Prop removal questions...

lewy2001 wrote: With the GT40 you can only set the static timing the rest of the time the GT40 ECM adjusts the timing depending on input from all other sensors it has a range of twenty odd degrees from memory that it adds to the static timing from the table in the ECM. Base timing per manual is 5 deg BTDC with Spout disconnected and engine at operating temp. I have played around with this and actually have tried other settings up to 10 BTDC. I had mine set to 8 degrees with the GT40 ECM. Tried this setting on another GT40 at GL and could hear a slight ping so set it back to standard. The GT40 also has knock sensor that will retard timing if detected.

Thanks, Lewy. I wonder what sort of advance increase you'd be able to achieve on good premium fuel. I run Mobil ethanol free premium 93 octane. I'm not messing with it regardless as I don't see any performance issues with my GT40. I know I don't need 93 but it's the only ethanol free fuel near my home (if you consider 17 miles to be near).

MrMcD wrote: I have never checked my GT40 timing assuming it was controlled by the computer and it has run very well since I have had it. 30 degree's seems very tame to me. I would think you would benefit from moving the total advance to 34-36 degree's. Try 34 and if you have no ignition rattle or pinging try 36. Timing should be all in by 3,500 RPM. for max power. If you bring it in too early you can cause detonation issues and risk damage so be conservative with changes.

You really can't adjust the total advance. Maybe by setting base timing a couple degrees heavy you may get more not sure if that would work.
"The distributor has no centrical or vacuum advance since the ECA controls the spark timing. Other than setting base timing no distributor adjustments are required.
   

If your boat is fuel injected we need advice from those that have adjusted the Fuel Injected GT40 on how to do it. If it is carbureted changing timing is simple but you will need a timing light. A set back Timing light is best so you can check the timing at idle and at all the RPM ranges.   It is also important to see your timing curve actuates very smoothly from idle to full advance.

I have never checked my GT40 timing assuming it was controlled by the computer and it has run very well since I have had it. 30 degree's seems very tame to me.
I would think you would benefit from moving the total advance to 34-36 degree's.
Try 34 and if you have no ignition rattle or pinging try 36. Timing should be all in by 3,500 RPM. for max power. If you bring it in too early you can cause detonation issues and risk damage so be conservative with changes.

GT-40 computer advances spark not distributor per say.

63 Skier wrote: I guess if it was me I'd take a look at, and likely change, the plugs, inspect the wires, cap and rotor, and maybe most of all get a timing light on it. Would be nice to know you have good ignition and are timed right.

Thanks for all the advice everyone.

The prop I had on before had a few decent sized nicks in it and I wasn't sure if that was affecting performance, turns out it was but not by much. With the new prop I now know I have an issue but figured it was just due to the low compression. Now that I know a tune-up could help I'll look into getting that done.

Should I just go ahead and replace the cap and rotor, wires and plugs? I'll probably start a new post on this tomorrow.

Not sure how to use a timing light, guess that something new to learn.

I would do what Jpass said and see if the numbers are the same now that you've been running it.
I know your not worried about getting into the compression problem until after the season but the other things may help get better performance until then.
Also take a peek inside the cap to see what kind of condition it's in.

gun-driver wrote: I guess we can start with what are the current compression numbers? Have you done anything to it like a tune up? How do the plugs look black, brown, wet, worn? Is the air cleaner/spark arrester clean?

Well that's interesting because I was not aware that most of the above should be done.. To all the service items the answer is no. The flame arrestor is dirty and I've been meaning to clean it but keep keep forgetting to take it out.

All i have done is the regular stuff. Oil and filter change, trans fluid change and fuel filter change. I also ran some fuel cleaner through the system.

I was going to change the spark plugs and I have new ones. I have been researching the doing a tune up the week but figured since I wasn't noticing any miss firing issues it wasn't to important. Same goes for wires. Do you think this could help?

I'll try pull the compression numbers from an old post but I'm on my phone now.

Edit: Here are the compression numbers from last year when I bought the boat.

1. 120
2. 100
3. 120
4. 110
5. 120
6. 110
7. 90
8. 120

KENO wrote: If it's Blarney you're talking about he states he's using the boat pretty much at sea level a handfull of posts back. If Denver's at sea level, we all have a lot of problems (except LC Gordon who now would have a better running boat) Now White Plains NY.........that's pretty much at sea level.

Yup, I'm in White Plains NY and I run my boat on Greenwood Lake. I think it's at 700ft, so no altitude issues.

And yes, I have a GT40. The boat does have compression issues. It's something I knew about when I purchased it. I haven't done a leak down yet since I don't have the money to fix the engine but hope to get it looked at some day.

Im pretty sure the compression issues that are affected my top end but really if there are any other suggestions to look at I'd appreciate the help.

MrMcD wrote: I think he stated he is in Denver, 6,000 foot elevation will rob some power.

That would make sense but his profile says NY that's what was throwing me.

tryathlete wrote: gun-driver wrote: What motor do you have? Looks like a GT-40 from his diary listing. He can gain an easy 3 mph with better compression, but it's a lot of work for 3 mph.

Those RPM numbers are way low for a GT-40 with that prop

gun-driver wrote: What motor do you have?

Looks like a GT-40 from his diary listing. He can gain an easy 3 mph with better compression, but it's a lot of work for 3 mph.

So looks like I gained 0.4 mph on the top end my WOT numbers are now 43.5 mph at 4560 rpm. Overall the prop is much smoother. I honestly can't notice much difference in hole shot but I haven't had the boat for long. Across the RPM range I have added about 0.5 MPH. (at 3000,3500, 4000) vs the stock OJ.

So overall the boat runs great. Good news is I don't have a slow hull, Bad News is I am probably missing a few ponies since I can only get up to 4450 RPM max and top speed is 43.5mph. This makes sense because I had low compression on a couple cylinders when I tested the engine before buying. That's something I plan to address in the future but for now I am just enjoying the boat.

Overall I am happy with the 422, hope my results will help other make a decision.

Blamey wrote: I believe I have the stock prop on the boat but I'm not sure how I confirm that.

Take the nut off and read what it says on the hub.

I'm want to start looking for a new prop for my 95 Sport and rather than start a new thread I thought I'd add to this one. After doing some reading it appears the 422 is probably what I need. I'm planning on using the boat mostly for wakeboarding but would also like to keep some top end speed as I am interested in learning to barefoot. I'll be running at pretty much sea level. At WOT I got 43.1 mph at 4560rpm both measured using perfect pass Stargazer.

I believe I have the stock prop on the boat but I'm not sure how I confirm that.

I'm probably a couple month away from buying so I am open to any kind of testing to get performance number to help make the right decision