Journey with Confidence RV GPS App RV Trip Planner RV LIFE Campground Reviews RV Maintenance Take a Speed Test Free 7 Day Trial ×
RV Trip Planning Discussions

Go Back   iRV2 Forums > RV SYSTEMS AND TECHNOLOGIES FORUMS > RV Systems & Appliances
Click Here to Login
Join iRV2 Today

Mission Statement: Supporting thoughtful exchange of knowledge, values and experience among RV enthusiasts.
Reply
  This discussion is proudly sponsored by:
Please support our sponsors and let them know you heard about their products on iRV2
 
Thread Tools Search this Thread Display Modes
 
Old 09-17-2020, 07:19 PM   #1
Senior Member
 
Vintage RV Owners Club
Join Date: Feb 2020
Posts: 142
Carburetors! What do you know about them?

I have a 454 on my 86 Winnebago and I really want to understand this carburetor. https://images.app.goo.gl/9JPGFMKeFZR2eL438 It looks identical to this. My question is with a mechanical fuel pump is it suppose to squirt gas every time I push the pedal even with out starting it or will I eventually dry out the fuel pump and result in no gas squirting into the carb.
Chieftain27 is offline   Reply With Quote
Join the #1 RV Forum Today - It's Totally Free!

iRV2.com RV Community - Are you about to start a new improvement on your RV or need some help with some maintenance? Do you need advice on what products to buy? Or maybe you can give others some advice? No matter where you fit in you'll find that iRV2 is a great community to join. Best of all it's totally FREE!

You are currently viewing our boards as a guest so you have limited access to our community. Please take the time to register and you will gain a lot of great new features including; the ability to participate in discussions, network with other RV owners, see fewer ads, upload photographs, create an RV blog, send private messages and so much, much more!

Old 09-17-2020, 07:24 PM   #2
Senior Member
 
Old-Biscuit's Avatar
 
Join Date: Nov 2015
Posts: 26,692
Mechanical fuel pump ONLY pumps when engine is running

Example of mechanical fuel pump ---cut way view
__________________
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
Old-Biscuit is offline   Reply With Quote
Old 09-17-2020, 07:31 PM   #3
Senior Member
 
Join Date: Jun 2016
Location: Omaha, Ne
Posts: 427
Quote:
Originally Posted by Chieftain27 View Post
I have a 454 on my 86 Winnebago and I really want to understand this carburetor. https://images.app.goo.gl/9JPGFMKeFZR2eL438 It looks identical to this. My question is with a mechanical fuel pump is it suppose to squirt gas every time I push the pedal even with out starting it or will I eventually dry out the fuel pump and result in no gas squirting into the carb.



Yes your carburetor will pump gas into the manifold every time you step on the pedal when the vehicle is not running, it pumps the gas out of the float bowl, once your float bowl gets low or empty it will stop until you turn the engine over and the fuel pump pumps more gas into the float bowl. The accelerator pump on the carb is what does this.
__________________
Curt
2015 Wildcat 295RSX
2014 Ram 3500 CCLB 6.7 cummins
wildcatter is offline   Reply With Quote
Old 09-17-2020, 07:33 PM   #4
Senior Member
 
fletch460's Avatar
 
Join Date: Sep 2010
Location: Groves,TX
Posts: 546
Yes, you will see gas when you press the pedal. Gas will squirt as lkong as fuel is in carb. when it gets low in carb, it wont. When you start the engine the pump will refill bowl in carb.
__________________
2004 Allegro Bay 37' W/8.1
fletch460 is offline   Reply With Quote
Old 09-17-2020, 07:39 PM   #5
Senior Member
 
Ljwt330's Avatar
 
Join Date: Jan 2018
Location: Capistrano Beach, California
Posts: 4,465
I believe you mean the accelerator pump on the carburetor, correct? If so, the carb has a fuel bowl that is filled with gasoline by the fuel pump. When the engine is running, fuel is continually pumped into the carb bowl to keep it filled to the proper level. There is a float and needle valve at the carb inlet that shuts off fuel into the carb even if the pump is still active.

Engine off, the carb accelerator pump will still shoot fuel down the carb throat if it is repeatedly depressed. Eventually, the carb bowl will be empty until the fuel pump is restarted and refills the bowl.
__________________
Larry, Eileen, and Finley
2004 Alpine 36FDDS
Third motor home, first Alpine, no need for another.
Ljwt330 is offline   Reply With Quote
Old 09-17-2020, 07:43 PM   #6
NXR
Senior Member
 
NXR's Avatar
 
Join Date: Mar 2019
Posts: 5,653
Wow, I used to rebuild Rochester four-barrel carburetors back in the '80s. I could buy parts and replacement jets at any good auto parts store.

This link may be of value: https://www.gmcmi.com/wp-content/upl...ice-Manual.pdf

From the responses above, so have other people.

HTH,

Ray
__________________
2020 Forest River Georgetown GT5 34H5
2020 Equinox Premier AWD 2.0L/9-speed
NXR is offline   Reply With Quote
Old 09-17-2020, 07:53 PM   #7
Senior Member
 
Old-Biscuit's Avatar
 
Join Date: Nov 2015
Posts: 26,692
It takes only a few squirts to empty that Quad carbs fuel bowl

The fuel chamber is relatively small in volume to reduce
fuel evaporation during hot engine "shutdown".

So w/o engine running/cranking just a few squirts available
__________________
I took my Medication today. HAVE YOU?
Dodge 3500 w/Tractor Motor
US NAVY---USS Decatur DDG-31
Old-Biscuit is offline   Reply With Quote
Old 09-18-2020, 12:16 PM   #8
Senior Member


 
Join Date: Feb 2020
Location: NY State
Posts: 3,089
Quote:
Originally Posted by Chieftain27 View Post
I have a 454 on my 86 Winnebago and I really want to understand this carburetor. https://images.app.goo.gl/9JPGFMKeFZR2eL438 It looks identical to this. My question is with a mechanical fuel pump is it suppose to squirt gas every time I push the pedal even with out starting it or will I eventually dry out the fuel pump and result in no gas squirting into the carb.
Gasoline has mass, and therefore it has inertia. When the throttle opens suddenly, it takes time for the gas to accelerate through the internal passages in the carb and the metering jets into the venturi to provide enough fuel to match the airflow. This leans the mixture. The accelerator pump squirts gas directly into the venturi to make up for this shortfall. It's actuated by downward pedal motion. The farther you press the pedal down, the more the throttle plates open, and the more gas the accelerator pump delivers, up to the point where the pedal is on the floor or you stop pushing it farther toward the floor.

The accelerator pump is a piston-based pump with check valves. Because it's mechanical. it relies only on fuel that's in the float bowl, as others have posted.

A secondary function is to provide some priming for cold starts. If you overdo it, though, the engine gets enough gas to wet the spark plugs, usually called "flooding" the engine. Your owner's manual should have cold start instructions.
__________________
John
1976 Southwind 28', '96 Winnie 34WK,
2006 Tiffin Allegro Bus 40QDP
n2zon is offline   Reply With Quote
Old 09-18-2020, 03:12 PM   #9
Senior Member
 
Join Date: Aug 2017
Posts: 2,093
The accelerator pump on the carburetor will squirt gas into the engine when the pedal is pressed even with the engine not running if there is gas in the float bowl.

Your engine may have a mechanical fuel pump mounted on it to supply gas from the gas tank to fill the float bowls in the carburetor .

You could have an electric fuel pump in the tank or along the frame rails to supply gas to the carburetor , or a combination of electric and mechanical pumps.
__________________
1993 Tiffin Allegro Bay 32'
Soppy is offline   Reply With Quote
Old 09-18-2020, 03:49 PM   #10
NXR
Senior Member
 
NXR's Avatar
 
Join Date: Mar 2019
Posts: 5,653
Quote:
Originally Posted by Soppy View Post
The accelerator pump on the carburetor will squirt gas into the engine when the pedal is pressed even with the engine not running if there is gas in the float bowl.
Right. Its purpose is to immediately make fuel available if needed rather than waiting on the fuel pump to catch up so there's no lag between stepping on the gas and moving.

Wow, that memory really came out of the cobwebs.

Ray
__________________
2020 Forest River Georgetown GT5 34H5
2020 Equinox Premier AWD 2.0L/9-speed
NXR is offline   Reply With Quote
Old 09-29-2020, 05:34 AM   #11
Senior Member
 
Vintage RV Owners Club
Join Date: Feb 2020
Posts: 142
Quote:
Originally Posted by NXR View Post
Wow, I used to rebuild Rochester four-barrel carburetors back in the '80s. I could buy parts and replacement jets at any good auto parts store.

This link may be of value: https://www.gmcmi.com/wp-content/upl...ice-Manual.pdf

From the responses above, so have other people.

HTH,

Ray
I’m trying to locate my air fuel mixture screws and cannot locate them. Ive adjusted the idle and choke but can’t find the air fuel screws.
Chieftain27 is offline   Reply With Quote
Old 09-29-2020, 05:56 AM   #12
Senior Member
 
Join Date: Jul 2014
Posts: 35,349
Air fuel mixture screws may be sealed behind round lead plugs. Look for them.

You can turn a sheet metal screw into the lead and then pull the plugs out.
twinboat is online now   Reply With Quote
Old 09-29-2020, 07:24 AM   #13
Senior Member
 
Join Date: Jul 2015
Location: Watertown NY USA
Posts: 6,446
Quote:
Originally Posted by twinboat View Post
Air fuel mixture screws may be sealed behind round lead plugs. Look for them.

You can turn a sheet metal screw into the lead and then pull the plugs out.

Most of the Q-Jet carbs which had sealed mixture screws had hardened steel plugs blocking access to the screws. (Tamper proof) (We used to call them "God's Metal") I still have the tools including a small hole saw to cut the base of the carb to get the plugs out. I believe they were made by a company called "Tomco".
With the base turned over you will see two dimples in the base next to where the screws are located. Using the dimples as a guide you can cut into the base with a hacksaw and knock a chunk of the base out to expose the idle mixture screws. Also some of these screws on later models had a head on them which required a special socket to turn the screws.
If you do gain access to the screws I highly recommend you turn the screws IN while counting the number of turns and record it when the screws are seated. Then remove the screws if you are going to clean the carb.
When you reassemble the carb turn the screws in until they are seated then back them out the number of turns you previously recorded. Fine tuning for best idle quality can be adjusted from there. Usually you will be backing the screws out some to richen the air / fuel ratio. Most Q-Jets were adjusted lean from the factory to meet emission standards. Back in the day we often used a tachometer and a vacuum gauge to adjust the Q-Jet idle screws.
Lynn
__________________
2002 Fleetwood Storm 30H on Workhorse P32 chassis 8.1 gas.
LETMGROW is offline   Reply With Quote
Old 09-29-2020, 09:19 AM   #14
Senior Member
 
Join Date: Jan 2020
Posts: 285
The way we adjusted the old Quadrajets was to take them off and put a Holley in their place.

They have retro fuel injection now.

Ethanol fuel doesn’t play well with carburetors. Especially if it sits for any time between use.
TMyers17 is offline   Reply With Quote
Reply



Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Would it be rude to tell them to turn them off ? Bug512 Just Conversation 54 09-30-2015 11:49 AM
You KNOW to store batteries where you can check them periodically, don't you? JohnBoyToo iRV2.com General Discussion 2 08-17-2015 04:24 PM
Altitude Compensating Carburetors Possum Vintage RV's 27 07-11-2012 01:03 AM
You don’t know what you don’t know! 62_inrightlane Class A Motorhome Discussions 12 03-19-2012 06:21 AM

» Featured Campgrounds

Reviews provided by


All times are GMT -6. The time now is 07:58 AM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.