Another Water-Cooled Twin

[johnlaudano]

I ran the engine again withe a reduced-size venturi of 6mm. it didn't make a difference in mixture sensitivity but it seems to allow more variation in fuel tank height without consequence.
I checked the valve timing and was very disappointed to learn of my great error in planning and design. I think the main problem was that both intake valves were open simultaneously which disrupted intake of fuel mixture. The secondary problem was excess valve lift. had i superimposed the cam diagram of the second cylinder onto that of the first cylinder during the designing, the trouble would have been avoided. There's always next time. But it does run and will work in the boat. The checked rpm rang was about 1000- 6000. low end can goes down with reduce ignition timing but throttle response is poor.
Attached is the cam diagram showing the current condition. Does anyone have examples of cam charts for various engines related to performance? or, suggestions for cam timing for a good idle and good low-end torque?

 

[Rustkolector]

John,
I highly recommend that you read Dave Bowes article A Few Thoughts on Valve Timing in issue 12 of the Model Engine Builder magazine. It has everything you want to know including the timing diagrams for low, mid, and high speed engines.
Jeff

 

[johnlaudano]

Thank you Jeff. Is there a good way to get copies of the article(s) or should I look for back issues?
John

 

[Rustkolector]

John,
The article is copyright protected so I cannot copy it, but Dave Bowes article is well worth the cost of a back issue. I suggest you contact MEB at www.modelenginebuilder.com
Jeff

 

[johnlaudano]

I finally got the engine to where it belongs.
It's got an improved camshaft and is ready for a run in a pond.
see the video here of the trial run.

 

[74Sprint]

John you did not say if the carb you are using was originally a alcohol or gas carb. Alcohol carbs need a lot more fuel than gas engines. Gas engine carbs usually use a longer less tapered adjustment screw so that they aren't so finicky. Try to find a new gas screw or make one.

Ray

 

[johnlaudano]

John you did not say if the carb you are using was originally a alcohol or gas carb. Alcohol carbs need a lot more fuel than gas engines. Gas engine carbs usually use a longer less tapered adjustment screw so that they aren't so finicky. Try to find a new gas screw or make one.

Ray

Ray it’s an alcohol carb with a reducer in the barrel. Yes it’s extremely sensitive but I’m not sure what shape another needle should be. Do you have a drawing of a good one?
John

 

[74Sprint]

I can, I have a similar carb 8mm but for gas, I'll get you a drawing later during the next week.

Ray

 

[dozerdroid]

John, nice boat! What kind of prop will you use ?

 

[johnlaudano]

It’s got an aluminum prop that’s has a modified diameter. It started as a 70m/1.4 prop

 

[johnlaudano]

For those interested in the finished boat underway, I finally have video.
It's running on glow fuel and glow ignition in these videos. Blue smoke in the low speed video is due to a low speed miss on one cylinder.

 

[74Sprint]

Cool