BW troubles

I would suggest to try this. Close your needle all the way down and snug. Holding the engine backplate facing you. I would put drops of oil on the screws and then begin to pressurize your tank with a syringe as if your trying to blow the engine up and cover the other vent with your finger. If the oil around the screws begins to bubble there's one problem. I'm sure your going to find more. Put a little oil around the tank as well where it meets the backplate. If you hear air leaking out the venturi screen than obviously the o-ring is suspect. A piece of dental floss in the v-groove of the tank will fix the leaking tank usually. As Jason stated, I found several metal backplate to have cracks around the screw boss in the casting. The engine is working until the fuel uncovers the crack and it begins to suck air. I'm also assuming the pickup is in the correct location. It can be knocked out of whack in the event of a crash. I like to wrap fine copper wire around the nipple and keep it tight as the ends of the tubing swells and becomes another situation for a leak. Ken

Liking that floss tip Ken

The tank to backplate seal is a problem as are the screws. Been getting airtight seal on the tank and backplate by turning the two together with polishing compound.
The screws i cover with RTV

Make sure back face of crankcase is flat/no raised metal around screw holes? Possible to get air leak between c.case and front of tank, even with a good gasket. Take it down with 400 grit emery paper on glass or flat metal surface. Countersink holes ever so slightly to prevent reoccurrence.

Sometimes the crankcase screw holes are only bored 3 or 4 threads deep even though the pilot holes are much deeper than that. It can cause a leak if the screws hit the bottom thread and tighten before the tank is pulled down snugly enough. I've added more threads with a 2-56 bottoming tap to get 8 or 9 turns on the screws and hold it all together more tightly.

Well,

Just tried pumping the tank full of air upon Ken's suggestion, guess what? Air leak around the venturi. Needle valve closed all the way. Funny thing is my good runner does the same. I use silicone tubing gaskets. Guess not anymore. I've always lapped my cases.

What do you guys use for venturi gaskets? Besides the real gaskets that is. I will check the other things mentioned but first things first!

Ron

I was cutting mine from silicone tube, but they weren't running worth a crap when I quit using them and went to Tee Dees. I knew they were leaking but I never bothered to find out where.

Ron, if I have a venturi gasket that is in question I replace it with a piece of medium fuel tubing. I make several at a times. I use a piece of 1/8" music wire about 2" long chucked into my drill press. I slip about an inch of tubing on the wire and the other 1" of wire is up in the chuck. I use a new single edged razor blade and hold it as perpendicular as I can to the fuel tubing. I turn on the drill press and cut myself some donuts. I cut a few that are slightly thicker than the stock gaskets. I cut several and weed out the ones that aren't so square. Try one that may be a bit thicker. Ken

I think I'll try that. I had been pushing the small silicone tube through a piece of brass tube, and using it like a guide for my razor blade.

Good suggestion.

What I am not so sure about is the silicone gaskets dont't fit into the little groove like the stock ones do.

Ron, the tubing which I was using was Prather medium pink. The Prather medium was close but it didn't fit exactly. Prather is no longer in business and the closest I've found is the pink that Brodak provides and it's not like the old Prather. Ken

Ok I found leaks from the venturi and crank gasket. I cut a new O ring and addes a gasket in front of the plastic reed holder. Now when I pressurize the tank the plunger in the syringe pops back up when I release the plunger. So the tank is sealed.

Guess what? Still runs like crap. The NV is wrapped with teflon tape and I installed a new steel reed. Now it burps and coughs when it runs.

Ron

next time your by a dart store stop in and for 3-4 bucks you'll have a life time supply

Ron,
You might want to tear it down completely, check # of head gaskets, condition of glowplug, remove and reinstall reed, use fuel line and washer on needle. Theres any number of guesses, but when you start from scratch you start to eliminate 'em.

If you can pressurize the tank like you said then the crankcase and tank are mated properly.
The teflon tape on the needle could leave some strands in there to clog it. I think you'd be better off with just the fuel tube seal for that. I like to take some brake parts cleaner and, with the needle out, blast the spraybar through both holes from both directions. Wear glasses and keep your mouth closed for that job. Make sure the sharp point isn't broken off the tip of the needle. I have had one of those lodge in there and muck up the works.

HI Ron,

All the foregoing is most likely what I would do. However my most unscientific method is to
swap parts between the engines. I would start by swapping tanks & go from there.
i.e. then swap backplates then swap needle valves... sooner (or later) you will find
the problem part(s)... Then the 'rougue' part can be either quarantined for further
detailed investigation or turfed in the bin. Best of luck.
Cheers, Paul G.

p.s. it's REALLY tough to trouble shoot on the internet as things like a badly out of balance prop
can give bad results where few would care to even look...

Mark Boesen wrote:

next time your by a dart store stop in and for 3-4 bucks you'll have a life time supply

I don't have a dart store near here however, if you could tell me the size I can find them just about anywhere. I like the o-ring idea as it saves me time and they look like a better fit.

I'll keep at it guys. Looks like my compression is low now too. Probably due to lean runs. Bummer.

Paul, I will swap parts as advised. I always run balanced props......


Rusty, I will go ahead and pull out the teflon. I haven't used the fuel tubing due to aesthetics, I suppose good runs are better than good looks.

Ron

Thanks for all these suggestions. I have two BWs that want to quit when I go inverted. Maybe now I can have them sorted for next spring.

cribbs74 wrote:I don't have a dart store near here however, if you could tell me the size I can find them just about anywhere. I like the o-ring idea as it saves me time and they look like a better fit. Ron

This http://www.theoringstore.com/index.php?main_page=product_info&cPath=303&products_id=11499 turned up on a thread here somewhere, so I bookmarked it.

I thought Matt or one of our esteemed vendors was selling o-rings now. As opposed to the too-thin round flat washers Cox used.

Joe Sesere posted this link back in February
http://www.theoringstore.com/index.php?main_page=product_info&cPath=0&products_id=11499
I jumped on it, and the work realy well for me.
About $.14 each with shipping for 50pcs.

Mark Boesen's photo
Bob