Engine Runs inconsistently

anm2 Fri Sep 06, 2013 3:07 pm

I have been bench testing a black widow and it will not hold a consistent setting. I have changed the venturi gasket and needle valve. I have also inspected everything else but don't notice anything that would prevent a good run. It starts easily, but it doesn't run steady. I have to fiddle with the needle to get a consistent setting, but it won't hold. Additionally, it won't run through the hole tank. It pulses and then cuts out. Does anyone have any ideas about the culprit. The engine is new and compression is strong. Thanks, Andy

Ken Cook Fri Sep 06, 2013 3:21 pm

Andy, I would try and air test the tank and components. Dismantle the engine by removing the backplate. Use a syringe with the plunger withdrawn and begine to apply pressure with the plunger. Try and pull the plunger back. You shouldn't be able to withdraw the plunger. If you can, the reed isn't seating properly and needs to be either replaced or flipped over. Check the tank for air leaks by applying air pressure to the tank with your thumb over one of the vents and I'm just guessing here that this is a true stunt vented Black Widow. Lapping the rear of the crankcase on a piece of flat glass using 400 grit and oil will give you a very flat surface and prevent air leaks at this juncture. The needle valve should be closed all the way down when applying air to the tank. If you here air coming out at the rear venturi area, the o-ring isn't sealing properly. I've had air coming out of the needle valve seat and this needs tubing over the needle. many times I've found the screws to be the problem as one or several are leaking. Placing a drop of oil on the screw heads will reveal bubbles. Check for tank to backplate leaks as well.

Is the head staying tight? Make sure your head is sealing properly. Lapping the head on a piece of glass will also insure a tight seal and prevent funny business there. Many times with backplates, I found them to be leaking regardless of style as I've had metal ones with pinholes and cracks within them as well. This is why pressurizing the tank with air can be most helpful to locate airleaks. This will cause the engine to run as your describing. Ken

anm2 Fri Sep 06, 2013 3:56 pm

Ken Cook wrote:Andy, I would try and air test the tank and components. Dismantle the engine by removing the backplate. Use a syringe with the plunger withdrawn and begine to apply pressure with the plunger. Try and pull the plunger back. You shouldn't be able to withdraw the plunger. If you can, the reed isn't seating properly and needs to be either replaced or flipped over. Check the tank for air leaks by applying air pressure to the tank with your thumb over one of the vents and I'm just guessing here that this is a true stunt vented Black Widow. Lapping the rear of the crankcase on a piece of flat glass using 400 grit and oil will give you a very flat surface and prevent air leaks at this juncture. The needle valve should be closed all the way down when applying air to the tank. If you here air coming out at the rear venturi area, the o-ring isn't sealing properly. I've had air coming out of the needle valve seat and this needs tubing over the needle. many times I've found the screws to be the problem as one or several are leaking. Placing a drop of oil on the screw heads will reveal bubbles. Check for tank to backplate leaks as well.

Is the head staying tight? Make sure your head is sealing properly. Lapping the head on a piece of glass will also insure a tight seal and prevent funny business there. Many times with backplates, I found them to be leaking regardless of style as I've had metal ones with pinholes and cracks within them as well. This is why pressurizing the tank with air can be most helpful to locate airleaks. This will cause the engine to run as your describing. Ken

Thanks Ken. I will try that. Not sure I can do it today, but I will get back with you. Thanks again. Andy

pkrankow Fri Sep 06, 2013 4:09 pm

Before you take it apart, run the needle in all the way and try Ken's above suggestion. Put 1 finger over the vent and the hose on the fill.

You can also try putting some fuel in it and some pressure. The tank shouldn't leak anywhere. The venturi shouldn't leak, the tank seam, the screw heads in the back, nothing.

If you are not satisfied, take it apart and lap. Assemble using anaerobic sealant if desired. I fill the rim of the tank, strike it off and clean the inside, then assemble and clean the outside. I also use some on the venturi gasket and the tank to case gasket. Be sparing.

Phil

jsesere Fri Sep 06, 2013 4:13 pm

What kind of shape is the reed in?

anm2 Fri Sep 06, 2013 7:20 pm

jsesere wrote:What kind of shape is the reed in?

Reed and all gaskets are brand new.

Ken Cook Fri Sep 06, 2013 7:34 pm

Andy, don't assume all is good just due to the reed being new. The best test is what I suggested using the syringe to blow and suck to insure all is good. You shouldn't be able to retract the syringe AT ALL. It really is that important and it will cause a crappy run if the reed isn't working properly. Ken

anm2 Fri Sep 13, 2013 4:35 pm

Ken Cook wrote: Andy, don't assume all is good just due to the reed being new. The best test is what I suggested using the syringe to blow and suck to insure all is good. You shouldn't be able to retract the syringe AT ALL. It really is that important and it will cause a crappy run if the reed isn't working properly. Ken

Ken,

I tested the engine, and it was the Reed Valve. It was a new reed valve, but it was not sealing properly. I replaced the valve, remounted the engine, and two flips later, the engine started, and gave me a consistent run throughout the full tank. Additionally, I tested for air leaks and found tiny bubbles coming out one of the screw heads. I did not know how to fix that, but it didn't seem to effect the engine run. Thanks for your assistance. Andy

pkrankow Fri Sep 13, 2013 5:15 pm

anm2 wrote:... Additionally, I tested for air leaks and found tiny bubbles coming out one of the screw heads. I did not know how to fix that, but it didn't seem to effect the engine run. Thanks for your assistance. Andy

Anaerobic sealant under the screw heads takes care of this nicely. Just need a drop under each and it spreads well when tightened.

If it is leaking ONLY when pressure is applied it probably is fine. If it leaks when fuel is in, but no added pressure is applied then the run time is reduced.

Phil

**Cribbs74** Fri Sep 13, 2013 6:07 pm

On a bench an air leak is not as critical. Once in the air though it creates all kinds of havoc.

Ron

anm2 Sun Sep 22, 2013 7:27 pm

Ken,

I had some time today so I put together four reed valve engines. Prior to assembly I tested each of the reed valves in the manner you suggested in this thread. I was surprised to find five of the reeds I was intending to use, were not sealing properly. Each time I removed and replaced the reed until I found one that held its seal when tested. Then I took the engines to the bench and started them up. All of the engines started and ran flawlessly. This was really helpful information and it will become a routine part of my pre-assembly check. Thanks to everyone who replied to my post. Andy

Ken Cook Sun Sep 22, 2013 8:19 pm

One thing to try, just flip it over and re test the reed. I found that it works many of the times. In addition, if your using the older circlip style tanks that retain the reeds, make sure the clip is orientated correctly so that it's not pinching the reed. I do two checks, I make sure the reed turns by just using the tip of my #11 blade with the clip in place, I also rotate the clip a few deg to make sure it's properly engaged within the groove. I owned a engine where the circlip almost exited out the side of the case. It actually stretched the extruded case. Needless to say that engine is no longer in use. Ken

ebeneezer Mon Sep 23, 2013 2:04 am

Thanks guys what an interestlng topic, Although I dont think I've ever encounterd any problems with any of my engines. I now plan use the checks mentioned when building/servicing an engine.

Cheers Mike Flying

SuperDave Fri Oct 11, 2013 11:18 am

The essence of effective trouble-shooting is start with the simple then, if needed, move to the complex.

Overlooking the simple things has caused countless thousands Cox engines to be discarded. Sad

SuperDave

**RknRusty** Fri Oct 11, 2013 12:02 pm

SuperDave wrote:The essence of effective trouble-shooting is start with the simple then, if needed, move to the complex.

Overlooking the simple things has caused countless thousands Cox engines to be discarded.

SuperDave

Yep, in my career as a copier tech, we had technicians that never grasped KISS. They would throw parts at a machine hoping one would stick, leaving countless thousands of dollars worth of molested boxes of parts and circuits in a slag pile for someone to sort out.

SuperDave Fri Oct 11, 2013 1:11 pm

Rusty:

re: KISS

It's one of the great trueism learned from experience in repairs. Those who don't apply it spend an awfully lot of $$$ needlessly.

SD

pkrankow Fri Oct 11, 2013 1:50 pm

I learned yesterday what the head gasket count can do to the operation of an engine. Lots of fun (not)

Phil

SuperDave Fri Oct 11, 2013 2:35 pm

Phil:

Stick around there's still lots to learn. Laughing

SD

Sponsored content

Engine Runs inconsistently

Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently

Re: Engine Runs inconsistently