Riptide 12 Finally gets wet!

[Preston_Hall]

Don,

Don't cut anything unless you fully understand. Well, not on my account at least.

Are you saying cut the spray bar off even with the side of the intake barrel opening. In effect, having no spray bar entering the opening at all like on a venturi?

No, No, No. Wait.

I have found low end needles to be useless and restricting to the fuel flow. Clay basically expained it. Take the carb apart and examine it. That may clear up a few things. The low end needle usually seats against the spray bar. Cut the low end needle itself off. Leave the part that threads and seals to the carb. Now, the high end usuallly seats to a hole drilled in the brass body that it srews into. So if you cut the spray bar back where it reaches the center of the carb you will be fine. I don't use a "third channel" needle but a remote needle. Remote meaning that it is a needle not attached to the carb. This shouldn't be that big of a deal.

And I'll say it again that the low end needles and spray bars in general are too restricting on any outrigger. Monos also as far as I am concerned, but plenty of people use them in this case. You never really go slow enough to justify having a low end. Low ends are made for idling and smooth accerations. We (boaters) are accelerated to substantial speeds during mill time.

If you need pics then I can get some some. (From my top secret carb) :lol: :lol: :lol: :lol:

 

[Eric Perez]

Don I have had the same problem with some of my 2-needle Carbs. I had the low-speed needle set in "car" mode, So that with a Carb opening of 1-2.5mm the engine would fire and idle well. I ended up opening the high-speed needle a bunch -To Finally get it to where the plugs where holding up.

A few tanks later the engine started acting up and was too rich. Adjusted the high-speed needle and the engine did not seem to react to adjustment. Then the needle pulled right out of the carb! That's how rich I had to have it to run at WOT

I then decided that the engine needed more fuel at mid throttle and opened up the low-speed needle. I ended up bumping up the idle to the carb close to 25% open to get enough air for the engine to fire and stay running.

Now the boat starts well and high-speed needle adjustments actually make a difference again.

Just thought you may want to try my non-destructive method before you permanently remove your ability to adjust the mid-end of your carb.

I know that I can throttle my engine to the point of loosing plane -then punch it to WOT and not have to worry about it loading up.

 

[Don Templeton]

"OK OK"

My problem is I have never used a carb before. Ackerman did all my engine work and I only used OPS .67 engines with venturi and exhaust throttle. Nothing but high speed needle!

I think where I went wrong was calling the needle on the end of the low speed mixture screw the spray bar when actually the spray bar is what injects the fuel into the carb after passing through the high speed needle.

If this is correct, I understand perfectly what you guys are tring to tell me. If not, I really need help! :blink:

Don

 

[Preston_Hall]

My problem is I have never used a carb before. Ackerman did all my engine work and I only used OPS .67 engines with venturi and exhaust throttle. Nothing but high speed needle!
I think where I went wrong was calling the needle on the end of the low speed mixture screw the spray bar when actually the spray bar is what injects the fuel into the carb after passing through the high speed needle.

I think we are on the same page now. You will loose the ability to let your engine idle on the stand. You just compensate by "burping" the throttle. You will also loose the ability to let the boat come to a dead stop and then get back on plane. But what do you want to do? Come across the starting line at 60mph or 10mph?

This modification to the carb just falls in line with the way we race these boats, wide open! Remember, these are engines designed for cars. If cars could run wide open all the time then you would see the same thing there. But cars rely on smooth accelerations so as not to upset the traction and steady idles so they don't shut down at the start or when they are upside down. A helicopter is also critical on smooth throttle transitions since it relies on steady RPM.

 

[Don Templeton]

Thanks Preston, Clay and Eric!

If I'd had the correct terminology to start with we wouldn't have had to go through all of this. :lol: :lol: :lol:

Don

 

[Eric Perez]

All this talk on low-speed needle got my gear going. Took some pictures of TRX 2.5 and Picco rotary carb at WOT.

Check out the position of the low-speed needle with respect to the venturi on the main needle between the different carb designs

A major eye opener for me. I rember some older engines that I had (More than 10 years ago) the low-speed needle was heavily tappered and never really got "out of the way" from the venturi.

Notice how the huge travel of slide-carbs puts the low-speed needle on a different zip-code from the venturi. You would think that it would have little effect on high-speed operation. I found out that it did make a difference. If the low-speed needle was too lean the engine would just quit when going to WOT and would always tend to lean out on the water. Richened up the low-speed and the engine growled "rich" until it reached WOT -cleaned out and turned that 1640 like it was not there... Still you can turn the high-speed needle half a turn and you will hardly notice the difference out on the water. Either I have a pickup restriction or I need to get a one-way valve for the pressure line going to the tank or I may need a remote needle that can handle more flow like Preston suggested.

The picco rotary carb was a litte more reponsive to needle tweeks. The carb opening is smaller than the Traxxas engine. This makes sense smaller carbs tend to be easier to setup, better feed through the venturi.

 

[Don Templeton]

Very interesting Eric:

Well I'm going to take prestons advice as well as yours. I've cut off the bar on the low end adjustment screw, however, I have a new one on its way from Tower.

I'm really hopeing I don't need the low end at all but at least i'm covered.

Don