| Slant Six Forum https://slantsix.org/forum/ |
|
| Tuning carb and a good lash adjustment https://slantsix.org/forum/viewtopic.php?t=49900 |
Page 1 of 1 |
| Author: | wjajr [ Tue Sep 25, 2012 4:10 pm ] |
| Post subject: | Tuning carb and a good lash adjustment |
Yesterday I fiddled with the Holley a bit more in a quest for leaner steady cruse (transition pre main jet booster kick in) which has always been on the fat side. I re-drilled the throttle plates once again, readjusted idle speed screw so no transition slot was showing allowing for a better leaner in park idle. Also this allowed turning in idle mixture screws back to 1 ½ turns. These adjustments lessened of a bit of a flat spot on tip in, but did not help in gear idle; something I have not enjoyed for some time. By chance I had left off a vacuum cap from center tap base of carb after removing vacuum gage the day before. What this small vacuum leak did was lean in park idle out to ideal zone on o2 sensor, and allowed engine to sit idling happily loping away in gear at 700-800 rpm. So I calculated the area of the throttle plate holes, and area of vacuum tap, re-drilled both throttle plate holes to made up for the additional air supplied via the tap. It worked perfectly. Today I was cleaning up the mess caused by boiling over after shucking both belts during yesterday’s acceleration test. I replaced both old belts as they were damaged. While adding some coolant with engine spun up to 2400 rpm I noticed it had an intermittent skip that is new. It appeared to be acting up as o2 sensor changed mixture readings to lean. I pulled the air cleaner, and observed the accelerator pump nozzle was dribbling, but did not dribble at 2000 rpm and lower. This odd as I replaced the old shooter the other day with a fatter, non-syphon type (25 to 28 shot). I’m not clear on how to stop the accelerator pump dribble, and could it be responsible for fat cruse mixture? I now have ideal mixture at idle, main jet booster, and during power valve enrichment, but still fat under light steady cruse… below 2800 rpm. It is now possible to feel when secondarys fully open, and hear a bit of the four barrel howl; a rather delightful feeling after all these years. The valve train seemed a bit noisy during the coolant project, I have had a bit of a weak sounding #5 from rear of car listening to exhaust, and the last several lash settings were conducted with non-running hot engine because it wouldn’t idle down slow enough allowing adjustments and stay running until now. I was able to lash most of the weak #5 pulse out of it, quiet down some of the clatter, and improve idle a bit with 0.016†intake & 0.020†exhaust settings. |
|
| Author: | emsvitil [ Tue Sep 25, 2012 4:16 pm ] |
| Post subject: | |
Blast out the accelerator pump passages. Some crud may be stopping the check balls from sealing. |
|
| Author: | DusterIdiot [ Tue Sep 25, 2012 5:17 pm ] |
| Post subject: | Lol... |
Quote: Some crud may be stopping the check balls from sealing.
If he's got a mid-80's or newer 8007 then he has a rubber umbrella seal at the pump instead of a check ball that that point...also none of my 8007's came with a check ball under the shooter, but I have used one of the 'needle' check valves that the bigger carbs come with instead to moderate the pump shot as well as keeping high vaccuum singal past the shooter from drawing fuel from the circuit...Changing the shooter style can also change this condition as well. -D.Idiot |
|
| Author: | Jeb [ Wed Sep 26, 2012 3:16 am ] |
| Post subject: | |
The umbrella style valves have been known to "pump" fuel through the accelerator pump circuit at certain harmonics. On my 2300 I had to drill a .010 hole at the top of the accelerator pump channel on the float side of the metering block. This is known as a kill bleed, and helps break the vacuum that is pulled on the nozzle. It also stopped it from pushing fuel out the accel pump nozzle during heat soak. I would try other methods though before you start drilling your metering block. The kill bleed is a last resort method. |
|
| Author: | wjajr [ Wed Sep 26, 2012 4:39 am ] |
| Post subject: | |
Ed: [quote]Blast out the accelerator pump passages.[/quote] I did flush out every passage in metering block a fortnight ago when changing out power valve, jets, accelerator pump arm, and discharge nozzle. This house cleaning is generally done whenever metering block is removed. DI: [quote]If he's got a mid-80's or newer 8007 then he has a rubber umbrella seal at the pump instead of a check ball that that point...[/quote] Yup, got the bumbershoot stile pump mechanism in it. One would think the [url=http://www.summitracing.com/parts/HLY-121-231/] “anti-pullover discharge nozzleâ€[/url] would have solved this problem… Perhaps I’ll reinstall the old nozzle as I don’t recall previously seeing this phenomenon… for what that is worth... LOL, and run a test. I’ll give Holley’s tech line a buzz later this morning. |
|
| Author: | Jeb [ Wed Sep 26, 2012 6:02 am ] |
| Post subject: | |
You can always swap your float bowl to the older check ball style. |
|
| Author: | wjajr [ Wed Oct 03, 2012 1:27 pm ] |
| Post subject: | |
Today I was back at that damn carburetor… After driving the car for 500 plus miles with a 512 jets installed, I have come to the conclusion that it was just a bit too causing surging under light acceleration, climbing long low percentage grades etc. so the 53 jets are back in. A short eight mile test drive route that has just about every grade change one will encounter, which brought out light throttle surge with 51 jets, did not produce any surge with the 53 jets. The A/F gage still shows middle rich light during steady small throttle opening on flat ground. Previously when jetted much richer engine would run on after shut down. 51 jet eliminated back spin to an occasional one cylinder sputter in park. Only one shut down cycle with 53 jets produced a one sputter-plus feeble attempt at back spin in park. Tires still spin easily when power braking, engine still pulls strongly much stronger when secondary’s fully open around 3800 rpm. While the infernal device was on bench I popped out the needle housed below accelerator pump shooter, flushed it carb cleaner, examined its discoloration which showed full sealing in its seat, and put it all back together… It now seems to be doing its job, time will tell. |
|
| Page 1 of 1 | All times are UTC-08:00 |
| Powered by phpBB® Forum Software © phpBB Limited https://www.phpbb.com/ |
|