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Obscure Perry Carb Feature - 4/18/2012 8:20 PM   
earlwb


 

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Status: offline 		Someone had asked me a question recently about what does the two screws and a little tiny brass rod do in a Perry Carb.
On some Perry carbs, not all of them, it appears to be just the Pump Carbs not the standard carbs there are what look like two screws inline and right behind the fuel inlet fitting.  The top screw has a narrow tip to the end, whereas the other short screw is fitted into a brass insert screwed into the carb. In between the two screws is a little brass rod.  


You can see it here in the carb body


Here are the two screws and the little tiny brass rod showing how they look when put into the carb.



Anyway, when I researched it I found that some Perry Carb instructions mentioned it in the exploded parts diagrams, but not in the parts list or in the instructions.
I finally located a set of Perry Instructions dated 1978 for my Perry Carb setup for a Rossi .60 engine. The screws and brass rod are called a "Slide Valve".
When everything else is adjusted on the engine and you bring it up to full throttle and then hold the plane inverted, if the engine runs a little rich, you can lean it out by turning the top screw (the one with the narrow tip) in 1/4 turn increments counterclockwise to lean the engine out more.  The default setting is to adjust the top screw out 2.5 turns from when it stops when screwed in.  The brass rod acts as a gravity operated valve when the engine is inverted and it obstructs the fuel flow going to the engine.

Anyway it is a pretty cool feature that I had never noticed before on the Perry carbs. I have a number of carbs and none of the instructions mention this feature in them or what to do with it, including other pump carbs too.



Here are some pics of the inner throttle body, spray bar and idle disc and how it looks outside of the Perry carb:
Front side of spray bar

Back side


Here is the instructions for my Perry Pump Carb for a Rossi .60 engine:






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RE: Obscure Perry Carb Feature - 4/18/2012 9:09 PM   
pe reivers



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Status: offline 		This is a feature I never saw in a Perry carb. Clever thinking!


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RE: Obscure Perry Carb Feature - 4/18/2012 9:16 PM   
turbo.gst


 

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Status: offline 		Good stuff Earlwb! Thanks for posting.

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RE: Obscure Perry Carb Feature - 4/18/2012 9:54 PM   
earlwb


 

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I got to thinking more about it and it seems to only work like this if the engine is mounted upright. If the engine is inverted then the slide valve is setup wrong for it. But it ought to work OK if you more or less reverse the slide valve adjustments. As you turn the engine/plane upside down to make the engine adjustments, once dialed in, and then flip it over right side up (inverted engine) and make the slide valve adjustment.
 Then if the engine is mounted horizontally, it would appear to only work depending on if the engine is inverted doing certain aerobatic maneuvers such as a knife edge on that particular side. Most planes knife edge with the nose high, so that is doubtful to work in those cases.



< Message edited by earlwb -- 4/19/2012 12:23 PM >

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RE: Obscure Perry Carb Feature - 4/18/2012 11:15 PM   
w8ye



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Status: offline 		I looked into this some 10 or 12 yrs ago. I had a Perry with these adjustments. I've since forgotten most of it.

I don't think the newer pump carbs have this feature?


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RE: Obscure Perry Carb Feature - 4/19/2012 2:39 AM   
Charlie P.



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Status: offline 		I've got two Perry carbs - one with that feature and one without.  Did not know that was what those screws did.

Thanks.

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RE: Obscure Perry Carb Feature - 4/19/2012 12:33 PM   
earlwb


 

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quote:

ORIGINAL: w8ye

I looked into this some 10 or 12 yrs ago. I had a Perry with these adjustments. I've since forgotten most of it.

I don't think the newer pump carbs have this feature?



You maybe correct. In their current parts lists and instructions they do not show or mention the slide valve.
So if you take it apart and lose one of the slide valve parts, there aren't any parts you can order from them now. They might still have some slide valve parts though, if anyone that works there now knows about it.  it is a pretty obscure feature. I haven't ordered a current version Perry Pump carb so I can't say for sure if they quit doing it or not. My example carbs are all older models. This may be a feature from way back in the old .60 engine powered pattern planes era.





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RE: Obscure Perry Carb Feature - 4/20/2012 1:46 PM   
DerFly



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Status: offline 		Very interesting Earl,

inhave just found this feature on my old pumped HB61 PDP

DF

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RE: Obscure Perry Carb Feature - 4/20/2012 4:18 PM   
earlwb


 

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Status: offline 		Yeah it was something I had never noticed before as well. At least until someone brought it to my attention.

Here are the instructions that came with a old Perry Carb for a Picco 90 engine.
They show the slide valve and parts in the parts list and exploded view but they don't tell you what to do with it.
This carb was made by Varsane before Conley bought the rights to Perry carbs.




Of course the Standard Perry Carb for a K&B 61 engine, from circa 1987, doesn't show or mention the slide valve at all.







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RE: Obscure Perry Carb Feature - 4/21/2012 4:00 PM   
oskartek


 

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earlwb,
              Do you think this feature will work on a engine set up not using a pump but using the
exhaust pressure to the tank?

Or, is the pump pressure greater than exhaust pressure as the pump is driven by crankcase pressure?


Thanx, Oscar



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RE: Obscure Perry Carb Feature - 4/21/2012 8:34 PM   
earlwb


 

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Status: offline 		The fuel pump provides for more pressure than muffler pressure does.
Generally the pump carbs have a larger bore inside as the pump provides the fuel instead of the engine sucking the fuel. Plus they have a slightly different mid range trim in the carb to account for the extra fuel pressure too.
The fuel tank is rarely inline with the carb as it is usually a little lower. So then the plane goes inverted the fuel flow increases causing the slight rich running condition. The fuel pump tends to aggravate the situation. So yes the slide valve would work for that. But the carbs are setup for pumps, so you probably wouldn't find a non-pump Perry carb with that feature on it.


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RE: Obscure Perry Carb Feature - 4/22/2012 7:48 AM   
proptop



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Status: offline 		This reminds me of when the Perry backplate pump / carb sets were first becomming available...mid 70's...
A friend bought one for his O.S. .60 FSR in his Kwik Fli III...(engine mounted upright)
He fiddled and fiddled with that slide valve adjustment for days...flying back and forth..upright, then inverted...burned a couple gallons...
After all that, he said that the adjustments didn't seem to make any difference...

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RE: Obscure Perry Carb Feature - 4/23/2012 5:24 AM   
oskartek


 

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quote:

ORIGINAL: earlwb

The fuel pump provides for more pressure than muffler pressure does.
Generally the pump carbs have a larger bore inside as the pump provides the fuel instead of the engine sucking the fuel. Plus they have a slightly different mid range trim in the carb to account for the extra fuel pressure too.
The fuel tank is rarely inline with the carb as it is usually a little lower. So then the plane goes inverted the fuel flow increases causing the slight rich running condition. The fuel pump tends to aggravate the situation. So yes the slide valve would work for that. But the carbs are setup for pumps, so you probably wouldn't find a non-pump Perry carb with that feature on it.



The reason I asked is a friend of mine has an old K&B, I think it's a .60 or .61? with this carb and pump but the pump is shot so he set it up with exhaust pressure to the tank, it runs fine when upright and stationary but as soon as he points the aircraft vertical it quits and when it is held inverted it goes blubbering rich.
I think he's looking for the K&B carb.

Happy flyin'  Oscar 

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RE: Obscure Perry Carb Feature - 4/23/2012 12:02 PM  1 votes
earlwb


 

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Status: offline 		Ok, he has a K&B engine with the fuel pump. The carb is a bigger bore carb designed for use with a fuel pump. It is dependent on a fuel pump to provide the fuel as it can't draw fuel very well itself.  What you can do is use a Perry VP-30 style pump with the engine and he will be back to normal again. You can even get a regular backplate and epoxy, using JB Weld, the fuel pump back into the backplate and it'll look almost like a original pumped engine too. Don't forget to drill a hole in the backplate for the crankcase pressure to get to the pump. You could also just put on the regular non-pumped engine carb and not use a fuel pump. The non-pumped engine uses a smaller bore carb. Perry says the regular carb is a 1300 and the pumped carb is a 9300 for a K&B .61 engine.


< Message edited by earlwb -- 4/23/2012 12:49 PM >

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RE: Obscure Perry Carb Feature - 4/23/2012 1:23 PM   
w8ye



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Status: offline 		From my experience with my PDP K&B 61's, they didn't run any faster with the pump carb than the regular one.

The limiting factor is actually the hole up through the center of the crankshaft.


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RE: Obscure Perry Carb Feature - 4/24/2012 4:21 AM   
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Status: offline 		Thanks earlwb,
                         I think he's found the K&B carb for that engine.

Happy flyin' Oscar

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