TOPIC: rejeting the carbs

I have a 1979 Johnson V4 115TL79R . Is it as easy as rejecting my carbs with jet off a V4 140TL79R to get more hp out of the motor ? As I look through the parts book both motors take it seams like the same parts. carb kit ,pistons ,rods crank ,etc. the only difference I've found is different part #s for the heads. just doesn't seam that easy . thanks in advance ..

I'm no expert by far but I don't think rejetting will increase horsepower. If you put in a larger main I think you would just increase fuel consumption and runability issues. Could be wrong. One thing I did find out almost 26 years ago was that if you shave the heads you get better spunk. Did that out of necessity. Had an older 80's Johnson that overheated and warped the heads, I put emery cloth on a flat board and proceeded to cut down the warp until it was flush again. There was a noticeable improvement in performance. Not recommending this though.
There are experts here that could be more informative.

Just resetting your carbs will not help & in fact will hurt your performance. The motor will just use more fuel as already mentioned. I have attached the parts pages of the blocks of the two motors so you can see the difference in the exhaust. The 140 has what is termed a bubble back exhaust system (think headers). See attachments. The first should be like your 115 & the second is the 140. These pictures are from 1977 because the 1979 books list all of the motors the same (even the 85hp). Later OMC made the 115 a bubble back motor & the 112 SPL. This all had to do,with rating HP changes after 1984. Hope that helps.

Dan in TN

Thanks for the info !! I was using a 79 book ,thats why I asked. Didn’t think it was that easy . I’ll just leave things as they are . Thats why I love this site so much info at a reasonable price !!!!!

Now it’s time for the OMC prop experts and performance experts to jump in... just let them know what you want... more whole shot for skiing or full loads, or more top end, or ??? A little of the right adjustments can at least fully unleash the HP you do have. Nice rig by the way!!

well like everyone I would like more top end (speed) . I pull grand kids on a tube , but when it just me I like the wind blowing through my hair > I run a 13 1/2 by 19 prop. I'm going to put carb kits in this spring , I'm the second owner and the PO said he never had them rebuilt . I've used sea foam in the gas ,sprayed sea foam in the carbs . thanks in advance. I bought the rig from the original owner last summer, well taken care off, just need some extra love , very lucky find !!!

I am thinking that if you are not pulling big guys like me doing deep water starts on a slalom ski ( which I am a big drag) ... compared to modern tubes that have bottoms that help them plane easily, I have seen people trying a bigger pitch prop that also has those holes behind each of the prop blades to help it slip a little at start to allow more rpm and therefore more hole- shot to plane off and then allows a bit more top end if your motor can spin it to proper rpm. The caution to this is if you pull kids at speeds less than full plane out speeds, that slipping may be undesirable... like maybe that 12-18 mph range give or take. I have not owned your model or brand, but have ridden in a couple with both 85 and 115s. Seems like the hull stays wet a bit more than some other performances boats when trimmed. More wetted hull surface robs speed. A prop that can be more of a bow lift prop could lift the hull a bit more when you are alone. You will hopefully hear from Glastron OMC people with this actual experience with this. They can also warn where the limits are to avoid chine walk problems at high speed or too aggressive of trim. I found that balancing my fuel load between both a front and rear tank. I used half the rear tank for skiing with full bow tank weight... then switched to front tank and ran it out skiing and cruising in afternoon. That left me light for evening speed runs. On my current boat of 20’ and only 25 gallon rear tank, I would only put 5-10 gallons in tank and leave spare cans on shore. This was like keeping an adult out of the back of the boat ... helps planing, pulling, and speed. Glastron OMC people can give you real numbers and ideas to try that fit your rig. You found a nice gem! Good luck.

Dr. Thanks for all the info. I’ll do carb kits , and then experiment with a couple props. I can always change props , run half tank of gas or maybe a gas can , trim out when I need to feed my need for speed Thanks again .

The nice thing is that your boat already looks fast just sitting on a trailer... and classic finish is an 11, so you should have tons of fun and lots of attention from lookers. Remember to add additional time at the boat launch for onlookers with questions about your cool boat.