Hopper Tanks

[BradV]

I posted recently regarding tuning issues with my new CMB1.0 / SprintCat. No matter what the needle setting is, the boat just launches and dies. See ->

PAST THREAD

After spendng time at the local boat club it seems the issue is fuel delivery ie placement of the fuel tank and remote needle.

The tank is sitting below the carb centreline (up front) and the advice I've been given is to fit a Hopper tank or header tank. It also seems I have an excessive distance between the remote needle and the carb and this needs to be kept to a minimum.

Hoping someone who knows more about it than me can tell me a bit about the theory of hopper/header tanks, their construction and proper placement, operation and recommended size.

Also is it true that the distance between the remote needle and carb needs to be minimal? It is currently only 2 inches but maybe this is excessive.

Finally anyone else had the same issue with the remote needle CMB carb and are there any other viable solutions?

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[Bart Drieghe]

Floatchamber and ( pipe ) pressure on the tank . Works in Europe , solves lots of things :

Constant fuel delivery

same ( or pretty much the same ) needle settings during the full run

no changing during the run .

Bart

 

[BradV]

Yep running pressure feed.

 

[Brian MAhoney]

Brad

Bart is suggesting you use a float chamber rather than a header / hopper tank. Should be possible in a cat without too much difficulty.

A header tank may help. I have had no problem with 2 inch fuel lines between remote needle and carb.

What remote needle are you using?

Brian

 

[BradV]

What's a float chamber guys?

Using the CMB remote needle that came with the motor.

 

[Bart Drieghe]

Brian's right , im suggesting a FLOAT chamber and not a HEADER tank .

Read this Brad and follow the links im giving in it , it'll show u what i mean .

http://www.intlwaters.com/index.php?showtopic=7283

Gr ,

Bart

 

[nigel]

G'Day again, I have a Sprint Cat with the CMB 1Cu. I have a 16oz tank right up in the nose, this feeds into a 2oz hopper tank. The hopper tank sits directly in front and below the carb intake, from the hopper tank fuel goes to a remote needle valve then to the engine.

I have found there can be no air bubbles in the hopper tank, be sure the hopper pick up is on the left if you do right circuits.

I had a similar problem the other day with my 67 cat, engine would start then die 20ft onto the water, it turned out that there was a small split in the pressure hose from the pipe to the main tank so try that.

Hope that may help.

Cheers Nigel.

 

[BradV]

Thanks Guys - Nigel I've sent you a message with my e-mail address as I would love to see pics of your boat.

The float tank looks like it would work too, but not very atttractive so I will go with the hopper.

I really do think my problem is fuel starvation caused by fuel sitting too low under the carb. The tank is pressurised and all tubing is in good order but it is a long run from the pipe to the tank. So even a 2nd pressure nipple and tube might be a good idea.

Is 2OZ a good size for a Hopper tank?

 

[TimD]

yes, 2oz is fine for a hopper tank.

The reason for short lines between a radio needle and the carb is that the changes to the needle are faster.

 

[EatMyShortsRacing]

Thanks Guys - Nigel I've sent you a message with my e-mail address as I would love to see pics of your boat.
The float tank looks like it would work too, but not very atttractive so I will go with the hopper.

I really do think my problem is fuel starvation caused by fuel sitting too low under the carb.  The tank is pressurised and all tubing is in good order but it is a long run from the pipe to the tank.  So even a 2nd pressure nipple and tube might be a good idea.

Is 2OZ a good size for a Hopper tank?

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Sorry but I really dont think your problem is where the tank sits. Pressure feed on a tank that size should fix any fuel delivery problems. One possible problem is that when you throw the boat in the fuel bounces around in the tank and you get an air bubble come through. A hopper tank will fix this.

Also you should be prepared to start with a much smaller prop just to find the tune on your engine. Once you have that then start going up in props. Yes it is good to have the mixture as close to the carb as possible, but I dont see 2 inches as all that excessive.

EMS Racing If you dont remember it, it never really happened!!!!

 

[BradV]

Guys

I just thought I would give you an update. Fitted a 2Oz hopper tank, sits about 1/4 inch above the carb centreline and moved the needle to about 1/2 inch from the carb.

Seems this has worked, I'm yet to run it in the water but the motor now runs up on the throttle without the splutter and stalling like it was.

Race day Sunday so it should be fun.

 

[dannyual767]

I've been following this thread as I've experienced the same problems . I'm thinking of going to hopper tanks on my boats as well. Let us know how it turns out on Sunday.

 

[Speedway]

So what happened?

 

[BradV]

Bloody disappointing actually so I couldn't be jacked writing about it.. But thanks for the prompt.

I got to the lake which is 1.5 hours away and realised I left my fuel at home. Only 2 guys on the day running nitro boats - one had a batch of 20% nitro that was 12 months old, the other had 75% with 5% PO and was determined to either blow-up his 67 Picco mono or set a new world record.

So I tried the 20% and it just didn't want to run at all. Started, hit the water, and died. 15-20 times until I threw the towel in. Wasn't game to try the rocket fuel for the obvious reasons.

On the upside another guy mentioned his issues with the CMB Evo and remote needle, his only started to run well when he went to 50% nitro. So I might top my 40% nitro up to 50% and see how it goes.

Anyone seen what 75% nitro/5%PO does to a 67 Picco in a Seducer propped to the max and tune pipe set just right? It was exhilerating stuff until the flex cable broke, 2nd quickest boat I've seen (other than a twin 45 hydro a few years ago).

 

[anthony_marquart]

I had a CMB Evo 67 that would do the same thing until I went to 50%. I'm pretty sure you will have your problem solved when you get the right fuel.

Bloody disappointing actually so I couldn't be jacked writing about it.. But thanks for the prompt.
I got to the lake which is 1.5 hours away and realised I left my fuel at home.  Only 2 guys on the day running nitro boats - one had a batch of 20% nitro that was 12 months old, the other had 75% with 5% PO and was determined to either blow-up his 67 Picco  mono or set a new world record.

So I tried the 20% and it just didn't want to run at all.  Started, hit the water, and died.  15-20 times until I threw the towel in.  Wasn't game to try the rocket fuel for the obvious reasons.

On the upside another guy mentioned his issues with the CMB Evo and remote needle, his only started to run well when he went to 50% nitro.  So I might top my 40% nitro up to 50% and see how it goes.

Anyone seen what 75% nitro/5%PO does to a 67 Picco in a Seducer propped to the max and tune pipe set just right? It was exhilerating stuff until the flex cable broke, 2nd quickest boat I've seen (other than a twin 45 hydro a few years ago).

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