Nova 45 DD going lean?

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Hi Jeff,

I ran 5 tanks out this morning with the pipe stinger opened up to .390. This made a huge improvement. I will open my second pipe even larger until I find a drop off and then shim back down with brass tube. I'm thinking the guys trying to run this pipe on a sport 40 boat with an extender to get the exhaust out of the hull may go even larger.

Thanks, John
Thank you John for being the guinea pig.

Thank you all for looking into this issue, I hope everyone get their boats running great. Thanks Andy Brown for really diving in an helping us out. I am always learning with model boats.
 
Well were all learning something and that's a good thing.

I will be heading out Thurs to play some more and see what we come up with, interesting I have been running my stinger at .390 for a long time always thought it was the standard for 45 engines?

We are running that dia. on Als boat right now.
 
Well were all learning something and that's a good thing.

I will be heading out Thurs to play some more and see what we come up with, interesting I have been running my stinger at .390 for a long time always thought it was the standard for 45 engines?

We are running that dia. on Als boat right now.

Pull the PTO off and you'll see what I mean!
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Well were all learning something and that's a good thing.

I will be heading out Thurs to play some more and see what we come up with, interesting I have been running my stinger at .390 for a long time always thought it was the standard for 45 engines?

We are running that dia. on Als boat right now.
Pull the PTO off and you'll see what I mean!
default_ohmy.png
Will do :)
 
Terry, The flow problem is Dynamic, not Static. Yes it will flow off the clock on the flow meter, but an accelerating engine sucking on very massive nitro and oil through small tubes will find itself with too little or too much fuel at varying points in the acceleration curve. It takes some time to get your head wrapped around it, but once you do your boats performance will improve.

Picture this! Liquid flowing through a long tube at a slow speed will require a relatively low pressure or suction. In order to cause the liquid to move through the same line at a high speed will require more pressure or suction. You might say that the engine is spinning faster so it will suck more. That is true, but here it the problem. The fuel and the air flow rate do not necessarily increase in the same proportion as the engine speed, and therefore suction, increases. It is the relationship between the length and diameter of the air passage and the length and diameter of the fuel passage that must match in order for the air/fuel ratio to remain constant over the range of rpm. However, we do not necessarily want the same A/F ratio as the engine speed increases.There is a load dynamic that comes into play here too, and understanding this relationship between the fuel passages and the air passages will allow one to "tweak" the system to get the correct A/F ratio map for a particular set up. It's almost like computerized fuel injection without the computer once one understands how to Tweak it.

Anyway, back to the Nova 46 specifically! A big part of these above problems with the Nova 46 are related to heat build up as the laps continue. As Martin said, the engine needs time to come up to temp, but in the cases I am reading here the Temp is continuously raising without stabilizing. In this case the heat needs to be released. Water cooling may not be enough, so the heat needs to get out of the pipe. This means a bigger stinger bore, but as you noted Terry, this will cause the fuel pressure to drop. This is the reason for needing the bigger spraybar, fuel lines, fittings.

But remember, what I wrote above. Just bigger is not best. The Spraybar can be too big. That will cause the engine to come off the corner strong and the go rich half way down the straight. This is the problem that I think Jeff is encountering. The easy fix for him will be to bore out the stinger rather than make a SMALLER spraybar.

Likewise, if the spraybar is too small the engine will come off the corner strong and sag lean halfway down the straight.

Ok, now that I have shared some of my speed secrets it's time I put some of my new ones into practice!... Time to go set some new Nitro records!
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Thanks for the help Andy and I do understand what you're saying but the motor isn't just leaning out on the top, it's surging up and down. I shoulda taken a video, would have been more "visual".

Everything we've done to make it easier for the motor to draw fuel has helped, it's not surging to the point of shutting off anymore but it's still doing it. It's not going rich, it's leaning out, sounds like when you get a pinhole in a tank or fuel line. It does have a fairly small cooling jacket and was coming in hot so we took the cowl off, it's not over heating.

I finally pulled it apart last night and "think" I mighta found something. The seal between the PTO and case is only a very small diameter O ring and there was some galling, similar to my 45 VAC backplate:

normal_DSCN0588.JPG


Could it be leaking when it comes up to temp?
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Sealed it all up with RTV and after Olly finishes his therapy sessions we're gonna try it again...
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I had a Picco 21 EXR that had a pin hole in the side of the case, in the middle of the side transfer port. I had all ready run the engine a couple of times before I noticed this stream of fuel squirting out the side of the case every time I revved the engine on the beach. I tossed it in the water anyway and it ran great, just like the two previous runs. I mean it was fast and did everything right. My thinking was Wow, This this is going to be really fast when I patch that hole. Fixed the hole and ran it a week later...NOTHING changed! Ran the same speed and performed just as it did the week before.
 
Well were all learning something and that's a good thing.

I will be heading out Thurs to play some more and see what we come up with, interesting I have been running my stinger at .390 for a long time always thought it was the standard for 45 engines?

We are running that dia. on Als boat right now.
Pull the PTO off and you'll see what I mean!
default_ohmy.png
Kinda reminds me of when you would blow the paper gaskets on the old motors.lol
 
Terry, The flow problem is Dynamic, not Static. Yes it will flow off the clock on the flow meter, but an accelerating engine sucking on very massive nitro and oil through small tubes will find itself with too little or too much fuel at varying points in the acceleration curve. It takes some time to get your head wrapped around it, but once you do your boats performance will improve.

Picture this! Liquid flowing through a long tube at a slow speed will require a relatively low pressure or suction. In order to cause the liquid to move through the same line at a high speed will require more pressure or suction. You might say that the engine is spinning faster so it will suck more. That is true, but here it the problem. The fuel and the air flow rate do not necessarily increase in the same proportion as the engine speed, and therefore suction, increases. It is the relationship between the length and diameter of the air passage and the length and diameter of the fuel passage that must match in order for the air/fuel ratio to remain constant over the range of rpm. However, we do not necessarily want the same A/F ratio as the engine speed increases.There is a load dynamic that comes into play here too, and understanding this relationship between the fuel passages and the air passages will allow one to "tweak" the system to get the correct A/F ratio map for a particular set up. It's almost like computerized fuel injection without the computer once one understands how to Tweak it.

Anyway, back to the Nova 46 specifically! A big part of these above problems with the Nova 46 are related to heat build up as the laps continue. As Martin said, the engine needs time to come up to temp, but in the cases I am reading here the Temp is continuously raising without stabilizing. In this case the heat needs to be released. Water cooling may not be enough, so the heat needs to get out of the pipe. This means a bigger stinger bore, but as you noted Terry, this will cause the fuel pressure to drop. This is the reason for needing the bigger spraybar, fuel lines, fittings.

But remember, what I wrote above. Just bigger is not best. The Spraybar can be too big. That will cause the engine to come off the corner strong and the go rich half way down the straight. This is the problem that I think Jeff is encountering. The easy fix for him will be to bore out the stinger rather than make a SMALLER spraybar.

Likewise, if the spraybar is too small the engine will come off the corner strong and sag lean halfway down the straight.

Ok, now that I have shared some of my speed secrets it's time I put some of my new ones into practice!... Time to go set some new Nitro records!
default_wink.png

Thanks for the help Andy and I do understand what you're saying but the motor isn't just leaning out on the top, it's surging up and down. I shoulda taken a video, would have been more "visual".

Everything we've done to make it easier for the motor to draw fuel has helped, it's not surging to the point of shutting off anymore but it's still doing it. It's not going rich, it's leaning out, sounds like when you get a pinhole in a tank or fuel line. It does have a fairly small cooling jacket and was coming in hot so we took the cowl off, it's not over heating.

I finally pulled it apart last night and "think" I mighta found something. The seal between the PTO and case is only a very small diameter O ring and there was some galling, similar to my 45 VAC backplate:

normal_DSCN0588.JPG


Could it be leaking when it comes up to temp?
default_rolleyes.gif


Sealed it all up with RTV and after Olly finishes his therapy sessions we're gonna try it again...
default_laugh.png
I recently ran a K-90 that had no backplate gasket and no O-ring. Also, the carb had none either. All just bolted up dry, no RTV. And the mating surfaces were not perfect. The engine ran consistent with no issues.

I don't think there are any problems because of Nova's small o-ring.

I think the real "air leak" problem is that BIG 11mm hole in the carb.
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Not that 11mm is too big for a .45 engine, but because it only has a .070" spraybar and it's in a sprort hydro, 11mm is too big.
 
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Terry, I guess I should have asked a while ago...have you guys tried a smaller carb? The Nova .21 carb will fit right on, but at 9mm may be a bit small. I can also get 10 mm carbs.

GQ
 
Terry, I guess I should have asked a while ago...have you guys tried a smaller carb? The Nova .21 carb will fit right on, but at 9mm may be a bit small. I can also get 10 mm carbs.

GQ
9 mm will run better than some would think. We have seen Gary Preusse run near 100 mph with the K&B 7.5 using the K&B red carb which is about 8.5mm.

When I set the first 100+ mph record in IMPBA I used a 10mm carb.

I understand that the "Go Fast " guys decided they liked 11 mm on the Nova .46, but a 9 or 10mm would make the engine work easily in a wider range of boats and conditions. Most of us know what Rod G. would have to say about this. "Smaller is better!"
 
Terry Keely wrote:

"Thanks for the help Andy and I do understand what you're saying but the motor isn't just leaning out on the top, it's surging up and down. I shoulda taken a video, would have been more "visual"."

Terry, I sorta overlooked this, because I was assuming that everyone is using header tanks these days or internal tanks in the metal tanks.

While it is probably not 100% of you surging up and down problem, if the tank does not have a header tank, the surging is the result when running relatively big carbs.

No amount or configuration of baffling in a metal tank will solve this. The header tank is a MUST for big carbs. A baffled tank will work if the carb is sized down much smaller.
 
I recently ran a K-90 that had no backplate gasket and no O-ring. Also, the carb had none either. All just bolted up dry, no RTV. And the mating surfaces were not perfect. The engine ran consistent with no issues.

I don't think there are any problems because of Nova's small o-ring.

I think the real "air leak" problem is that BIG 11mm hole in the carb.
default_smile.png


Not that 11mm is too big for a .45 engine, but because it only has a .070" spraybar and it's in a sprort hydro, 11mm is too big.
That was my 1st thought way back but I kinda got sidetracked from that after looking at the 11mm carb on my 45 VAC. We did try the stock carb with the low end needle, idled and transitioned better but still surged.

Terry, I guess I should have asked a while ago...have you guys tried a smaller carb? The Nova .21 carb will fit right on, but at 9mm may be a bit small. I can also get 10 mm carbs.

GQ
That's the next thing to try I guess, I have a 10mm OS 6B and an old 10mm Picco carb to try. It may just be the problem.

Terry Keely wrote:

"Thanks for the help Andy and I do understand what you're saying but the motor isn't just leaning out on the top, it's surging up and down. I shoulda taken a video, would have been more "visual"."

Terry, I sorta overlooked this, because I was assuming that everyone is using header tanks these days or internal tanks in the metal tanks.

While it is probably not 100% of you surging up and down problem, if the tank does not have a header tank, the surging is the result when running relatively big carbs.

No amount or configuration of baffling in a metal tank will solve this. The header tank is a MUST for big carbs. A baffled tank will work if the carb is sized down much smaller.
He's running a long (6" or so) rectangular tank in the sponson with an internal hopper (one of Walt's). Because of the plumbing he might be pulling fuel through 12" or more of line before it exits the tank. Even though Walt used 5/32" tubing it might just be too much to ask combined with the large carb. The "surging" might not be an air leak at all but just expecting too much in the "fuel delivery" department.
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I think he's completed his 5th round of therapy and might be willing to attempt another session this weekend.
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Hi Terry,

I'm thinking with the draw being that far maybe you might want to shim the stinger down to develop more pressure in the tank to push more fuel to the engine. If I recall Mike Betke had a fuel draw problem on his scale boat and Marty Davis suggested that and it worked.

Thanks, John
 
Not to say that any of my findings are what is going on with your engine but I have had this problem before on several occasions and with different causes.

One time I found a crack in the fuel pickup line (inside the tank) about 1/2 to 3/4 inches from the top of the tank where I had bent the tube around to point into the portside-rear-corner of my tank. While the tank was full, no problem. She was bad. But as soon as the fuel level fell down below the hairline crack, the engine began pulling just enough micro air bubbles into the fuel line to cause the engine to act a total fool. I had made the mistake of thinking that I had properly tested the tank because I tested it by submerging it in water and blew into it, pinched the lines off and no bubbles came up. I then pulled a slight vacuum and it held that as well. So I counted the fuel tank out as being part of the problem soon into the process since it "tested good". I looked at every part of the carb, measured everything, changed out all the parts of the engine and looked for crankcase cracks with black lights and ziglow, ran tons of fuel though it and finally changed out the "perfectly good tank" and BOOM the problem was gone! That took a long time to find.

On another occasion I put a large bore carb on one of my K&B 7.5 engines and since I knew this may cause some fuel drawing issues, I went ahead and before I ran it, changed the fuel lines out for large lines thinking I was making it easier for the engine to get fuel. When I ran the engine, It was obviously having fuel delivery problems and I blamed the carb and everything else I could think of for being the problem but one day for some reason I put the small fuel lines back on it and the carb starting working!

I thought what the crap is going on here? The only thing that could explain this is even though the larger inside diameter should deliver more fuel, the larger bore carb did not have enough draw to pull the extra fuel weight up to the carb. That took a few years off my life too.

I hope you find the problem with your enine. Things like this can totally smoke your brain stem.

-Carl,
 
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Hi Terry,

I'm thinking with the draw being that far maybe you might want to shim the stinger down to develop more pressure in the tank to push more fuel to the engine. If I recall Mike Betke had a fuel draw problem on his scale boat and Marty Davis suggested that and it worked.

Thanks, John
Yup, that might help. Don't like going smaller than 3/8" tho as it can add excessive heat to the piston and cause other problems. The 6280 we tried had a 3/8" I/D stinger.

Not to say that any of my findings are what is going on with your engine but I have had this problem before on several occasions and with different causes.

One time I found a crack in the fuel pickup line (inside the tank) about 1/2 to 3/4 inches from the top of the tank where I had bent the tube around to point into the portside-rear-corner of my tank. While the tank was full, no problem. She was bad. But as soon as the fuel level fell down below the hairline crack, the engine began pulling just enough micro air bubbles into the fuel line to cause the engine to act a total fool. I had made the mistake of thinking that I had properly tested the tank because I tested it by submerging it in water and blew into it, pinched the lines off and no bubbles came up. I then pulled a slight vacuum and it held that as well. So I counted the fuel tank out as being part of the problem soon into the process since it "tested good". I looked at every part of the carb, measured everything, changed out all the parts of the engine and looked for crankcase cracks with black lights and ziglow, ran tons of fuel though it and finally changed out the "perfectly good tank" and BOOM the problem was gone! That took a long time to find.

On another occasion I put a large bore carb on one of my K&B 7.5 engines and since I knew this may cause some fuel drawing issues, I went ahead and before I ran it, changed the fuel lines out for large lines thinking I was making it easier for the engine to get fuel. When I ran the engine, It was obviously having fuel delivery problems and I blamed the carb and everything else I could think of for being the problem but one day for some reason I put the small fuel lines back on it and the carb starting working!

I thought what the crap is going on here? The only thing that could explain this is even though the larger inside diameter should deliver more fuel, the larger bore carb did not have enough draw to pull the extra fuel weight up to the carb. That took a few years off my life too.

I hope you find the problem with your enine. Things like this can totally smoke your brain stem.

-Carl,
Seen the split inner tube before, that'll drive you nuts! One of the 1st things we did was empty a full tank looking for bubbles, none.

We did try large line and it didn't change a thing and went back to medium, never woulda thought large line could cause more restriction!
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I didn't make sense to me either. I guess it was right on the edge and that made just enough difference to get it all to come together. You can bet I didn't change it again.

An engine that is coming in can be a little funny right before it settles down and the heat becomes stable.

-Carl
 
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Marty said might be break in related my 46nova outboard the needle was all over the place hard too get to the water 3gallons later motor is getting sweet love it had problems dieing when the needle got close too much water thanks glenn
 
Not break in, not pipe or stinger dia, not fuel tank(tried more than enough of them, and yes with hopper), , not needle valve or placement(isolated didn't change anything), not temperature, not seals, not fuel, not plugs , we are not new at this.lol.

If the .430 carb is to big for the .07 spraybar would the problem not start shortly after the engine cleans out and reaches temp, and if the carb is the problem would not running at 3/4 throttle solve the problem?
 
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Can someone out there snickering please share a successful setup ? And one wonders why guys don't want to run nitro !! Even the latest technology engine with all the best peripheral parts and this is a common problem . Share . Almost seems as frustrating as the CMB 101 deal .
 
Can someone out there snickering please share a successful setup ? And one wonders why guys don't want to run nitro !! Even the latest technology engine with all the best peripheral parts and this is a common problem . Share . Almost seems as frustrating as the CMB 101 deal .
Hey Tom, I wish I knew what the magic fix was for this boat, but I don't. There are a lot of very smart folks tossing out some great ideas and I know the guys working on the boat are very smart. I know these motors can be a bit sensitive to setup, but there are a lot of guys with them running great straight out of the box. I understand they were running pretty good down in Fl at the Nitro Shootout with completely stock motors with just the standard setup most guys do. I also understand that some very good boaters have had the same kinds of problems as we are talking about. I think we are all gonna learn a little after this is over. And I am working so this kinda stuff may be a thing of the past with the Nova 46 motors.

GQ
 
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