Dockman

Hey Peerpsi I will post them rpm's tonight but the were no better then I have already seen. What pitch is a 7016 prop? I don't understand these prop pitches as for Chris (Dasboata) should my prop is a 6717/3 with 400 pitch???

PEERPSI

First half of the number is diameter of the prop second half is pitch. 7016 is 70 mm with 1.6 pitch. 7016 might be a good one to try. So were your RPM's higher, lower or about the same?

Dockman

About the same.

Dockman

I edited post #20 and put in the rpm's.

PEERPSI

Prop 6717/3 = 45.3 @16062 66.4%

Prop X472= 44.4 @16131 64.8%

Prop Prather 275= 41.6 @16078 67.5%

Your efficencies. Prather was the best but I'd say obviously you're too high for all three.

70% of the prop in the water for the 6717 would be 5.2875 mm gap, x472 6.0375 and 275 6.4875. Given that you were at 8 mm it's not surprising the prather did best. Try again with all three at 6 mm. Maybe try another 1/4 and then 1/2 inch on the pipe, further out. You're still not getting the RPM's despite having had less prop in the water. Make only one change at a time.

Dockman

I think my motor may need new ring in it? Today never did get over 15500 rpm's and by the end of my running it was getting worst and worst. It was also getting harder to start, had to give it a quick choke each time.

stackeddeck

Sorry to barge in but I have to give my stock Zen a choke everytime to get it started as well.. it is only had about 1-2 tanks ran through it... Is something wrong?

Thanks

Dockman

Even after it warms up? I have run about 3 gallons in my RCMK and tonight is the first time Ihave had this problem. My buddy chokes his everytime (RCMK)and he has not run it much. But mine is also losing speed ad rpm's. I guess there is a chance that it is idling to high but that don't hve anything to do with the slowing down?

PEERPSI

Sounds to me like you are running to lean and it's heating up to the point were it's nearly seizing. I've had mine through two summers and no issues. I tend to run it at the stock recommended needle settings from either the factory or engine builder.

Needing a choke to start it each time does not sound entirely unusual. Sometimes I need to choke sometimes not. Depends on how long I let it cool down.

dicko

I usually choke my engines each time to get them to start, it's not unusual at all.

stackeddeck

Ok sounds good. Thanks guys

Dockman

I have thought that it may be to hot? It don't sit more then 5 minutes between test runs and it runs about 30 seconds out of water while putting the lid on. Before I bring it in I round it around just a little at slow speed to cool it down. Rings are cheap and I may have one if the Zen's are the same as a RCMK?

philip clemmons

Anyone tested aerodynamics (speed) with and without the canopy?

Dockman

I have tested with and without canopy. One time it went 2 mph faster and the next time it went slower. When I get my boat running real consistent my plan is to test the canopy again and also I want to test without the wing. I think you had asked early about running just one rudder? If it was you, I have tested this also? I have the shorter rudders and let me tell you LEAVE BOTH OF THEM ON. I may one of these days try it agian and drop the single rudder about 1/2"?

philip clemmons

I may test the canopy this weekend too, with the other 5000 things I want to try! I hope to see 5o this weekend. Gotta test 5 props, strut, pipe length, and tune the engine too!

How long is "long" and "short" on the rudders?

I did ask about them, as many have suggested running just one. Just ordered my 333 oz/in servo today Should turn OK with that! I think the linkages and grommets (x 2) are half the issue, with them being so tight. Hard work for the servos.

PEERPSI

I don't see why you could not get it to work with just one rudder. You would need to change the servo's though. I tried one rudder on mine after breaking a servo horn and it wasn't strong enough. I work on CNC controls for a living, repairing, retrofitting and system design. I have to say I'm not a big fan of the two servo system Proboat used. It's impossible to eliminate all back lash which in my mine leads to one servo fighting the other. One large 1/4 scale servo should be all you need.

Dockman

I have had no issues with 2 servos. When I tried one rudder I simply just removed it and left both servos connected. I also left the tie bar connected from side to side. The boat is wild with just one rudder and done a 360 at about 3/8 throttle. Remember my rudders are shorter then yours and I think that may have something to do with it? I would love to remove one rudder because I think it would be good for a few mph.

Dockman

Hope you have about 8 hours for that much testing? I would set the carb needles at factory settings, pipe at 13", install best prop you have, & adjust strut height 2mm, 4mm, 5mm, 6mm, etc. After you find the best strut height play with your props. The hardest thing about the strut adjusting is getting the trim exactly the same each time (I use a smart level). Take notes on each and every pass then post them on rcu when done.

PEERPSI

Trying each prop at each strut setting may not be the best way to go. What would be better is trying each prop at 70%, 60% and 50% summersion in the water. Use the prop calculation sheet I made to figure out what the numbers are for each propeller. Once you figure out which propeller you can acheive the best efficency with then try optimizing RPM's. Pipe length, carb settings, reduce parasitic losses etc..

philip clemmons

My pipe is at 12 1/4, and some are as short as 11 3/4............[X(]

Little different setup than most...................

You say "best" prop, I wish I knew what that was...............lol

PEERPSI

Try a 7015 3 blade to start with. Are you using a zero band or 2" band pipe? 13" should be a better number at center of band if you're running a full mod engine.

Dockman

What props do you have? I agree with peerpsi 7015/3 if you have it? In the end you will be using a 7015/3, 7016/3, or 6717/3 for a prop. So if you have one of these then use it and test something else until you get it dailed in then play with props. Peer can you send me a picture of your throttle setup and tell me where you got it at? Mine is still the stock crap and it has finally went by the waste side.

Dockman

PS I' am not rying to tell you what to do. Peerpsi and I have done a lot of testing and we are only trying to eliminate some of the beginner stuff for you. I hope you did not take the beginner thing wrong as for I' am new to this sport this year. Peerpsi has helped me tremdously but I was confused at first. ONE CHANGE AT A TIME.

PEERPSI

I'm actually still using the OEM setup. Because the 257 has it's throttle linkage on the opposite side I modified the OEM bracket, moved it to the opposite side of the carb and rotated it 180 degrees. I got rid of the OEM o-rings that held the cable in place and used tygon fuel line glued overtop of the throttle cable for stops to hold it in place. I used the collar that came with the engine on the throttle linkage to make an attachment point. The collar uses 4/40 pitch screw so I used a computer style D shell standoff to make a cable pinch. I'm at work now but I can post a picture later.

PEERPSI

Actually didn't take long to find the pictures. If you look at where the cable meets bracket you will see a nut that the cable collar threads into. That nut was drilled and tapped on the bottom to secure it to the OEM bracket. The bracket was then bent up around the nut to help hold it in place. The collar on the throttle arm has a screw to secure it to the throttle arm which you can just sort of see in the picture. The cable pinch is just a standoff from a D shell PC connector, the part that you tighten your cables into on the back of a PC, cross drilled with a set screw pinching the cable. I may have locktighted that but I'm not sure.

One other thing, there is a little nub that helps locate the carb diaphram. I needed to file that done so the bracket would sit down properly.