Warbird Information Exchange

DISCLAIMER: The views expressed on this site are the responsibility of the poster and do not reflect the views of the management.
It is currently Fri Dec 06, 2019 3:46 am

All times are UTC - 5 hours


Classic Wings Magazine WWII Naval Aviation Research Pacific Luftwaffe Resource Center
When Hollywood Ruled The Skies - Volumes 1 through 4 by Bruce Oriss


Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: Mon Feb 13, 2017 11:40 pm 
Offline
Corporal

Joined: Tue Feb 02, 2016 6:41 pm
Posts: 16
On SNJ-5 with NA-Y9E carburetor:
When engine not running (cold), throttle movement is smooth throughout its travel. When engine is running and have reached its normal operating temps., when throttle lever is moved about 1/4 to 1/2 inch from idle the throttle "hangs" (feels like binding) and then, upon being forcefully pushed towards the open position, the RPM jumps to 1100. The carburetor has just returned from having its accelerator pump repaired and was bench tested and calibrated. Throttle operating linkage system was checked and no binding was discovered and the operation is smooth.
Any ideas as to what may be happening?


Top
 Profile  
 
PostPosted: Tue Feb 14, 2017 3:18 pm 
Offline
Been here a long time
Been here a long time

Joined: Sun May 02, 2004 1:16 am
Posts: 10434
First thing to check is whatever was touched. Are you sure the throttle arm on the carb is in the right orientation?


Top
 Profile  
 
PostPosted: Wed Feb 15, 2017 10:35 pm 
Offline
Corporal

Joined: Tue Feb 02, 2016 6:41 pm
Posts: 16
bdk wrote:
First thing to check is whatever was touched. Are you sure the throttle arm on the carb is in the right orientation?


Checked throttle arm position and it's OK; checked the whole throttle lever linkage from cockpit to carburetor and found per specs (drawings.) Disconnected the throttle linkage from the carburetor and ran engine while operating the throttle arm on the carburetor manually and the problem persists.


Top
 Profile  
 
PostPosted: Thu Feb 16, 2017 12:19 pm 
Offline
Been here a long time
Been here a long time

Joined: Sun May 02, 2004 1:16 am
Posts: 10434
zedzil wrote:
Disconnected the throttle linkage from the carburetor and ran engine while operating the throttle arm on the carburetor manually and the problem persists.


Sounds like you have the source then. Maybe the accelerator pump piston (seal) is getting hung up in the accelerator pump cylinder (assuming it isn't a diaphragm type pump)?

At idle there is a lot of suction force on the butterfly so there might be some problem there that you can't feel statically. If the overhauler removed the butterfly from the shaft it may have been replaced in a slightly differently location than it was before (tolerance between the screws and the butterfly) and could be dragging on the housing, but only noticeable under vacuum due to wear between the shaft and the bushings.


Top
 Profile  
 
PostPosted: Fri Feb 17, 2017 12:49 am 
Offline
Corporal

Joined: Tue Feb 02, 2016 6:41 pm
Posts: 16
bdk wrote:
zedzil wrote:
Disconnected the throttle linkage from the carburetor and ran engine while operating the throttle arm on the carburetor manually and the problem persists.


Sounds like you have the source then. Maybe the accelerator pump piston (seal) is getting hung up in the accelerator pump cylinder (assuming it isn't a diaphragm type pump)?

At idle there is a lot of suction force on the butterfly so there might be some problem there that you can't feel statically. If the overhauler removed the butterfly from the shaft it may have been replaced in a slightly differently location than it was before (tolerance between the screws and the butterfly) and could be dragging on the housing, but only noticeable under vacuum due to wear between the shaft and the bushings.


The carburetor was removed and sent to a shop. We'll see what the findings are. I am only afraid that the overhaul shop will not be able to operationally test it and thus, after all the work of installing it, I might have the problem again. Hope not.


Top
 Profile  
 
PostPosted: Mon Feb 27, 2017 9:29 am 
Offline
Lance Corporal

Joined: Thu Jun 09, 2011 9:29 am
Posts: 38
Do you have any updates on the carb issue?


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 5 hours


Who is online

Users browsing this forum: No registered users and 1 guest


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group