Holley 770 Questions

[Mattsvtcobra]

Originally Posted by cycleguy55

Yes, that's the way an automatic choke operates. It will be fully open from when it was last run - the heating element in the choke pulls it open. After it's shut off the bimetallic coil cools and applies spring tension to the choke mechanism. The first touch of throttle will release the spring tension and pull the choke plate closed tight. Once it's started engine vacuum will pull the choke open to the set point of the choke pull-off mechanism. After that the bimetallic coil will continue heating while the ignition is on, allowing the choke plate to open further and further until fully open. There's also an interaction with the fast idle cam to keep the idle speed higher until the engine is warmed up.

More here: https://forums.holley.com/entry.php?...rel-Carburetor

This article has good instructions on adjusting carbs. It shows a pull-off adjustment you won't find on Holley's official pages - it's the adjustment I used on mine to make it run properly.
https://www.chevelles.com/threads/ad...#post-11389045

Thank you greatly. I'll be checking these out tonight. Appreciate the info on why the flaps are open at shutdown.

[Dwight]

cyclegue55 said WD-40 is for cleaning. I agreed.

A better lubricant is Kroil - An industry proven penetrating oil that has no equal

Penetrating-Lubricating Oils

Lots of places sell it.

[Texasdoc]

I use a thin coat of white lithium grease on the base plate and arms.

[Mattsvtcobra]

Originally Posted by MaSnaka

Do you have a mechanical timing advance on the distributor?? MSD. I noticed my RPMs were hanging up while lifting my foot. I cleaned and lubed the exterior of the carb (AED) and it would still happen occasionally. I had an epiphany and thought what if the mechanical timing on my distributor was hanging up. That would increase RPMs. So I popped the cap, everything looked good but I gave it a shot of wd40 where the weights and springs move. Problem gone so far. BTW- I have no vacuum advance on the distributor.

Hope this helps...
John

So I thought I had it all worked out. 1st ride after some WD-40, the problem was gone and it drove as it should. 2nd ride, it was doing what it was doing before and bogging bad. I took the air cleaner off and repositioned it a bit because its always hit the top of the distrib (working on getting a small riser to get it off of there) as well as opened the cap and closed it and the car ran great on the 3rd run. But any ride after has been where the RPMs climb.

Say I buy lube and not just use WD-40, put the air cleaner on a riser... Is there something I'm missing here?

EDIT: Just got back from a quick ride and the RPM's are not falling or fall slowly. I've tested all throttle linkage while in the garage and everything seems free. While on the ride, I used my big toe and the one next to it to grab the side of the pedal and it seemed to make the RPMs come down like they should.

*The weird thing is that on the past 5 trips when it was running good or bad I noticed one thing. If I felt it was good and the RPMs fell quickly, the car would run really well and responsive with minimal low RPM bog. If I felt it was running not so well and the RPMs would hang, there would be quite a bit more bog at the lower 2k range when I floor it. The engine would run a little more rough it feels and is noticeable in the car. Also, the start up would be almost instant if it was going to run well, and it would take some cycles for it to fire up if it was going to have not a good of a run.*

[jhv48]

Sounds like you’ve isolated the problem in the advance mechanism. One way to test if the timing is hanging up is to hook up a timing light and watch the timing pointer after blipping the throttle. Should snap back to initial setting. If slow to return then the advance is hanging up somewhere.

[Mattsvtcobra]

Thanks Jim! I will check with a timing light. Also someone in the ignition section suggested that I may have too strong of springs on the weights in the distrib, so I need to look into that too.


Question. The car drove decently today and had some hang up/RPM climbing on me when pushing in the clutch, but every time that happened I could pull the throttle back up with my foot and the RPMs would instantly drop to idle. Any idea what could be getting hung up? I've traced every thing on the throttle cable and I have 2 springs that seem to snap back well. Is there something I need to look into lubing or replacing?

[Bobcat]

I think you`re backwards on your distributor springs .... too weak will not pull the weights back as quickly and the advance will not return to the base setting quickly . The stronger weights will pull the weights back quicker , but also change your advance curve .
Check the MSD spring curves for where the advance comes in with the various spring combos . If your idle is too high , then it may have the advance already starting to come in .
Personally , I think you need to put a light film of lithium base grease under the weights to free them up and help keep corrosion to a minimum .

[cycleguy55]

I'd be concerned about using ANY kind of lubricant that would attract or hold dirt, carbon particles, etc. Clean the advance weight pivot points and either leave them dry or sparingly apply something like a dry film lube. Powdered graphite could work - if it wasn't conductive. I have a spray lube that has PTFE (Teflon) in it - the carrier evaporates and leaves the PTFE behind. The one I have is by GUNK Liquid Wrench, but WD-40 makes it, as do B'Laster, 3-IN-ONE and probably every other maker of general purpose lubricants.

[MaSnaka]

Matt do you have a cable or linkage connecting the pedal to the carb?? When you say you lift the pedal and the RPM goes down sounds like there is a bind somewhere between the two. Then you say you can tell by start up whether it will run good or have the RPM hang up. Vac advance on the dist? Vac leak possible or bad diaphram?? The air cleaner should not be resting on the dist. I have the oval Cobra air cleaner and it clears my dist by about a 1/4" from the side but is nowhere near sitting on top. I have the FE motor which might make a difference. Does the air cleaner contact the choke horn?? Could cause air flow restriction on acceleration. Trying to think outside the box.

John

[Mattsvtcobra]

Originally Posted by MaSnaka

Matt do you have a cable or linkage connecting the pedal to the carb?? When you say you lift the pedal and the RPM goes down sounds like there is a bind somewhere between the two. Then you say you can tell by start up whether it will run good or have the RPM hang up. Vac advance on the dist? Vac leak possible or bad diaphram?? The air cleaner should not be resting on the dist. I have the oval Cobra air cleaner and it clears my dist by about a 1/4" from the side but is nowhere near sitting on top. I have the FE motor which might make a difference. Does the air cleaner contact the choke horn?? Could cause air flow restriction on acceleration. Trying to think outside the box.

John

Do you have a cable or linkage connecting the pedal to the carb?? When you say you lift the pedal and the RPM goes down sounds like there is a bind somewhere between the two.
--- It's weird, it seems to happen once the engine has warmed up. So something is changing when heat becomes a factor. That's why I wasn't sure if the carb had something that needed to be checked or lubed. Can a lubricant just be sprayed where I see levers moving and also down the throttle cable?

Then you say you can tell by start up whether it will run good or have the RPM hang up. Vac advance on the dist? Vac leak possible or bad diaphram??
---No vac advance

The air cleaner should not be resting on the dist. I have the oval Cobra air cleaner and it clears my dist by about a 1/4" from the side but is nowhere near sitting on top. I have the FE motor which might make a difference. Does the air cleaner contact the choke horn?? Could cause air flow restriction on acceleration.
---Mine does not clear. Not sure what you mean by the choke horn?


Trying to think outside the box.
--- I really appreciate it!

[MaSnaka]

Hi Matt,
I use the silicone spray and lube the external moving parts on the carb with it on occasion, really not very often.

Air cleaner and choke horn- choke horn is the shroud surrounding the choke plates on the top of the carb. Rises about 1 1/2" above the carb opening. Some air cleaners being low profile to fit under the cobra hood, the inside of the air cleaner top is either making contact with the choke horn or very close to it. This can restrict air flow into the carb as you approach wot when the engine is sucking in the most air.

Do you have a phenolic spacer between the carb and the intake manifold? This insulates the carb from heat which might be causing some deflection in your linkages. I have only heard of them being used to prevent the fuel from boiling in the carb but maybe.

John

[Mattsvtcobra]

First off... I want to say thank you to everyone on this post that gave ideas on what rabbit hole to go down. The car is back in order and I'm just getting around to post this update, but I'm not sure which of these fixed it. I tinkered with each area individually, but it wasn't until I tore everything apart at the same time... that any and all of these fixed it.

1) Just spraying wd-40 in the distributor seemed like it would temporarily work, but it was not until I took the springs out and removed the weights. You could not see the rust build up on the posts that the weights sit on or the rust in the little bushing that is on top of the weight.
- Sanded with super fine sand paper and put a very small amount of silicone spray.

2) I cleaned up the cap and rotor posts as well. Carbon build up on the posts, but not a lot.

3) Adjusted the auto choke and fast idle cam but did take it all apart to make sure that it was clean and freely moving.

4) The throttle shaft on the base plate had a small amount of wiggle to it. It seemed to be holding the throttle linkage up and wouldn't fully go back to starting position. This was a PITA to find, but glad I finally did. May eventually replace this part but for now it is working well. I sprayed some silicone on the main throttle shaft and at the next start up, the idle was very high then came back down. I was 100% sure I had a vac leak happening and would not of expected to look at this shaft potentially binding.

SO happy the RPM's don't climb on me anymore when driving! Back to having a fun and responsive throttle.

[Anthony]

Originally Posted by mattsvtcobra

first off... I want to say thank you to everyone on this post that gave ideas on what rabbit hole to go down. The car is back in order and i'm just getting around to post this update, but i'm not sure which of these fixed it.

------

so happy the rpm's don't climb on me anymore when driving! Back to having a fun and responsive throttle.

excellent !!!!!

[Dwight]

this is one of the best if not best solvents. WD40 is for cleaning not oiling

Kano Aerokroil Penetrating Oil

[Mattsvtcobra]

After much debate and a ton of research, I ended up scrapping the carb and going with a new one as at a min I needed a baseplate and a carb rebuild kit. Brent Lykins built a QuickFuel HR650 for me and it was instantly better. Off idle bog= gone and it is very snappy now!Wish I would of just done that at day 1.

[MaSnaka]

Excellent!!

[Mattsvtcobra]

Originally Posted by MaSnaka

Excellent!!

Yes! Glad I went that route.

So the car had a few good runs and 1 funky one. So in monkeying around, I found that the distributor was barely loose, and I mean barely. I think it was twisting here and there, but could never figure it out.

1) Reset timing and clamped her down good!
2) Put lighter springs on the weights and checked total timing
3) Messed with the 4 corner idle until I was able to get max vac. She didn't like that very much when I took it for a test drive. So I went home and bumped it up, but it is way too rich so I will mess with the air bleeds. Ran like a bat outta hell!


The car starts up immediately again and runs well Thanks for the suggestions!