Poor Performance from Suzuki 115

badbass · Dec 7, 2004

First of all hi to everyone. I am new on the site and do not have much experience with outboard motors, but I am very techically inclined so I can do all the work that you would suggest. i traded my 85 Hp Suzuki in on a 115 Hp Suzuki (97 model) to go on my 15ft bass boat. I tought that this motor would scream on this hull but much to my disgust this motor tops out @ 4400 rpm's with a 17' prop. When i put my 19' prop on she barely touches 4000 rpm's.

The only thing I have tried is to change the plugs and to set the carb screws 2.5 turns out from full stop ( all the way in towards rich) Please help me to solve this problem Thanks Rudie Potgieter

JB · Dec 7, 2004

Re: Poor Performance from Suzuki 115

Howdy, Rudie. Welcome to iboats.

My guess is that your engine is running on 2 or 3 cylinders. To confirm this, disable each spark plug, one at a time, while at idle. If the idle speed drops that cylinder is making power. If not, that cylinder is not making power. Test plugs from cylinders not making power for a hot, blue spark. If all plugs are sparking hot, but one or two cylinders not making power, spray/squirt some premix fuel into the carb that fuels the dead cylinders. If idle picks up briefly, overhaul that carb. If you have dead cylinder(s) but neither test above reveals a cause, do a compression check. All cylinders should be above 100psi and within a range of 10-15%. Let us know what you have found. If it is not resolved, we can use that info to suggest more steps. Good luck,

jim dozier · Dec 7, 2004

Re: Poor Performance from Suzuki 115

Sounds like you need to go to a smaller pitch prop. You went the wrong way on pitch (17 to 19). Go the other way. You should aim for ~5500rpm. Check to see that it is firing on all cylinders. You are right that engine should scream on that boat. Also where is the cavitation plate in relation to the bottom of the hull? The carb screws are for idle air mixture only and won't affect WOT.

badbass · Dec 7, 2004

Re: Poor Performance from Suzuki 115

I will try testing power on the cylinders. That sounds logical enough to me. my cavitation plate is running at 1" above the bottom of my hull. Rudie

badbass · Dec 9, 2004

Re: Poor Performance from Suzuki 115

Ok I have done what you asked. I have numbered the cylinders from top to bottom. Number 1 cylinder had a slight drop in rpm's, maybe about 50 rpms. The same was followed by 2,3.... but number four cylinders just about stalled the engine when I disconnected the plug lead. All the cylinders have a blue spark and number 1-3 cylinders jumped slightly when i sprayed some premix in there. If you are going to say overhaul the carbs, please give some info on how to and what to. Also if the jets need to be done please tell me what jets should be in there so I cab check if they are correct. Thanks Rudie

JB · Dec 9, 2004

Re: Poor Performance from Suzuki 115

Wow, Rudie! Sounds like you have one cylinder pulling the others along, but the others are not completely dead. Time for a decarbonization and compression check. Check compression both before and after the decarb. After we know about the results of that we can move forward. I wouldn't suggest tearing into the carbs until you have a service/repair manual to work from. Let us know, and good luck.

jim dozier · Dec 9, 2004

Re: Poor Performance from Suzuki 115

Do as JB says and AFTER you receive your manual (available at iboats at the bottom of this webpage) you will be pulling the 4 carbs off and disassembling them. They are not complicated inside. Clean all the orifices and jets with carb cleaner AND compressed air. Replace the parts (gaskets and float valve) that come in the rebuild kit. Reinstall and reset the idle air mixture screw and floats to the manual specs. When you get this thing running right you can check the rpm and whether or not you need a smaller pitch prop.

badbass · Dec 9, 2004

Re: Poor Performance from Suzuki 115

Should i use a specific marine decarb product or can I use some sort of replacement. Also which manual is the best to go for I have seen seloc on i boats and have run into clymer on other pages. I would also like to invest on a stainless prop. Any suggestions. I would try and determine pitch after the motor is running fine but in the meantime would like to do some shopping. I have spoken to some guys that say you cant work according to your alluminium prop pitch and use the same stainless pitch. How would I know with one to choose.

JB · Dec 9, 2004

Re: Poor Performance from Suzuki 115

It would be best to use a specific decarb product, Rudie. DeepCreep is one that comes to mind, but most dealers will have one that works. Your best manual will be an OEM Manual, though either Clymer or Seloc could do as a substitute. Think about props after you have all 115 horses healthy. Your boat suggests a 19" to 21" prop for starters, but on-the-water testing is the only way to optimize. Good luck.

badbass · Dec 10, 2004

Re: Poor Performance from Suzuki 115

I have noticed one more fault that i believe confirms what JB has been saying. I pulled the plugs today and found that only the bottom cylinders plug had black carbon inside the plug, the other three were only slightly coloured ( light brown). I could only get hold of Quiksilver Powertune... But the dealer says it works like a dream. I will take the boat out in the morning and decarbon the motor first, after that I will replace the plugs and also spray some carb cleaner in there and see if it works. What do you think the plugs colour means. Rudie

jim dozier · Dec 10, 2004

Re: Poor Performance from Suzuki 115

JB is recommending the decarbonization to help clean the carbon off of the piston rings which may help the compression. Its difficult to say without a picture but the plugs generally reflect the mixture at shutdown. Sounds like a couple of the cylinders are burning leaner thant the others. Don't bother to spray carb cleaner down the throat of the carbs. If you want to waste money send it to me. You need to pull the carbs apart and then use the carb cleaner. The dirt or crud is in the orifes and jets which are upstream of the carb throat. I can say with some certainty that your carb throat isn't dirty. P.S. Have you obtained your manual yet?

badbass · Dec 10, 2004

Re: Poor Performance from Suzuki 115

Unofortunately for me getting a manual anywhere would take at least four weeks, and with the festive season coming up i am sure I wont see that manual before the end of January

I will post the reply from the compression test and the decarb process. Thank you all so much for the help so far I realy appreciate it Rudie

badbass · Dec 11, 2004

Re: Poor Performance from Suzuki 115

I done the decarbon process and tested compression this morning. All the cylinders are around the 94 psi mark. The shop that i bought the motor from said that the powerhead was overhauled from top to bottom, but I am starting to wonder if this is the case since this motor performs like *@#%. I also replaced the sparkplugs with new NGK BR8HS plugs, the motor is now running around the 4900rpm mark , this is a improvement but still not what I want. I wont get my manual for a while still and I dont know what to do with the carbs rebuild. Rudie

JB · Dec 11, 2004

Re: Poor Performance from Suzuki 115

What was the compression before the decarb, Rudie? 94psi on all 4 is a reasonable result for an engine with fairly new rings. If compression was a problem before, it isn't now. Which prop were you using on this last test run? If it was the 19", try the 17" again. That should get you around 5500rpm, which would be in acceptable range.. Test the sealing of the gaskets between the intake manifold and the crankcase and over the bypass passages for pressure leaks. Soapy water painted or sprayed on the gasket edges should not make any bubbles. Also, do a retake on the power-at-idle test to see if those other three are now making power. Let us know, and good luck.

badbass · Dec 11, 2004

Re: Poor Performance from Suzuki 115

I did not really see much difference in the compression i took readings this afternoon and came in at about 97psi. There is a noticeable difference in the motors performance but I would like to have that rpm's with the 19 pitch prop

I was using the 17 pitch for the test. The power at idle test now shows that the other three cylinders drops slightly more at idle than they did before. Could I have carboned up this motor running double mix for the break time? I will check the rest of the tests tomorrow and will post back. I will also go the office and get the camera to send you some pictures of the plugs that jimd asked for. Rudie

DJ · Dec 11, 2004

Re: Poor Performance from Suzuki 115

badbass, Your carbs are fouled. Very typical, for that engine. Trust me I am the former owner of a 140 Suzuki (108 cid block) same as your 115. Rebuild them now or rebuild your powerhead a little later. Clogged carbs will cause a piston melt down.

badbass · Dec 11, 2004

Re: Poor Performance from Suzuki 115

DJ, Thanks for the warning. I was planning on going out on monday morning to order the rebuild kit. I've always believed in preventative maintenance

Rudie

badbass · Dec 13, 2004

Re: Poor Performance from Suzuki 115

This is the plugs as they came out. From left to right as they came ou from top to bottom, I hope this helps

jim dozier · Dec 13, 2004

Re: Poor Performance from Suzuki 115

Which cylinder is the fuel pump connected to? If your fuel pump diaphragm has a hole in it, it will inject unmetered fuel into the cylinder to which it receives its pressure pulse (the cylinder intake port its bolted to). This causes that cylinder to run rich. The spark plugs for cylinders 1-3 look about right, #4 looks a little rich or carbon fouled. When you pull the carbs for the rebuild you might as well inspect the fuel pump diaphragm and install a new one which is relatively inexpensive and easy to do.

badbass · Dec 17, 2004

Re: Poor Performance from Suzuki 115

Ok I know I am getting myself into trouble here but please help. the guys that I bought the motor from offered to help fix the motor but it has been standing there for a week now and no improvement at all. I tried to order the carb kit but the guy at the counter looked at me all funny and said that have to order all the parts from an exploded view of the computer one by one, Now I would like to know what you would consider as very important to replace on the rebuild as this is going to cost me a arm and a leg to rebuild these carbs buying the spares one by one Rudie

Poor Performance from Suzuki 115

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