Hot rod V4s

[FMP]

X flow , I have one which runs a max 35° at WOT. The mechanical advance doesn't come close to this unless the throttle is full. So if I'm coming on plane and open it up at 1000rpm it's got max advance. It's all throttle position. Cruising at 3800-4800 no where near 35°.
The ign advance is directly related to control input, the throttle is cammed to follow. It's aggressive enough that light part throttle control input puts the boat on plane without heavy advance. The curve is matched to porting and gearing.

In race form these ign were held at max, the best fuel was used and throttle really didn't get closed during racing.

I can say that trying to manually advance the ign on a 25 Merc two stroke to max and back with light throttle advance will cause a knock every time it's pushed. I tried this once to see if any advantage could be had.

[olboatman]

I agree with FMP about racing (circle) ign. being locked at max as that is how we ran our BSH. Didnt idle worth sht but came out of the corners with vengence! All timing was done with a dial indicater before TDC......those were some great days as there were way more motas around than money!!!!
Gary

[Umassot50]

That's an interesting scenario. It tolerates 35 degrees at Max rpm? Every two stroke I've worked on will tolerate more timing under load than it will at peak rpm. These are mostly engines with expansion Chambers though. The scenario I described with electronic TPS and rpm controlled advance map only puts in max advance when throttle goes wot and rpm is below peak. You basically tune the map all over so cruising rpm and less than full throttle is not max advance. I'll still maintain that the engine will handle more advance at lower rpm than it will at peak revs. And varrying based on Tps is what an electronic system does. A mechanical system of advance won't do that. I'd be interested to see what modern rpm/tps based ignition system maps look like. Tuned pipe two strokes aren't unlike outboards in that peak cylinder pressure still happens at peak torque where volumetric efficiency is at it's best. Everything below peak tourque can usually benefit from more ignition advance than it can handle at peak torque.

[powerabout]

yes drag guys use a old choke solenoid to retard the ignition at top revs

[Freddie Webb]

Umassot50 what you are describing has been tested and you would be very surprised how smart Omc and Mercury are when it comes to their timing settings. Powerabout I have one of those setups with the choke solenoid and if you want it and I can put my hands on it you can have it if you pay the shipping cost.

[Freddie Webb]

Powerabout it works by the solenoid holding it to where you want it advanced to as long as you hold the momentary switch. When the button is released the timing retards to where you want it.

[FMP]

Would be interesting to try an electronic map system out on one of these xflows. In normal spec the engine I describe does mechanically back the advance off a couple three degrees at WOT. I found it performs better holding it max without issue and having a couple more degrees total. Having more on the low end as well, just needed some fine tuning to get the idle rpm in gear.

[NWolf]

Just throwing this out there. In the case of my motor I set the timing 4 degrees retarded at cranking speed with the timing at full advance. When I checked it in the water it was 8 degrees retarded. Exactly backwards of what everyone said would happen. Just sayin..

[FMP]

Looks like it moved back 4° when you don't have it full advanced. Guess you can't just set it at its fully seated position at cranking speed.

[frank jackson]

OMC ignition must be set running under load at 5000 plus rpm .......Any time you change a component in the system you must retime ......

[gfinch]

OMC ignition must be set running under load at 5000 plus rpm .......Any time you change a component in the system you must retime ......

Only way to be sure!
Wayne Taylor described the timing change thru increasing RPM, "The flywheel. It's like a sea gulls wing. As it (the flywheel) rises, the timing changes."
Thank you Wayne.

[flabum1017]

Only way to be sure!
Wayne Taylor described the timing change thru increasing RPM, "The flywheel. It's like a sea gulls wing. As it (the flywheel) rises, the timing changes."
Thank you Wayne.

Or as in the looper, when the magnet comes loose........ so does the rod

[baja200merk]

Yamaha ignition looses ~1* for every 1000rpm over 6k. 18* at 6k ends up down around 16 at 8k no I did not like checking this theory but watched with my own eyes.

I went to Yamaha after my Omc double fired on a ported motor with only a few hrs on it took out a cyl at 4K. I was pissed. Never mind how much more reliable Yamaha was for me.

[Umassot50]

I grabbed a spare omc wheel. Basically I need to attach a small trigger plate like this to the underside of the flywheel. I'd like to keep it all contained under the wheel like stock. Then I can disable the mechanical advance but make it a fine adjustment to rotate the trigger coils to dial in the baseline.

[upyours]

Yamaha ignition looses ~1* for every 1000rpm over 6k. 18* at 6k ends up down around 16 at 8k no I did not like checking this theory but watched with my own eyes.

I went to Yamaha after my Omc double fired on a ported motor with only a few hrs on it took out a cyl at 4K. I was pissed. Never mind how much more reliable Yamaha was for me.

I went through the same issue with my v4 changed it before I lost the motor saw basically the same results