 64cv
"5th Year" Silver Supporting Member
Posts: 647
Reg: 06-05-08
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 05-02-12 05:19 PM - Post#2221687
What are the symptoms you'd see if the accelerator pump squirter is too big?
Brad
Life is an optimization problem; make the most of it!
'64 Impala Convertible, Blueprint 383, Tremec TKO 5sp, 4-wheel disc brakes. |
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 Rick_L
Honored Member
Posts: 24808
Loc: Katy, Tx, USA
Reg: 07-06-00
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05-02-12 07:16 PM - Post#2221753
In response to 64cv
Hard to describe.
Usually when you're messing with the squirter size, you had a flat spot or hesitation which prompted you to change to a bigger one. And the normal recommendation would be to increase the squirter size one available step at a time. When the hesitation goes away, just stop, or if going the next size doesn't help, go back to the previous one. One size too big may just give you a puff of black smoke. More than that puts you back in a hesitation similar to the too small squirter.
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66cayne
Frequent Contributor
Posts: 1810
Reg: 08-06-08
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05-03-12 06:00 AM - Post#2221879
In response to Rick_L
Yeah, it's not only squirter size that is important but also the shot duration and atomization, which is controlled by the squirter type, pump cam and the pump shot size. It all needs to be balanced. You are usually better off with a longer duration lower volume shot size. I think most stock duel feed Holleys come with a .025 squirter. The largest I have ever run is a .035 squirter/with a 50cc pump. And that was on a Holley 950DP feeding a 468 BBC with a big solid roller cam.
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bobb
Super Senior Member
Posts: 4628
Loc: paradise
Reg: 09-05-03
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05-03-12 07:48 PM - Post#2222201
In response to 64cv
if you go down 2 sizes and there is no performance dropoff, then i would say they were too big.
| 70 L camino 350 all forged,174 baby blower, g-force 5 spd, road rage suspension. Pray first before all else fails. |
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64cv
"5th Year" Silver Supporting Member
Posts: 647
Reg: 06-05-08
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05-05-12 05:33 AM - Post#2222623
In response to Rick_L
Rick L,
Yeah, I'm chasing down a dead spot at low rpm cruise that I've always had; feels like a lean surge. I have an understanding of the five circuits in the carb, idle, transfer, main, power, accel.
I've got it narrowed down to a problem with the transfer circuit. Idle, main, power and accel are fine. During all my tuning I went up one pump squirter size and plan to return it to stock; just trying to think ahead what that will do.
I actually got rid of the surge by retarding timing all the way down to 11 deg btdc. That caused a new problem though, sometimes the car would stall out really bad when accelerating from a dead stop with light throttle. Won't restart w/o flooring the accelerator (like it's flooded.)Not acceptable. I'd like to go back to that timing setting if I could get rid of the stalling. I'm thinking it's caused by squirting too much fuel when pulling away from a stop. We'll see what happens.
What I'd really like to do is make the transition circuit a little bit richer but I've never heard of a way to do that. I understand about exposing too much transition slot on a low vacuum engine like mine. I've done a lot of experimenting with drilling the throttle plates and I've got it just right so that the secondary throttle is adjusted to spec and the primary throttle is almost completely closed exposing almost no transition slot.
I've gone richer and then dialed back down on idle, main, power and acceleration with idle mixture, bigger jets, lower # power valve, bigger pump squirter and bigger pump cam but transfer (low rpm cruise)is too lean no matter what. Less timing cures it but I can't live with stalling out I got at that setting. Hopefully the stalling is caused by the too big pump squirter rather than the timing and will go away when I go back to the original squirter.
Brad
Life is an optimization problem; make the most of it!
'64 Impala Convertible, Blueprint 383, Tremec TKO 5sp, 4-wheel disc brakes. |
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Rick_L
Honored Member
Posts: 24808
Loc: Katy, Tx, USA
Reg: 07-06-00
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05-05-12 03:50 PM - Post#2222860
In response to 64cv
I think you may be trying to hard.
You commented that retarding the timing helped. Usually that is the opposite of what you would do. This indicates to me that for whatever reason your tuning combination was way off. I would put everything in the carb back to the way it came out of the box. Make sure you don't have vacuum leaks or malfunctions in your mechanical or vacuum advance units. See how that runs and tune from there.
The transition slot shouldn't affect anything except that if it's exposed at idle it will richen the idle.
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acmsal
Senior Member
Posts: 233
Loc: san jose,ca.
Reg: 02-19-02
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05-06-12 02:52 PM - Post#2223179
In response to Rick_L
I went thru months of messing with my carb, turned out I had a vacuum leak at the the intake manifold. Just spray some carb cleaner around the intake and see if the idle doesn't rise.
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64cv
"5th Year" Silver Supporting Member
Posts: 647
Reg: 06-05-08
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05-13-12 09:09 AM - Post#2225439
In response to Rick_L
Pulled the plugs and everything looked ok, a little bit rich all over though. Took out the bigger pump squirter and went back to stock; much better. Not as prone to stalling and flat spot gone. Too many variables though. The weather's warmer and this car with the air gap manifold has always liked warm weather better.
The car originally ran lean at power. Went up a total of six jet sizes and it still ran lean but the fuel mileage was terrible. Following Grumpy's advice I went down two power valve numbers from stock; much better! Lot's more power and plugs indicate I'm not running lean.
I'm running at 3 jet sizes over stock now and my take those out later and see what happens.
Bottom line: 383 with a 234/244 cam, dual plane air gap manifold and a Holley 670 Street Avenger.
1) had to drill the throttle plates to get the transition slot and earlier performance issues under control.
2) had first erronously compensated by going up six jet sizes.
3) took 3 jets out and went down 2 power valve numbers to cure lean.
4) tried a bigger squirter, worse not better.
5) will go back to stock jets and see what happens.
So I'm pretty close to stock carb except for power valve and drilled throttle plates.
Brad
Life is an optimization problem; make the most of it!
'64 Impala Convertible, Blueprint 383, Tremec TKO 5sp, 4-wheel disc brakes. |
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Rick_L
Honored Member
Posts: 24808
Loc: Katy, Tx, USA
Reg: 07-06-00
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05-13-12 04:48 PM - Post#2225560
In response to 64cv
3 jet sizes up is still too rich for most setups if you run a power valve.
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 navygunner08
"2nd Year" Silver Supporting Member
Posts: 644
Loc: New London, CT
Reg: 02-13-11
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05-15-12 12:30 AM - Post#2226026
In response to Rick_L
Have you thought about buying a wide band O2 sensor, so you know exactly what your A/F ratios are?
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64cv
"5th Year" Silver Supporting Member
Posts: 647
Reg: 06-05-08
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05-15-12 05:54 PM - Post#2226299
In response to navygunner08
Navygunner08,
That's a great idea and yes I have thought of it. What's holding me back is finding someone competent to weld an O2 sensor bung into my stainless steel exhaust and the price of the sensor/gauge.
Have to agree with you though, there's no substitute for real data.
Brad
Life is an optimization problem; make the most of it!
'64 Impala Convertible, Blueprint 383, Tremec TKO 5sp, 4-wheel disc brakes. |
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navygunner08
"2nd Year" Silver Supporting Member
Posts: 644
Loc: New London, CT
Reg: 02-13-11
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05-16-12 05:27 AM - Post#2226445
In response to 64cv
That is very understandable. Is it a show car?
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64cv
"5th Year" Silver Supporting Member
Posts: 647
Reg: 06-05-08
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05-17-12 02:53 PM - Post#2226900
In response to navygunner08
No, not a show car. It's a driver. Been everywhere but on a trailor.
Brad
Life is an optimization problem; make the most of it!
'64 Impala Convertible, Blueprint 383, Tremec TKO 5sp, 4-wheel disc brakes. |
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navygunner08
"2nd Year" Silver Supporting Member
Posts: 644
Loc: New London, CT
Reg: 02-13-11
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05-20-12 01:12 AM - Post#2227744
In response to 64cv
Is it the car in your pic? If so it looks really nice.
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