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nelson - 10/6/2002 6:53:38 AM   
jlong34016


 

Posts: 365
Joined: 4/14/2002
From: columbus, OR,
Status: offline 		I have a qm-40 nelson with an os 7d carb. The pressure tap off the header is not completely drilled thru to the inside. Does this engine just suction feed? or do i need to drill this out and pressurize the tank. Thanks.
       Post #: 1

put a hose on it and blow... - 10/6/2002 7:57:38 AM   
splatt



Posts: 651
Joined: 1/30/2002
From: splattsville, MN,
Status: offline 		does it pass air? then leave it alone. The hole does not go completely thur to the center. I think theres 2 parts to those mufflers and the vent goes to the back half. But if I'm wrong hopefully someone will pounce on me and correctly give the right answer

(in reply to jlong34016)
       Post #: 2

nelson - 10/6/2002 9:05:23 AM   
jlong34016


 

Posts: 365
Joined: 4/14/2002
From: columbus, OR,
Status: offline 		No air moves at all.The fitting is in the header portion of the tuned muffler.

(in reply to jlong34016)
       Post #: 3

nelson - 10/6/2002 7:45:57 PM   
Jerry-B


 

Posts: 39
Joined: 1/29/2002
From: Ramsey, MN, USA
Status: offline 		The pressure tap hole in a Nelson muffler is not drilled all the way through, that is if you push a small wire in the hole it won't go in more than 3/8ths of an inch. The hole is only drilled into the same hole the mounting screw goes into, if you put to long of a mounting bolt in it you can block the hole. If you put a piece of fuel
line on the pressure tap you should be able to blow through it, if you can't take the mounting bolt out and try again, if you still
can't blow through it, push a small wire through the Mounting hole, it shold go in at least 7/8ths of an inch.

_____________________________

Jerry-B

(in reply to jlong34016)
       Post #: 4

nelson qm40 os 7 D carb - 10/7/2002 12:41:15 AM   
jlong34016


 

Posts: 365
Joined: 4/14/2002
From: columbus, OR,
Status: offline 		Ran today without pressure on tank. Seems to work fine. Didnt tach but with 7.4 x 8 it was easily over 20,000.

Took muffler bolt out and still no flow.

(in reply to jlong34016)
       Post #: 5

nelson - 11/15/2002 11:19:32 AM   
DrewTelford


 

Posts: 45
Joined: 1/6/2002
From: San Diego, CA,
Status: offline 		You should be able to blow through the pressure fitting. Some brand new mufflers are like yours, with the hole blocked. I've had 2 like this in recent years, and here's what I did:

Remove the muffler, and gently drill through the pressure fitting with a 1/16 inch drill until it goes through into the muffler bolt hole (won't be much). Be sure to clean out the debris after drilling. I wash them in the sink under high pressure hot water, towel dry and finish drying with a hair dryer or heat gun.

You should be able to turn that 7.4 x 8 at 24,500 or better on a new motor, but don't burn it up hunting for peak RPM on the ground, let it run rich about 600 RPM down from peak, and pinch the pressure line for 1/2 second to peak it to check the RPM but don't hold it. (You can pinch the fuel line too but it's harder to see the actual peak RPM.)

Whatever you do, NEVER run it lean and it will last a long time.

Good luck,

Drew

(in reply to jlong34016)
       Post #: 6

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