IR GRB-125 Running questions

hamel01

Member
Hi All,
So I bought a new to me 1960's IR GRB-125 Rotatory Screw Compressor. It was is pretty rough shape cosmetically so I have since tore it down and repainted/repaired the unit. I have put new gaskets in the air sep flushed the compressor oil, rebuilt the carb.... Before i tore it down the regulator was not working to slow the engine down and unload the compressor. In the tear down i found that one of the copper lines going from the regulator to the air control valve was broke. I have since fixed that but now i can not get the unit to run right. With all the carburetor linkage hooked back up the unit will start and run at what i would call a fast idle. As soon as the internal air pressure reaches around 45-50 psi the unit stalls out. I am unable to pull the throttle out to speed it up as the air regulator will not let it move. If I disconnect the air regulator from the governor linkage I am able to control the engine speed and can keep it running while it builds air but I have to constantly control it manually. According to my manual i should be able to pull the throttle out to the warm up speed when first starting it so the engine has enough power to over come the air pressure build up. I am not able to do this as long as the air regulator it connected.

Before tear down it had a broken throttle cable put you where able to pull it to speed the unit up and it would sit there and run at a high speed... I am assuming i am missing something very simple but i can not find it. Is any one familiar with this units and would not mind spending a few minutes on the phone? Or maybe you know of a shop that still deals with these??
 
The UL 88 regulator is out of adjustment. Someone most likely screwed with it thinking that was the problem rather than the line that broke. I will bet when you pulled on the copper line the flange was broken on the end.
 
Yep! The flange was indeed broke. So your thought is that I need to readjust the UL 88? I have the book that details it but my biggest question is how do i know the RPM when there is no RPM Gauge?
 
There will be an lock nut on a square head bolt loosen the nut and turn the square bolt in 1 and 1/2 turn. Start in compressor. See if any improvement.
 
No change. I should be able to move the throttle when it is off right? Right now i can not move it at all when off and only a bit when it is running. I am fighting the ul 88 all the time.
 
That is a really strong spring that you are trying to move by hand. The UL88 is to shut the inlet door on the air comp then slow the engine back to an idle. You do have air coming out of the copper line going to the UL88 when the air comp is running. yes?
 
OK here is an update.

I disconnected the governor and the linkage from the UL88 and ran it by hand. I am able to control everything just fine and the compressor runs perfect. What i did notice though is that when i open one of the air valves to bleed off some air i see the UL88 arm move as if it is calling for more engine speed. The interesting part is if you follow the linkage that movement (if connected) would slow the engine down by closing the carb. So to me someone has something backwards. I think... Here is a pic of the linkage and the back of the carb. Does it look like yours?
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Just working on my memory. Look at the year on your air tank. I think I remember the grb coming out in 1963. I thought the 1960 was a gra. This was a two stage air comp. I use to work on these at the Nevada test site, and others. I worked for the largest IR dealer in the USA.
 
Here are the pic's. It is definitely a GRB-125. It appears to me that the linkage going to the carb is just backwards. When the machine is shut down the carb is at idle. When the UL88 equalizes (when the compressor has no demand for air) it pushes the carb to wide open instead of idle, well it would try to if i could get the thing to run that long...

That being said i can not see how it could be connected any other way...
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Did you trying to screwing the adjustment screw/ bolt in. that should counter the air pressure from the back side of the regulator. the covered cap nut regulates to top pressure This does not look as it has been disturbed by the dirt and paint.
 
Yeah I tied turning it in and out. It made no difference. I have not messed with the other adjustment screw and I agree that it appears that it has never been touched. The UL88 appears to be moving as it should but the linkage just appears to be backwards..
 
I don't even know what a rotary screw compressor is, (assume it's one of those big air comps for running drills and such), but if it looks to be hooked up backwards, it wouldn't be the first time someone "fixed" a carb and put the linkage back on upside down.
 
My mistake!! I meant to say Vane compressor and not rotary screw! Slight case of fingers moving faster than my brain!!
 
I got it!! After finding another unit in my area to look at it was determined that who ever worked on the carb before put the arm on upside down. After flipping it and a few trial and errors it is now working correctly and runs like a charm!

Thanks for the in sight!
 

I also have a grb -125 which I just got running. it takes off great and builds pressure and at 100 lbs the motor dies. I do not hear any pressure release happening. it just doesn't want to idle. I took apart and blew the carb passageways with compressed air. the ul 88 controller has the forward (front-engine end) adjustment all the way in. the radiator side has about 3/4 inch threads showing.
any adjustment info that I could get would be great!

thanks
 

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