Problem .90 rigger

[jaso]

Hi All, Just putting up this post after re-running my .90 rigger today.

Well first off this is what I done after the replys I got to my last post on this boat and the problems I've been having. I sealed up the holes around the boom tubes,

up graded the fuel lines, leghthened the pipe 10mm and a general complete check over of the fuel system- carb,tank,pressure pick up etc.

Today I had a lot more success obtaining a constant fuel mixture and no lean offs in flight or loading up. Actually once it leaned off and surged alot but, I brought it straight in and discoverd it was low on fuel. East fixed.

Anyway now I can put it in the water and get it up and going ok but still struggles a bit so after a bit of head scratching and a closer look at the front sponsons, we discovered that the angle of attack seemed very flat on the riding sufaces. As soon as I got home I looked at my .21 rigger and you could see the difference from a mile away! So know I'm going to have to do some mods to enable this attack angle to be adjusted more than what the builder has alowed in the built in adjustment.. I'm not sure how it ended up like this because the tub tube holes were already drilled and also the sponson tubes mounted and glued in.

There is a mounting block at the bottom of the tub that shims can be put in and angles modified but I already had the tubes set to the lowest setting and there is no room to adjust any lower at the rear tube. If I lift the front any higher I think the sponsons would be to high in relation to the tub and also the rear sponsons.

Any thoughts on this before I go ahead . I was thinking of adding a riding surface to get more angle or with some help from my Dad, using a mill machine to remove some of the material from the rear block in the tub and elongate the holes some more. My Dad was a fitter and turner and he has a fully set up workshop at home( Very Very useful).

 

[Don Ferrette]

Easy fix. Remove sponsons & boom tubes. Elongate the FRONT boom tube holes upwards about 1/8 to 3/16" from where you are now. Don't go straight up from boom mount block as sponson movement will be in a soft arch so as you elongate the hole go just slightly towards the rear of tub. Put it all back together & shim the front boom up to get what you want. You'll be surprised how little it takes to get to what you need so you should be fine with the sponson vs. tub heights. Which prop did you run?? I'd start with the 1667 & drop your head clearance to about .012". Glad to see you moving in the right direction now.

 

[jaso]

Don, Yeah that was with the 1667 and I was also wondering about the head clearance. I know with the .21s a little extra clearance can mean the diff between no torque and it having enough to to the job and be user freindly, Being able to back off the throttle quick and get straight back on the pipe when your ready to . I spose this is still important with a big motor as well?

 

[Don Ferrette]

Yup, the head clearance matters, even on the big motors. I'm running .011" head clearance on 60% nitro with my CMB 90. Granted the motor is not stock either but the point is to run the tightest head clearance you can without detonation. B)

 

[TimD]

If it's a stock 1667 then a CMB90evo would have no trouble swinging that prop unless the pipe was way too short. set your head clearance to 16 thou.

If the boat is running too wet as you suggested with the sponson angle post then that will induce more drag too and make the prop less responsive.

 

[Don Ferrette]

Tim-

Why do you run so much head clearance?????

 

[TimD]

Don,

I don't personally - but I know it should be a safe starting point and he can rule out clearance at that height and concentrate on the rest of the setup!

We have some seriously fast CMB 90's in my club - did you meet Bill Annabel at Slidell or the nat's? I'm sure anyone who did see his twin can vouch for this.

Jaso,

1 word of advise with the CMB - don't try to make really big rev's with it as the cranks develop runout - they have heaps of torque so use a big prop to load it up and you can't go wrong. MAC's 90 pipe at 305 -310mm + H48 or H50 on a rigger is prolly the most common setup here.

Tim.

 

[Don Ferrette]

The only thing I'm worried about is too much clearance will give it a soggy bottom end. If he starts out a little on the fat side & gradually leans in it should be ok with a little tighter head clearance. Key here is patience & not having an itchy 3rd channel needle finger! B)

 

[TimD]

... too much clearance will give it a soggy bottom end.

Don,

Agreed - but most likely it will still get up on 16thou' . It should be able to or something else in the setup is wrong. What bowl volume are you running on yours with the 60% juice?

Tim.

 

[Don Ferrette]

"What bowl volume are you running on yours with the 60% juice?"

To be honest I've yet to measure it. The motor was done by Frank Orlic.

 

[Don Ferrette]

"Agreed - but most likely it will still get up on 16thou' . It should be able to or something else in the setup is wrong."

True. I think he will see a big improvement once he jacks up the sponsons and loosens it up some. B)

 

[TimD]

One thing I forgot earlier :blink:

Jaso - did you paint the front and rear sponsons and if so so you have sharp edges on the ride pads?

Tim.

 

[jaso]

Tim, No the sponsons are painted with epoxy, a product similar to west systems and the edges are nice and sharp as they should be. Just on another note, if the head clearance is a bit slack, will this make the engine a bit harder to get along with when using a colder type plug? On Sunday I tried one of my old plugs just to see the difference in the start up and running/ needle adjustment on the stand before throwing it in the water. It seemed to like this plug alot better than the Mc9s I've been running. It was a Cippolia (think thats close to the spelling) red.

I used to run them in my .21 rigger and I found them to work well at the time( ten years ago I'm talking). Anyway I sort of thought this was a bit off and this made me wonder about the head clearance again. I mean lower comp ratio and its goint to be harder to get a colder plug to be happy right? Any Ideas on this or advice? I think nearly everyone is using the Mc9s in most things around here anyway. Also if this is a problem plus the sponson problem I guess it all adds up right? B)

 

[ampba 237]

no there not painted but it sucks it's self hard to the water it has no chance at the angle it's at.

 

[jaso]

Yep thats what I'm thinking and hoping is the main cause of my troubles

 

[Don Ferrette]

I think with the attack angle set right so it loosens the boat up will be a tremendous help. BTW- what is the strut angle?? Also what was your head clearance set at again?

 

[TimD]

Re: Cipolla red's.

These are a cold plug - colder than an MC9, But they do perform well if the motor is set up right and you are running lots of nitro. They are my plug of choice. I suspect that maybe the MC9 might have "gone off" a little. Did you try a new one?

If your engine ran started and ran ok on the cipolla then the head clearance isn't an issue.

Do any of the guys you race with have a digital level or angle finder? It would be interesting to know what the sponsons and strut angles are.

 

[Don Ferrette]

Digital level, the best piece of gear I've bought in a LONG time. After having one I don't see how I could ever do without. Not cheap, but worth every nickel!

 

[TimD]

They seem to be made of unobtainium here in Oz :unsure:

Anyone know a source for them?

 

[jaso]

Don, strut angle is at 0 degs and head is at 15 thou.

Tim, I tried another Mc9 but it was the same as the other. I thought the Cippola was hoter than the Mc9, it did seem happier on the stand with the red. Not as spluttery as the Mc9 at the same needle setting and trying to quit.