Nova 45 DD going lean?

[SayMikey]

Jeff is running a Zoom carb wrap around motor,but has the same concerns.Tomorrow we will spend the day diggin

 

[aaron alberico]

Jeff

Are you sure it's surging and not richening up in the straights?

As in the turns you say it clears out and goes hard(in turn is more load=more heat, burn fuel better) what is your stinger I.D ? Sounds like you might have to open it up! Thst could be cause why half way down straights it sounds like it's surging! To much back pressure will cause this problem..

Regards Aaron

 

[Jeff Schindler]

It could be richening up, I really don't know at this point. I am running the 46 muffled pipe and the stinger on the muffler exit is .360 inch. I haven't measured the real stinger before the muffled section. Also I have about 6 inches of .500 brass slipped over the outside of the stinger to get the exhaust out the transom. My boat seems to unload the prop in the turns, it's a sport 40 running a Prather 235 w/ a little cup added. When I straighten up coming out of the turn, the prop loads back up. If I am too lean it will bog coming out of the turn, but my problem is when it's rich enough to pull off the corner, it coughs and nearly goes down at 1/2 track, so it could be richening up.

I know if I get this fixed, the boat will be awesome.

 

[mtruex]

If you can't get it rich enough on the water look at the fuel system, 5/32 tank tubes, large fuel lines and fittings. Make it as rich as you can and still keep it running on the beach, if it comes on the pipe and sounds clean right away it's still too lean. My experience with the 46 is it needs to have a distinct rich cackle sound for a lap or so to build some heat.

 

[Andy Brown]

Terry,

I ran mine today, no dice. Motor sounded rich on the bank but very solid. It was flowing a reasonable number, I was hopeful. The boat took off from the launch a little more sluggish, which it usually jumps right up on pipe and is hard to tame. It milled well, and when I pulled the trigger it went as fast as ever, but at 1/2 track it just coughs and nearly dies. It surges from 20 mph to 55 back to 20 in 400 ft. It goes like hell thought the turns, but it has to be starving for fuel down the straights, I can't figure this one out. The plugs come back without even being frosted and there is no sign of load. Hmmmm My water is restricted at the outlet, but I will try clamping it down to a dribble tomorrow.

I dinged up my turn fin so I only go 1 run in today. I'm going to put a camera on the engine bay tomorrow and see if i can spot what is going on.

Jeff, I'm not sure, but from what you are saying the boat is doing it sounds like your engine is actually going rich down the straight, not sagging lean. Does it sound like that to you or can you actually tell that it is sagging lean down the straight?

Some boats load the prop in the turns and some boats unload the prop in the turns. If your boat loads the prop in the turns then slowing down in the straight IS a rich condition due to the prop UN-loading in the straight.

 

[Andy Brown]

It could be richening up, I really don't know at this point. I am running the 46 muffled pipe and the stinger on the muffler exit is .360 inch. I haven't measured the real stinger before the muffled section. Also I have about 6 inches of .500 brass slipped over the outside of the stinger to get the exhaust out the transom. My boat seems to unload the prop in the turns, it's a sport 40 running a Prather 235 w/ a little cup added. When I straighten up coming out of the turn, the prop loads back up. If I am too lean it will bog coming out of the turn, but my problem is when it's rich enough to pull off the corner, it coughs and nearly goes down at 1/2 track, so it could be richening up.

I know if I get this fixed, the boat will be awesome.

Ok I just read this post Jeff. Yes, it sounds like it IS going rich down the straight and your prop is actually LOADING UP in the turns which helps to burn the fuel. As soon as you straighten the rudder the prop UN-loads and the engine goes rich down the straight.

Since you are running the stock carb with the .360" stinger I highly suspect that your .500" X 6" pipe is adding too much pipe pressure. This is making your problem different then Olly's and the others. Basically the opposite.

Drill your muffler outlet to .375" and see if the situation improves. If it gets better, but still tends to go a little rich down the straight drill it to .390".

The Nova 46 gains more heat after a few laps of running then any other engine I have seen. It is very important, as Martin Truex mentioned, to keep the engine rich and allow it to come up to temperature with a few laps of running.

 

[Andy Brown]

Well Olly & I were back at it today, it ain't air leakin' around the carb and it ain't the pipe. The stock carb with the low end needle idled and transitioned better but it's still surging.

He threw the venerable 6280 on it at 10 1/4 and it did the same.

We're gonna drill out the spray bar as Andy suggested but I don't see how that could be it as it flows off the clock without the needle in the line.

We're down to the tank (doubt it) or something inside the engine...

"We're gonna drill out the spraybar as Andy suggested but I don't see how that could be it as it flows off the clock without the needle in the line "

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!

 

[Terry Keeley]

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!

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:

Could it be leaking when it comes up to temp?

Sealed it all up with RTV and after Olly finishes his therapy sessions we're gonna try it again...

 

[Olly]

OK - therapy ain't working

I'm ready to give up and give it a Viking funeral, but Terry is enjoying the challenge. LOL.

On a brighter note - my new Beta 21 in my mono is showing potential

Thanks to everyone for your input on this.

Olly

 

[SayMikey]

Darn Olly if you give up on the boat,im a player

 

[Walt Barney]

Olly,

Don't give up on this project, there has to be and answer, Has the new tank arrived yet?? as I have completly changed the inside workings to help with the fuel flow , if that is the problem, If you try this tank and it still sags, I don't think it could be the tank, Is the pressure tap in the muffler drilled out to as big as possible???, if the tap is drilled out you may have to go to a different brand to get it big enought, not looking for pressuer but to keep the volumn up.

Walt Barney

Tanks 2 U

Walt 's Hobbies

Darn Olly if you give up on the boat,im a player

 

[Jeff Schindler]

I have not changed the o-ring on the back plate, and I'm not a fan of how they use the o-ring. The only backplate I've seen that uses an o-ring right is the techno power. It might be leaking.

 

[Terry Keeley]

I have not changed the o-ring on the back plate, and I'm not a fan of how they use the o-ring. The only backplate I've seen that uses an o-ring right is the techno power. It might be leaking.

Seemed to me like the O ring was small for the groove it seats in in the case. The backplate on the wrap around motor would seal the same as the PTO on the DD, not subject to quite the same vibration tho. Also, most of the after run oils we use deteriorates regular rubber O rings.

Seal it up with RTV and see if that does it!

 

[ALLAN YUEN]

Olly Did you take disassemly engine and check any very thin cracked on crankshaft ?

very poor airflow through then run lean

 

[Jeff Schindler]

Well, mine ran good yesterday, 55 mph strong until the tank ran out. The system only flows 35 pts on our Boris gauge so there is still something not right, but the driver is happy for now.

 

[John Beardslee]

Hi Jeff,

How much did you open the stinger? Or what seemed to make the difference?

Thanks, John

 

[Jeff Schindler]

Hi Jeff,

How much did you open the stinger? Or what seemed to make the difference?

Thanks, John

John, The only thing I changed was I had to fix my turn fin because the 1st heat race on Saturday I hit something running wide and out of the way. I couldn't get the boat to run right. Waiting to see how Olly & Terry faired. I am going drill out my stinger to .375 as Andy suggested. I can always sleeve it back with K&S.

 

[John Beardslee]

Hi Jeff,

I tried .375 yesterday with a slight improvement and have now opened to .390 to see if it is any better.

Thanks, John

 

[John Beardslee]

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

 

[Marty Davis]

John:

Do you think that any of your problem could be related to "break-in" and not stinger diameter?