.21 valvola engine question.

[tmunn]

Guys,,,

Had a very sucessfull day today with my pt ss21 .I removed my twin tanks and front radio box and installed a rear radio box and front tank.

Some of you guys know i was having issues with my tank setup and when it transfered from one tank to the next was causing me fits..I ditched it for now ..maybe later.I installed the rear more spacious radio box and am more happy with that. Everything is comming together nicely and i am pleased.

I do have one issue with my engine that is confusing me.If i am driving around at WOT it seems like the exhaust makes a different sound than when I am at 1/2 throttle more deeper or something.

The engine will actually speed up when i cut the throttle to around 1/2 or so.When I apply the throttle fully open you can notice the boat sounds different and the speed decreases.

I have tried richer and then leaner but i figured i had better ask before I did some harm to the engine becuse i did not know what i was doing and got it too lean.

Thanks

Terry

 

[Brad Christy]

Terry,

Does the carb have a low speed needle? If so, take it out, cut off the tapered needl portion, leaving only the threads. Apply some Loc-Tite and tighten what's left back into the hole. This should solve the half-throttle surge problem. BTW.... you will no longer have that useless low speed needle after this. How convenient.................

Thanks. Brad.

Titan Racing Components

BlackJack Hydros

 

[tmunn]

Brad

I find that i have had to open the low speed needle open quit a lot to get the engine to start.By removing the taper on the needle and leaving only the threads, won't this alow too much fuel into the engine at low end and idle.

I am just nervous to do this that's all but will do waht I need to to make it work

Thanks

Terry

 

[Buckshot]

I'd start with cutting the LSN also. As Mr Christy stated it is useless.

-Buck-

 

[tmunn]

This particular model has the LSN needle that takes a 5/16 " socket or wrench I use my socket driver on it.

This is the one i cut the tapered portion of the needle where it transitions to threads.

Stupid question but why do they put it on there

Thanks

Terry

 

[mark voorhies]

This particular model has the LSN needle that takes a 5/16 " socket or wrench I use my socket driver on it.
This is the one i cut the tapered portion of the needle where it transitions to threads.

Stupid question but why do they put it on there

Thanks

Terry

It closes the spray bar off at low throttle settings so you can idle without loading up motor with fuel.

I.E. leaner at low throttle.

 

[steve wood]

we havn't used a low speed needle on a boat in over 25 years. the are only useful on the bank

 

[Tim_Duggan]

What pipe and how short is it?

 

[tmunn]

The pipe an ops 3280 at 8.75".

I will remove the tapered portion before my next outing.

 

[FloridaScaleBoater]

JEEZE;

And to find out I've been paying an extra $75.00 for an OS 9B carb for my 67's just to get that "USELESS LOW SPEED NEEDLE"

Boy I must be stupid!!!!!! NOT

So, someone please explain to me how the low speed needle is affecting the wide open throttle position of the carb, at W.O.T. the low speed needle is rotated all the way over, and out of the spray bar (spray bar is un-obstructed---full fuel flow) only restricted by something between the hi-speed needle and the tanks.

Now, Terry may have the low speed needle set too lean for the half throttle position, making it scream??

Terry, I'd leave the low speed needle in, and find were the REAL problem is!!!

It is still in the carb of my Valvola in the new MONO.

Rick Bellinger

 

[Marty Davis]

we havn't used a low speed needle on a boat in over 25 years. the are only useful on the bank

Steve:

I am surprised at your answer....

A low speed needle is a super valuable asset to being able to mill slowly. If that is not your drivng style, then you are correct.

That IS my driving style, so it is VERY useful to me.

One additional advantage is that the low speed needle will allow you to launch your boat with the mixture correct rather than super rich. It makes launch much easier.

Marty Davis

 

[Marty Davis]

Sounds like either the prop is to big or the pipe is to short. Both will do EXACTLY what you describe.

Marty Davis

 

[Jerry Wyss]

Runs faster @ half throttle is a problem I have with two o/b powerheads, both buggy engines on Thunder tiger

lower units. They are also both O.S.'s, the VZ-B (with VZ-M P/L & button) and 30VG , they seem to start doing

that weird act as the day get's warmer, as I think about it. They are the only two o/b engines I have outa 6 that

have the angled squishband in they're buttons,, don't know if that makes any big difference but it's worth mentioning.

All the 21 o/b power heads have the O.S.20J with idle circuit in place,, my other 4 have never had this problem

no matter what weather or temp. They all have similar port timings and button volumes minus the 30VG, which

has a sleeve that screams "Don't Cut Me!"

It's making me think at some point these two engines are just not getting enough air to mix with the fuel. I

addmit, I'm not much of a carb guy, that science baffles me to no end.

Rod Geraghty is the only one I know that has experience with this kinda stuff, maybe he could shine some light

on this subject.

Marty Davis, "pipe too short", could very well be in my case, Tim D was saying the same thing in a PM a while back,

Thanks!

 

[tmunn]

I will leave the LSN the way it is for now.I like the easier to launch reasoning and for a newbie that is good

i will lengthen the pipe and try that I am currently at 8.5 I mad a mistake in an earlier post.

I will go to 8.75", try that and what happens.Then I will try another smaller prop or 2 if it still does it.

I am currently running a x440.Now I have an M440 as well as a x438 to try.

I have the day off so i might get out today it beautiful outside.

Thanks everyone ...didn't ean to start a feud.

Terry

 

[Buckshot]

All we need is a dump valve.........W.O.T. all the time. B)

All kidding aside, I haven't ran with a low speed needle for as long as I care to remember and have not had driveablity or launching issues. I guess my junk dosen't run fast enough or I guess I don't run a big enough prop to need a LSN.

-Buck-

 

[steve wood]

we havn't used a low speed needle on a boat in over 25 years. the are only useful on the bank

Steve:

I am surprised at your answer....

A low speed needle is a super valuable asset to being able to mill slowly. If that is not your drivng style, then you are correct.

That IS my driving style, so it is VERY useful to me.

One additional advantage is that the low speed needle will allow you to launch your boat with the mixture correct rather than super rich. It makes launch much easier.

Marty Davis

i think chris has only one throttle position. wide open. mill slowly? whats that?

our 9b os has the low needle removed

 

[FloridaScaleBoater]

To each, his own.

I guess?

Rick

 

[Marty Davis]

we havn't used a low speed needle on a boat in over 25 years. the are only useful on the bank

Steve:

I am surprised at your answer....

A low speed needle is a super valuable asset to being able to mill slowly. If that is not your drivng style, then you are correct.

That IS my driving style, so it is VERY useful to me.

One additional advantage is that the low speed needle will allow you to launch your boat with the mixture correct rather than super rich. It makes launch much easier.

Marty Davis

i think chris has only one throttle position. wide open. mill slowly? whats that?

our 9b os has the low needle removed

Steve:

There are so many ways of racing... I have seen people be very successful using many methods. That is the main reason that I stated about driving styles. For me, having a low speed needle is important. For some, it is useless. The same thing is in play with mixture controls. Some use them with great success, and some hate them.

Many ways to accomplish equal results...

Rod Geraghty was mentioned. He can accomplish the same outcome on a carb, WITHOUT a low speed needle, by using an "air bleed". Takes many years of experience and "touch" with a carb.

Marty Davis

 

[Preston_Hall]

Marty,

What do you do when the low end needle makes it physically impossible for the engine to flow enough fuel at top end?

 

[Chris Wood]

Hey marty,

I havn't used a low speed.. But i guess i felt like i really never needed one.. Last few years I have noticed that it mills really well and i can slow down ALOT without it, that is why i havn't used one.

I will say, i am using the nova rossi carb.. with all the low speed stuff cut out.. Now with that being said..

I noticed about 2 yrs ago. I used to use a barrel for the nova carb that dad made that rotated in the barrell.. I switched it to the barrel that nova sends that rotates and also screw's in and out.. THAT helped the throttle ablility a TON.

chris