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Questions on high speed jets.

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Brian4591

Contributing Member
1996 Evenrude 225. No matter what prop i try 25p, 24p, 23p it does not seem to change any high rpms at WOT. The max rpms I get is 5000rpms. I have checked rpm gauge to another one and no differance. The only thing i gain is 2mph from a 23p to a 25p . My rpms should go up when going to a smaller pitch prop but it dont.
My questoin is do I start changing high speed jets? If so do I go bigger or smaller and how far in size of jet. What about running it to lean and rich and how do I tell if it is to rich or lean. Do I have to adjust timmimg too?
The boat is a Stratos 290fs 20'5"
When trying the 23p prop I can trim up till it blows out and even then my rpms wont go over 5200 rpms.
It starts and idels great and take off is very quick to plane on any prop but no top rpms. Looking to get rpm range of 5500 to 5800.
What to try?
 
Brian
I am new here so I am sure a more senior and knowledgeable member will respond.
I have recently been through this same scenario and am wondering have you had this motor long? Have you seen it turn 5500 rpms?
Let us know.
 
No i have not seen it more that 5100rpms and I have only had it for a year. The person before me used it for ski, tubing.
 
Look at your plugs after a high speed run, if they are dark you are at least getting fuel, maybe too much.I had one oversize jet out of 6 that was holding me back.
It would be a good idea to check for fuel restriction, proper spark, sucking air in fuel system.
I found a problem with pretty much everything in a boat I got in March. Everything I fixed t got a little better until Sunday when my stator quit.

Veterans keep an eye on this thread, I don't want to lead someone down the wrong trail.
I had never touched an outboard before March, I read every page of the Johnson forum and learned a lot.

Good luck and keep us updated
 
compression check first,spark test second,start with the basics,troubleshooting 101. Running an engine to lean it will damage motor,running too rich it will carbon foul
 
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If tach will not read above 5000 rpm when prop blows out you have a bad tach,regulator or stator. Its not a jetting problem...
 
Replaced Stator, power pack, plugs,fuel line , primer bulb,fuel filter. Checked tach to another one and they read the same.
 
A word of advice..... DO NOT start tinkering with the jets on that engine. They are precisely set up for that model to provide maximum performance regardless of whatever propeller might be installed or if the engine's installed on a bass boat or a 24 foot barge.

To fool with those jets will result in either a lean running engine or what we call a "Wash Out", in either case, a condition that will result with a need to overhaul the engine (blown pistons, scored cylinder walls, burnt bearings,etc).


(Compression & Spark Test)
(J. Reeves)

1st - Regardless of what problem one might encounter, always start with the basic troubleshooting procedure. Check the compression which should be in the range of 100+ psi (somewhat less on the smaller hp engines) and even on all cylinders.

2nd - With the spark plugs removed, rig up some type of spark tester whereas you can set a gap to be jumped. On magneto ignition systems.... and also the Battery Capacitance Ignition system OMC engines from 1968 to 1972, set the gap to 1/4". On the solid state OMC ignition systems from 1973 to the present, set the gap to 7/16". The spark should jump the gap with a strong blue lightning like flame..... a real strong blue snap!

NOTE: Checking the spark via using the spark plugs is a waste of time and proves nothing. The above stated gaps must be used for a proper test.
 
Brian4591 said:
Replaced Stator, power pack, plugs,fuel line , primer bulb,fuel filter. Checked tach to another one and they read the same.
Click to expand...

What about the rectifier tach gets it's signal from that. You seem to have replaced everything but even if the jets were wrong you still should have seen a difference in the rpm.
 
What about reeds. Could my problem be bad reeds. My compression is 112,110,110,109,111,99. One cylinder is low but not that low. Or is this my problem. I just cant seem to figure out why this 225hp wont go over 5000 rpms even from three different pitch props. I should see some rpm change at WOT. I have two tachs installed and both read the same. I feel that if I can get this motor to get 5600rpms that more of the boat will come out the water and have much more speed by like 8 to 10 more mph. I hear guys running 200hp on the same boat i have and they get 60 + mph. I am only getting 50 with a 225hp. Was also thinking of raising the motor one more hole but not sure if that will help. Water psi is at 30 at WOT i dont want to lose that psi. Any sugestions?
 
You need to test your rectifier before anything, if the tach is not working correctly which it sounds like it's not how do you know your actual RPMs. Is your speed GPS or speedo. If your reeds were bad you would see fuel coming back through the carbs.
You have a list of things to check

#1 are the carbs opening all the way
#2 is the timing correct.
#3 is your link and sync correct
#4 are your carbs clean
#5 Check you RECTIFIER/REGULATOR
 
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I have tested everything according to service manual that i can with the tool and meeters i have. The rectifier is the only thing i didnt check. Dought that is the problem but i will check. Anything else to check. All carbs are clean n sync. Could VRO fuel pump be week on top pressure? I have no way to ckeck it.
 
Do the carbs open all the way have you physically checked them to make sure they do. It is possible to linc and sync and not have the carbs open all the way. I am not there I can't tell you what's wrong with your motor I can only tell you what to check if you don't want to or can't that is a problem. You need to diagnose things not just guess.
 
the fuel pump is only mentioned in one thread #14,Fuel pressure needs to be checked at WOT.Auto parts store might rent a pressure gauge. Ditto on Flyingscotts posts #13&15
 
I am unable to find a pressure gage for fuel pressure. Is there any other way? Going out fishing today. Will see how boat runs today.
 
Normally, fuel pump pressure gauges are combined with vacuum gauges. Auto parts stores should have them. But don't confuse with fuel pressure gauges designed for fuel injection systems.
 
Great day fishing. Motor ran good but still no top end. I put my 23p prop on first and ran 4900-5000 rpms with only 48mph then i switched to a 25p and got 5000-5100 rpms and 51mph. Now I know that the rpms should be higher with the smaller 23P prop but it is not. I scrached my head and put the 23p back on for the day but still only 48mph and 4900rpms. The props are the same brand and same 14 1/4 round just different pitch. Im so confused. Guess maybe the 23p might be out of tune or the 25p. But even still the engine will not rev any higher than 5100 rpms when I trim to high and eiher prop blows out. When the prop blows out it should rev at least 400 more rpms but it dont. Or am I wrong. Wish i had a 19p just to see if i can get the motor to rev to like 5800rpms at wot. Thought about not puting a prop on and just put motor in the water and run it in gear and carefully push the throttel to see if it will go to 5800 rpms but am afraid of blowing motor or even damage the lower gearbox because there is no load on shaft. I did rev motor once today to see if the rpm gauge would go over 5000 and i seen it hit 6000. I dont like to rev the motor like that but i had to try. Any sugestions?
 
had same problem, found one of the high speed jets had backed all the way out of the years it would not run over 52 WOT till i screwed the high speed jet all the way back in, it was flooding one cyclinder now im running 65 plus
 
I purchased a pressure/vacuum gauge to check things on my son's outboard from Amazon. Less than $20 and it delivered the next day. Also, most national chain auto parts stores have a spark gap tester for less than $10. You can adjust it from 1/4" up to about 3/4". I would not recommend replacing the high speed jets, but I would certainly recommend pulling them out to see if they have a fine layer of varnish type buildup on them. I also purchased a jet cleaning tool on Amazon. It's like a very, very fine file that has the jet size on each one. It's like a Swiss army knife, with lots of different sizes. Be sure not to use a larger size and over bore the hole. But I have used it to clean some pretty nasty carbs that were actually under-sized because of some build-up from sitting and/or bad gas. If that's your problem, this would give a similar result as using larger jets, but actually your end result would be correcting your jets to the propper size.
Keep us up to date on what you figure out.
Nobody has asked, but when did you last change lower end oil? My son had a 90 HP Johnson that simply wouldn't reach high RPM's. He replaced all sorts of parts. While drinking a beer and leaning against the boat trying to figure it out, I put m foot on the prop and kicked it to watch it spin. It didn't move! I checked and it was in neutral! We drained his lower unit and it was a mixture of clumps and water! The lower unit had been taking in water for quite some time. That was HIS failure to reach high RPM's. Check that out too.
 
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