I don't have a test wheel; what is the best way to set timing at 5000 RPM

[astampfel]

Taking the advice from this forum, I purchased an OEM manual for my 1990 90 Hp Johnson VJ90TLESB. For the link and sync procedure, it says to use a test wheel. I've looked on the internet a little for a test wheel, but haven't had any luck.So, short of having a test wheel, how do I get 5000 RPM under load? Do I go 40 mph and adjust the timing, or should I strap my boat to the trailer and put it on the boat ramp with my engine intake covered? I've tried to adjust the timing at 5000 RPM with the engine out of gear (neutral), but I can never get to 28 deg BTDC. I can adjust it from 32 to 30. Even if I get to 28 deg BTDC, I'm at a no load condition. Has someone figured out what the adjustment is for the BTDC degree amount in neutral compared to under load? For example, 30 deg no load equals 28 degree under load?

 

[ezeke]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

The best way is to take the rig to a shop that has the correct equipment and have tham set the timing.

 

[wilde1j]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

Very bad idea to run any motor 5000 RPM in neutral, unless you don't mind parts scattered all over the place, like shrapnel.

 

[DJ]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

Did you look here?

http://forums.iboats.com/showthread.php?t=228183

 

[5150abf]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

I have used Joes method on my 50 and it worked like a charm.

 

[emdsapmgr]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

Years ago, I watched an OMC factory service person time an engine on the trailer at the boat ramp. Ran the engine/boat into the water just deep enough to cover the lower unit water intakes. Maybe 70% of the prop was in the water. Started it up and ran it at 5000. Must have shot water for 50 feet. You have to be careful, as the engine runs, it can suck down the water level around the intakes, so the initial depth is critical.

 

[ezeke]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

You should check before running up at a boat ramp; many jurisdictions prohibit the practice because of the damage to the ramp bed, and some impose heavy fines.

 

[mamm7215]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

What I did with the muffs on (or use a big barrel) was disconnect the throttle linkage from the timing arm, start motor, manuall advance the timing arm (without moving the throttle). The RPM's will increase but not to 5000. Maybe 2000-2500. I only do this for long enough to measure the timing mark with a timing light. Then adjust the stop if needed. Worked good for me. Read about that on a thread here not too long ago...

 

[emdsapmgr]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

If you set the timing at only 2000-2500, the engine is probably running with too much timing now-unless you set it for less than the factory spec. The electronics on that ignition system cause the timing to creep upward as 4 degrees as the rpm's increase to 5000. It's ideal to set the max advance at 5000, when the timing already includes that system increase of 4 degrees.

 

[mamm7215]

Re: I don't have a test wheel; what is the best way to set timing at 5000 RPM

Ahh, so I'd notice a bit of a stumble at top rpm then...