[mrfuzzy]

hi guys, here's the newest problem:
at idle, when i floor the gas pedal, carb stumbles for a second, then goes like hell. i had a 35 shooter in it, changed to a 25, same thing i'm playing with the acc. pump cams. anyone know what color would work best for my combo?? 70 396 4 spd. 3:31 posi, square port heads, fact. intake, exh. manifolds . comp solid lifter cam 532 lift. car runs great like i said, just the stumble at idle. thanks. ( 780 dual feed holley)

 

[blasttime]

Hope you meant 35 to 37 squirter. Try 2 more degrees timeing . Back down squirter when you see black smoke. 50 cc pump has fixed lots of stumbles for me.

 

[Xtreme70SS396]

Blue cam works best for a nice quick shot. As said, get rid of the 25 shooter, 35 should have been good for you - but if it stumbled at a 35 on a manual tranny I'd also be inclined to say your timing is not where it should be (around 18° without vacuum can at idle)

 

[mrfuzzy]

been driving it for some time now, that's why i'm wondering about the timing. car starts and runs fine all day, just when i step on the gas. last time i checked the timing from what i remember everything was in at about 3000 rpm, want to say 38 degrees.

 

[Xtreme70SS396]

I'd bump UP the squirter, but try the blue cam. Here's a chart showing the amount of gas and timing of when it squirts in (you want more earlier) compared to other cam colors:

 

[mrfuzzy]

went to the blue cam and 28 shooter, still bogs!!

 

[Xtreme70SS396]

But better, correct? Go to the 31 shooter next.

Plus, those passages can get plugged - when you hit the throttle by hand, watch and make sure the gas comes out strong and steady from the shooter.

 

[mrfuzzy]

tried 31 and 35 shooters, still bogs!!! passages are clear. this is starting to bug me.

 

[mrfuzzy]

here's what i did. i had a small squeeze bottle that i filled with gas. then had the wife hold it over the carb and squeeze it while i hit the gas. flat spot seems gone. i thought 35 was the largest shooter???

 

[wotr]

here's what i did. i had a small squeeze bottle that i filled with gas. then had the wife hold it over the carb and squeeze it while i hit the gas. flat spot seems gone. i thought 35 was the largest shooter???

If it had backfired,, your wife would have been gone,,,,, worth it???? LJ

 

[Xtreme70SS396]

They do make larger than 35. You ARE driving the car while doing this, right?

How do your plugs look? Clean, or black? It's odd that a stick car would need much more than you've already tried, unless there were other issues.

What's your idle speed? Do you know what the transfer slot is, and how to check it? You might have your throttle blades set in such a way that it's creating this problem, too.

 

[lg1969]

Use the blue cam but set the screw at #2 setting. Make sure there is no play on pump lever

 

[mrfuzzy]

thanks for the input guys, i will try the blue cam set at #2 pos. mark thanks for the chart. lj, i have insurance on the wife, if it would have backfired, i'd be shopping for a ls-6!! just kidding. there was enough for 1 squirt, about a teaspoon. i'll let everyone know what happens, hope it's not raining tommorow. thanks again!

 

[mrfuzzy]

finally got a chance to test drive it today, blue cam set at #2, and went with 31 squirter, runs great. thanks everyone for your help!!

 

[charbilly2001]

Use the blue cam but set the screw at #2 setting. Make sure there is no play on pump lever

The pump lever is supposed to be adjusted to 0.015" clearance at idle. Not "no play".

 

[Xtreme70SS396]

The pump lever is supposed to be adjusted to 0.015" clearance at idle. Not "no play".

I don't think this is correct. The .015" play is supposed to be on the top end (full throttle) so you can't damage the diaphragm if you're somehow able to push it further. At idle, the arm is supposed to be in contact with the cam without any play.

 

[mrfuzzy]

mark you are right. the holley carb tuning dvd states to check it at full throttle.

 

[lg1969]

The pump lever is supposed to be adjusted to 0.015" clearance at idle. Not "no play".

I have set my with no play, and I have not blown pump diaphram in the 35 years I been driving with the dual quad tunnel ram set-up. thank you.
Mrfuzzy, Have a blast out there and party, party, party! :hurray:

 

[job68327]

Just curious as I have a 750 dp and want to try to customize my pump cams,should both acc. pumps have the same cams?also is the nozzle another spot to tune and does it have to be in relation to acc. pump?Thanks as I just picked up two cam kits and want to try later today.

 

[Xtreme70SS396]

Both cams do not have to be the same - the front will have the off-idle impact, as you will have that same bog when just cruising (Not opening the secondaries at all). The back will need a big enough shot to compensate for the secondaries opening, which on a Holley are the same size as the primaries - so logic would say at WOT they should certainly be close to the same size if not the same, but you may not need the same size if you just lean into the throttle, as other factors come into play. I think you might need an A/F meter to really tell.

The nozzles affect how quickly the pump shot comes out, not the size of the total shot. For example, if you have a 35cc shot of gas, a 35 nozzle will be able to let out more gas earlier in the shot than a 25, even though the total will be the same. Similarly with the pump cam, but the cam can also affect how much the arm goes up and therefore the amount of the shot, too.

The tough part of tuning a carb is every adjustment has an effect on all the other stuff. Timing has to be done first, too. For example, if your idle is too rich, you won't need as much of a shot off-idle as someone with a lean idle. Fix the idle, your bog may return. That's why it's important to change one thing at a time.