Decarb and WOT questions...

[ineedacottage]

I was reading the Decarb FAQ and I was wondering what the purpose of a separate gas tank was? Could I not just add the seafoam to my existing gas tank?

The reason I wanted to do a decarb is the idle is a little rough on my 1990 90hp Johnson. She has a tendancy to stall...if the motor is trimmed up when I start it, it will hold the idle better and if I trim it down while idling (in or out of gear) it will often sputter and stall. I have no problem starting it again especially if I raise the fast idle lever a bit and run it at fast idle for 3 - 5 seconds. She will not usually stall then after that. I was hoping a decarb might take care of this...

My other question is (now that I have a working tach) do I need to adjust something to get to the correct WOT range? It currently tops out at ~4900 - 5000 rpm trimmed all the way down; when I trim it up I can get ~5300 - 5400 rpm with just me and gear(wake board, skis, knee boards, life jackets) and full tank of gas. The boat is a 16' Stuery X150. I read that I should be getting closer to 5800 rpm. What would I need to adjust to achieve that?

I forgot to add that most of my boating is tubing, skiing, wake boarding etc in the 3000 - 4000 rpm range...

Thanks a lot for your help!

 

[darrklim2]

Re: Decarb and WOT questions...

They're going to need the size of your current prop at least to be able to help you.
Also I don't see anywhere that you say what type of engine you have.

 

[ineedacottage]

Re: Decarb and WOT questions...

They're going to need the size of your current prop at least to be able to help you.
Also I don't see anywhere that you say what type of engine you have.

I did mention the engine (1990 90hp Johnson) , but I did forget the prop - oops :redface: - it is a 13-1/4 X 17.

Thanks!

 

[iwombat]

Re: Decarb and WOT questions...

Sure you could do it in your existing gas tank. The reason for the separate tank is so you don't have to either drain your built-in to 1 gal or add 23 cans of seafoam to get the right mixture. It's a lot easier to get the 1gal-1can mixture with a portable. Then, whatever doesn't get used up can go right into the main.

 

[ineedacottage]

Re: Decarb and WOT questions...

Sure you could do it in your existing gas tank. The reason for the separate tank is so you don't have to either drain your built-in to 1 gal or add 23 cans of seafoam to get the right mixture. It's a lot easier to get the 1gal-1can mixture with a portable. Then, whatever doesn't get used up can go right into the main.

Thanks iwombat - that is sort of what I thought, but I did not know if there was another reason...just wanted to make sure. The tank I have is sort of the portable type (5 gallon removable). The boat does not have a built in tank. Thanks again for your help!!

 

[Dennisanoka]

Re: Decarb and WOT questions...

I have the same engine and same prop size. My wot RPM's trimmed were 5200Max., on a good day. My engine appeared to be a bit low on the transom. When it was in the all the way down position the cavitation plate was below the hull by about 3/4", I raised it 1.5" (2 holes) and I now get 5600 on any day. It still holds, in decent high speed turns. Now my boat is not your boat and our props are different manf. but you may want to look at your engine ht. Just to let you know I tried a 13x15 and while it got me out of the hole faster I lost top end and I could over rev the engine if I ran it to wot. I also use a 13x19 as a spare and it gives me the same speed as the 13x17 but it starts to cavitate at 5400 rpm. So if your engine is as high as it can go without cavitating you can try a 13x15 and you'll get about 200 more rpm, which is also about where you want to be.

 

[ineedacottage]

Re: Decarb and WOT questions...

I have the same engine and same prop size. My wot RPM's trimmed were 5200Max., on a good day. My engine appeared to be a bit low on the transom. When it was in the all the way down position the cavitation plate was below the hull by about 3/4", I raised it 1.5" (2 holes) and I now get 5600 on any day. It still holds, in decent high speed turns. Now my boat is not your boat and our props are different manf. but you may want to look at your engine ht. Just to let you know I tried a 13x15 and while it got me out of the hole faster I lost top end and I could over rev the engine if I ran it to wot. I also use a 13x19 as a spare and it gives me the same speed as the 13x17 but it starts to cavitate at 5400 rpm. So if your engine is as high as it can go without cavitating you can try a 13x15 and you'll get about 200 more rpm, which is also about where you want to be.

Thanks Dennisanoka! I'll take a look to see exactly where it sits. Now I'll show my ignorance some more - is the cavitation plate the flat piece above the prop?

I have never experienced any cavitation on my boat at any speed and no matter how sharp I turn.

One thing I forgot to mention was that my skeg is slightly bent - would that affect WOT or does it only affect steering characteristics? It happened the first year I owned the boat and that was about 8 or so years ago...I had a small pieces knocked out of one of the blades in the prop from that as well - I bought a new one this year and that is what is on there now and that is in perfect shape...

 

[Dennisanoka]

Re: Decarb and WOT questions...

yes that flat piece above the prop is the cavitation plate. The bent skeg probably will not affect wot that much but it will provide some drag but on the other hand just how bad is it?

 

[iwombat]

Re: Decarb and WOT questions...

Anything that puts turbulence on the prop will cause problems. As dennis says, how bad is the bend?

 

[Dennisanoka]

Re: Decarb and WOT questions...

Iwombat- it is important to qualify your statement about Alaska being colder. Anchorage for instance is alot warmer than Minnesota in the winter. But okay I got your point, they do have areas that get alot colder than here.

mdbauer62- can you post a pic of the skeg with a straight edge along side?

 

[ineedacottage]

Re: Decarb and WOT questions...

A guestimate with a straight edge a long it would put the bend at about 3/8" in total - it might even be less (1/4"), but it is a little hard to gauge as the skeg is tapered.

The cavitation plate is about 1/2" below the hull...when trimmed all the way down should the plate and the hull be close to parallel or does that not matter at all?

 

[Dennisanoka]

Re: Decarb and WOT questions...

I would raise it one or two holes. One maybe be enough. Two maybe be good too but it could be too much. This is a little trial and error, because all set ups vary some. I raised mine two right off the bat because I reasoned it might save me from doing it again. Since if one showed some improvement I'd have to try one more. It's up to you, you're a little closer in RPM to where you want to be than I was.

Regarding the skeg: I'd at least take it off at the end of the season and straighten it. I don't know if you can do it on the engine or not. My driveway got mine once and I straightened on the engine it but it probably wasn't like yours. Mine was bent towards the tip not the whole thing. Post a picture if you can.

 

[ineedacottage]

Re: Decarb and WOT questions...

By raising it one or two holes, you mean the bolts that go through the transom, right? Not the pin that looks like it controls how far you can trim the motor down?

What is the best method of raising the motor - I think it weighs in the neighborhood of 350 lbs or something...I do not want to risk dropping it !

I have been told that I am better off not trying to straighten the skeg as it could very well break...?

I'll get some pics of the skeg - it is bent a little more towards the bottom I believe...

Thanks a lot for your help!

 

[ineedacottage]

Re: Decarb and WOT questions...

Here are a couple pics of the skeg with slightly different angles:

http://i192.photobucket.com/albums/z258/darceybrown/Picture_3483.jpg

http://i192.photobucket.com/albums/z258/darceybrown/Picture_3479.jpg

And by raising the motor, do you mean the holes at the top of the pic with the bolts through the transom or do you mean the holes on the bottom that look to me like they just adjust how far down you can trim the motor...

http://i192.photobucket.com/albums/z258/darceybrown/Picture_3484.jpg

Thanks again for your help!!

 

[iwombat]

Re: Decarb and WOT questions...

Transom bolts is what he's talking about.

 

[iwombat]

Re: Decarb and WOT questions...

Looking at the picture, that's really not much of a bend. I doubt it's contributing to your WOT issue in any significant way. You should also be able to bend it back with some steel/wood straight edges and c-clamps

 

[ineedacottage]

Re: Decarb and WOT questions...

Transom bolts is what he's talking about.

That's what I thought...what's a good way to lift the motor without risk of dropping it...?

Looking at the picture, that's really not much of a bend. I doubt it's contributing to your WOT issue in any significant way. You should also be able to bend it back with some steel/wood straight edges and c-clamps

Yeah, I did not think it was too bad...so you think I could straighten it...is there no risk of it breaking or weakening? I assume you slowly tighten the c-clamps around the wood/steel until it is straight?

Thanks a lot for your help!!

 

[iwombat]

Re: Decarb and WOT questions...

That's what I thought...what's a good way to lift the motor without risk of dropping it...?

I use an engine hoist. Does it have a lifting ring on it? Some do, some don't. Barring that, a couple of friends can help you slide it up. Just loosen the lower bolts.

Yeah, I did not think it was too bad...so you think I could straighten it...is there no risk of it breaking or weakening? I assume you slowly tighten the c-clamps around the wood/steel until it is straight?

Thanks a lot for your help!!

That's about right, you may need to put in some shims over the hump to over-bend it a little bit past even. It'll spring back a little doncha know. Yes, you'll work-harden it a bit, but not enough to weaken it significantly with such a small bend.

The real risk is weakening it at the top. The c-clamps and jigs will help you avoid all that.

 

[ineedacottage]

Re: Decarb and WOT questions...

I use an engine hoist. Does it have a lifting ring on it? Some do, some don't. Barring that, a couple of friends can help you slide it up. Just loosen the lower bolts.

Yeah...I seemed to have misplaced my engine hoist...

I'll get a couple of my buddies to help me lift it - just have to make sure we are lifting on something strong enough...

That's about right, you may need to put in some shims over the hump to over-bend it a little bit past even. It'll spring back a little doncha know. Yes, you'll work-harden it a bit, but not enough to weaken it significantly with such a small bend.

The real risk is weakening it at the top. The c-clamps and jigs will help you avoid all that.

Having never done this before some of these question may be stupid but here goes...

How many c-clamps should I use?
And where is it best to place them?
And is this something I would slowly tighten a turn or 2 and leave for a few hours or can I just tighten all c-clamps at an even rate continuously until it is straight?

Thanks a lot for your help!

 

[Dennisanoka]

Re: Decarb and WOT questions...

ineedacottage,

My engine did not have a hook on it for hoisting. I asked my two sons 18 & 20yrs. old to lift it but they said "ya right dad". So as usual dad was on his own. I'm not saying this was perfect and you may have trouble following what I did but it worked and I avoided any calamity.

I happen to have a floor jack and was able to do this myself. I put the floor jack on a sturdy platform(I had some 6"x6"x3'beams) so it could go high enough. I then nailed blocks into the platform so the floor jack could not move when I jacked it up.(doing that is important) I put a block between the floor jack and the very bottom of the transom. I raised the engine so that the center of gravity was forward to keep it from falling backwards when it was loose.(that part is also important) I only loosened the bolts that are in the slots, removed the ones in the holes and raised the engine. When the next holes lined up I put the bolts back in.

It only took about 15 minutes