[quicksilver97ta]

I just rebuilt this carb with a Holley kit, I believe the list # is R4788 but it's not stamped. Bought it used many years ago. 830 cfm, jets are 80/80 and squirters are 31/31. I dont know much about Holleys but this is a very simple carb. I finally got everything buttoned up and started her up yesterday. Intake is a T2. Both are new to this engine combo.

Idle and slower throttle response is just fine. Rolling into near WOT briefly felt awesome.

Squirters appear to function normally.

Snap the throttle, primaries only- produces a slight bog/hesitation.

Snap the throttle, getting into secondaries- produces backfire into carb and fire in secondaries.

Car never did this before with my tri-power and I didn't pull the distributor to do the swap.

Is the backfire in the secondaries a result of the bog in the primaries? What does it need? Larger front squirter? Suggestions please.

[regamble]

Start with the hesitation. Your squirters sound about right for setups like this I've seen, but what accelerator pump cam are you using and what position? An 830 is a pretty big set of holes to draw vacuum through effectively and maintain a decent draw on the idle circuit, so what motor is this on? I know an 830 on almost anything under 450hp is going to have some issues. My son's Ranchero with a 425hp 429SCJ runs it's absolute best with an 800cfm. By the time you get enough fuel going into the carburetor to balance out the huge venturi, it's running rich.

The backfire. I'm going to use a different term here called "off fire" and that is when a cylinder fires with the intake valve open but not the same as detonation or pre-ignition. A backfire through the carb can only be caused by combustion with an intake valve open. That said, if it's running extremely lean or extremely rich at idle, when you open the throttle it can cause a cylinder to "off fire" causing a pop through the carb. Basically, in each of the two scenarios, if it's very lean each cylinder is going to be much hotter than normal and when the squirters flood the runners with fuel it can ignite the moment the intake valve opens causing it to "off fire" and POP. In the other scenario, if it's very rich, it could be causing a near wet foul and when the excessive air hits the runners it dry's the excessive fuel causing a cylinder to fire as soon as the fuel/air ratio hits optimum.

Lastly, one thing I've encountered is incorrect vacuum advance timing. If the VA signal is premature or delayed it can cause both of the issues you are finding here. It may be, once again, incorrect carburetor, or a number of other things. Most Holley's have a screw on the secondary butterflies that allow you to open them just enough to remove vacuum from the VA and still idle on the idle circuit. If that setting is wrong it will cause VA issues, hesitation, and secondary jumps or inconsitencies.

Holley has a phenominal tech help line. Email them your application and problems and they will email you back with good information. Be as specific as possible. And no, you don't need to have a new carb to ask. I have used their help line on a number of 30+ year old carbs and they're always helpful and courteous.

Anyway, kind of long winded, but I hope this helps.
Rob

[quicksilver97ta]

30cc pumps, yellow cams, pos 2 on primaries, pos 1 on secondaries. Day shift?

[regamble]

You can try changing the position of your cams first since that's the easiest. I would move the secondaries to the second position for sure. Is that a 2 position or 3 position throttle? Day shift? Nah, every shift.

[shaker455]

Originally Posted by quicksilver97ta

I just rebuilt this carb with a Holley kit, I believe the list # is R4788 but it's not stamped. Bought it used many years ago. 830 cfm, jets are 80/80 and squirters are 31/31. I dont know much about Holleys but this is a very simple carb. I finally got everything buttoned up and started her up yesterday. Intake is a T2. Both are new to this engine combo.

Idle and slower throttle response is just fine. Rolling into near WOT briefly felt awesome.

Squirters appear to function normally.

Snap the throttle, primaries only- produces a slight bog/hesitation.

Snap the throttle, getting into secondaries- produces backfire into carb and fire in secondaries.

Car never did this before with my tri-power and I didn't pull the distributor to do the swap.

Is the backfire in the secondaries a result of the bog in the primaries? What does it need? Larger front squirter? Suggestions please.

That does not look like an 830 but I can help you ID it.

Look at the driverside of the mainbody casting, just under the aircleaner gasket surface on the primary.

There will be a raised casting letter and number like for example "P-11"

Tell me what you have?

[quicksilver97ta]

P-32

[shaker455]

Okay that is an 850 mainbody list # 4781

To make it and 830 you would have to have the 1-11/16" throttleplate base and the plate numbers are stamped from the bottom 172.

An 850 is 180.

Can you tell me what you got?

Are you running powervalves both front & rear?

[quicksilver97ta]

Thanks for the reply. Those stampings must be on the bottom because I can't see any, I'll look next time I pull the carb. Yes p.v. Front and rear.
I bought this carb from a guy I knew back around '90. I was under the impression that it was not that old at the time and out if the box stock. Other than that all I remember was he told me it was an 830. I searched holley's web site last week and found an 830 with the 31 squirters f/r, 80 jets f/r, yellow pump cams, front on 2, rear on 1. This is exactly like this carb is so I thought I probably found the right list #.

[shaker455]

Yes there on the bottom.

PV's F&R are nice but if you have a lot of power it will uncover the rear PV so you may want to consider a plug and simply jet up.

Yellow cams you say?...how about some close up pics of that?

Whats your engine combo?

[quicksilver97ta]

Check my sig for my combo, see if you can make sense of that, I wrote it HIS style, lol. Ask away if its unclear. The 'yellow' is from memory. I do know that what I read on the Holley site matches what I have. IIRC they look kind of tan to me. I'll get a pic as soon as I can.
So if I I block the rear pv how much should I jet up? Also do you you care to take a wag at why it hesitates and/or back fires and what I might try?

[shaker455]

I want to determine carb size before advising but I don't want you backfiring.

Go 81/88 rear plugged

Test your front PV to make sure it works.

What size you using?...with that cam maybe a 4.5" or 5.0" PV

How's that MalloryUnlite it set up? initinal, mech adv, total

Vacuum advance hooked or disc?

Ported or full?

More than likely you have pink #330 cams and they are faded.

Do you have any factory Holley bronze sintered filters in the fuel bowl inlets?

[quicksilver97ta]

It idles in drive with about 11" of vacuum. 6.5 pv's are what came in the kit so thats what's in there. Dist is a Mallory dual point w/ vac adv limited to 12*, mech limited to about 18*. I drop it in and set the total (sans vacuum) to about 31. Then it idles down to about 13*, then I plug in the vacuum adv (manifold) and it adds it's 12*.
It ran great this way with my previous set up which was a 66 tripower jetted to 421 specs.
I've got jets I just need to pick up the part that pv blocker. Hmm, I just thought for sure it needed more pump shot. Does the Holley idle circuit get affected by jet size?

[shaker455]

It might need more shot so once you post a cam pic I can tell you what you have.

Some basic jetting will tone that stumble as well

Do you have pink # 330 cams on the shelf you can use?

[quicksilver97ta]

Finally got to work on this car again. I should have reread this thread as I just missed a couple of things Shaker mentioned but here's what I did. Shaker you there?

1. Changed front jets from 80 to 82
2. Changed front squirter from 31 to 37
3. Blocked rear pv
4. Changed rear jets from 80 to 86

Notes:
1. Forgot to inspect butterfly stampings
2. Cams are brown

These changes helped a lot. No more backfire. No more hesitation in the primaries. There is a slight stumble, almost like a gargle, when snapping the throttle getting into the secondaries. I then changed the rear squirter from a 31 to a 37 and that gargle got worse, taking much longer to clear up. That defiitely seemed like the wrong direction so I changed the rear squirter to a 28 but didn't get to test it. Also, I borrowed a friends tunning kit and have access to a ton of different cams, pv's, and jets now.

[johnta1]

I'd try leaving the 37 squirter in the rear and put the 31 in the front.

When the primaries just start to move the front squirter should squirt immediately.
Same for the rear squirter, once it starts moving it should squirt immediately.

If there is a lag there will be a bog.

Then also the front should squirt until the secondaries open also.

Then there is all the stuff shaker said also.

[shaker455]

Yep I'm here!

If you got the brown cams then you must have 50cc pumps.

So if thats the case then there will be no cam changes unless you want to try position# 2 at some point.

You gargle may be a bit rich or the dist taking too long to react to your snap and with that cam I feel some of your problem is contributed to your low initinal timming of 12 or 13 degrees.

I would suggest setting your initinal @ 18 degrees and recurve your Mallory to 18 degrees mech adv.

Maybe go back to the 31 shooter in the back rather than the 28.

What size PV did you go to?

Pop some plugs and see what color they are?

[PunchT37]

Originally Posted by shaker455

Yep I'm here!

If you got the brown cams then you must have 50cc pumps.

So if thats the case then there will be no cam changes unless you want to try position# 2 at some point.

You gargle may be a bit rich or the dist taking too long to react to your snap and with that cam I feel some of your problem is contributed to your low initinal timming of 12 or 13 degrees.

I would suggest setting your initinal @ 18 degrees and recurve your Mallory to 18 degrees mech adv.

Maybe go back to the 31 shooter in the back rather than the 28.

What size PV did you go to?

Pop some plugs and see what color they are?

Jeff, if you look at his accel. pump arms, they look like the 30cc type. Should he dump the brown cams?

[grandville455]

I am running A true 850 now from my 830 Annular and I am jetted at 75/86 and my AIR/Fuel is about perfect and that is with close to 580 hp! I can't believe u need that much jet? Put the 50 c.c pump up front with about a 35-37 shooter or so and a 30 c.c in back with a 31 shooter. Sorry Jeff your the one that told me to buy the books What is the rest of the combo setup?

[shaker455]

"Oh no" not Darby!

Don't listen to this guy...his car is slow!...LOL

Hey Darby, still don't know his carb size due to the base and I'm glad your car is running good.

If your heads really flow well and you have big cubes alot of times you will go down on jetting...maybe like you..

Otherwise you still don't get it!...HaHa!

Back to the books and the track buddy!

[shaker455]

Originally Posted by PunchT37

Jeff, if you look at his accel. pump arms, they look like the 30cc type. Should he dump the brown cams?

Wade,
I see the arms but he'll have to tell us if he's got 50cc pumps and I commonly use the 30cc pump arm on 50cc pumps to assure aircleaner clearance.