Retarding timing to gain wot rpms

[Abomb27]

Hi, I have a 1996 Four Winns Fling with an OMC 115 turbojet. The boat runs well except that it tops out at 4,800 rpms and 36 mph. Factory specs for this motor is wot is between 4,500 rpms and 5,500 rpms. My question is how far can I retard the timing out of factory specs before doing any damage. I'm trying to get it to run at 5,500 rpms which will put me in the 40mph range. Thanks

 

[boobie]

Re: Retarding timing to gain wot rpms

Retarding the timing you will lose rpm. Find the spec for the wot timing and set it to that. Advance it to much and you're looking at blown piston time. Is it running on all 4 cylinders ??

 

[Abomb27]

Re: Retarding timing to gain wot rpms

All 4 cylinders are firing. The factory timing is 28? btdc. The only other thing I am doing is replacing the coils they looked slightly melted from a previous overheat.

 

[boobie]

Re: Retarding timing to gain wot rpms

Set it at 28 *

 

[Abomb27]

Re: Retarding timing to gain wot rpms

thanks Boobie. what else do you think I can do to gain those extra rpm's?

 

[boobie]

Re: Retarding timing to gain wot rpms

Is your tach accurate ??

 

[Abomb27]

Re: Retarding timing to gain wot rpms

Yes I checked it against a hand held tach and they were the same. Also I have a fuel consumption chart for the fling that I downloaded and it gives the rpm, relative speed, and the account of fuel being used. My rpms and speed right on with the chart. I just can't hit the higher numbers of 5500 rpms and 40 mph.

 

[Faztbullet]

Re: Retarding timing to gain wot rpms

the only other thing I am doing is replacing the coils they looked slightly melted from a previous overheat.

If engine has been hot (which most turbojets has) it may be lacking hp due to some engine wear/damage.

 

[Abomb27]

Re: Retarding timing to gain wot rpms

I am going to use the boat for a couple more weeks till it's starts getting cold. Then I am going to pull the motor and redo everything. I really like the boat it's alot of fun. I want to have it perfect for next season. I wanted to see if there were any tweaks to get running at max performance.

 

[Faztbullet]

Re: Retarding timing to gain wot rpms

Use it as it was designed....its not for wake jumping and 180's.

 

[Abomb27]

Re: Retarding timing to gain wot rpms

Im not one of those morons that jeopardize the safety of other boaters. I just want it to run at its full ability. Which factory specs are 40mph @ 5,500 rpms. I mainly cruise to the beach with my thing son and wife. The only time I hit wot is by myself. I like this boat because it's only 15' so it's ready maintenance. I bring it home flush it, wash wax and ready for next time.

 

[Abomb27]

Re: Retarding timing to gain wot rpms

I believe regardless of the age of the motor that if it's not running to factory specs then there is a problem

 

[keefallan]

Re: Retarding timing to gain wot rpms

I had a 16' cajun center console(stand-up bass boat basically). It had a 112 special on it. With just a sst2 prop(junk) and trimming the motor out(way out) it got it to run almost 53. I have a heavy bowed 18'6"work boat(ken craft) with the same motor(with 135 heads though). It pushes 40. Something doesn't seem right to me. Have you done a compression check? What about prop pitch? Motor height? Are you trimming the motor out when you run it wide open? You really should go faster than that(unless that boat is just a tank). A 15' boat can't weigh that much. What year is the motor?1996?

 

[Abomb27]

Re: Retarding timing to gain wot rpms

It's a 1996 jet boat so doesn't have trim. Only weighs 1,000lbs. I know it loses some mph having a jet but it should hit 40mph. Plus the guy before me out on a performance kit on the jet drive which is supposed to give it an extra 3-4mph. I also have boisen power reeds which made it really smooth out specially idling. One cylinder is low 105 120 120 110, part of the reason I'm gonna rebuild it over the winter. Im gonna set the timing to 28? on the water like boobie said. Then run it. It can't be off more than a couple degrees, I have it set at 26? at cranking speed.

 

[Tim Frank]

Re: Retarding timing to gain wot rpms

It's a 1996 jet boat so doesn't have trim. Only weighs 1,000lbs. I know it loses some mph having a jet but it should hit 40mph. Plus the guy before me out on a performance kit on the jet drive which is supposed to give it an extra 3-4mph. I also have boisen power reeds which made it really smooth out specially idling. One cylinder is low 105 120 120 110, part of the reason I'm gonna rebuild it over the winter. Im gonna set the timing to 28? on the water like boobie said. Then run it. It can't be off more than a couple degrees, I have it set at 26? at cranking speed.

According to your thread title and posts, you are looking to retard the timing and want to know the practical limit....for more performance.
You know the spec is 28 deg. BTDC, but you have already reset it to 26 BTDC.
There are two problems (at least here) :

1) You are ADVANCING the timing....not retarding it. You may not actually know what you are doing.
2) The boat is not new ....just new to you. There could be any number of factors that could be in play of which you are unaware...waterlogged hull....bad install by the PO of the "performance kit".....and so on.

Have you checked the condition of the impeller?
I'd do that before messing with the timing on a whim.

 

[Abomb27]

Re: Retarding timing to gain wot rpms

I read a statement on another site that said retarding the timing will increase wot rpms. I want to find out if anyone else has heard of this. Obviously timing advances with the throttle. And my timing is 26? at cranking speed, which in the water should translate to 28?. A little more background. I had rebuilt the carbs, replaced fuel lines from fuel tank all the way to the carbs,new starter, New solenoid, New battery and wired it for duel batteries, New bosien power reeds, new spark plugs, and wires, pulled the flywheel checked the shear pin, cleaned the magnets on the flywheel, pulled the jet replaced the o rings checked the impellar for nicks, changed the gear fluid. Short of rebuilding the motor I wanted to see if I missed something simple. So it's a little more than a whim. I might be stubborn but I have found everything I would need to rebuild the motor. So whether it's new to me or not there is no reason this motor should not hit its factory specs.

 

[Abomb27]

Re: Retarding timing to gain wot rpms

The article that peaked my interest stated that advancing the timing a few degrees helps low rpm performance and retarding the timing a few degrees helps wot. I would like to find out if there is any truth to that. From someone that really understands timing mechanics. And I can practically recite my boats service manual in my sleep, so quotes from the manual I have already. Thanks. From what I understand and I could be wrong but timing retards a little naturally at wot. Thanks for all the replies.

 

[Tim Frank]

Re: Retarding timing to gain wot rpms

. And my timing is 26? at cranking speed, which in the water should translate to 28?. ........

"Should translate...."??????
What does that even mean?
Can you describe the process that you used to set the timing to 26 degrees?

 

[Abomb27]

Re: Retarding timing to gain wot rpms

You can not set the timing to exactly 28? while cranking the motor because it is not the same as the motor running at wot. It should be 2-4 degrees less. Then checked on the water with a load on the motor. So 26? at cranking speed should translate to 28? on the water with a load on the motor.

 

[Tim Frank]

Re: Retarding timing to gain wot rpms

You can not set the timing to exactly 28? while cranking the motor because it is not the same as the motor running at wot. It should be 2-4 degrees less. Then checked on the water with a load on the motor. So 26? at cranking speed should translate to 28? on the water with a load on the motor.

Wow.

I'm not gong to try to type out ignition timing 101 instructions....you seem so sure of yourself that I would probably be wasting my time anyway.
You are saying that your timing range from near-static to WOT should be ~ a net of 2-4 degrees.
As a disclaimer, I am not sure what power plant is in that rig, so I am not type-familiar, but those numbers make no sense whatsoever.

I would suggest that you swallow your pride and buy the OEM manual so that you can get the timing where it should be.
That ain't 26 BTDC at "cranking speed", whatever that is.