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UMS Gas Radial Engine Enthusiasts Rabbit Hole

Old 01-04-2024, 09:02 AM
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Default 7-50 ums

To the gentlemen with the 7-50 UMS engines..
Were you able to get your problems worked out.
I picked up a used (very little if any) one and have it setup to test run. Life keeps getting in the way.
It has the stock UMS carb.
I am going to start out with Lawnboy 2c oil, Seafoam, and non-ethanol fuel at 32:1

Question for Tom...do you think the Saito carb like used on the 5-55 would be a good fix if this one has issues?
Old 01-04-2024, 09:35 AM
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Well John, I hope the Saito carb will improve things. Usually do! -Tom They have gotten so expensive.
Old 01-27-2024, 10:04 PM
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Default Twin UMS 7-50 project

Originally Posted by partshunt
thank you for that information. Mine will come with the UMS carb, not the Walbro but it is an option The 50cc 7 cyl the UMS carb is standard , optional is the Walbro as you probably know. . ... thanks... Joe
Just ran across this forum, and boy do I need you guys! Iíve embarked on a challenging project, a 1/6 model of the Sikorsky S-38. Iím planning to fit the 7-50 ignition and throttle servo in the nacelles, and Adrian tells me he will shortly have a pump option that will allow me to put one large fuel tank in the bilge. Thatís the layout as it relates to the engines.

Iím currently breaking the first one in and having quite a time finding reliable settings. Iím about halfway through the 2-hour break in period, mostly at about 2000 or less, 10 minutes at a time. It generally idles pretty well, having richend it up per Adrian. But it seems no matter where I set the high speed needle, it either has rpm excursions or sometimes just dies. Running it up a bit (to about 3,500 momentarily) results it intermittent white smoke out of the ring. Overall, itís too inconsistent to put on an airplane and when itís stopped, there is fuel visible in the air intake. Iíbe been all over the place with these adjustments, and I can continue the break in, but Iím concerned about getting it running perfectly, like the video by some seller in England (Malvern Links, as I recall, home of the Morgan Ö been there, had 4!). Any help on tuning in this group! I realize itís a difficult thing to do remotely, but any thoughts/tips would be appreciated.
Old 01-28-2024, 07:02 AM
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Originally Posted by Maxam
Well John, I hope the Saito carb will improve things. Usually do! -Tom They have gotten so expensive.
Which Saito carb did we use on the 5-55 Tom? And would the FG-60R carb be a good choice. It seems most people have problems with the 7-50 stock carb and the MMM WT option does not seem to be the fix either.
Jon
Old 01-28-2024, 08:36 AM
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Default Saito carb for the R90-3 or R12-3

Do not order the FG carb, it pumps based on pulses from a one cylinder engine. If you try it, use the FG -11 carb due to the smaller choke area. -Tom
Old 01-30-2024, 12:58 PM
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I have the UMS 5cylinder 55cc engine I purchased from Adrian and when I received it I had problems with it running properly and eventually sent it back to Adrian who apparently managed to get it running again. However, once I received it back from Adrian I have not made any attempts to try and run it. I'm in Anchorage Alaska and we are dealing with a terrible winter with gobs of snow and cold. That plus I recently had a new knee replacement done. Therefore, I have not been able to do any testing of that engine. I am also purchasing the Morris Mini Motors Walbro carburetor kit to replace the UMS carb that came with this engine. I'm hoping things will work out OK once I am able to get some methods of doing some test runs later on.
Old 02-15-2024, 05:00 AM
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Originally Posted by S-38 Flyer
Just ran across this forum, and boy do I need you guys! I’ve embarked on a challenging project, a 1/6 model of the Sikorsky S-38. I’m planning to fit the 7-50 ignition and throttle servo in the nacelles, and Adrian tells me he will shortly have a pump option that will allow me to put one large fuel tank in the bilge. That’s the layout as it relates to the engines.

I’m currently breaking the first one in and having quite a time finding reliable settings. I’m about halfway through the 2-hour break in period, mostly at about 2000 or less, 10 minutes at a time. It generally idles pretty well, having richend it up per Adrian. But it seems no matter where I set the high speed needle, it either has rpm excursions or sometimes just dies. Running it up a bit (to about 3,500 momentarily) results it intermittent white smoke out of the ring. Overall, it’s too inconsistent to put on an airplane and when it’s stopped, there is fuel visible in the air intake. I’be been all over the place with these adjustments, and I can continue the break in, but I’m concerned about getting it running perfectly, like the video by some seller in England (Malvern Links, as I recall, home of the Morgan … been there, had 4!). Any help on tuning in this group! I realize it’s a difficult thing to do remotely, but any thoughts/tips would be appreciated.

I ve had exactly the same experience with this engine, after many days and hours trying, following the advice of all the experts, setting the needles etc, Walbro carb aka MorrisMiniMotors, pump, no pump, changed ignition unit, checked for air leaks you name it I tried it. This engine, my one at least just would not run consistently across the whole expected rev range. Not the mention the black Sh--ite that came out the exhaust. My worst engine experience in 30 years. Decided life's too short to waste any more time on it. I got larger UMS engines and these are fine, but the 7-50 with UMS carb is a dud. I wish you good luck with yours.

Last edited by Edhamp; 02-15-2024 at 02:20 PM.
Old 03-03-2024, 05:40 AM
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Default Question on the Phoenix Waco for my UMS 100

Aaron, (Hyjinx) Sent you a PM.. Thanks -Tom
Old 03-03-2024, 05:42 AM
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Default Information on Phoenix Waco

Hyjinx, Are you still happy with your waco? Sent you a private message. -Tom
Old 03-03-2024, 10:49 AM
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Hi Tom. PM returned.
Old 03-03-2024, 11:35 AM
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Originally Posted by Edhamp
I ve had exactly the same experience with this engine, after many days and hours trying, following the advice of all the experts, setting the needles etc, Walbro carb aka MorrisMiniMotors, pump, no pump, changed ignition unit, checked for air leaks you name it I tried it. This engine, my one at least just would not run consistently across the whole expected rev range. Not the mention the black Sh--ite that came out the exhaust. My worst engine experience in 30 years. Decided life's too short to waste any more time on it. I got larger UMS engines and these are fine, but the 7-50 with UMS carb is a dud. I wish you good luck with yours.
I have the 5-cylinder UMS 55cc radial engine that I purchased from Adrian down there in Florida and I have experienced pretty similar situations as well so far. I think a lot of the problems I had with trying to make it run were due to the crappy UMS carburetor. I got to the point of not even being able to get it to run and sent it back to Adrian. He supposedly got it running again and sent it back. I'm here in Alaska and we are having a terrible winter with gobs of snow. Therefore, I have not even tried to run this engine yet again. Plus, I've also had another knee replacement surgery that took precedence. Luckily, now my knee is far enough along that I can begin to do other things again. I have also purchased a Walbro carb and pump kit from Morris Mini Motors and it should arrive any day now. I think I can get my test stand set up in my garage here with a couple of silicone tubes running the exhaust out underneath my overhead door to do some test runs with this engine. I will try to add here what I experience once I get to that point.
Old 03-06-2024, 06:42 AM
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Default Ums 55 or 75

Long time modeler and looking for my first radial.
I'd like to get the 55 but posts indicate it will need a pump and walbro carb to run properly.
The 75 is probably a better choice in that respect but bigger then my requirement.
I see the 75 comes with a Walbro carburetor. Do you need to buy a pump also to run well?
Old 03-06-2024, 12:48 PM
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To pump or not to pump. That is the question and it all depends on the brand of radial you have. On a Moki, the carburator impulse pressure comes from within the area of the cam ring, which over time, gets clogged with cam grease. Bad news because now the impulse pressure to the carb is blocked and has no where to go. The solution is to run a pump.

On a UMS engine, the carb impulse pressure (vacuum) comes from the #1 & #5 intake ports (in the case of a 5-cylinder radial. #1 & #7 on a 7-cylinder) and therefore, do NOT require a pump. I have several UMS radials (5-100's and a 7-260) and do not run pumps on any of them. NOTE: There is nothing wrong with using a pump on your UMS engines and many people I know use them. Some say their engines seem to run and idle better with one. So, consider it a form of insurance. YMMV.


Moki radial. This line get clogged with cam grease thus requiring the use of a pump.

UMS radial. Pump is not rquired since the impulse pressure (vacuum) to the carb is coming from two intake ports.

Last edited by okcrcpilot; 03-06-2024 at 01:41 PM.
Old 03-06-2024, 01:24 PM
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okcrcpilot,
Thanks for the great info.
Old 03-06-2024, 01:27 PM
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Default UMS 55 five cylinder

Has anybody have success running the UMS 55cc 5-Cylinder motor either stock or with a pumped walbro?
Old 03-06-2024, 01:31 PM
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Thanks to Maxam for your pm reply info. I couldn't reply till i get my newby 5 post requirement.
Old 03-06-2024, 01:49 PM
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Robert, I have had OK success with the the 5-55 with its stock carb and no pump (cannot use a pump!!!). The carb is not great but there is a trick. The choke area is too large for the engine. Make the full throttle position on the transmitter = only about between 1/2 and 3/4 throttle on the carb. Then the engine will run reasonably well with little power loss. -Tom
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Old 03-06-2024, 01:56 PM
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And so for my 5th post to allow me responder privileges.
I want a radial in a 5 cylinder configuration running gasoline.
My first choice was the Saito FG73r5. What worried me was weekly posts on Facebook of the Saito gas radials with photos of the bent up rods.
Next in the hunt is the UMS 55-5 that is perfect size for my application but appears it will need a Walbro carb and a pump. I'm willing to do that but i can't find good comments on it's operation in either configuration.
Next leads me to the UMS 75-5 stock with a walbro carb. Seems to have happy owners.
So a question comes back to my first engine. Is there a reason the saito radials are bending rods, is this really that common, or a user operational error?
Old 03-06-2024, 02:01 PM
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The Saito better have 16-1 oil ratio. Then you are OK.
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Old 03-06-2024, 02:28 PM
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Robert, follow Tom's recommendations to the letter and you can't go wrong. He has more knowledge and experience with radial engines than anyone else on here and I've lost track of the number of times he has helped me out. UMS 5-55 no pump and proper throttle settings are the key.
Re-read post #242 if necessary.

Last edited by okcrcpilot; 03-06-2024 at 02:32 PM.
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Old 03-06-2024, 02:32 PM
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anyone with experience on the UMS 5-180 gas engine?
do, do not, servicing etc.
Old 03-06-2024, 09:26 PM
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Originally Posted by GIJon
To the gentlemen with the 7-50 UMS engines..
Were you able to get your problems worked out.
I picked up a used (very little if any) one and have it setup to test run. Life keeps getting in the way.
It has the stock UMS carb.
I am going to start out with Lawnboy 2c oil, Seafoam, and non-ethanol fuel at 32:1

Question for Tom...do you think the Saito carb like used on the 5-55 would be a good fix if this one has issues?
I just thought I would warn you about using that Saito carb on the UMS 5-55 radial engine. I have the same engine, but I ordered a Walbro carb from Morris Mini Motors and am waiting for it to arrive in the mail any day now. However, I also have a Saito RG 60cc R3 radial engine that I bought from Morris Mini Motors and I had them install a Walbro carb on it as well. So......I have the Saito carb left over in the box. Anyway, my point is I saw somewhere on an RC forum that you need to make an adapter to be able to install the Saito carb on to a UMS radial engine. The guy who did this had his own machine shop apparently and made his own adapter. So........be forewarned.

I might also add that I had crummy results in running this UMS engine when I first got it and I think it was caused by the crappy carb that UMS puts on this engine. I think it is nothing more than a glow type carb and doesn't do a very good job of providing fuel to the five different cylinders. That's why I decided on getting a Walbro carb kit (includes a fuel pump too) from MMM to see if it will work a lot better. I'd be interested to hear back from you on anything you have done with your engine so far. Thanks.......

Last edited by Gozonablat; 03-06-2024 at 09:30 PM.
Old 03-07-2024, 05:43 AM
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Thank you Gozonoblat for ratting my brain. I believe you are referring to me with the Saito carb modification. Yes when I had the 5-55, I did make an adapter for the Saito r90-3 GLOW carb which has a very small choke area. This little engine is only 15cc. It did work better than the stock carb but there were concerns that the o-rings could handle gasoline. Thank you for bringing this up, Robert D, are you reading this?? This engine may not be in your best interest. I do not have a machine shop but a friend does have a nice old metal lathe I used to make the adapter.
Again Gozonoblat, thank you for bringing this up so Robert is not misled. The "expert" forgot thus messing things up here. Sorry Robert.
Old 03-07-2024, 10:14 AM
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Originally Posted by Maxam
Thank you Gozonoblat for ratting my brain. I believe you are referring to me with the Saito carb modification. Yes when I had the 5-55, I did make an adapter for the Saito r90-3 GLOW carb which has a very small choke area. This little engine is only 15cc. It did work better than the stock carb but there were concerns that the o-rings could handle gasoline. Thank you for bringing this up, Robert D, are you reading this?? This engine may not be in your best interest. I do not have a machine shop but a friend does have a nice old metal lathe I used to make the adapter.
Again Gozonoblat, thank you for bringing this up so Robert is not misled. The "expert" forgot thus messing things up here. Sorry, Robert.
Hey!! Not a problem. It's best to spread the knowledge around to the guys who need it with their attempts at doing some mods. I was wondering if those O-rings you mentioned worked out OK with gasoline. I still have not received my Walbro carb kit from MMMs and I hope it did not get lost somewhere in the USPS system. At least I have a good rapport with the owner of MMM and can chat with him using WhatsApp. He is supposed to be sending me a tracking number today.
Old 03-16-2024, 07:02 AM
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Default 7Cyl 50cc

I recently bought a 7-50 from Adrian @ CH Ignitions. Even after reading about it's problems I purchased due to size restrictions. This is my first radial and will be testing it on the stand this week. I spoke with Adrian a couple days ago and he is well aware of its shortcomings and is working on the solution. In the mean time I will get some run it in some and see what happens .

The carb body is very robust with a small venturi compared to my 2 stroke glow engines. I do understand multi cylinder engines sometimes share a carb that is equivalent to an individual cylinder but other than the f-90 r3 15cc Saito carb has anyone tried any others?

After reading through this thread on the 50 & 55 no one has mentioned the exhaust pressure tap for the fuel tank. Has anyone used this as it was included in the hardware pack and the exhaust ring has accommodations for it?



Chris

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