons are made to weigh the same as the original stock bore ones. Unless you go more than .030 over, you don't have to worry about rejetting the carb that feeds that cylinder. Just hone the other 5 cylinders and install new rings on the 5 pistons. If you are going to get into a complete teardown, you'll probably want to be working from an original factory service manual. Check out this website: outboardbooks.com

 

[10Rams]

Thanks alot man. I was debating on just junking all of it. but i think ill give it a try. Might take all winter but i will post up if i ever get it back running. Thanks again!