10R75C Power problem

[cst756]

Hello, Im new and of course have a question hoping to get some input.

I got a 10r75c yesterday, and put it on the water today, got it cranked and went on up the river (about 20 minutes full throttle). Seemed to be doing pretty good. I had to turn around (got a little lost), so I eased off the throttle and made my turn, and went to increase the throttle, but the boat wouldnt gain power seemed to be bogged down, except for these small (one second long) "burst of power", I referred to it as "I think I can, I think I can" , but never would. However; if i maintained full throttle it would finally catch and start going fast after a couple of minutes. After that as long as I didn't ease off the throttle it would run seemly good. I had to turn around a couple of times on this hour long trip and each time I slowed the boat it would lose power except for the little burst power, and eventually would get right and go (with no skips or anything I could feel).


I have learned alot about this motor from this forum, but think i got too much at one time. I look at the plugs and they were wet, i guess its the fuel mixture. Is that normal, or should they be dry? Is it because the coils arent firing enough or something (they look pretty old). Or is it something worse.

thanks for any help

 

[Monte1961]

Re: 10R75C Power problem

Befor you start throwing parts and yer money away, do a few simple checks. Test compression with known good tester1. Get a spark tester and check both wires with sparkplugs removed.2. If all checks good, might look into carb/fuel related providing lincNsync are good! Post yer results!

 

[tallwill38]

Re: 10R75C Power problem

Just by the symptoms that you listed sounds like trash in the fuel system somewhere.A lot of people have a misconception that trash in the fuel system will either pass through by itself or that just running a cleaner in the fuel will clear it out.If there is trash in the float bowl it ain't going to get out on it's own no matter how much you run it.Best thing is a thorough inspection of the entire fuel system from the tank vent to the fuel discharge point inside the intake.Check the simple stuff first as always check the filter and get a light into the tank to inspect for fuel contamination look for water or trash in the bottom ect... I am not up on model numbers of engines so I don't even know what a 10r75c is I assume thats the model number but if you could post more information someone here will more than likely be able to help you figure this out.Good Luck

 

[cst756]

Re: 10R75C Power problem

OK. Its a 75 Johnson 9.9. I had to order the rewind spring so I'm waiting to put that on and make it easier to pull. Ill post up what I find out.

 

[OptsyEagle]

Re: 10R75C Power problem

If you are using Champion spark plugs switch them to NGKs B7HS. Seems crazy but if you search this site you will see many posts on the 1974 to 1976 9.9HP/15Hp series hating Champion spark plugs. My 1975 9.9 did the exact same thing with Champion UL81C plugs and once I switched to the NGKs the problem went away. When I put the Champions back in the problem returned. The wetness on your plug is probably from its intermittent firing.

Pretty easy test anyways.

 

[cst756]

Re: 10R75C Power problem

I picked up some ngk br6hs. They had the b7hs in stock but was scared they would be too hot. I think I will grabs set and see.

 

[OptsyEagle]

Re: 10R75C Power problem

With NGK the lower number br"6"h is hotter then the higher number br"7"h. I use the 7's but I run her hard and don't troll too often. If you troll the 6's would be better. I have not heard anyone with problems and both 6's and 7's are used by many.

Put in the NGK BR6H and see if it makes a difference. You may have another problem but as I said, it is an easy test. You will only notice the difference running with a load on the boat. Please let us know your findings.

By the way, what plugs were you previously using?

 

[cst756]

Re: 10R75C Power problem

Well I decided to go get some earmuffs and see if the plugs help. I still feel the same skip but thats ok I have ran into other problems attempting to track this problem down. I got it running and then did a compression test (per testers instructions), I checked the top cylinder and it would jump up but then lose pressure immediately. I tried a couple of times and same thing. I moved to bottom cylinder and got a reading of 85 on the first pull and it topped out at about 90, but the gauge stayed up at the number. I decided to check the top one again and wouldnt you know it, it held a pressure of 90. I don't understand that (cheap tester).

Well while I was preparing to do the compression test (motor running, warming up), I noticed that no water was coming out of the hole, its was coming out from the bottom steering pivot point (? I dont know the name). But I checked on the water the other day and water seemed to be coming out the right hole great. So now I think I have much bigger problems possibly causing my initial problem.

I hope this video helps, Ihad run it for about 5 minutes prior to this. Please help me not lose my mind. Oh yeah, I put my finger up to the water hole and did feel a little air coming out, but no water

 

[cst756]

Re: 10R75C Power problem

I think I know about my water now from reading a little more. Should have searched a little better.

 

[OptsyEagle]

Re: 10R75C Power problem

I can't really add much since I don't really hear the skip you are talking about unless that is what killed the motor (or you did, I could not tell).

With an intermittent cylinder a boat test is best since these motors run remarkably well on one cylinder but the loss of power is easily observable when it is pushing a boat, not when it is idling on muffs.

Your compression seems fine. You could do an external spark test and see if your ignition is firing on both cylinders, a spark that can jump a minimum of a 3/8" gap. If it does, it doesn't mean that you still don't have an intermittent spark failure, but if it doesn't jump the gap, it should help guide you to the source of your problem.

 

[cst756]

Re: 10R75C Power problem

I replaced the rewind spring. And after testing the spark it looks like my problem is the bottom coil. Going to replace both. They both look pretty old. Ill post up after the next test run