Flame outs on launching

[Rod Fonda]

Been running my Kand B 7.5 rigger on 30%,15%castor,OS R6 cold plug,.010" squish ,runs well,,gets on pipe about 20 feet away,,So I tried some 60%,,12% castor fuel,same prop and engine dies after launching about 10-15 feet,,tried rich lean etc 3rd channel,,after 4 failed launches I managed to get it going,,ran very well,,carby is about .400" bore,,outboard carb adapted/bored out,low end needle,disc valve modded to open 5 deg early,,just wondering why the flame outs with the higher nitro ,,any ideas welcome ? lol

 

[Norm Doerr]

Pull the pipe out a half inch, find the needle then a new pipe length.

 

[Rod Fonda]

Pull the pipe out a half inch, find the needle then a new pipe length.

Cheers Norm,,pipe is around 10"

 

[Terry Keeley]

Richen it up and try a hot plug if you have one, or you could try pulling a coil out of your R6 to make it run hotter.

 

[Rod Fonda]

Cheers Terry,,I did wonder about the plug being too cold for higher nitro,,just didn't have a hotter one on the day,,the coil pull trick sounds like it might help,,otherwise it runs well and keeps going if it launches,,even without a hopper tank,,just 2 horizontal tank baffles,,mixture stays constant

 

[K F Wheeler]

I ran K&B 45's in my Sport 40 for a couple of years when I first started racing. Until I felt there wasn't anything more I could learn from them. Can tell you they don't like 75-80% nitro with about .010" head clearance! Buddy tried and it blew the case to pieces!! I ran K&B HP plugs. Always worked well for me. Ran 40-45% nitro.
Norm is right about pipe length. 10.5" was what I ran at. Boat would be on pipe and on plane within about 4 foot easy. Pipe at a longer length worked. But took longer to get on pipe. Found no advantage to running longer than the 10.5" Just took longer to get on pipe. Lightest engine I ever had. Favorite prop was a X450/3. This is back before ABC props were so available. Always felt like it should be able to run a little more prop. Never found what I liked better. Went to the Picco Blackhead back then. A lot heavier engine but the torque more than made up for it.
Hope this helps...

Ken

 

[Rod Fonda]

Cheers Ken,,Yes they are very light and very thin case haha,,I used to race a Kand b.45 sprintcat years ago on 50% 9.75" pipe and homemade crank with .035" more stroke pulling an x450/2,,also using an exhaust throttle,which seemed to work well..its a wonder I never split a case lol,,,,,,I might have to try one of those HP plugs
So with all the spare parts I accumulated over the years I thought I'd slap a rigger together and have some fun,,runs well with 10" pipe and 30% but finicky on 60%,,at least it costs less to run on 30% haha

 

[Wasted wages]

They don't call 'em Ka-Boom's for nothing!!

 

[Timbo Whalen]

They don't call 'em Ka-Boom's for nothing!!

Richardson rod, plenty of lube, and above average button clearance readily lengthens the fuse.

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[brad nichols]

I stoll have some 45 K&B's running on 50% with 18% oi. I would of guest low oil but you say it runs good if it launches so maybe crap in tank or needle. They always run great before the Kaboom!

Brad

 

[Rod Fonda]

I stoll have some 45 K&B's running on 50% with 18% oi. I would of guest low oil but you say it runs good if it launches so maybe crap in tank or needle. They always run great before the Kaboom!

Brad

Cheers Brad,,launches/runs well on 30%,,but not so on 60%,like its struggling to burn the higher nitro under load,I havn't had a chance to run it since,,I'm going to try the coil pull trick and/or hotter plug as Terry suggested next time,,Ive only broken 1 rod above the bigend and a crank through the pressed in pin area,,been lucky haha,,

 

[boatworx]

What prop are you running? Where are you running ?

 

[Rod Fonda]

What prop are you running? Where are you running ?

A cut down 2117-19-38,,Its lake Gilwarna at Lansvale,,Oh..its you Brian,,cheers mate,where have the years gone haha,,I got back to the boats a cpl years ago,,sometimes take Phil Allison for a run,,Are you still in the Monterey area?

 

[Norm Doerr]

Lap the rotor, If it is a disc intake, lap and set the clearance. How is the liner/piston fit? Carb sealing around the neck? Many fun things which are best diagnosed in person.

 

[Frankor Jagerstack]

A cut down 2117-19-38,,Its lake Gilwarna at Lansvale,,Oh..its you Brian,,cheers mate,where have the years gone haha,,I got back to the boats a cpl years ago,,sometimes take Phil Allison for a run,,Are you still in the Monterey area?

Unless you have hook in your sponsons that motor should pull that prop without any problems. How heavy is the boat, and are all of your ride surfaces sharp and flat? Where is your strut set? If the motor doesn't have any pinch left that could also cause headaches. Can't tell what pipe you're running but 10.5 seems pretty long, what is the length center of case to the center of the flat section? If possible you may want to try a different pipe. CMB nitro pipes run well at around 9.5" center of case to weld.

 

[Rod Fonda]

Lap the rotor, If it is a disc intake, lap and set the clearance. How is the liner/piston fit? Carb sealing around the neck? Many fun things which are best diagnosed in person.

Yeah Norm,,might be the piston/ liner,,not much pinch left,,piston/liner has 2 boost holes I drilled,,I can hear crankcase compression leaking on the downstroke through the ex port..disc seems ok ,,around .003"/.004" clearance,,I spose I just assumed if it ran ok on low nitro.it would run on higher %,,When I used to use an ex throttle,they were good at masking worn piston /liners lol,,seems more finicky running a carb only

 

[Rod Fonda]

Unless you have hook in your sponsons that motor should pull that prop without any problems. How heavy is the boat, and are all of your ride surfaces sharp and flat? Where is your strut set? If the motor doesn't have any pinch left that could also cause headaches. Can't tell what pipe you're running but 10.5 seems pretty long, what is the length center of case to the center of the flat section? If possible you may want to try a different pipe. CMB nitro pipes run well at around 9.5" center of case to weld.

Cheers Frankor,,sponsons are flat,,I was careful not to add any hook or weight anywhere,,and a Kand B is a lot lighter than a CMB,,strut is sitting on bottom of ski,,pipe is an old rossi 60.ran it for years around 9.5-10" and using an ex throttle,,yes,I thought it should pull that prop based on what I have read on here,,might have to go back to the drawing board on the engine and try another piston/liner

 

[Grimracer]

if your Piston to Liner fit is wore... its not going to launch on the "prop you expect it to"

Do the bump over TDC process to check it

Grim