01/13/2008

Hello Everyone!

I'm putting the finishing touches on my Midwest Cap232 project with a Brison 2.4/40cc engine. The motor last ran 2years ago... Well lo and behold... It won't run now....

The fuel system is brand new. And as of yesterday I confirmed the plumbing is correct and working.

The Brison Ignition is working, if you prime the motor by turning the prop with your thumb over the carb it will pull enough gas to fire and run on the prime then stop...

The motor was stored in the house on the airframe and was clean and dry... The diaphram appears to be pumping but the carb doesn't appear to be sucking gas on its own...

Any ideas???

Thanks,

Ed "Hibrass" Harley

Usually it's a bad diaphragm........if it's still working you might see if the carb fuel jets are open....these can lacquer up and close off if a little fuel residue was left for a period of time.

Ed, it seems to me, from what you describe, that the pump in the carburetor is not working. Remove the single screw from the plate and look at the rubberized sheet. Make sure that the U shaped check valves are not stuck and lie flat against the casting. Make sure that the screen is clean. Screw the needles in until they gently seat. Count the turns. Move them back out to the original setting. If you don't have any luck here then get a carb kit from Ralph Cunningham at RC Ignitions.
www.rcignitions.com

Checklst, I will check that next.. Thanks!

Ken, I'm not sure what single screw you are referring to? My diaphram is held down with 4 separate screws... Unless I'm looking at the wrong thing which wouldn't surprise me.. LOL I will try and grab a quick picture on my carb setup and post it in my gallery..

More soon,

Ed

http://www.rcuniverse.com/gallery/ga...memid%3D168694

http://www.rcuniverse.com/gallery/ga...memid%3D168694

Lets see if these work...

Ed, the carb plate that I'm talking about is the one opposite the one with the 4 screws. The one with the 4 screws covers the diaphragm which regulates fuel flow to the carb. In all likely hood the diaphragm is not causing the problem you described.

The side with 4 small screws is covering the diaphragm that controls your bowl level and main jet. There is a metal disk on the inside of that diaphragm. When the bowl begins to get sucked dry, the outside air pressure pushes down on that diaphragm and it pushes on a little lever. The other end of that lever is connected to the main jet. When the lever is pushed, it raises the jet and allows more fuel to pass into the bowl. The pump (other side of the carb) is pumping and pushing against the jet all the time, but it can't push the jet open until the bowl diaphragm pushes down on that lever and raises the jet out of the seat. Fuel rushes into the bowl and fills it up. The fuel displaces the space previsouly occupied by the diaphragm. That forces the diaphragm to raise back to a neutral setting, and then the pressure on both sides is equal. That lowers the jet back into place and fuel flow into the bowl stops.

The side with one large screw is the side where the actual pump diaphragm is located. The pump diaphragm has two little tabs that cover small holes in the carb casting. These little tabs flutter up and down via the crankcase pulses and thats what pumps the fuel.

There is actually a diaphragm AND a gasket on both sides:
On the side with the pump (1 big screw in the middle) the pump diaphragm (thin one) must be placed flat against the casting of the carb FIRST. Then the gasket (spacer) is placed on top of the pump diaphragm. If you put them in backwards, the little flapper valves on the pump diaphragm can't touch the carb body and then they won't seal up on each successive crankcase pulse. No pumpy. No fuel. Engine no worky.

On the side with the bowl diaphragm, you must place the thicker gasket on the carb body first. This is nothing more than a simple spacer. It prevents the actual diaphragm from setting too close to the lever and pushing down on it constantly. This would cause the main jet to remain out of it's seat and flood the bowl continuously. Engine no worky. Put the big gasket on FIRST and then place the diaphragm on top with the metal disk INSIDE (pointing to the carb casting).

[sm=spinnyeyes.gif]

You guys rock!!

Now after the thunderstorm passes maybe I will have a chance to get outside and see if the lower pump diaphram is ok... If it is bad where is a good place to get replacement parts???

Thanks again,

Ed

You should be able to get a rebuild kit from any small engine shop. Lawn & Garden shops, saw shops, snowblower shops etc..

You will need to know the carb model #
It's located right next to the needles, or exactly on the opposite side from the needles. Usually a few letters and a number.
Examples:
HDA 137
WT 25
WA 174
Something like that. Give that ID number to the guy at the small engine shop and they should be able to get you a kit for it. They cost around $8--$15.

Be careful when you start to work on the side with the 4 small screws. Under that diaphragm is a metal lever that sits on a metal rod. It pivots back and forth on the metal rod. There is a tiny phillips screw that holds it all together. UNDER that lever is a teeny tiny spring. If you loose that spring-- your hosed --go buy a new carb. [] BE CAREFUL when you take that little screw out. Take it out slowly and move deliberately. Maybe even do this inside a ziploc bag in case the spring goes flying. It's very small and if it gets loose--it usually goes flying across the room and is all but impossible to find.

You need to take it out in order to replace the jet.

Rcpilot,

Thanks for the heads up... I have had the Carpet Monster eat plenty of parts over the years so I will take extra care on the Carb. The weather hasn't cleared here yet but I was speaking to my neighbor who owns his own lawn service and it is amazing what you learn... There is a small motor shop just around the corner that I didn't know about.. LOL I have lived here 16 years... LOL

Thanks again,

Ed

Quite often, when an engine sets up, the needle valve mentioned above will stick to the seat and not open. If the cover with 4 screws has a hole in the middle, you can sometimes free the needle by pushing the diaphram down with a small punch. If the vent hole is off to the side, remove the cover and push down on the diaphram. They will free the needle. This will solve the problem, IF the diaphrams are not damaged, and the passages are not clogged.

Make sure the pulse passage is not misaligned or blocked. i.e. has the carb been repositioned 180 degrees or does the carb gasket or adapter gasket block the passage?

JD

Well Guys!

Thanks for the advice, I popped the bottom pump cover off the carb and lo and behold....! The screen was stuff with some fluffy crap... I have cleaned it up and will retest it this afternoon!

More soon,

Ed

Ok.. Retest since cleaning the carb and pretty much the same results but it seems to prime easier... In the meantime I did some checking on Needle settings and the Hi speed seem pretty close to suggestions and instructions but the Low speed was only out 1.5 turns...

So once my hand recovers I will take it back out and try again later...

Ed

When you found the gunk on the filter screen, did you remove the screen and clean it? Could you hold the screen up to the light and see that it was clear?

No I didn't remove it... I will go back and check that before the next attempt...

Ed

Good idea because a clear film can be on it and you might not be able to see it unless you hold it up to the light. If so, you might be able to clean it with Berrymans Chem Tool or some other good carburetor solvent. You can also screw the needles out and remove the diaphragm and needle on the other side and give the carb block a good spraying down with the Chem Tool. This will help dissolve the gum in the carb. Be sure to do this with good ventilation.

Be real careful with the screen because it can disappear in a heart beat. Ask me how I know.

Well I won't be working on it for a couple of more days but I will double check the screen. And I defiantly watch out for the magically disappearing carb parts... :-)


Right now I'm hip deep in CubScouts and Derby cars... LOL

Ed

Pinewood Derby. Brings back fond memories.

Well guys I'm back!

The engine runs! I got a rebuild kit and replaced both diaphrams and Success! So far with just beginning needle tuning it is turning a Xoar 20x8 to 6800RPM and it is idling at 1200RPM.

I'm syked! With a little more time I will be ready for maiden, I still need to add a vent loop to the tank to prevent some drainback on nose down positions...

Ken,

Pinewood derby is a lot of fun.. I have a 8 and 7 year old so we have a blast... This our best finish was 4th out of 135 so we were pretty happy!

More later,

Ed "Hibrass" Harley

Congratulations on the 4th place. Quiet an accomplishment.

Well Folks!!

It flies!!! Very well I might add! After more tweaking on the motor it rips a 20x8 Xoar to 7k! On my 13lb 7oz bird it pulls verticle with no limits!



http://www.rcuniverse.com/gallery/ga...memid%3D168694

I'm very happy, Thanks for all of the help!