69 Holley Tri-Power Carb Questions

[Stuart F.]

My son recently purchased a new set of tri-power carbs for his 69 L-89 for the sake of having proper numbered carbs for possible judging (the ones I rebuilt for him were operating perfectly fine, just for the record). Now we have these new ones to sort out. It seems that these new Holley's are assembled by people who just jumped off their Donkey's or Water Buffalo's (I'm married to a former water buffalo driver so I can say that). I see at least a couple days doing bench fixes before we can ever install them, to say nothing about sorting them out in operation.

I wonder if anyone else has made such a purchase and then tried to install them themselves.

The first problem we ran into today was the simple little vent valve mechanism atop the float housing. Compared to his current center carb (a replacement as noted by it's 4 digit number instead of 3 digits on new), the actual valve rubber is much larger in diameter. When assembled to the rod and return spring mechanism, there is no way the rubber would ever seat over the vent hole in the bowel. There is no way to bend the rod to bring this about, and we didn't expect to bend it for an adjustment until after we had the idle speeds all set (high and full warm) and the end carb throttle return linkage adjusted, etc. The only way we could see around this is to raise the air vent rod clamp at least 1/16'' of an inch. What ever spacer we'd use would have to fit under the full clamp including the rod because the clamp is open (U shaped) under it to position over the rod.

Well, that's just the beginning. Just another reason to add to many others as to why I hate Holleys.

Any thoughts?

Stu Fox

[Timothy B.]

Re: 69 Holley Tri-Power Carb Questions

Hi Stu,

That's the hot idle compensator and it's to vent fuel vapor to atmosphere instead of through the main vent located inside the air cleaner area, that would cause the idle to become rich and slow. Can you use the old rubber seal and rod assembly?

[Stuart F.]

Re: 69 Holley Tri-Power Carb Questions

Tim;

Thanks for the response. Using the old vent valve and linkage may be what we end up doing if all else fails. My son still wants to find a new home (sell) the old replacement set of carbs to somewhat offset his investment expense in the new ones and to please his accountant (wife) so we're trying to find a way to make them both work. We were also not able to get the self locking nut off the center carb pivot for the linkage that is used to provide a safety closing of the end carbs so he ordered a new linkage kit for it which was reasonably priced.

Thanks again. Enjoy your spring and summer.

Stu Fox

[Stuart F.]

Re: 69 Holley Tri-Power Carb Questions

Spent a few hours this morning adjusting the vent valve of my son's new tri-power center carburetor. I worked on it on the bench as if I had to do it on the car I wouldn't walk for a few days. I had the linkage on and off at least 20 times using a padded vice to bend both the valve rubber seat end and the throttle linkage end w/o damaging it's new appearance. I finally got it to work perfectly using an initial throttle setting matching the settings of the old rebuilt carb off the car. I don't know who Holley has put these carbs together, but they are obviously w/o a clue as to what they are working on or what it's supposed to do. As a result, I don't have much confidence in how they will operate on the car. Holley does not provide any written instructions with the carbs so we'll have to research our old materials (can do) and draw on our recent experience with the ones I rebuilt and sorted out on the car. Now all I need is a level driveway (I hate these things!).

P.S. Tim; I can't quite see how this vent valve could be called a hot idle compensator. Any air in would be in the float chamber, not below the butterfly's.

Stu Fox

[Timothy B.]

Re: 69 Holley Tri-Power Carb Questions

Stu,

The hot idle compensator vents out to atmosphere the hot fuel vapor from high temperature evaporation. If the primary float bowl used the main vent that is located inside the air cleaner restarts could be difficult like a flooded engine because the only place for fuel vapors to go would be out the tube and drawn down inside the carburetor.

Have you ever seen how these bowls get fuel stained around that hole? I believe that is the remains of fuel vapor so I bet they help. Most aftermarket Holley's don't have them, it's probably spec'd by the OEM's.

[Stuart F.]

Re: 69 Holley Tri-Power Carb Questions

Tim;

Perhaps we are speaking apples and oranges. My understanding of what constitutes a Hot Idle Compensator (based on my limited understanding of the Carter AFB's) is a means to bleed in additional air below the throttle butterflies to increase idle speed under super heated conditions. Typically, the ones used on the AFB's are located in the secondary section and use a bimetallic spring which lifts a valve off it's seat to admit air into a chamber leading to a vacuum channel in the base of the carburetor below the throttle butterflies. Now, our 63's with Model 3461s AFB's also have what are commonly referred to as Vapor Vents (unique to the 3461s and maybe the 62 equivalent) which are small holes through the carburetor body that lead from the outside of the body to small ports situated immediately above each of the four butterflies. These are similar and perform the same function as slots cut in base-to-center section gaskets of certain model Rochester two barrel carbs. Their purpose was to vent fuel vapors from the throttle bores immediately above the butterflies to improve hot re-starts. I believe the Vapor Vent valves on the Holley's are there for this same purpose. As I recall, immediately below that vent opening in the Holley float chamber, is a screwy looking brass baffle which may be designed to preclude liquid gas splashing through the vent. I may be wrong on this, but am not about to re-open one of the beasts to prove it.

The center carb on my son's 69 L-89 tri-power has such a Vent Valve, but I believe the 67 version of this setup does not (perhaps other years and/or different engines are so equipped).

Stu Fox

[Timothy B.]

Re: 69 Holley Tri-Power Carb Questions

Hi Stu,

I thing it's Holley's version of the same thing only a different way to go about it.

[Steve G.]

Re: 69 Holley Tri-Power Carb Questions

They are two different ways of dealing with the same issue, fuel vapour out the vent in the throat.

Ideally, the bowl should always be vented to the throat only. The idea is that the air pressure in the throat is always the same as what's pushing down on the fuel in the bowl. This helps to offset the affects of a restricted air filter. When the air pressure in the throat is reduced by the restriction so is the air pressure pushing down on the fuel in the bowl. They will tend to not run as rich with the air cleaner restricted. There may be other influences beside restricted air cleaners, but that as I recall was the major one.

The AFB's and I think Q-jets, among others opt to keep the benefit of the throat vent. Instead of venting off the vapour they let the vapour enter the airway and add extra air to balance off the rich mixture . Everything remains under the air cleaner and in the throat.

The Holley chooses to forgo the throat venting benefits at idle and let the vapour escape to atmosphere rather than go down the throat.

A third option is similar to the Holley solution, but more controlled where the external venting is controlled by a bi-metalic spring so that it only vents to atmosphere when it needs to, not just anytime it's at idle. If I remeber correctly Thermoquads used that.

Steve

[Wayne M.]

Re: 69 Holley Tri-Power Carb Questions

Stu -- Here's the hot idle vent on my late '69 tri-power set-up ... 3940929 LIST 4055-1, dated 981. Had the same problem (the rubber seal/seat [tit]) broke off the arm).

L68 4sp late 69.jpg

[Stuart F.]

Re: 69 Holley Tri-Power Carb Questions

Wayne;

Yours looks like the larger diameter rubber valve that I've seen. My son's original replacement center carb had a much smaller valve rubber that was easier to adjust so that it fit flat to the housing when closed (throttle open). His new center carb has the same larger diameter valve like yours. To get that to close flat I had to bend down the very end of the rod that holds the rubber (the portion of the rod that is flat) and only that portion. I thought I would have to raise the rod itself off the housing using a spacer. I tried that, but it was not possible to keep it lined up and held in place just with the one small screw. Once I got that to seat flat, then I had to spend additional time and effort to get the linkage to engage the throttle end of the rod enough to lift the rubber off the housing to permit entry of air (or release of vapor).

Note:My criteria was to manage this adjustment without leaving any nicks, scratches, or scrapes on the the rod or the hold down clamp, and to NOT damage the rubber. On that point, I decided early on NOT to try and remove the rubber from he rod. I'd sprayed it with silicone spray and tried to pop the teat out of the rod, but it was not inclined to come out easy so I quickly dropped the idea.

Stu Fox

[Stuart F.]

Re: 69 Holley Tri-Power Carb Questions

Well, finally got it running again. Words to the wise:

1) Check all fuel bowl screws for tightness EVEN ON NEW CARBS!!

2) You can not tighten the fuel lines too tight EVEN ON NEW CARBS!!

I spent so much time adjusting the vent valve with the center carb on the bench and didn't think the assemblers could also leave one bowl screw finger tight on a NEW CARB. We used new steel fuel lines assembled on the old carbs a while back, which is not easy, then changed them to the new carbs and tightened them what we thought was tight. However, the new carbs use a different type of body fitting (that holds the filter in the bowl) and when we cranked the engine to prime the carbs, each fitting leaked badly. We really had to "torque" them down tight which you'd never expect of flared fittings like these.

All's well that ends well though. The new carbs solved several problems and sure look a whole lot better, besides being correctly dated and numbered.

Stu Fox