Low RPM at WOT 115 Johnson

[jakedaawg]

Did we everbdo a spark test on this yet?

 

[mustanghorizon]

Ok so reporting back: The boat is still performing the same. The boat has a brand new stock prop. All 4 carburetors were rebuilt. The gas is OK, with no water in gas. The throttle plates are all opening all the way. Spark test showed spark in all cylinders. Compression is all cylinders is 130 psi. I have tried pumping the fuel ball when driving WOT, to no effect. What else do you think I could be missing?

 

[mustanghorizon]

Cleaned the electrical connections on the coils today, and saw about a 200 RPM increase, as well as 3 or 4 mph. Is there a chance that the boat is getting enough spark at WOT. And as far as max timing, is that something that could just change overnight without adjusting anything?

 

[mustanghorizon]

Problem Finally Fixed: It took me a while to figure out that I was missing a high speed jet in one of the carburetor bowls. Boat runs great now, 46 MPH at 6000 RPM. Thanks to all for the help.

 

[jakedaawg]

So glad you found it. Sorry for steering you in the wrong direction. There are limits to diagnosing when all we have are questions and answers.

I even run in to issues when a customer brings one to the shop but doesnt tell the whole story. In no way am i implyong that you did anything remotely similiar, just saying that a lack of info and being able to hear see and feel can make net diagnosis problematic and frustrating.

Once again, congratulations!

 

[Tim Frank]

Problem Finally Fixed: It took me a while to figure out that I was missing a high speed jet in one of the carburetor bowls. Boat runs great now, 46 MPH at 6000 RPM. Thanks to all for the help.

???? Something is not adding up.
How on earth did a high speed jet go missing?

Also, you mention that you are running 93 octane. That is not the recommended fuel and can increase carbon build-up as it runs a bit cooler.
Regular is better.....and cheaper.

 

[Joolz]

Also, you mention that you are running 93 octane. That is not the recommended fuel and can increase carbon build-up as it runs a bit cooler.
Regular is better.....and cheaper.

Old post but came across while searching for compression test and noticed this last line.
Are you folks in accordance with the above? I've been running premium (in Canada it's 91 octane) from Costco as it is the ONLY premium that I know of that contains no alcohol. Unfortunately Canada is now following the US lead in adding alcohol (methanol?) to our gas. Isn't it a really bad idea to have this in a motor? I hear all sorts of headaches methanol causes to motorcycles to folks in the US and that's something we've been spared here up north. Well, till now. Concern is with alcohol turning to gunk inside the carbs while stored for the winter.

Getting alcohol free premium from only one source is a headache (and as mentioned, costlier too). If indeed the consensus is that running regular (89 octane and I think up to 10% alcohol) is preferable please let us know. Motor in question is a 1983 Johnson 115 HP 4V.

 

[Tim Frank]

Old post ....

It is. But that didn't seem to stop you from reopening it. That will not amuse the Mods.
Below are some additional forum policies in hopes of all iboats members will follow, Thank you.

1. Please do not reply to old topics or hijack existing topics. Old topics of a technical nature are like a library book, Please do not write in them.

Getting alcohol free premium from only one source is a headache (and as mentioned, costlier too). If indeed the consensus is that running regular (89 octane and I think up to 10% alcohol) is preferable please let us know. Motor in question is a 1983 Johnson 115 HP 4V.

There are many discussions on this topic available in here. Just do a search and form an educated opinion.
If you try and get a discussion on this started, it falls into the "natural vs. synthetic oil....Champion plugs vs. NGK etc. " hot-button category and may start several skirmishes.
That will not amuse the Mods either.

 

[Joolz]

My bad. Hadn't realized it wasn't good etiquete to reopen an old thread - and a hijack on top of that too!
K, will search about. Probably should have done that to start with, but your line above really caught me by surprise (a pleasant surprise but now more confused than ever). Cheers.

 

[Tim Frank]

I use 87 octane gas as specified in my owners' manual. At the end of the season I pull the plug on the carb and drain it for the off season. Outboards run pretty cool, really, so no benefit from higher octane.
I have never experienced the issues that some people attribute to ethanol fuel ....EXCEPT....I had a lawn mower that the fuel line failed. Probably ethanol related and an older machine before they had ethanol resistant components. Replaced the line with new ethanol-resistant fuel line and no hitches since.

Not to confuse the issue, but in my small air-cooled motors I do use 94 octane, and in my chain saws use non-ethanol pre-mix that I buy in small cans, 1 litre at a time.