Looper exhaust porting

[Captain75]

Agree,I'm guessing that waters cooold..

73-74 degres right now

[Captain75]

Break-in and fine tuning still in process. Haven’t dared to open her up full yet, but the midrange power is amazing If you bury the throttle when crusing at 3000-3200 you really feel and hear the new power!
I have increased the mains a bit to be on the safe side (drilled to .081”), still running #26 mids and #106 pullovers.
Right now tryin to create a usable test wheel from a damaged 21” aluprop iot be able to confirm the wot timing.

[Captain75]

Finally got some time to get some time on the water! Trying to figure out the best prop size for the engine. What would be the right wot rpm to aim for iot not put to much stress on the motor? Exh Port timing equals the 250hp.

[Captain75]

Just went to Greece for a weeks vacation with family and friends, so no boating for a while. Despite that, I found some time on the water yesterday that included a couple of short but successful wot bursts. The motor runs strong all the up from idle, which was my intention due to the heavy hull, so I’m quite happy!
Also had time to get the kids small raceboat ready for the water. A month to late, but better late than never. Some pics:

Snap-off wheel removed


Total length 10ft, 188lbs(without motor)
Tohatsu 30hp
41mph+ carrying one adult (187lbs)
A really fun toy that really allows you to feel the speed when sitting so close to the water surface.

[Captain75]

Back on the water again, motor runs strong. Although had some minor problems yesterday; suddenly the idle rpm went to low and the motor sounded blubbery, tried to clear it by giving it some revs in neutral, but it didn’t have that instant response like before and it also sneased a bit in the above water exhaust!?
In gear it blubbers a bit when throttled up and then explodes and runs like a champ!
What could be causing this? Bad ignition coil that doesn’t deliver spark at low rpm?
Greateful for ideas, this makes it a bit hard to handle around the docks.

//Anders

[Captain75]

Back on the water again, motor runs strong. Although had some minor problems yesterday; suddenly the idle rpm went to low and the motor sounded blubbery, tried to clear it by giving it some revs in neutral, but it didn’t have that instant response like before and it also sneased a bit in the above water exhaust!?
In gear it blubbers a bit when throttled up and then explodes and runs like a champ!
What could be causing this? Bad ignition coil that doesn’t deliver spark at low rpm?
Greateful for ideas, this makes it a bit hard to handle around the docks.

//Anders

Checked all the coils this evening, all fireing!
Idle timing at 4btdc iot obtain 650rpms in gear.
I read somewhere that it should be like 4 deg atdc?! In that case, If I need 4deg btdc would mean that the idle mixture is way fat?? First time for me with these idle adjustment screws.
Any tips or pointers on the adjustment? Motor sits deep, idle relief exhaust barely above water.

[FMP]

If it dropped off all of a sudden as you said something probably changed. Fuel pressure in range, not spilling fuel at idle? It was deep in the water before and idled fine.

[powerabout]

Checked all the coils this evening, all fireing!
Idle timing at 4btdc iot obtain 650rpms in gear.
I read somewhere that it should be like 4 deg atdc?! In that case, If I need 4deg btdc would mean that the idle mixture is way fat?? First time for me with these idle adjustment screws.
Any tips or pointers on the adjustment? Motor sits deep, idle relief exhaust barely above water.

I never look at idle timing its just the method to adjust idle speed but ensure the carbs are still closed.

[Captain75]

If it dropped off all of a sudden as you said something probably changed. Fuel pressure in range, not spilling fuel at idle? It was deep in the water before and idled fine.

Spilling fuel...good thought!
I will check! Pressure is 5.5 at idle

[Captain75]

Spilling fuel...good thought!
I will check! Pressure is 5.5 at idle

Going out on the lake today, youngest son want’s to sleep in the boat next to an island in the archipelago, therefore I will have plenty of time to check the idle issue. I will also try this new toy, probably a bit more gentle on the motor than the 22” raker, at least during break in. I’ve never tried 4blade before, so this will be interesting. Otherwise, these props are fast and definately worth their money, at least with an application like mine.

[Captain75]

Going out on the lake today, youngest son want’s to sleep in the boat next to an island in the archipelago, therefore I will have plenty of time to check the idle issue. I will also try this new toy, probably a bit more gentle on the motor than the 22” raker, at least during break in. I’ve never tried 4blade before, so this will be interesting. Otherwise, these props are fast and definately worth their money, at least with an application like mine.

The motor still want’s to stall when throttled up fast from idle, especially in reverse!?
I don’t really know where to start, is it a good idea to richen up the adjustment screws and compensate the lost revs with more idle ignition advance?
It might stall due to being rich already, but being lean seems more logic because the problem only appears when you stab the throttle fast going from idle(=instantly a lot of air and a weak signal)
I need ideas and pointers because I’m totally new to these adjustable throttle bodies.

[Captain75]

Just came home from a 160 mile, partly offshore cruise, so I feel the break-in process can be concluded as positive.
I managed to find and solve the electrical problem I had last week; it was tired piece of wire, a one that had been bent so many times that it got parted inside the isolation.
Below is a pick that points out the wire that was broken making it impossible to kill the motor. The wire runs from the powerpack to the shift interruptor.

In the end of the recent trip I had some idle problems that seemed to be fuelrelated: suddenly the motor idled too slow and when the key swich was pushed it picked up speed and idled normal for a couple of seconds. Pump, carbs and throttlebodies have been cleaned and controlled thereafter which resulted in a new filter (before pump) I Also adjusted the throttle body idle screws from 5.5 turns out to 7 turns which together with a bit more timing advance gave a better idle and better throttle response.


Btw: over 60000 views!! Not really what I expected when I posed the exhaust design question back in 2013...

[Captain75]

Checked today after work.
Motor cold, not running since yesterday.
Butterflies closed(forgot...)
Had to run with all plugs in, Otherwise the starter releases before I get a proper reading?!

#1: 142
#2: 137+
#3: 140+
#4: 137
#5: 142+
#6: 137

I will start by running mains drilled to .078,
#26 midrange orfices, 106 pullovers.

End off season over here, so I pulled the boat out off the water the other night.
After messing a bit with backfiring and slightly bad idle after a long trip late this summer, I decided to take compression reading before pulling the p-h iot to access the adapter för some mods.
It didn´t exactly show the numbers I wanted...
All cyls except #5 had appx 95-100psi. #5 had 145psi

Probably explains the rough idle etc...
What could have happened? Is it possible the end up with stuck rings after just one season, as a result of running too rich?

If I did something wrong during the honing process that would have shown at the above compression readings after a couple of hrs running time!? But after a summer of boating without hard wot runs feels strange. The consistent numbers, apart from #5, makes it even more strange!?
Opinions?

[gfinch]

"All cyls except #5 had appx 95-100psi. #5 had 145psi"

Did you mean to say 45psi? Should have been able to hear that low hole while cranking before it started up. Also when I had a compression problem the starter bendix would usually kick out.

Pull the head and look. Any easily seen damage? Stuck rings is possible but you won't see it. You could put the piston at TDC and then push it from side to side.... see if it springs back to center on it's own. Try the others, are they the same? Honing, probably not the cause unless you honed it to the next side over.
Look on the bright side...Now you can tear it down and slap a set of DBR sleeves in it.

[FMP]

Measure the bores, if you are lucky and no damage maybe a quick hone and five sets of rings. Measure the old ring end gaps and compare your preassembled numbers. Could too much oil during first break in cause it?
Are you getting any water spray under the cowl into the carbs?