Advice sought for fuel pump for a Moki 180cc Radial

[Nigel castle]

I have just bought a very nice 1/3 scale Paulo Severin Jungmeister (used) fitted with a Moki 180cc 5 cylinder radial. There is a small in-line electric fuel pump fitted between the tank and the Carb inlet which runs continuously when the ignition is on. It is not the APS pump that I think Moki recommend. I can't see what make it is in the position its installed.
I have successfully started the engine on two occasions and I had one successful flight (very nice model to fly).

However after the flight I could not get engine started again a third time and we noticed fuel was leaking from behind the engine when the pump was running. I've dismantled enough to check the plumbing etc. All Tygon joints and connections look good and there are no splits. Again when the pump is running with model on bench it looks like the fuel is just being pumped into the carb and is coming out of the air intake (not easy to see but I'm pretty sure that's what is happening). There is no T piece anywhere in the system to allow fuel to re-circulate if the carb is essentially closed. The pump seems to have only an inlet and an outlet (with no return to fuel tank connection).
I have also noticed that the tubing that goes from the crankcase at the front of the engine to the carb (which I assume is to feed the carb diaphragm pump with pressure impulses??) is still in place. I would have thought a pumped system would make this redundant??
I hope i have explained things clearly enough.. My questions..

Does the fuel supply need to be pumped? If so why.
Will the engine run without a pump (I'm assuming yes....). If so what are the disadvantages.
What is the correct way to rig up the pump to prevent it just pumping fuel away (as seems to be happening).
Have I misunderstood whats going on?
How do other Moki 180cc Radial owners rig up their fuel supply.
Any other advice or thoughts for me (particularly for starting by hand).

Many thanks
Nigel Castle (potential LMA member in waiting).
P.S. I was inspired to get a model with a Radial Moki after hearing a model (Yak I think) flying at Elvington this year. What a lovely noise they make...

[BRIAN RAWCLIFFE]

MOKI RADIAL.
Nigel, before you do anymore testing of your engine there is one thing you must do if only to eliminate that it could be the starting problem. It will require the engine to be removed from the airframe, then you will have access to the carb, remove the carb and take off the fuel input cover. Inside you will see a very fine gauze filter approx 6 mm dia. Lift it out and check to see if is blocked.. note. you can clean them, but I would strongly recommend fitting a new one, hopefully it may cure the starting problem. I have some spare new filters, if you send me you address I will post one to you, or whatever arrangement you prefer. Brian Rawcliffe LMA 042.

[Nigel castle]

Hi Brian. Sorry I've only just found your reply (the email alerting me was in my junk folder)! Thanks for responding. After receiving advice from another experienced LMA Moki owner (Jon Horne) I have removed the pump. This has obviously stopped the fuel being pumped away when the engine wasn't running(I don't really know if it was still being pumped away when the engine was running??)
I then tried and failed to start it again. Then (again after advice from Jon) I noticed some black greasy material oozing from the breather hole at the back of the pressure pulse piston housing on the crank case at the front. The tube between this and the carb was clean. I removed the housing over the piston, cleaned out a fair bit of greasy black gunk and made sure it was clear. On reassembling the engine then started perfectly as per the instruction manual and ran very sweetly.
There does seem to be a group of Moki owners who like to use a pump and another group who don't. In any case the pump was not the reason it wouldn't run. However I'm going to continue at least for now with the engine as per manufacture. It certainly sounded like it was running and picking up revs very nicely without a pump fitted and I'm sure it was designed to run without a pump. Do you know what model of Walbro Carb it is in case I ever need to replace the pump diaphragm & filter etc??
Thanks again
Nigel

[BRIAN RAWCLIFFE]

Nigel. Sorry but I do not know what walbro carb is used, but I think you will find that the filter Is the same for all, and the offer still stands. I bought my 150 new in 2007, 50-1 mix, 4.8v ignition battery, no pump, 26"x 16" prop, perfect every time. Enjoy it. Brian..

[Nigel castle]

Thanks Again Brian.. I will take up you very kind offer thanks. My address is: 9 Bridge Ave, Otley, West Yorks. LS21 2AA

I had more issues today. I started the engine no probs and had one flight but felt like the engine wasn't peaking out at full revs. I have been advised that the carb would probably need re adjusting after the pump was removed. I set the high needle to full revs then richened about 1/3 of a turn but could not get a steady reliable tickover by adjusting the low end needle or a reliable pick up on throttling up. I went back to the manuals default needle settings but still had issues. I'm going to take the engine out, remove the carb and hope to get a refurb kit for it with new diaphragms (if available). Meanwhile your filter may do the job?? I'm pretty sure the throttle linkage and servo are good but I'll triple check them as well. Cheers Nigel

[Doug Allardyce]

Hi Nigel, Your engine likely has the Walbro WT225B carb fitted. The ident No is embossed/stamped on the same face as the fuel inlet nipple. As Brian already intimated you should check the carb inlet fuel filter, also remove the cover where the air festo fitting is attached and clean out any residual moly grease. The crankcase air pump and festo tubing will need regular cleaning until the engine has had a decent amount of running.
The engine should run fine without a pump provided the tank is reasonably close with its centerline at or above carb level. If using a pump it must have a return to the tank. What size and make of prop is fitted? Is the cowl baffled?
The radials don't like prolonged running on the ground and are very sensitive and slow to react to needle settings. (1/8th of a turn can often be two much).
The best starting technique is to forget everything you know about petrol two strokes, as using the usual Ignition on/choke closed flip until it fires on a radial can easily flood the lower cylinders.
The best method is Ignition On, Choke Closed, 1/3 Throttle, Rotate Prop firmly until you feel the first bump of ignition - then select idle, choke open and flip. The engine should start within a couple of flips.
Hope this helps.
Kind regards,
Dougie

[Nigel castle]

Thanks Doug. I found something online that suggested the engine has a Wabro WT-621 carb. I've ordered a refurb kit that is apparently good for all WT series carbs so whichever one it turns out to be I should have the correct diaphragms etc.. However doing that is just a belt and braces shot in the dark reaction.
It sounds like I may just need to spend more time adjusting the carb? The centre line of the tank is pretty much in line with the carb, the cylinders do have very nicely made baffles between them and the prop is a Wooden Menz 28" x 16" two blade.
I have been using the exact starting method you recommend (except I was told full throttle when grasping the prop and turning over looking for the 'bump'). It now usually starts OK but I can't get a clean steady tickover and nice transition from low to high revs (it often cuts or loses revs). I've tried going both richer and leaner on the low needle to sort this with no success.. One interesting observation was that after I removed the pump and flew it it was running reliably, transitioning from low to high revs just fine with a nice steady tickover.. However I felt it wasn't giving me full revs and power. I leaned the top end out and realised it had been very rich (I think I got over a full turn leaner before the revs maxed out -then backed off a bit to avoid it being too lean!). I did find a LOT more revs.
That was however when the issues I've described started. I have checked and cleaned all the plugs (which were quite black and showing signs of rich running) and I've checked the tappet gaps which were all good and the sparks (again all good). It seems this engine likes running rich (or at least can be trusted not to cut when its too rich).
My plan now is to wait for the refurb kit. Replace the diaphragms and filter etc...then start from the default needle settings - hope springs eternal.. All suggestions welcome..

[Nigel castle]

All Just a short update. I've now got the engine and model sorted and I've had 10 good flights without issues. Its a fantastic thing to fly, sounds wonderful and looks and can be flown very scale in the air.
I would like to thank all those who have helped me particularly Doug Allardyce, Brian Rawcliffe and Jon Horne.
In case anyone else has similar problems these are my conclusions.

Note: The seller told me the engine had not been run for at least 3 years before I bought it and hadn't had much running before that.

I don't think the pump was causing any issues when the engine was running (but was running continuously - even when the engine was not- with no return line to the tank. As a result it was building up pressure and pumping away fuel when the engine was not running (leaking from the air intake).
Having removed the pump and sorted the following issues I can absolutely say that the Moki 180cc radial does NOT need a pump to run correctly. I suppose if the tank were in a poor location and could not be moved (low to the engine or a long way back) a pump might be of use?? If so make sure it doesn't pump fuel away when the engine is not running! I think having a line T'd into the system that allows fuel to circulate around the tank to relieve pressure on the carb inlet if the carb is 'closed' might help - but I really don't think a pump is of any use.

The root of my issues in the end was simply that the diaphragms in the carb and the filter needed replacing. The standard Walbro WT refurb kit includes all the parts you need. The carb on mine (I assume its standard) is a Walbro WT-621. The pump was a red herring taking my eye off the 'simple solution'. After servicing the carb it was a standard high and low needle adjusting procedure to get it running properly.

Other learnings:
Keep an eye on any black grease coming from the crank case pump to the carb (it oozes out of the bleed hole at the back of the small piston housing on the front of the crank case). Clean out the line and the piston housing as required. Apparently this can cause issues particularly with new engines with less than 15hrs on them. This can block the pressure line feeding the carb diaphragm pump (it's possible this may be why an electric pump was originally fitted??). Thanks for that one Jon..
Use quality oil at 50:1 such as Bel Ray H1-R.
Lubricate the exposed valve gear before each session.
Keep an eye on the exhaust nuts which can work loose after several flights.

Obviously run the engine on E5 petrol (not E10 which can rot old type diaphragms in the carb) or use Aspen (which being a tight Yorkshireman I dont!).
Thanks again all...