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UMS Gas Radial Engine Enthusiasts Rabbit Hole

Old 05-28-2024, 03:50 PM
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Yes, the Motorex leaves an oily mess. I'll try the Amsoil Dominator oil and and an electric fuel pump in about 3 weeks.
You'll notice in the photo the fuel tank positioned high to give me more pressure at the carb. And the messy oily stains on the start stand.

Last edited by Robert Dochterman; 05-28-2024 at 03:54 PM.
Old 05-29-2024, 05:51 PM
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I ran a bit of fuel through it with Stihl Ultra (couple flights as I ran low at the field and used some of a mates mix) about the same. No biggie to me, it cleans up easy with "tub of towels".
Mine runs without the pump with a head pressure like you have going on there. Not well enough to fly though when the tank is in its normal position in the fuze. Even with very short feed line. Not a huge fan of the ob pump, but it is warranted. On my engine anyway.
Old 05-30-2024, 05:54 AM
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I ordered this pump. A friend uses it on his Kolm with good success. Only 3 days from across the big pond.
https://micropumps.co.uk/product/m400k-v/
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Hyjinx (05-30-2024)
Old 05-30-2024, 11:24 AM
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Quite reasonably priced. I have been using APS pumps on all my set ups. Had a bad experience with them on a warranty issue once. Let me know how this unit works out please.
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Old 06-04-2024, 07:42 PM
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Default Ums 5-55cc

I
Originally Posted by Maxam
So I got the 5-55 from Adrian 'cause it is cute and a nice small size. Got it mounted up and used a 22x10 prop. The engine can turn it to 4500rpm. True hp at this rpm is 1.5. Sure it can develop more hp at a higher rpm but then much smaller prop. The UMS glow style carb has the classic way over rich condition at mid throttle. The trick of adjusting the throttle mixture at half opening still was unsatisfactory. I made an adapter on the lath for the Saito 90r3 carb and that was the ticket! Beautiful ideal mixture at all throttle settings with immediate response. All cylinders at same temp. A 4oz tank runs the engine for 15 minutes with some part throttle settings. The question now is will the seals in the Saito carb hold up on gas? Reliable idle at 1000rpm

-Tom
Does the Saito carburetor need a fuel pump with the 5-55 UMS
Old 06-04-2024, 10:22 PM
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So I got the 5-55 from Adrian 'cause it is cute and a nice small size. Got it mounted up and used a 22x10 prop. The engine can turn it to 4500rpm. True hp at this rpm is 1.5. Sure it can develop more hp at a higher rpm but then much smaller prop. The UMS glow style carb has the classic way over rich condition at mid throttle. The trick of adjusting the throttle mixture at half opening still was unsatisfactory. I made an adapter on the lath for the Saito 90r3 carb and that was the ticket! Beautiful ideal mixture at all throttle settings with immediate response. All cylinders at same temp. A 4oz tank runs the engine for 15 minutes with some part throttle settings. The question now is will the seals in the Saito carb hold up on gas? Reliable idle at 1000rpm

-Tom

I have the exact same engine and purchased it also from Adrian. I had problems with it early on (I've had this engine now for almost a year I think). Right after I first bought it I was able to get it to run kinda. I eventually could not get it to even pop during my attempt to try and start it. I eventually sent it back to Adrian and he worked on it and later on sent it back to me. However, because of where I live (Anchorage, Alaska) and it was winter time here with gobs of snow. Plus, I had to have a knee replaced during this time as well. So......I could not do anything with the engine until recently. I also purchased a Walbro carb and fuel pump from Morris Mini Motors and now have that installed on the engine. Several days ago I finally got the opportunity to try and run it. Well.....I managed to get it started and running.......sort of......It ran like crap and I could not get it to get up over 3500 RPMs and several of the cylinders were way cool......like 113 degrees Farenheit on #5, #1 138, #4 133, #3 160, #2 164. So......I am not happy with this performance. I'm thinking about going back to the original UMS carb and manifold to see if I can get it to run better than it is with this Walbro carb set up. If you have any suggestions about what I could do please post them up here. Also, you mention making an adapter (or had a friend make it for you) to be able to use a Saito 90r3 carb and you state the that carb worked out really well for you. Well, I have a leftover carb from a Saito 60r3 after I purchased a Walbro carb for this engine. I bet the 60r3 and the 90r3 use the same carb. Maybe you could have your friend make an adapter for me as well.........eh?? I am going to be contacting Adrian here in the next few days to see what he has to suggest for me to do to help this UMS 55cc radial run better.
Old 06-05-2024, 12:01 AM
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Default UMS 5-55CC with Saito carburetor needing external fuel pump?

[QUOTE=Maxam;12724700]So I got the 5-55 from Adrian 'cause it is cute and a nice small size. Got it mounted up and used a 22x10 prop. The engine can turn it to 4500rpm. True hp at this rpm is 1.5. Sure it can develop more hp at a higher rpm but then much smaller prop. The UMS glow style carb has the classic way over rich condition at mid throttle. The trick of adjusting the throttle mixture at half opening still was unsatisfactory. I made an adapter on the lath for the Saito 90r3 carb and that was the ticket! Beautiful ideal mixture at all throttle settings with immediate response. All cylinders at same temp. A 4oz tank runs the engine for 15 minutes with some part throttle settings. The question now is will the seals in the Saito carb hold up on gas? Reliable idle at 1000rpm

-Tom... Does the Saito carb on the ums 5-55cc need an external fuel pump, similar if using a walbro carb on the ums.
Old 06-05-2024, 02:54 AM
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Initially my 7-50 (which also has the glow style carb) ran perfect out of the box. It had a really good top end , low idle and transition was good. After a gallon or so it all went south. I checked and rechecked the valve lash and it didn't help. I ended up taking the exhaust ring off and by doing so it was easy to see how each cylinder was doing individually by feeling the exhaust gasses from each. I noticed all 7 were firing at low rpm but 4 were dropping out above 2800. It turned out that the plugs were not working properly. After installing new plugs it is now running perfectly again. I guess the plugs fouled out due to the heavy black sludge during the break-in process. The cylinders with the bad plugs also had lower compression then the others due to not firing through the entire range hindering the rings from bedding in.

If you have UMS 5-55 or 7-50 and it was running well on the initial runs but has problems now I urge you take the exhaust ring off , find the problem cylinders and replace the plugs. Swap the plug from a known good cylinder to bad one and vice versa and see what happens. You could just install a new plug on the cylinder that isn't operating properly but that plug could be defective.


Chris
Old 06-05-2024, 03:57 AM
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Originally Posted by dodgers72
Initially my 7-50 (which also has the glow style carb) ran perfect out of the box. It had a really good top end , low idle and transition was good. After a gallon or so it all went south. I checked and rechecked the valve lash and it didn't help. I ended up taking the exhaust ring off and by doing so it was easy to see how each cylinder was doing individually by feeling the exhaust gasses from each. I noticed all 7 were firing at low rpm but 4 were dropping out above 2800. It turned out that the plugs were not working properly. After installing new plugs it is now running perfectly again. I guess the plugs fouled out due to the heavy black sludge during the break-in process. The cylinders with the bad plugs also had lower compression then the others due to not firing through the entire range hindering the rings from bedding in.

If you have UMS 5-55 or 7-50 and it was running well on the initial runs but has problems now I urge you take the exhaust ring off , find the problem cylinders and replace the plugs. Swap the plug from a known good cylinder to bad one and vice versa and see what happens. You could just install a new plug on the cylinder that isn't operating properly but that plug could be defective.


Chris

Hi Chris...... Hmmm......what you say here proves to be very interesting and may certainly apply to my situation too. I just looked at my engine and I think it would be pretty easy to remove the Keleo exhaust ring and adjust each individual exhaust stack so it points out away from the cylinder head giving me a really good way to check the warmth of the exhaust and how each cylinder is firing at various RPMs. My problems could also be due to spark plug failures. Wow!!! This could easily be the very same thing that is causing my problems. Hope so, because it would be an easy fix. I spent a fair amount of $$$ on this Walbro carburetor and fuel pump system from Morris Mini Motors and so I hope that Walbro carb ends up not being the problem. I use Walbro carbs on several of my 2-stroke engines and they seem to be flawless there and the many YouTube videos I have viewed showing guys running radial four stroke engines with these carbs very successfully tells me they should work just fine. I will keep you posted here on what I end up doing with this engine to try and solve my problems and will see if your suggestion turns out to be the answer. Thanks a bunch.

By the way........ I hope these spark plugs aren't all of the problem as these little buggers are not exactly inexpensive to replace. But......We'll see on that.

Last edited by Gozonablat; 06-05-2024 at 04:02 AM.
Old 06-05-2024, 05:48 AM
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You can buy two off these for $25 each from Amazon and put the sensor directly on the side of the spark plug.
i found various infrared thermal gun just about useless because of the cone angle of the readings

​​​​​​​


.
Old 06-05-2024, 07:18 AM
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Originally Posted by Gozonablat
Hi Chris...... Hmmm......what you say here proves to be very interesting and may certainly apply to my situation too. I just looked at my engine and I think it would be pretty easy to remove the Keleo exhaust ring and adjust each individual exhaust stack so it points out away from the cylinder head giving me a really good way to check the warmth of the exhaust and how each cylinder is firing at various RPMs. My problems could also be due to spark plug failures. Wow!!! This could easily be the very same thing that is causing my problems. Hope so, because it would be an easy fix. I spent a fair amount of $$$ on this Walbro carburetor and fuel pump system from Morris Mini Motors and so I hope that Walbro carb ends up not being the problem. I use Walbro carbs on several of my 2-stroke engines and they seem to be flawless there and the many YouTube videos I have viewed showing guys running radial four stroke engines with these carbs very successfully tells me they should work just fine. I will keep you posted here on what I end up doing with this engine to try and solve my problems and will see if your suggestion turns out to be the answer. Thanks a bunch.

By the way........ I hope these spark plugs aren't all of the problem as these little buggers are not exactly inexpensive to replace. But......We'll see on that.
Gozonablat , I hope it turns out to be the plugs like mine. I had read the troubles you had with the 5-55 before I purchased the 7-50 but took a chance as my airframe required the size of the 50. I was pleasantly surprised with the first few runs and thought I just got lucky. But then the gremlins appeared.

Taking the ring off definitely lets you feel the health of each cylinder. I could tell by the puff of exhaust from each one (even when they were all firing) which were stronger. I believe , when fully broken-in they will even themselves out . Hopefully after it's fully broken-in the black exhaust residue will diminish completely and the plugs will last longer. I even considered trying the iridium plugs (even more $) but decided to wait until I have a few more gallons through before trying that.

Good luck with the 55.


Chris
Old 06-05-2024, 12:49 PM
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Originally Posted by Robert Dochterman
You can buy two off these for $25 each from Amazon and put the sensor directly on the side of the spark plug.
i found various infrared thermal gun just about useless because of the cone angle of the readings




.
Hello Robert,
I just purchased two of these gadgets from Amazon and I'm going to test them out on my UMS 5-cylinder radial engine that I'm having trouble getting to run properly. I also have one of those infrared thermal guns and it's going to be interesting to see how it compares with the readings taken with this digital thermometer that has the individual thermocouples. I have another Saito 3-cylinder FG 60cc r3 engine and I'm sure this gadget will come in handy with that engine as well. Plus, it will just be fun to learn how to use this thing too. Thanks for your suggestion here.
Old 06-05-2024, 01:04 PM
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Yep, i just pull back the spark plug boot about an 1/8", place the probe tip against the spark plug and head, then push down the boot to hold it in place. Works very well and consistent readings.
Old 06-05-2024, 01:04 PM
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Originally Posted by dodgers72
Gozonablat , I hope it turns out to be the plugs like mine. I had read the troubles you had with the 5-55 before I purchased the 7-50 but took a chance as my airframe required the size of the 50. I was pleasantly surprised with the first few runs and thought I just got lucky. But then the gremlins appeared.

Taking the ring off definitely lets you feel the health of each cylinder. I could tell by the puff of exhaust from each one (even when they were all firing) which were stronger. I believe, when fully broken-in they will even themselves out. Hopefully, after it's fully broken-in the black exhaust residue will diminish completely and the plugs will last longer. I even considered trying the iridium plugs (even more $) but decided to wait until I have a few more gallons through before trying that.

Good luck with the 55.


Chris
I hope my problems are also solved by the same method you ended up doing but I guess we will see. You may have noticed from a post I made to Robert Dochterman about me purchasing a couple of digital temperature monitors from Amazon. I think they will be very helpful in determining which cylinders I'm having problems with. I am starting to think that maybe these 4-stroke radial engines are more trouble than they are worth. I am building a large Phoenix Stinson Reliant that I wanted to use a Saito FG 60cc r3 engine in but I also have a couple of 40cc twin 2-stroke engines that would probably work OK in this Stinson too. If I can't get one of these radials to run correctly I might just give up and use one of my 40cc 2-stroke engines. They certainly seem a whole lot more troublesome-free.

Oh!!!! Just another thought here. When I was first considering buying one of these UMS radials, I also was thinking hard about getting a UMS 50cc 7-cylinder engine but changed my mind and got the 5-cylinder one instead. I can't remember now what it was that changed my mind but I think I made the right decision. We'll see though.

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Old 06-05-2024, 01:18 PM
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Originally Posted by Robert Dochterman
Yep, I just pull back the spark plug boot about a 1/8", place the probe tip against the spark plug and head, then push down the boot to hold it in place. Works very well and has consistent readings.

OK...............COOL!! Thanks for this suggestion. You should take some photos of you doing this and post them here. I think that would be super helpful for guys that are checking in here. When I get around to accomplishing these tests with my engine I'm going to do my best to take a bunch of photos and get them up here.
Old 06-17-2024, 02:16 PM
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Originally Posted by Gozonablat
OK...............COOL!! Thanks for this suggestion. You should take some photos of you doing this and post them here. I think that would be super helpful for guys that are checking in here. When I get around to accomplishing these tests with my engine I'm going to do my best to take a bunch of photos and get them up here.


Old 06-17-2024, 02:17 PM
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Old 06-17-2024, 10:37 PM
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Default UMS 7-90cc

Hi,

Hoping someone can give me a bit of advice. I have a new 7-90cc radial that's almost finished running in. I have to run it very rich to get it to run over half throttle. Also when idling it often start / stops as if the ignition is cutting out, especially when left idling for a while. The engine will sometimes not come back to idle straight away (holding 3000rpm for 20 seconds). I have checked for air leaks as that seemed the obvious problem but to no avail. I'm wondering if the issue is plug fowling as the oil ratio is high for running in and going to the regular oil mix will solve some/ all of the issues. Any advice appreciated.

Regards

John
Old 06-18-2024, 11:16 AM
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I have not been getting notices when someone posts lately....Rich123, No do not use a pump with the Saito carb. John Shiell, are you using a fuel pump? The pulse system is not reliable. Robert D. I have completed my Waco with the baffles 5-100 as pictured in post 287. I ran the engine on the ground at all throttle settings including full for a good while. The baffle is effective. Temps reaching 215 F. -Tom
Old 06-18-2024, 11:31 AM
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Originally Posted by Maxam
I have not been getting notices when someone posts lately....Rich123, No do not use a pump with the Saito carb. John Shiell, are you using a fuel pump? The pulse system is not reliable. Robert D. I have completed my Waco with the baffles 5-100 as pictured in post 287. I ran the engine on the ground at all throttle settings including full for a good while. The baffle is effective. Temps reaching 215 F. -Tom
Darn!! I ordered these Digital temperature measuring devices from Amazon and I have received them recently. However, it looks like the ones I ended up with are a different model so I won't be able to use them and I need to send them back to Amazon and try to get the correct model. Stupid me. I should have paid more attention to what I was doing when I ordered these things
Old 06-18-2024, 08:31 PM
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Originally Posted by Maxam
I have not been getting notices when someone posts lately....Rich123, No do not use a pump with the Saito carb. John Shiell, are you using a fuel pump? The pulse system is not reliable. Robert D. I have completed my Waco with the baffles 5-100 as pictured in post 287. I ran the engine on the ground at all throttle settings including full for a good while. The baffle is effective. Temps reaching 215 F. -Tom
Hi Tom. No I don't run a pump and the manual says I don't need to. Are you saying that the engine won't run reliably without a pump? Seems UMS should include one if that's the case?
Old 06-19-2024, 01:51 PM
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Yeah John, yes you really do need the pump. The pulse system is marginal at best. You will be burning your engine up attempting to go to full throttle with inadequate fuel delivery -Tom
Old 06-20-2024, 04:16 AM
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Originally Posted by Gozonablat
Darn!! I ordered these Digital temperature measuring devices from Amazon and I have received them recently. However, it looks like the ones I ended up with are a different model so I won't be able to use them and I need to send them back to Amazon and try to get the correct model. Stupid me. I should have paid more attention to what I was doing when I ordered these things
I used these.
https://www.amazon.com/gp/aw/d/B0C39TKV4X?psc=1&ref=ppx_pop_mob_b_asin_title
Old 06-20-2024, 04:29 AM
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If you want to check the health of your engine, valves, piston, compression, it's easy with a simple gauge setup.
1. A gauge that reads from 0- 125psi. Mine is only good for 100psi.
2. A check valve.
3. A glow or spark plug drilled out and thick walled tube sealed in to it.
4. Hose.

Remove all spark plugs and screw in the modified glow plug. Attach hose. Ignition off of course. Turn engine over with a starter and record readings. Repeat for each cylinder. Mine all read 95-100 psi but I need to repeat with a higher psi gauge.

Old 06-20-2024, 04:39 AM
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Originally Posted by johnshiell
Hi Tom. No I don't run a pump and the manual says I don't need to. Are you saying that the engine won't run reliably without a pump? Seems UMS should include one if that's the case?
The obvious reason i needed a pump was on the test stand my 5-100 would peak at 2 turns out. At 2.5 turns it richen a bit. Then the rest of the way out to 5 turns had no effect on the mixture, at wide open throttle. On the test stand I could raise and lower the tank 8" and it sound like I was using the throttle stick. So you can imagine what would happen on take off when the nose pitches up in a climb.

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