Chevy Tri Five Forum banner

41 - 60 of 85 Posts

·
Registered
Joined
·
6,932 Posts
Discussion Starter #41
without being there to see how it acts can't say for sure but go up 1 step at a time. put the out of the box squirter in. and slow down the secondary. you timing sounds decent where it is.
And what primary pv? Need it be high flow?

If I just do what you wrote, I'll be back to backfiring when quickly opening the primary throttle. I was assuming somehow a different PV was going to help that?

I got hung up working/cleaning the catastrophe of a shop yesterday and never got to recheck the secondaries for any blockages. I had put air through the metering block again when it was apart again, but didn't double check the carb body.

I don't know about the choke. It seems to start fine without a pump and with the choke open 1/2", but the fast idle cam is on the lowest fast idle and it stalls in gear. Maybe I'll try wiring the choke open and turning the adjustment richer so I get a higher fast idle? Just to test it anyway. (I'm into experimenting, I know, you hate that) Why is it that it starts with no pump or much of a choke? I had a similar problem with a Q-jet and since it was old and I really didn't care about it much, I drilled and cut two large slots in the choke so it could breath a little while on fast idle. But this carb is fairly virgin so I hate to do that to it. It is not too much fuel pressure leaking into the intake. It just simply starts in less that 1 revolution with the choke probably not doing much at all at cranking speed and 1/2" open.
 

·
Premium Member
Joined
·
13,331 Posts
And what primary pv? Need it be high flow?

If I just do what you wrote, I'll be back to backfiring when quickly opening the primary throttle. I was assuming somehow a different PV was going to help that?
You have to start somewhere, just throwing fuel at it is not the answer. start with the power valve and smaller squirter first and only work the primarys, this may need a slight jet increase too. the standard 125 series power valves are all you need. when you open the throttle manifold vac drops. this is what causes the PV to open. the higher the number the sooner it opens. once you get this sorted out then you can move on to the choke.
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #43
If I were Tony I'd get a new mechanical secondary double pumper and go from there. I like having total control of the butterflies instead of some automatic thing. You can teach your foot to give the engine what it needs, and when you stomp the pedal you KNOW them fly's are definitely wide open. A bog can be worked out easier too.
I had a really old Holley 800 spreadbore double pumper on it that ran well. I just got this carb for $50 so I had to buy it for the challenge.

The secondary bog is really a no brainer. All I have to do is slow the secondaries a little bit, maybe I'll do that while I'm messing around today waiting for some deliveries. Still, it will almost open like a mechanical, sure never as fast, it can't without a rear squirter, but I can't believe people drive the Holley vac secondaries as they come from the factory. It takes, I'm guessing, about 3 to 5 seconds depending on the spring used for the secondaries to open all the way. My way right now it's starting to open with a quick blip of WOT. When I slow it down it will still be less than 1 second, and it won't bog. I know, when you are used to a double pumper, saying less than 1 second sounds like a long time, but it's a lot better than 3 to 5 seconds.

If you or anyone with a Holley double pumper could check something for me I'd greatly appreciate it. When opening the throttle by hand, does the primary squirter continue to squirt when the secondaries are opening? ... all the way open?
 

·
Premium Member
Joined
·
13,331 Posts
If you or anyone with a Holley double pumper could check something for me I'd greatly appreciate it. When opening the throttle by hand, does the primary squirter continue to squirt when the secondaries are opening? ... all the way open?
with the right pump cam and squirter the primary will continue to deliver fuel to about 90% throttle
 

·
Premium Member
Joined
·
12,565 Posts
I had a really old Holley 800 spreadbore double pumper on it that ran well. I just got this carb for $50 so I had to buy it for the challenge.

The secondary bog is really a no brainer. All I have to do is slow the secondaries a little bit, maybe I'll do that while I'm messing around today waiting for some deliveries. Still, it will almost open like a mechanical, sure never as fast, it can't without a rear squirter, but I can't believe people drive the Holley vac secondaries as they come from the factory. It takes, I'm guessing, about 3 to 5 seconds depending on the spring used for the secondaries to open all the way. My way right now it's starting to open with a quick blip of WOT. When I slow it down it will still be less than 1 second, and it won't bog. I know, when you are used to a double pumper, saying less than 1 second sounds like a long time, but it's a lot better than 3 to 5 seconds.

If you or anyone with a Holley double pumper could check something for me I'd greatly appreciate it. When opening the throttle by hand, does the primary squirter continue to squirt when the secondaries are opening? ... all the way open?


I had a really old Holley 800 spreadbore double pumper on it that ran well. I just got this carb for $50 so I had to buy it for the challenge.
Long time ago I had one of those and really liked it. Stomping open those huge secondaries would produce that BAH-WAA!! sound like no other, and take the tires to the very edge of adhesion.

For 50 bucks I don't blame you for grabbing and trying the 'new' one.

If you or anyone with a Holley double pumper could check something for me I'd greatly appreciate it. When opening the throttle by hand, does the primary squirter continue to squirt when the secondaries are opening? ... all the way open?
To honestly answer your question..no. The primary shot turns to a dribble and ends just before the primaries are fully open, BUT, the secondary shot starts just as you tip in the secondaries. Work the foot in just the right way and there isn't much of a gap between the two.

One of the things I really like about a mechanical secondary carb is that you can feel the extra pressure with your foot as you start to tip the secondaries in. Might be just me, but I really like that type of control.

With your big squirter, it would be best to have a big acc pump (50cc) to keep up with it. The downfall of that is the many trips to the gas station to keep up with THAT thing. To true hotrod guys it don't matter a bit though. lol
 

·
Registered
Joined
·
23 Posts
Have you tried tuning the secondary with different springs? You have done a lot of work and a whole lot of trial and error to have bypassed that simple tuning option. I'm sorry if you think this is a step backwards but a good holley tuner can make a vacuum secondary perform as good if not better than a mechanical secondary.
 

·
Registered
Joined
·
7 Posts
My 2cents
Its always better to try to leave the power valve in the carburetor I don't think I ever heard you mention what your manifold vacuum is ,that would address what size power valve to use . I usually start at least two steps below my manifold vacuum .
Unless it's a smog 454 your vac carb should be right there .
 

·
Registered
Joined
·
7 Posts
Also.....
A back fire threw the carb is the fastest way to damage a PV.
I would check that vacuum and replace PV with correct new size 🤗
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #49
Got some higher PV's today but it's raining so no sense in messing with it. Back a while I said the idle vac is 12. I'll go up on the primary PV and increase the jets 2 sizes and see what happens. The pv's are not blown out by the backfire, I'm certain this has the backfire protection in it since it's not that old. And it would be running very rich if a pv was blown. Turning down the idle screws will still stall the motor, that's the Holley check for a blown pv.

I did slow down the secondaries and the bog is almost gone. I'm going to wait and see what happens before I slow it any more.

Also yesterday at light throttle, maybe 50mph, with the slightest increase in the throttle it had a little hiccup. Just a tiny, tiny bog. Only did it with the tiny increase in the throttle. If I gave it just a little more, it didn't do it. I'm thinking that the accelerator pump check valve may be leaking down a little and it's missing the first part of the squirt. But I didn't try looking at it with the air cleaner off yet. I could have missed cleaning that, I don't really recall it.
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #50
Went over the accelerator pump circuit from one end to the other. In the bowl there was a little tit in the casting under the rubber valve that looked like it could let it leak. I removed it and got the entire surface smooth. Then up top I managed to get the needle out from under the squirter without loosing it and although I didn't find any dirt, I blew it out better then flushed it out with gas in the pump. It started raining so I just backed it out of the garage half way and ran it a while. Took a look at the pump shot and holy hell it's shooting a LOT. Although I only looked at it before when it wasn't running, and yesterday I only looked at it while it was running, but it looks like double or triple the amount of fuel as before. I had also installed an 8.5 PV and increased the primary jets 2 sizes. Didn't get to try it because of the rain.

I let the accelerator pump sit overnight to drain down if it was going to. It didn't. It's giving one hell of a squirt this morning when not running. I'll be honest and say I didn't put the factory squirter back in yet, but after seeing what it does now, I will put the .040 factory one back in it. I'm just thinking out loud here and wondering if the smaller squirter will give it a longer pump shot. Not sure if .040 is small enough for that.
 

·
Registered
Joined
·
35,756 Posts
With a really big squirter size like an .040" you will run out of pump shot before the throttle is all the way open - unless you have the big 50cc pump. I don't recall you ever mentioning which one you have.

Also with most intake manifolds .040" is too big. .028" or .031" is a better starting place.
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #52
OK today's update.

8.5 primary PV and increased the primary jets 2 sizes.
Put the *factory* .040 squirter back in, I don't have anything smaller yet.
Took it out for a drive.
Cruising 45 to 65mph A/F 12 to 13:1
WOT is 15-16:1 (and no knock or ping!?!?)

It runs very well despite the numbers. I didn't think I had slowed the secondaries opening enough, but I didn't get any bogs, so they may be OK. Secondaries are very responsive for vacuum, can't hardly feel a delay.

I find it hard to believe the o2 sensor could be bad and reading both too high and too low, BUT, I think I have a spare I can install if you think it could be throwing the gauge off both ways. I may have time tomorrow afternoon and I think the weather should be good.

Watcha think?

Oh RickL, the pump is the small one but it gives a strong squirt the entire throttle range.
 

·
Premium Member
Joined
·
13,331 Posts
OK today's update.

8.5 primary PV and increased the primary jets 2 sizes.
Put the *factory* .040 squirter back in, I don't have anything smaller yet.
Took it out for a drive.
Cruising 45 to 65mph A/F 12 to 13:1
WOT is 15-16:1 (and no knock or ping!?!?)

It runs very well despite the numbers. I didn't think I had slowed the secondaries opening enough, but I didn't get any bogs, so they may be OK. Secondaries are very responsive for vacuum, can't hardly feel a delay.
from this I would say things are close, the reason it my be going lean at WOT is that after the pump shot is gone it needs more jet on the secondary side. it may also be that for your combo the high speed bleeds may be slightly too big. does the carb have removable bleeds or are they the pressed in type?
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #56
from this I would say things are close, the reason it my be going lean at WOT is that after the pump shot is gone it needs more jet on the secondary side. it may also be that for your combo the high speed bleeds may be slightly too big. does the carb have removable bleeds or are they the pressed in type?
The air bleeds are pressed in. :( It just came to mind that I could peen the air bleeds, then with a drill make sure they are both the same. I googled it and I'm not the first one to think of it.
 

·
Premium Member
Joined
·
13,331 Posts
The air bleeds are pressed in. :( It just came to mind that I could peen the air bleeds, then with a drill make sure they are both the same. I googled it and I'm not the first one to think of it.
I wouldn't, it is real easy to screw up the bleeds and the left and right might be the same but the idle and highspeed are always different and it only takes a slight change to make a big difference.
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #58
I wouldn't, it is real easy to screw up the bleeds and the left and right might be the same but the idle and highspeed are always different and it only takes a slight change to make a big difference.
I put in an email to Holley so I'll see what they say in a few days. But you probably know, can I pull the air bleeds, tap it, and install replaceable ones?
Or would I need a new metering block? I wouldn't mess with the primaries.
 

·
Registered
Joined
·
35,756 Posts
Why are you hung up on changing the air bleeds? Just put some bigger jets in the back and see what it does.

You're probably a bit rich at cruise too.

You might want to look at the plugs before you do anything.
 

·
Registered
Joined
·
6,932 Posts
Discussion Starter #60
Why are you hung up on changing the air bleeds? Just put some bigger jets in the back and see what it does.
Because I tried bigger jets and they didn't make any difference! And if you saw, I was told they are probably too large.
 
41 - 60 of 85 Posts
Top