1967 427 Holley 2300C Carburetor issue?

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

I think I've solved the problems. Yesterday I reinstalled all 3 after cleaning. Much better. However still a bit of a stumble. Partly due IMO to not at normalized engine temperature, only up to about 120* F, but after more research, reading my Holley books and reviewing suggestions, I removed the accelerator pump nozzle this morning and did some measurements and comparisons to the original one I have here. Both are stamped "21".

The new one's holes are less than 0.021", maybe 0.018-0.019". The old one is 0.021" or a tad more for sure. It looks like someone opened it up when I see it magnified.

I just installed the original that measures 0.021", stumble is almost totally gone. I just spoke to my carb restorer and Holley test consultant and he said I could open up the new one to up to 0.025" and it'd be ideal. I'm going to take his advice.

I must say I've become a bit smarter after diagnosing these problem. My Holley comfort level has dramatically increased.

Rich

[Ken A.]

Re: 1967 427 Holley 2300C Carburetor issue?

Stock OE was .028, .035 is ideal. By the way, those are the wrong squirters-you want the "tube" type.

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Stock OE was .028, .035 is ideal. By the way, those are the wrong squirters-you want the "tube" type.

Thanks Ken, Gone all day and just got back on the wire.

Yes I know we talked about that but I'm going to take baby steps to 0.025" before I go all-in. Since it's a easy thing to drill out I can do that at a later time after the car is more complete with it's cooling system.

Here's the clip from this morning before I took off for the afternoon.....

https://youtu.be/YhRC1fFlLno

Much better but ran out of time to make more changes.

Thanks,
Rich

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Update....

Friday I re-installed the nozzle after drilling out to 0.025". Ran it up. Much better flow but overall still something wrong.

I found more issues. As suspected, the secondary carburetors are a additional problem. Their throttle plates are not properly sealing in their bores. I can cause the engine to stall by covering the air horn on the rear carb. I took some airflow measurements to see the problem. Obviously, to me, this is why I still cannot get a good adjustment on the primary carb and why it's running too rich. Under higher RPM's the primary venturis are not atomizing properly. Airflow is being stolen by the secondaries.

Off they come again. I've been told by the experts that the throttle plates themselves may be defective causing them to not be contacting the bores properly.

I did a quick clip of my diagnosis.

More to come. I'm working with my vendor to help him help me and future replacement Holley users. I really don't know why these things end up in my lap but maybe it's just my destiny in life.

Rich

[Stuart F.]

Re: 1967 427 Holley 2300C Carburetor issue?

Rich;

What I've been told and have read; the front and rear carbs are supposed to idle some, but I never knew or was able to test the actual flow amount which you have done (and have the gauge with which to do it). I'm sure you know this as you have delved into Holley's lately far more than I would care to do. I don't remember ever having any problem with multiple carb progressive linkages on Rochesters or Carters, specially if I have made sure the butterfly's were lapped in properly. Holley is supposed to have a special idle circuit in the end carbs to prevent any bogging on tip in. Perhaps you can ask others to test their air flow on their tri carbs (if they are able) to compare with what you are getting (as shown in your video).

Stu Fox

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Stu, Part of my research, of which the available data is VERY limited, has told me that the early 2300 secondaries actually had a idle circuit and idle mixture screws.

From the 1967 CSM. The depiction of the secondary 2300 is not used on Corvette.
DSCN3041.jpgDSCN3042.jpgDSCN3043.jpg

I'm unsure which applications used those carburetors. These secondaries here do not have those adjustment features, by design.

This is how I understand it after my research and discussions with a few Holley rebuilders. At each bore there is a idle hole. That hole MUST be blocked from air above at idle. If I understand correctly, to prevent corrosion from non use, the carb will draw a minimal mixture at idle below the throttle plates when not vacuum activated. The throttle plates MUST remain closed. When throttle plates are closed no additional fuel enters the manifold. Those are closed, but because the plates are not sealing it is allowing them to attempt to draw a fuel/air mixture into the manifold. This is also evident by observation that there is much unspent fuel puddling in the manifold inlet passages, particularly at the front of the manifold which may be tilted forward somewhat.

I'm going to remove the rear carb and inspect again. I have another earlier replacement 2300 secondary here, actually two, and may try one for a comparison. I agree that it would be good to get others to compare to, however without knowing the condition of their carburetors and entire fuel system, it may be still a unknown.

Rich

[Timothy B.]

Re: 1967 427 Holley 2300C Carburetor issue?

Rich,

Is there a throttle blade stop screw on the passenger side of the end carburetors like on the four barrel. Does the engine idle down to a slow rpm and how far out are the emulsion screws on the center carburetor.

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Rich,

Is there a throttle blade stop screw on the passenger side of the end carburetors like on the four barrel. Does the engine idle down to a slow rpm and how far out are the emulsion screws on the center carburetor.

Timothy, No stop screws on the secondary carburetors. Nor emulsion screws. The engine idles down but spec is 750 RPM. IIRC I run out of idle screw adjustment at around 800-850. The Primary(center) carb emulsion screws are set to 1 1/2 turns out, adjusted in 1/4 turn increments leaner(in) with hardly no effect until near the stops. The right side emulsion screw still continued to have little effect on idle. I think I discovered why earlier.....

I removed the rear carburetor. This exhibited the high air input at idle as measured using my air flow test gauge. Upon closer examination using a brighter lamp, I see that the throttle plate on the right side was not sealing properly, and the left wasn't ideal as well.

Lights off in the shop and used a led lamp into the bore.
PA180001.jpgPA180002.jpg

As shown, light is still showing at the plates to bores, while holding the throttle shaft tight.
PA180004.jpgPA180005.jpgPA180006.jpg

I disassembled the base from the body. I found a Holley document to verify my procedure which is a guide to replace and adjust new throttle plates. I used it as reference for the process. I filed the edges of the screw tips slightly to allow removal. Using a #1 Phillips bit, I removed the plate screws.
PA180007.jpgPA180008.jpgPA180010.jpgPA180012.jpg
PA180013.jpgPA180014.jpgPA180015.jpgPA180016.jpg

After spending over a hour or more trying to get a tighter plate to bore fit, I got it better than it was, but not a perfect seal. The Right plate cannot be sealed tight. The left appears fine. So I swapped the R & L plates and tried again. Similar results. I took some caliper measurements of the bore on the right side and I'm seeing a variation. I'm not sure if it's designed that way or not. I will have to call and check in the morning, and try to discover a tolerance spec for the plates and the bores.

Rich

[Timothy B.]

Re: 1967 427 Holley 2300C Carburetor issue?

Rich,

Bottom line is you should be able to fine tune idle A/F with the emulsion screws on the center carburetor so it's getting fuel somewhere.

Does the primary carburetor close down to almost close off the transfer slot, that's where you want it almost out of sight. Are there little dribble holes in the secondary carburetors .022 +- below the transfer slots.

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Rich,

Bottom line is you should be able to fine tune idle A/F with the emulsion screws on the center carburetor so it's getting fuel somewhere.

Does the primary carburetor close down to almost close off the transfer slot, that's where you want it almost out of sight. Are there little dribble holes in the secondary carburetors .022 +- below the transfer slots.

Yes the emulsion screw adjustment is changing idle quality. If I get near closed on each side I loose vacuum reading and smooth idle. I get best around 3/4 to 1 turn out, but the right side isn't as crisp of a change as the left. Again, I feel that the F & R poor quality throttle plate sealing are causing much of my trouble. As shown above, the rear "right" bore and plate are not optimum.

Yes the secondary has both the idle hole(dribble hole) as well as a transfer slot. I may be wrong, but the slot is not used as there's no low-to-high speed changeover circuit in the secondary. The throttle plates, at rest in their bores, sit below the slot at all times until activated.

It all just seems so simple after the fact. I can't get a good Primary carb adjustment because basically I have vacuum leaks........i.e. The 2 Secondaries are stealing air from the Primary because they're just not shutting OFF completely.

Yesterday I read my 2 well aged but NOS looking Holley books cover to cover again for clues to the 2300/3660 Secondary operations details and specs. Not much in there.Operation is basically the same as the back side of a 4150, so most of that same information applies.

Rich

edit.....Attached is the Holley document regarding throttle plate replacement for future reference.

[Peter M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Hi Rich,
This may be a dumb question, but have you considered making two block off plates and removing the end carbs. Then evaluate the center carb. If satisfactory install one of the end carbs and evaluate and then the other end carb. I know you will figure it out.
Kind Regards,
Pete

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Hi Pete, That's actually a great question and I had not thought of that.

I do have 2 other 2300's here I may try, but your idea is a very good alternative. Makes sense as the secondaries will never get activated in my test environment anyways, only under load when driving. Which is a bit of time away.

Thanks,
Rich

[Peter M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Hi Rich,
For what it's worth I think those throttle blades should seal tight in the throttle body when closed.
Kind Regards,
Pete

[Richard M.]

Re: 1967 427 Holley 2300C Carburetor issue?

Hi Rich,
For what it's worth I think those throttle blades should seal tight in the throttle body when closed.
Kind Regards,
Pete

Pete, yes absolutely, and that's what I've been fighting with since last night and for quite a while today. I get one set, but the other won't give a tight seal no matter what. I'v been at it for hours already today. I think I've reached then end of any possibility that these will work, as I feel the plates and the bores are the problem, or both. Also, there is so much play in the throttle shafts to the bores that it makes it worse. Original carbs have similar shaft play, but add that to, IMO, defective parts and I think I'm fighting a losing battle.

I just finished setting the plates the best I can and will try one more time on the engine.


Rich

[Stuart F.]

Re: 1967 427 Holley 2300C Carburetor issue?

Rich;

Back in the day, I always did a hand lapping of the throttle blades using oil and light sand paper on the high spots - similar to the way you are doing it using a light - as part of my process of "blue printing" dual WCFB Carters for racing. I would remove the vacuum butterfly's from the secondary and actually increase the secondary rat trap throttle return spring tension with one more turn. The end product was a base that had positive sealing throttle blades, but you could just snap the primary throttle arm and get quick positive opening and closing of the secondary's. It took a lot of time and patience, but was well worth the $150. I charged to do a set (good money back in the late 50's).

Stu Fox