New 9.8 4stroke: Rev limiter during break in period?

[Mcboatface]

After much self-debate about the new 9.9/15/20 family vs carbed 4s 9.8, I just bought a new 9.8 for my light 12ft aluminum vee. I have about 5 gentle break-in hours on it and just got a little inductive hour/tachometer, which showed me some surprises.

It runs 16mph at less than half throttle (100lb boat plus 170lb me). Manual says I can now do short blasts of “full” throttle. When I do, revs go from 2800 at half throttle up to 3000 at full then fall slightly to about 2800ish. Speed doesn’t pick up much, maybe 3 mph.

Specs say say it should hit 5-6k rpm and I know I’m not overpropped in my tiny boat. Does this thing have a rev limiter keeping it under 3k while breaking in? I think I have the tach set up right, it’s saying 1k at neutral idle and 800 in fwd idle.

 

[GA_Boater]

Owner's Manuals tell you stuff like that.

 

[Mcboatface]

Nope.

 

[GA_Boater]

Nope.

Then it isn't rev limiting during break-in. The book would say that to stop unnecessary warranty claims for poor performance.

 

[pvanv]

Tach is probably wrong. Idle spec is 950 in N, and 900 in gear. Many people set that a hair higher for better warm-up, unless they have an RC setup with neutral warm-up lever.
Max WOT RPM is 6000. Recommended top RPM of 5000 to 6000. Higher is better. There is an ignition-staggering rev limiter, which engages at about 6250.
This is a siamese ignition coil; Both plugs fire once each revolution -- that means once at the power stroke, and again on exhaust... If you set the tach correctly, you should be OK.

 

[Mcboatface]

That’s got to be the issue - thanks Paul. Will try the other tach modes and report back. Also, if I’m hitting high cruising speed at less than half throttle, then quickly bouncing off the governor, then I take it I can go up a prop pitch or two

 

[Mcboatface]

Interesting. So, let’s say 5000 rpm. Gear reduction is 2.08. Stock pitch is (I think, couldn’t find the mark in the dark on the water) 8.3. Assume 10% slip. Comes up to 18mph on my napkin calculator. So, no way was I getting fuel cut at 3k rpm at 18mph. Tach has to be wrong.

Reset tach setting to 1 pulse : 1 rotation and got (seemingly) accurate rpm readings over 4300rpm. Below that, rpm readings were doubled. Weird. On the previous setting I had before, described in first post, rpms seemed right at lower rpm but obviously were wrong at high rpm. Not sure if I have a bad tach or if there’s a quirk of this ignition system I don’t understand yet. Anyone else w similar issue or recommend alternative tach? Im using the hardline products one from amazon.

This is whole thing is a little disappointing with respect to my break in period - I was under half throttle as instructed but well over the prescribed 3k rpm for a lot of the break in. I hope break-in engine loading has a greater influence than engine rpm on future longevity.

 

[pvanv]

Since you have a siamese coil, it's 2 pulses per revolution. Remember that both cylinders fire during compression, and they both fire on exhaust. And each plug wire sees the same signal. So each compression gives 2 pulses, and each exhaust also gives 2 pulses.

As for break-in, the thing is to allow bearings to mate, and rings to seat. After about 2 hours, the bearings are pretty good. Then you have to "run it like you stole it" while as warm as possible (with 10w-30 oil -- not over filled by even a drop) to seat the rings. You should be OK.

 

[Sea Rider]

Yep, induction tach must be set to 2 pulses per revolution in order to read correct rpm throughtout the whole rpm range. Portable OB's delivered with a prop are usually medium pitched ones. Doesn't mean that that's the ideal prop for your combo, after break end period ends will need to go for a prop maximization.

Ideal is to prop your OB right with a less prop pitch ir order to rev at max 6 K wot rpm range when at full throttle. Report the max wot rpm achieved as loaded to start propping it right.

Correct OB height, trim and deck weight distribution is a must have to get the max fun out of any underpowered portable OB.

Happy Boating

 

[racerone]

A siamese coil fires once each revolution !!-------And one spark on each plug every revolution-------On one cylinder it fires properly on compression.-----On the other cylinder the spark does nothing as it is the exhaust stroke.

 

[pvanv]

A siamese coil fires once each revolution !!-------And one spark on each plug every revolution-------On one cylinder it fires properly on compression.-----On the other cylinder the spark does nothing as it is the exhaust stroke.

No. Since it's a 2-cylinder, both plugs fire twice each revolution. One is after compression, while the other is on exhaust.

 

[racerone]

I do not think so---------It is a 4 stroke and therefor 2 revolutions to complete the cycle.------Therefor each sparkplug fires every ONE revolution !!!-----Think it trough mate.

 

[Sea Rider]

OP needs to test the induction tach set to 1 and 2 sparks per revolution to determine which setting reads max wot rpm range around 5/5.5K K rpm. My vote is for 2 sparks per revolution as stated by Paul.

Happy Boating

 

[racerone]

Each sparkplug fires once per revolution of the crankshaft !!!-----Both plugs fire at the same time.-----One spark plug does some good and ignites the mixture.-----Other cylinder sparkplug fires on exhaust stroke.----AKA a " wasted spark " system.

 

[pvanv]

Each sparkplug fires once per revolution of the crankshaft !!!-----Both plugs fire at the same time.-----One spark plug does some good and ignites the mixture.-----Other cylinder sparkplug fires on exhaust stroke.----AKA a " wasted spark " system.

Right. And since you are seeing both plug wires (siamese coil) you see two pulses per revolution. Just as though you were monitoring the wire from the CD to the coil.

 

[racerone]

No----The CDI puts out one pulse per revolution that fires both coils at the same time.-----If you had a tachometer sensor on a sparkplug wire you would set it like a 2 stroke motor.

 

[Sea Rider]

Set the tach to 180 deg firing which corresponds to 2 sparks per revolution and voila!!

Happy Boating