Holley 770 Questions

[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

[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

Gave mine a shot of wd-40 last night before bed per your suggestion. Just got back from taking my son to a friends house and we took the Cobra the RPM's increasing on me is gone! They fall back down to idle as they should. Thanks for replying and helping me!

Originally Posted by Anthony

Like gaz64 stated, I think it’s a fast idle cam issue. As your carburetor looks spotless, I don’t think the fast idle cam is binding. Maybe the spring in the choke housing has changed over time? Anyways, I think the choke needs adjusted, as the fast idle cam is connected to the choke linkage.

Here’s how I do it. The engine has to be cold. Take the air cleaner off. On the passenger side of the engine, Loosen the 3 screws on the perimeter of the choke housing, That are clamping the adjustment plate tight. Grab the throttle linkage and manually open to full throttle, and the choke should spring into the closed position. While holding the throttle fully open, with a standard screwdriver, adjust/ twist the loosened choke adjustment plate to where you see the choke plate start to open. I usually adjust it so there’s about a 1/4” gap between the edge of the choke plate and the carburetor housing, so the choke is almost, but not completely closed. Let off the throttle, and tighten the 3 choke plate hold down screws. See if that helps.

Regarding the engine bogging, pull the distributor cap and check for corrosion

When I took off the air cleaner, I noticed that the butterfly was open. The car has not been started for about a week. When I started your procedure, it closed and was up just a touch. Should the butterfly be open like that when the car is turned off?

[cycleguy55]

Originally Posted by Mattsvtcobra

When I took off the air cleaner, I noticed that the butterfly was open. The car has not been started for about a week. When I started your procedure, it closed and was up just a touch. Should the butterfly be open like that when the car is turned off?

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 operating on the choke pull-off mechanism will pull the choke open to the set point. 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

[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.

[Dwight]

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

Kano Aerokroil Penetrating Oil

[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.