175 2 stroke wont rev past 2k

[gohawks688]

Took the boat out for a test run yesterday and it would not rev above 2k rpm or plane out. It started fine and didn’t seem to stumble or hesitate.

I have recently done some work on the motor….

Deleted oil system and switched to premix gas. Oiling system shouldn’t have an effect on max RPM. Neither should deletion of oil system warning module.

New impeller and gear oil. I don’t think it is possible to put the lower on with the gear position reversed. Boat shifts fine into all gears.

Fuel should be in decent shape. Full tank in September non ethanol with stabil.

I verified butterflies are opening fully and linkage has no binds.

All three carbs were rebuilt last year.

Here is my list of things to verify in order of likelihood/ease.

• Verify no air leaks in fuel line. I had to reconfigure lines when deleting oil system. Fuel could be restricted or have air leaks.
• Check anti siphon valve. could be restricting flow.
• Spark test.
• Verify timing.
• Fuel pump rebuild.
• Ignition tests (switch box, stator and trigger per manual) I have a DVA adapter.

Any thoughts guys?

 

[gohawks688]

Og804616 is the serial number.
Is there any type of limp mode on the motor? Shift interupt switch have any effect on max rpm?

 

[jimmbo]

Are you getting a Spark that can jump a 3/8" gap on all cylinders?
When were the carbs rebuilt the previous Season, beginning, halfway thru, during winterizing?
Are all the carbs delivering Fuel thru the Main Circuit?
You say you rerouted lines, which lines? The fuel Lines, or were you messing with the Recirculation Lines, and/or the Cold Enrichment Lines?

 

[gohawks688]

Are you getting a Spark that can jump a 3/8" gap on all cylinders?
When were the carbs rebuilt the previous Season, beginning, halfway thru, during winterizing?
Are all the carbs delivering Fuel thru the Main Circuit?
You say you rerouted lines, which lines? The fuel Lines, or were you messing with the Recirculation Lines, and/or the Cold Enrichment Lines?

Have not checked spark with the tester yet.it is one of the items on my list. I know this can help identify switch box issues as well
Carbs were rebuilt at the beginning of last season. Full tear down and rebuild.
As far as the fuel lines I deleted the section that has the T fitting for the oil injection. So the only new connection would be fuel inlet to fuel pump. It has a hose clamp on it so there shouldn't any leaks. I did not mess with enrichment circuit. I also deleted the oil pump, oil tank lines ( I put a vacuum cap on the crank case vacuum for the oil tank) and oil warning module/wiring.
I wish I would have thought to try the choke circuit while on the water to see if more fuel would increase rpm.
I guess I couldn't tell if all carbs are delivering fuel. How do I test that?

 

[Dukedog]

Og804616 is the serial number.
Is there any type of limp mode on the motor? Shift interupt switch have any effect on max rpm?

none on that motor..
test stator........

 

[jimmbo]

I used to have someone else drive the Boat, and with a air silencer off, shine a light down the carbs. You should be able to see fuel leaving the Main Nozzle. Wear Ear Protection, those thing are Loud. Dumping a bit of Premix into the carbs, when the problem is occurring might reveal a Lean Carb

On my 115, I had one Switchbox go bad, and the engine had no power. , Another time on of the carbs was severely flooding, that too really killed the power too, however that was 35 yrs ago and the details have faded. I do remember changing out the Switchbox with one from a Box full of them the Dealer gave me(they would switch both when one was bad. Something about a Bias issue). The first one I tried, the engine fired up and It was firing on all 6. The Carb had a float that had went a little Cockeyed, a bit of prying with a screwdriver, and a few taps with a Hammer on the bowl set everything good again.

 

[dingbat]

Run through the testing for the switch box and stator to make sure you didn’t loose the high speed portion of the stator.

Limits rpm to less than 2k

 

[gohawks688]

Run through the testing for the switch box and stator to make sure you didn’t loose the high speed portion of the stator.

Limits rpm to less than 2k

I hope to get some time this week to run through the stator and switch box electrical tests per the manual.

 

[dingbat]

I hope to get some time this week to run through the stator and switch box electrical tests per the manual.

Coming in from offshore......all of a sudden rpm dropped and the boat shut down. Turned the key and it fired right back up. Let it idle for a minute then tried to get back on plane, stumbled and stalled. Needed up limping home at 1,500 rpm.

 

[gohawks688]

Coming in from offshore......all of a sudden rpm dropped and the boat shut down. Turned the key and it fired right back up. Let it idle for a minute then tried to get back on plane, stumbled and stalled. Needed up limping home at 1,500 rpm.

that sounds very similar to my problem. fires right up. but just wont build rpm feels sluggish wont pass 2k. starts right up and idles nicely.

 

[gohawks688]

got a chance to do some trouble shooting tonight. Weather is crap so sticking to non running checks. nothing standing out yet.

• No air leaks found in fuel lines i modified. bulb looks good. gets firm.
• As far as i can tell no anti siphon valve.
• static resistance tests of stator, trigger and coils all sat.
• removed one carb. clean as a whistle inside. Will remove and clean other 2 just to be safe.

Still to do
rebuild fuel pump. ( kit on the way)
spark test
running ignition electrical checks
clean other two carbs.

One thing I am wondering... I removed the oil system partly because i couldn't get the alarm to stop beeping. Based on my research the alarm can be set off from ignition components that are in poor condition. maybe this is a data point towards a bad switch box or stator?

 

[jimmbo]

A faulty switchbox will certainly kill the engine's ability to make power
but if you are consistently getting spark on all Cylinders, it is hard to condemn a Switchbox
Inspect the Wires between the Coils and the Plugs, Inspect the Plugs for any Cracks in the Porcelain. Inspect all the Connections and wires between the Switchboxes and Coils

 

[gohawks688]

A faulty switchbox will certainly kill the engine's ability to make power
but if you are consistently getting spark on all Cylinders, it is hard to condemn a Switchbox
Inspect the Wires between the Coils and the Plugs, Inspect the Plugs for any Cracks in the Porcelain. Inspect all the Connections and wires between the Switchboxes and Coils

I will be trying to check for good spark at all cylinders tonight. I will check plugs and wiring at that point as well.

 

[jimmbo]

Just keep in mind, a Good Spark is one that can jump 3/8". I know that plugs are gapped much closer, but 0.030" in an atmospheric pressure many times Sea Level, is like 1/4" at Sea level. Compressed Air is a better Insulator

 

[gohawks688]

STATUS UPDATE
Did a spark test tonight. STBD bank has spark Port bank does not. that would definately keep me from building power.

Is it safe to say switch box is causing this?

The switch boxes are unbolted from the motor right now to allow voltage readings on the inner box (this shouldnt have caused my loss of spark on one bank should it?)

 

[gohawks688]

So i swapped inner and outer switch boxes and the condition switched banks. I think i found my issue

 

[Faztbullet]

Swap em as a pair and only OEM,Serria ,EMP (Prufrex) brands,,no Amazon Chinese knockoffs

 

[gohawks688]

Well I'm back with the same symptoms not sure if it's the same problem. Boat has been running great since the switch box replacement until last outing. Was on plane running about 4k rpm all of a sudden dropped off plane and started running poorly. Boat would not plane or build rpm just as before.
Once home I expected to find one bank of cylinders with no spark... All cylinders have blue spark using spark tester. So it doesn't seem to be switch boxes.
Nothing seems out of under under the cowl, no loose vacuum lines.
Both cylinder heads are warm evenly, it seems all cylinders are firing.
Checked compression 115 on all.
Based on good spark it doesn't seem to be electrical?
Struggle to see how it could be fuel related, the problem hit so suddenly I struggle to think a carb could clog that instantaneous. I guess opening up the carbs again it's my next step. During last troubleshooting early this year I cleaned carbs and put on new fuel pump.
Any ideas ?

 

[jimmbo]

When you lost the spark the engine and the Switch Boxes were warm. When you tested them they had likely cooled down. Get the Wife's Hair Dryer, heat the Switchboxes up for several minutes, and see if the spark vanishes. Other parts, like the Trigger are also susceptible to heat. The carbs on the are usually not prone to sticky Floats like the I6 carbs are

 

[gohawks688]

Symptom persisted today on a test run. Components would have been cool to start test run. So I don't think it's a heat issue.
If it's not spark what else could cause my symptoms? Could the advance module be limiting timing?