Quick question on Holley secondary diaphragm check ball
 

Checking over everything on my Holley rebuild before putting it back on and suddenly dawned on me that I didn't see the check ball when I replaced the secondary vacuum diaphragm. So pulled the cover off and no check ball. Got to looking closely at the housing and I cannot pick up any trace of a relief groove in the check ball seat. This is the best photos I could get due to the recessed area and light.

http://i125.photobucket.com/albums/p...psd8xou9vz.jpg

If it originally had a check ball shouldn't the bleed groove be clearly identifiable? I may have lost it when I opened it up earlier but I sort of doubt it. Now I'm thinking it should not have one as the ball will seal the seat and prevent vacuum operation of the secondarys. It seems to have a very light spring from the original holley restoration about 25 years ago.

This is a 1969 service 3247 4150.

Thanks

Anyone know the answer.

A bit further away but more light in this photo.

http://i125.photobucket.com/albums/p...psfdakfmub.jpg

Check ball
 

Dan:

My April 1965 2818-1 did NOT have one. No groove in the seat either. The 65 supplement manual has an exploded view of the Holley -- NO check ball.

Exactly when the check ball & groove were added to dampen secondary action -- somebody like Greg T. would be able to answer.

Another difference with these early 2818s is the little baffle on the primary bowl. Just a bent piece of thin metal. Now THAT is a hard one to find if you need it!

Mike

I think your thinking is correct, no groove with the check ball and the servo will not get a vacuum signal. Just curious, does this Holley have the little brass tube that extends into the primary venturi air flow on the passenger side.

There is a little tube (I guess - it's hard to see the end) extending into the primary venture about 3/32 - 1/8 inch long. What's its significance?

I tried a vacuum test putting a check ball on the seat, a plastic cone vacuum fitting to a Mityvac on the carb side and my finger over the housing port above the ball. Pumping my vacuum gun on the carb side it did get vacuum past the ball I could tell as I pulled my finger away - but as to the metering it may be very little just past the casting finishes. Think I'll leave the ball out - I think I would have noticed it if there had been one in there. If I have a bog I'll no what needs to be done - put a check ball in or a heavier spring.

thanks.

I think the check ball was added in the early 90s, and your older vacuum can is correct without one. If you need a late model check ball can, I have one dichromate finish from a 1997 vintage model 3310 you can have. Replaced it with a QFT adjustable can a couple years ago.

I put it back on for now without a check ball. I looked in the 66 shop manual and in an exploded diagram of the 4150/4160 it showed one. But in the photo and description of the vacuum diaphragm itself, there was no ball shown or mentioned. Not sure what spring is in it that Holley installed - seems to have remnants of gold paint but it might just be old yellow paint.

The purpose of the 1/8" brass tube that extends into the primary venturi is to allow a strong venturi vacuum signal to the secondary vacuum servo. There is another hole in the secondary venturi just behind it which acts to bleed off some of that signal until the air flow in the primary venturi creates enough low pressure to overcome the spring above the servo diaphragm. As the secondary's start to open and air rushes in the secondary venturi that small bleed hole reverses and adds to the vacuum signal to the servo and further opens the secondary's.

Most people remove the check ball, which allows the secondary to open fast, with your low rear gear I doubt if there will be any problem without the ball.

Well, it's up and running and seems OK. Short shakedown run since I replaced some fuel lines due to slightly rounded flare nuts and also a new water temp sender, and I didn't want to stray too far without checking for any seeps or leaks. I don't usually jump on this thing all at once so I bet the secondarys will be fine. Engine seems a bit crisper at idle and low speed with smaller primary jets but idle vacuum is still around 8-1/2 in after adjusting idle mixture. I don't think this cam can do any better than that.

You are correct. If there is no bleed groove in that seat, there will be no check ball. The purpose of the check ball when a groove is present is to limit the rate of secondary opening, but to unseat to allow rapid closing of the secondaries when letting off the gas. Some applications used the check ball, others did not, like the 2818 Holley used with the L76.