Return to the home page...

Go Back   Moyer Marine Atomic 4 Community - Home of the Afourians > Discussion Topics > Fuel System

Reply
 
Thread Tools Display Modes
  #1   IP: 64.203.32.52
Old 12-27-2008, 01:27 PM
Dave Neptune Dave Neptune is online now
Afourian MVP, Professor Emeritus
 
Join Date: Jan 2007
Location: Grove, Oklahoma
Posts: 5,035
Thanks: 711
Thanked 1,289 Times in 839 Posts
Cool Carburator parts

Good mornin' fellow A-4 opperators and mechanics. I have been working on fuel consumption on my A-4 and have deciced to take a different tack. I am changing the main jet rather than using an adjustable one. I feel that if it is running right it is right. I have played around by changing the orifice diameters since I have access to a machine shop and a vast array of reamers. I have filled the jets and re-reamed to a smaller diameter with a good deal of success. I finally reached a point where I was loosing throttle responce and a few RPM (@.038") by going leaner (4 steps). I decided to contact Zenith and see about ordering foctory jets of a smaller diameter which they stock for the late model carb. I ordered the next two sizes down and the stock jet (#'s 21, 20 & 19). I now have the time to play with them during the holidays as my shop is closed. When I recieved the parts and the jets numbers were the same however the jet was a little shorter in length about an 3/16 of an inch, the actual metering orifice is inside the threaded area not the extended nose. My question is has anyone out there used the shorter jets or did I get the wrong ones? The threads are the same and I don't see any reason that they would not feed the emulsion well passage any differently.
By the way my A-4 was frozen tight when I bought the boat 22 years ago. I pulled the head cleaned the water passages and did a valve job as one had a rusted groove in it. I used a "dead blow" hammer and a soft piece of pinewood to knock the pistons loose and have been running ever since as a raw water cooled boat in southern California. When I got the motor running the compression was 55 to 70 psi and last year checked at 90 - 100 psi. Truely a durable motor!!!!!!!!!

Thanx Dave Neptune
Volador 1970 E35-MkII
Reply With Quote
  #2   IP: 142.68.109.160
Old 12-27-2008, 05:17 PM
rigspelt's Avatar
rigspelt rigspelt is offline
Afourian MVP
 
Join Date: May 2008
Posts: 1,187
Thanks: 0
Thanked 19 Times in 17 Posts
Quote:
Originally Posted by Dave Neptune View Post
I decided to contact Zenith and see about ordering foctory jets of a smaller diameter which they stock for the late model carb. I ordered the next two sizes down and the stock jet (#'s 21, 20 & 19). I now have the time to play with them during the holidays as my shop is closed. When I recieved the parts and the jets numbers were the same however the jet was a little shorter in length about an 3/16 of an inch, the actual metering orifice is inside the threaded area not the extended nose. My question is has anyone out there used the shorter jets or did I get the wrong ones? The threads are the same and I don't see any reason that they would not feed the emulsion well passage any differently.
I just started taking my carb apart to refit it (my first carb rebuild). Old carb and new-to-me boat, so I want to start fresh. I took out the main jet just now: it is stamped #24 and is longer than the main jet in the MMI kit, which is stamped #21. I gather from Don's notes that the extension on the longer #24 main jet is not an issue, however I understand also that if I replace the old #24 with the new #21, then I had best change all the other jets and nozzles to the current specs too, except the idle jet if removing it could lead to damage.

Here is a picture I just took of the two main jets, the new one in the MMI rebuild kit (21), and the one in my carb (24).
Attached Images
 
__________________
1974 C&C 27

Last edited by rigspelt; 12-29-2008 at 04:32 PM. Reason: longer not shorter
Reply With Quote
  #3   IP: 64.203.32.52
Old 12-27-2008, 08:08 PM
Dave Neptune Dave Neptune is online now
Afourian MVP, Professor Emeritus
 
Join Date: Jan 2007
Location: Grove, Oklahoma
Posts: 5,035
Thanks: 711
Thanked 1,289 Times in 839 Posts
Thumbs up Jets

Thanx for the heads-up! I think that the longer jets were to accomodate an adjusting needle. According to the people I spoke with at Zenith they did not install anything but the #21 jet in the A-4's with the fixed jet for marine use. They used a #24 and a #22 in the early style with the adjustable jet. All of the fixed jet carburators were shipped with the #21. If you are using a #24 you are 3 steps rich. Someone befor you may have changed it or removed the adjusting needle assembly and added a plug. I have seen this on a few early carbs I have done for others. Have you had any fouling problems?

They used a few different "well-vent jets" over the years however they varied with the positions of the discharge holes just above the butterfly valve. They also stated that there is only one "emulsion tube" available and is the only one they installed in these carburators early or late models. I was told by an old A-4 mechanic I have known for many years that he would install a #20 in any A-4 carb if people were confused by the adjustable jet or complained about fuel usage. He said that the smaller jet worked better as we tend to "LUG" these engines due to the availability of usable props. I have used many props over the years and couldn't achieve a comfortable cruising speed at or nera 2000rpm. This would be consistant with the findings of most contributors on this site.

I installed an Indigo prop at the start of last season and am in the process of fine tuning the carburator set up. It really made a big differance in overall performance especially in reverse.
Just an FYI for those interested. The jets for these carburators are base on metric diameters. IE #24 =1.4mm----#21= 1.1mm-----#20=1.0mm --#19=.9mm and so-on. These numbers are good according to my measuring capabilities. I rebuilt some jets in my shop and tried them with a great deal of success, now I want to install a standard jet at or near what I have been using so I can recomend a standard part number. I can control the diameter of the jet just fine, it is the length of the orifice that I can not control which adds "DRAG" to the flowing fuel influencing the mix slightly. IE my .9mm may flow more or less than the factory #19 (.9mm) jet with a fixed length. I have been recording my performance changes by measuring manifold preassure versus RPM with a Vacuum gage as a fixed base. U-know the like the old farm tractor days to set the load on the motor.

David
Reply With Quote
  #4   IP: 142.68.109.160
Old 12-27-2008, 08:54 PM
rigspelt's Avatar
rigspelt rigspelt is offline
Afourian MVP
 
Join Date: May 2008
Posts: 1,187
Thanks: 0
Thanked 19 Times in 17 Posts
Quote:
Originally Posted by Dave Neptune View Post
Have you had any fouling problems?
This old boat is "new" to me. I only know that the engine was running "OK" prior, and I ran up the engine prior to purchase, and then had a mechanic give it a check. The plugs looked OK when I bought the boat last spring, but I don't know how long they had been in. So I have no had experience with it under load and longer runs. I am glad, however, that I went ahead with this carb job. Don's notes compendium and manual are full of tidbits about the Zenith carbs used in the A4s - he did a lot of research, and a Zenith engineer dug up the history for him. You are adding a lot of interesting insight now too.

Update: Got all the old jets and nozzles replaced with MMI's rebuild kit parts. Easier than I thought it would be, thanks to Don's notes and the helpful photos at http://home.earthlink.net/~ultratom/...rb_rebuild.htm.
__________________
1974 C&C 27

Last edited by rigspelt; 12-28-2008 at 09:51 AM. Reason: Update
Reply With Quote
  #5   IP: 192.60.230.88
Old 12-29-2008, 10:25 AM
High Hopes's Avatar
High Hopes High Hopes is offline
Afourian MVP
 
Join Date: Feb 2008
Location: Fairfax, VA
Posts: 530
Thanks: 0
Thanked 1 Time in 1 Post
Quote:
According to the people I spoke with at Zenith they did not install anything but the #21 jet in the A-4's with the fixed jet for marine use. They used a #24 and a #22 in the early style with the adjustable jet. All of the fixed jet carburators were shipped with the #21.
Hmmm.... Something is amiss. My carb had a #24 jet as well.

That being said, Bob Hess's specs show the following.

1948 – 1968 Zenith 61-M2AE7:
main jet #24, Zenith C52-6-24 & adjustable needle assembly
idle jet #10, Zenith C55-6-10 (.019 in drill size)
well vent jet #22, Zenith C77-18-22 (.043 in drill size)
main discharge nozzle #50, Zenith C66-26-1-50

1969 – 1984 Zenith Bendix 68-7:
venturi #16
float needle & seat #25
main jet #21, Zenith C52-7-21 (.041 in drill size)
idle jet #12, Zenith C55-22-12 (.023 in drill size)
well vent jet #21, Zenith C77-18-21 (.041 in drill size)
main discharge nozzle #55, Zenith C66-114-4-55 (3 x .039 in drill size)
idle bleed hole, fixed plug (.039 in drill size)

Don identifies a #21 as well.

My Carb had already been rebuilt. Could it be that the rebuild kits were incorrectly packaged? My conclusion was that after a rebuild or two, with various jet replacements, the carburetor is pretty much guaranteed to be out of whack.

BTW, Don's adjustable kit works like a champ. Adjustment is easy and not critical. It cleaned up the carbon build up problem with the plugs. All I know for sure is that a #24 runs too rich in my configuration.

Steve
Attached Images
 

Last edited by High Hopes; 12-29-2008 at 11:17 AM. Reason: more info
Reply With Quote
  #6   IP: 192.60.230.88
Old 12-29-2008, 11:30 AM
High Hopes's Avatar
High Hopes High Hopes is offline
Afourian MVP
 
Join Date: Feb 2008
Location: Fairfax, VA
Posts: 530
Thanks: 0
Thanked 1 Time in 1 Post
Jim,

Is the June Bug your boat? I am dying for Spring to come. Now I watch sailing vids like those at the link to placate my sea-bound yearnings - or to torture myself. I am not sure which. I got my boat and A4 tidied up just in time to put them on the hard.

Steve
Reply With Quote
  #7   IP: 64.203.32.52
Old 12-29-2008, 01:56 PM
Dave Neptune Dave Neptune is online now
Afourian MVP, Professor Emeritus
 
Join Date: Jan 2007
Location: Grove, Oklahoma
Posts: 5,035
Thanks: 711
Thanked 1,289 Times in 839 Posts
Question Hmmm

Steve, over the many years the A-4 has been in use they used two basic carburators the 5 screw and the later four screw. The only time the #24 was used was in the Adjustable-jet configuration or the 5 screw carb. Many of the operators just didn't have the experience or the skills to properly adjust. These carbs were manufactured during a time when fuel was very inconsistant and not nearly as forgiving due to additives. Even the outboard motors of that time were all adjustable due to the deposits that could be found in the earlier fuels. The jets needed tweeking from time to time because the orifices would become contaminated from the fuels available. Most 4 cycle engines got away from the adjustable Hi-speed jets by the early fifties and the outboards by the mid fifties ( now most outboard's with carbs are even a fixed idle jet as well). Many of the early A-4's leaked a lot of fuel from the adjustable jet because of the lack of proper adjusting and maintenance causing a fire hazard! The coming of the fixed jet models was considered an improvement allowed by the improvement in the quality of the additives in the fuel. Many of the early models owner/operator/mechanics just plugged the old carbs and did not change out the jet. When you have the #24 without the needle they are deffinately to rich, but they tend to start much easier when cold, enter the spark plug controversy(going from the JC8 to the JC12's helped to resist fouling). When I did my first carb rebuild I reduced the #21 jet to .041" and continued using the J8 heat range plugs with no fouling. I have never had a fouled plug and have been operating like this for 22 plus years. I have been reading much of the fuel consumption experiences on this site and decided to try the adjustable jet. It worked well except when ever I would check there would be a drop of fuel on the assembly so I decided to go back to the fixed jets. I sent the jet back to Don and I think it had a faulty packing. Since that I have done a lot of research with my lil' A-4 by changing jets and recording fuel consumption. All of the work I had done went out the window when I installed the Indigo prop since it changed the operating RPM range so much. Previously I had used 5 different props and two of those at different pitches and diameters. Now that I have the Indigo I have tried 4 differet jet configurations (re sized jets---I own a carbide reamer mfg company) with varying results. Now that I have finally gone to lean I have decided to go to a Zenith jet (one over and one under what I am using) just so I can add the info to my files incase anyone wishes to do the same. Don has most helpful since I started the Indigo project and was a little surprised of some of my findings.

The trouble with most of the carburators out there is that so many have been rebuilt so many times over the years that who know's what was original and what was added incorrectly.

The Idle jet and the vent well jet you have listed are actually "Air correctors" which inject air (not fuel) into the Idle or Hi-speed passages to broaden or narrow the range of the fuel jet whether an adjustable or a fixed hi-speed jet, the idle jet is only adjustable and is the needle valve for the idle. Most important is to have the proper "Air corrector jet" for the model carburator in use. There were many different configurations of the two basic carbs offered.

I will check with Zenith again regarding the emulsion well since they told me only one was available--maybe they ment for the late model carb.

I may play around with the Hi-speed Air corrector in the near future to see if I can decrease the influence of the idle circuit above 1200/1400 rpm.

Just as a note I am using a PCV kit, electronic ignition and now the Indigo prop. The electronic ignition is one I adapted from my racing days, this one is photo-electric (lite-switch) and was made for a rotary (Mazda) operating at 11,000 rpm and should be sufficient. It has been working for about 22 years so far and outlived two coils.

Looking forward to your comments!

Thanx for the info Steve
Dave Neptune
Reply With Quote
  #8   IP: 142.68.109.160
Old 12-29-2008, 04:56 PM
rigspelt's Avatar
rigspelt rigspelt is offline
Afourian MVP
 
Join Date: May 2008
Posts: 1,187
Thanks: 0
Thanked 19 Times in 17 Posts
Quote:
Originally Posted by SteveMarkowski View Post
Hmmm.... Something is amiss. My carb had a #24 jet as well.
Very interesting. Glad now that I installed the new MMI rebuild kit, and that I was able to easily remove the old idle jet. Here are my numbers:
Fixed main jet was 24 now 21.
Idle jet was 2 or 12, now 12.
Main discharge nozzle was 45 now 55.
Well vent jet was 23 or 25, now 21.
Float valve seat was not numbered, now 25.

Some numbers were damaged by prior screwdrivers, but my guess that is all of mine were the same as your originals -- perhaps from the same rebuild kit in the past, with main jet 24 instead of 21.
__________________
1974 C&C 27
Reply With Quote
  #9   IP: 70.108.168.221
Old 12-29-2008, 06:12 PM
High Hopes's Avatar
High Hopes High Hopes is offline
Afourian MVP
 
Join Date: Feb 2008
Location: Fairfax, VA
Posts: 530
Thanks: 0
Thanked 1 Time in 1 Post
Hi Dave,

Thanks for the tutorial. It's nice to know we have an expert among us.

Quote:
The only time the #24 was used was in the Adjustable-jet configuration or the 5-screw carb.
Somehow, Rigsy and I got a #24 main jet on a 4 screw carb.

Quote:
When I did my first carb rebuild I reduced the #21 jet to .041" and continued using the J8 heat range plugs with no fouling. I have never had a fouled plug and have been operating like this for 22 plus years.
This is where I want to be. I am planning to switch back to the JC8's. The top of the head gets exceptionally hot compared to the rest of the engine.

Steve
Reply With Quote
Reply

Thread Tools
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

Forum Jump


All times are GMT -4. The time now is 09:02 PM.


Powered by vBulletin® Version 3.8.9
Copyright ©2000 - 2024, vBulletin Solutions, Inc.


Universal® is a registered trademark of Westerbeke Corporation

Copyright © 2004-2024 Moyer Marine Inc.

All Rights Reserved