Scale RCM 1/3 Scale Champ Build

[49dimes]

The carburetor is a Walbro WT962, Used on a DLE 20? Even smaller than i throught

Can you contact ROTO-MOTOR or a US Dealer and find out what carb they updated to? May be the same carb but with a pump cover that has a pulse connection.

BTW the WT 813 is a 20-23cc carb. The WT 962 is a 25-26cc carb.

Here is a site that actually matches the application of size engine to carb for manufacturers like sthil, echo, and others. The thing to remember is when using this chart is that the carbs are made specific to the application and differ in the way controls attach(choke lever / thro lever) and are adjusted(needles) and how it is pulsed (internally / externally)
and if it has remote or attached priming bulbs
https://www.carbtech21.com/v/vspfiles/downloadables/walbro kit reference.pdf

 

[TonyHallo]

Thanks for the list, I saved it so I can find it when needed. Looked at an old thread, back in 2014 the WT-456 and WT-994 were installed. Not sure what was first, towards the end of thread some two years later one person stated his Roto 85 ran fine out of the box, I seen one in a Hanger 9 Decathlon about two years ago and ran great, that's what convinced me.

 

[TonyHallo]

Both exhaust pipes are identical so the pipe for the left side was lengthen 7/8" to match the right side, 3 1/2" extensions were added to both. The pipes exit in the scale location and are vertically coped. I ordered a 26"x8" Falcon prop to dress the front. My wood is scheduled to deliver tomorrow so work begin on the fuselage, stab and rudder but as Snoopy1 has said the weather getting nice outside so might table this for a while and finish work on the Byron Glasair and a Cessna float plane.

 

[Snoopy1]

You are right about the good weather is coming and always remember there are not that many good weather days in a year to go flying so we need to make the best of it.

 

[49dimes]

Same here (Flying weather) but at the "opposed" end. Hope summer does not march in here like it did last year and last 6 months .
Fall, Winter and Spring used to grant a rather judicious flying season down here. Who says Global Warming is Fake News...

 

[TonyHallo]

We had a very wet flying season last year, grass grew like heck. All the small plane flyers bitched, my response, you need a bigger plane.
The spruce arrived today, began pinning the left side down. Ordered 6' long longeron stock to avoid splicing, looks like each side will take 3 pieces of 6' stock.

 

[Alky6]

Maybe you guys have concluded this discussion, but given the usable rpm ranges of a 26cc two stroke and the roto 85cc 4 stroke, I think the carb size on the roto 85 is reasonable, IMHO. Not to say it couldn’t be improved...but seems reasonable to start with.

 

[49dimes]

Maybe you guys have concluded this discussion, but given the usable rpm ranges of a 26cc two stroke and the roto 85cc 4 stroke, I think the carb size on the roto 85 is reasonable, IMHO. Not to say it couldn’t be improved...but seems reasonable to start with.

You are correct. And the chart is only a quick reference with out having to go and do all the math and figure CFM and volume ratios that would best match the 14.2 storch ratio for gas. The biggest thing I think is that ROTO pulsed the carb on their "updated engines" from the crank case instead of using the pulse made from the top of the piston through the intake valve. When you do it like that it allows more of a negative (Vacuum) pulsing action than a positive and negative pulse action resulting somewhat of an inconsistent pumping action in the carb.

 

[TonyHallo]

The crankcase is vented to allow drainage, the drain tubing is provided with the engine, the drain is larger than regular fuel tubing. Suspect this is required for bottom end lubrication, recommend 30 to 1 premix.

 

[acerc]

The crankcase is vented to allow drainage, the drain tubing is provided with the engine, the drain is larger than regular fuel tubing. Suspect this is required for bottom end lubrication, recommend 30 to 1 premix.

And if I am not mistaken changing the size and length of that drain tube will drastically affect the engine.