stock carb RCMK Rz 254

[chinslip]

Hi all. haven't posted in a long time. I've attached photos from the stock carb from my RZ 254. Last summer was frustrating as I was unable to properly adjust my carb for optimal performance. I got great tips from all good peeps on the site but still having trouble with this. With the pics I've attached, could someone tell me what carb this is and what base settings it should be at? (It has only 101 stamped on it...no other markings) I have a gas scale T6 with a stock RZ254, 2" aluminum torque master pipe, coleman fuel and a 2716/15' prop. I'm not new to adjusting carbs on small engines like weed trimmers and such, but normally do this with the engine under load and and fine tuning the carb until it sounds right...but with an RC boat I can't do this. Could any one pls help me out here? How do you pros do this?

thanks

Norm

 

[u60]

That looks like a walbro 257 carb. They are good carbs. A good starting point is 2 to 2 1/4 turns on the low side needle and 1 turn on the High side needle. That should get you close. Make sure the diaphram is in good shape. If the carb has been sitting for a while its probably worth replacing. It's really easyto do. Once the carb is set there's not really much adjusting necessary. If you're still having issues try running gasoline with a higher octane rating. We run 101 octane in our gas motors. It works really well. Ours are modified but we have run the 101 in the stock versions as well with good results. Plus it smells like racing gas instead of what my weed eater smells like when I'm finished trimming the yard

Fred

 

[chinslip]

Thanks for the quick reply Fred. Would my running camp fuel alter the carb settings at all?

N

 

[u60]

I doubt it. But I have never used the Coleman fuel. Give it a go and see how it works.

 

[harvknox]

Norm,I am just getting my T-6 going.I believe in your earlier posts you said you have Mike's framing kit and your own glass cowl,fins,wing,canard,etc.I don't know the weight of your boat ,but mine weighs 21.5 lbs.without any red paint or clear.Your's is probably somewhere close.I started out with an RCMK-RZ,modded with a stock carb..This was a 929 not a 257.The carb number is stamped on the side of the carb to the right of the fuel inlet,with the diaphragm up.Is your motor an EVO version RCMK-RZ,which comes with a 929 carb or earlier?The reason I ask,is you are going to need all the power you can beg,borrow,or steal.I am not familiar with your prop,but does it allow the motor to rev up?You may have trouble tuning the engine because you are underpowered,and the prop is lugging the engine down.I have now installed a Gizmo modded K-30 with a modded 257 carb.This made a major difference.Also what is the strut depth,and the ride attitude of the boat?Give us a bit more info and someone will figure it out.Or certainly give an opinion.

Harvey

Harvey

Harvey

 

[chinslip]

Hi Harvey, nice to talk to you again. The carb is in fact a 929. I can see the stamp plain as day. I don't know anything about the engine other than the RCMK 254 on the side. Should it have any identifiable markings if it's an evo? I've always felt the the prop was too big. The engine has never reved up to where it should be...regardless of carb, pipe or strut adjustment. I was thinking of buying a different prop but don't know what to buy...2-3 blades 10* 15* stainless copper??????

Does the 929 require different adjustment?

I'll weigh the boat after work but I'll fairly sure it's close to 20 ,22lbs

later

N

 

[jwo]

That prop is to large for a stock engine in a hull that is 20lbs. Try a prather 270 or a octura 1667. a good 3 blade for a stock engine is a 6518. I run a 6518/430 on my Tempo VII. It is a stock Zen and is 20lbs. The carb settings should be close to the same 2 low 1 high. You might be able to go 7/8 on the high with the right prop.

 

[harvknox]

Norm,the easiest way to spot an Evo motor is on the upper water jacket.The Evo has water fittings that are 90 degrees to the bore.The older model prior to Evo had the lower water fitting at 90 degrees to the bore,and the upper water fitting slanted down at a 45 degree angle.The Evo also has a circular machined surface surrounding the spark plug,extending out as 4 machined legs past the jacket attachment bolts.The older model had cast surfaces.There are internal differences which make more power than the older model.

There are a couple of threads on gas scale setup which may answer some of your questions,or raise more.Some of your problems are also mine,so I would also like as much input as possible.

The first started by Phil Thomas 12/11/11,titled "Gas Scale Hydro Builds".The more recent posts may apply more to your boat.

The second started by me 4/15/12,titled"Gas Scale Setup" is all about my T-6 which should be similar to yours.

If you have the older stock motor,I believe you will have trouble getting the boat to perform.Even the modded Evo did not do much for my boat.

Remember our T-6 hulls have more wetted surface than John's TempoVII,and it will take more HP to get the T-6 going.

Fred ,if you are following this thread,I'll get the exhaust pictures to you soon.

Harvey

 

[u60]

Thanks Harvey- Fred

 

[chinslip]

Thanks guys so much for the info. Sure beats the "my quad is faster then your quad" sites. OKAY...so it's an evo, does this mean more power? Also, my boat weighs 20lbs even, race ready...(no fuel) You need to remember that I don't belong to a club and don't race others on the weekend. I'm a solo weekend warrior and don't need to follow any regulation for boat building and setup. Therefore I've added a small heel at the rear of both sponsons and at the rear of both rear shoes to try and raise some of the wetted surface that you talk about. They are barely noticeable. Harvey, do you agree with JWO's prop recommendation? Is the 6518/430 prop a 2 or 3 blade?

thanks

N

 

[chinslip]

correction, my boat weighs 20lbs minus the tri wings at the back

 

[harvknox]

Norm,good that engine is an Evo,but I believe you said it is a stock Evo.We'll come back to this.The rear fins and wing probably will not add more than a pound to the boat,but it's all at the rear.One suggestion made is to set the wing to give some lift,if your boat is dragging its tail.Mine does.My cg with no added weights is about 2" behind the front sponson.All my 1/8 scales have a cg about 1" or less behind the sponson.At this time I am not adding any weight.

I have used a 6518 3 blade with 5.2 pitch.It was too much for the modded Evo.I also tested a 6518 3 blade with a 4.0 pitch.It did much better,but not great.These are Propworks West props.My strut depth varied from 7/8" to 1 1/4" during this period.I'm testing some Voodoo props on the modded K-30 which have diameters equal to Propworks West larger dia,have less blade area,but more pitch.The boat is starting to move.These props are too much for your engine.

I don't have any suggestions for your boat,engine combination.My only suggestion would be for a prop that will allow the engine to reach a reasonable RPM.Sorry ,I don't have a tach to give you you more data.

Back to your engine,I have the modified jug and piston from my modded Evo RCMK-RZ that I could offer to sell you.I don't think it's a good idea,since it did not work for me.Let me know if you are interested.I would not go this route.I would try to get the most power you can find,even though you are building a sport boat.

Harvey

 

[chinslip]

Thanks for the offer Harvey but I,ll stay with my stock engine. I still believe that a smaller prop will do wonders and this is where I need help. I don't want to buy 1/2 dozen props just to find one that works. So would a smaller dia prop work better (and how much smaller) or do I need a lesser pitch. 2 or 3 blade?

Thanks

N

 

[harvknox]

Norm,I am not a prop guru.Maybe the guys in the Northwest can chime in.I believe they have gone through the evolution of stock to modded engines on gas scale,and can remember what they used in the begining.They might also say what hull was tested.

Harvey

 

[chinslip]

Also...what,s this about a ride pad on the stuffing box? I just read it in your other thread. Any pictures? I don't,then have any rules to follow. ha

 

[chinslip]

i Harvey...I'm looking at everything that might help me here. Do you remember you pipe length with your RZ? I can only get 11.5 with my present header. Guys on this site have hinted that my pipe length might be too short and should be closer to 13 but my header is too short for that. Any ideas? Also what about this ride pad that I heard about on the stuffing box?

Thanks

Norm

 

[harvknox]

Norm,my T-6 is apart for sanding and painting.I assembled the exhaust system to measure it.I am using a Gizmo 2" flat band aluminum pipe.The pipe length from the face of the engine flange to the start of the flat band is 12".The RCMK ball and socket rear exhaust header is only 6" long,and will not permit a pipe length over 12" without causing the rear O ring to leak water into the pipe.I cann't give you a comparison in pipe performance since I've used two differently spec'ed engines with the same pipe.

I believe that the ride pad you mentioned from the other gas scale thread refers to something similar used on the JAE riggers.You should be able to find a picture on IW.If my understanding is wrong,someome please point Norm in the right direction.

Harvey

 

[chinslip]

Thanks for all your help guys. I wouldn't have been able to do this without you. I went to the lake today for the first time this year with all your setup tips and results were spectacular. The boat has performed beyond expectations. Now I have to fix the rear wings as they flew off when the boat flipped over from excessive speed. I kept the original prop, increased pipe length as long as it would go, adjusted the carb to your recommendations and added small ride pads at the sponsoon transom and at the rear shoes. I'm so happy with the results I can't wait to go back with a camcorder.

thanks again

Norm