383 stroker timing/performance and temperature

Discussion in 'Troubleshooting & Diagnosis' started by erhan ergin, Apr 25, 2020.

  1. erhan ergin

    erhan ergin Veteran Member

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    I am not clear on what PV has to do with idle? I changed the PV from 8 to 2.5 because of rich condition, it helped quite a bit, I may have gone a bit overboard but I do not believe PV is the issue here. Also I already drilled the holes on all 4 throttle bodies. I can open up the secondary a bit more but the transfer slots will be exposed again. Will going to a bigger air bleed help, say to 78 for instance (from 65) or is that too big of a jump? I assume air bleed impact is much less compared to the air fuel mixture screw thus I am looking at a big jump.
    Thanks
     
  2. G72Zed

    G72Zed Veteran Member

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    Either you have a PV chamber leak, internal leak due to casting porosity, or the "engine" may have the wrong cam timing events combined with CR. Drilling the throttle plates to get it to idle is not a good sign, I have actually have had to weld them up or change them out more times than I can remember..., and these are on some big cam'd 500-650HP SB engine.

    Your 7 in of vacuum at idle makes me wonder. does this carb have the Billet base plate, if so, i have seen these carbs so poorly machined in width and length that I had to insert Trans slot restrictors in some locations and not others....sorry if it was mentioned, but is this a dual plane or single plenum ?
     
  3. 80sz

    80sz Veteran Member

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    The 6.5 will just be under your vac reading and should be good, and isnt really effecting idle. Pull bowl and check if pv is bottoming out, 2 gaskets won’t hurt it. Might have a leak. Jump 5 on iab. See how it goes,do a big jump see what it does.
     
  4. erhan ergin

    erhan ergin Veteran Member

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    It is a dual plane edelbroke performer EPS. The carb is a brawler 650cfm, it is the billet shiny junk. I am still not clear on PV. I replaced the PV due to the low vacuum. I went from the stock 8 (or might have been 6) to a 2.5 as I was seeing as low as 5.5in vacuum before I bumped the idle timing. The rule of thumb is to half the idle vacuum to come up with the PV size.
    Most people here suggested there is a vacuum leak somewhere but I could not find any leaks. Also there are many posts all over the web about these huge cam'd strokers with low vacuum issues. People having power brake issues, idling issues etc.
    I am short of getting an older Holley and throw the current carb to trash but I am afraid the issue is with the bad cam profile and possibly junk aluminum heads on this engine.
     
  5. pomartin

    pomartin Veteran Member Gold Member

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    If there is no choke plate youill not get it to idle cold if carb is tuned proppey.

    Try putting a thin wire (from cooper wires) into idle feed restrictors- this will lean out idle cirtuit affecting idle and cruise. It has same effect as drilling air bleeds but it is easely reversible.

    The lean spike at WOT can be fixed by using propper pump cam or if neccesery bigger pump... assuming your transition slots are already in specs
     
  6. G72Zed

    G72Zed Veteran Member

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    First off, toss that "half the idle vacuum to set PV opening point" rule of thumb out the window, made no sense 40 years ago, and still doesn't. Holley put it in there, and I'm sure the original guys wish it was never said, or maybe Holley just wanted more sales.

    And just for shytz and giggles, try a 1" open spacer with new gaskets like Fel-Pro #1900, just to see what it does, make sure your timing is right.

    The reason why is that intake, with no open spacer, your engine is only seeing 1/2 of that carb, and may be just over signaling the idle port and trans slot. Just think why GM put 780 cfm Holley's with "down leg" boosters on there 302/350's in the LT1 Vettes and 67-72 Z/28's of the day.

    I have said it in many other post's that I have chimed in on, I've done many of these "Brawlers", I just modified & built one a few weeks ago on a 455 Pontiac. The IFR's are in a high set position, and were in the huge 36+ zone for size....and the transfer slots were machined wrong amongst other issues, this needs to be corrected. Dyno tested the 455, air hat, dual WB's, now high 13's at idle, 14.7- 15.2 at 2,200- 2,500rpm, and WOT at a safe 12.85.

    Some of these "Ultra-Warrior-Brawlers" are just screwed up from the get-go, and some are OK to good, pending the owners view on "what is good or acceptable".
     
  7. erhan ergin

    erhan ergin Veteran Member

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    I did the following changes
    1- Replaced the PV from 2.5 to 3.5
    2- Replaced the idle air bleeds from 65 to 78

    The impact of this is as follows:
    1- The air fuel mixture screws had to be backed out from 1 turn to about 1.25 turns otherwise it was too lean. I think this is due to the 65 to 78 air bleed change.
    2- When the car is in Park it idles around 1k RPM but when I put it in gear it dies. It will not idle in gear.
    3- If I increase the idle speed to about 1.2-1.3k in park and then the car will idle in gear. The rpm numbers are from my timing gun not the tach. At this rpm timing is around 32 degrees. I had originally set the idle timing to 28 at 900rpm

    There is a spacer under the carb in addition to the gasket, it is about 1 inch high. I am running out of ideas. Any suggestion is appreciated.
     
  8. 80sz

    80sz Veteran Member

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    The big jump in iab did what I expected, you will turn out screws more to compensate, this is good tho your getting more gas in on idle circuit. Back off idle screw till engine almost dies. Try to turn in or out the mix screws to get idle back up. What is your initial timing. Your lean spike is the low pv. Main function is open when you floor it, loss of vacuum ,pv opens to dump in some gas to rev up motor to not stall. You went so low it delays this action of opening when you loose all vacuum when throttle blade go wide open and vac is lost for few seconds
     
  9. G72Zed

    G72Zed Veteran Member

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    The PV will not change the area you are struggling in for the most part. The factory came with 71's for HSAB, (31's for HSAB) you should not have to get into changing bleeds for the most part. And when you start this, it becomes a "cat & mouse" game real quick, especially if your not real experienced in this area, multiple WB and dyno tuning helps big time, even then, it takes work.

    The last "Brawler" I repaired required moving all the IFR's to the low set position and one IFR was at .042 LOL, and had to install TSR (trans slot restrictors) as well. Then, the PV channels need to be lined up and the Metering blocks need a good going through and mod the E pak as it's ugly as shyt!, and more small mods repairs was required. This is the same carb that a customer told me to "toss it in the trash" as it used fuel like a dump truck and was great at washing down his fresh bores.

    Look at it this way, the 650 Brawler BR-67212 is $445 @ Summit Racing , if you need a carb expert to get this fixed up, your into more cash, it becomes a "5$ shine on a 2$ shoe", and even then, it may be screwed up enough that it will just be "ok".

    The similar "old school" Holley carb, 650 4777-C, is $573 @ Summit Racing, how can the "Brawler" carb with all aluminum construction, polished like chrome, clear sight glass, changeable idle & high speed bleeds, true Billet metering blocks and baseplate with black anodizing with all the bells and whistles be $128 LESS than the old caveman zinc relic, there's a reason why.

    Unless your engine is so poorly matched that no carb can work, it would be worth testing with a known well tuned carb just to make sure. I do this all the time at the dyno...it's a regular thing.
     
  10. erhan ergin

    erhan ergin Veteran Member

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    I have some questions based on my observations on my camaro's idling/performance/temp issues.
    As I mentioned in a few posts ago I replaced the idle bleeds with 78 (original was 65). I also have a A/F gauge.
    What I am realizing is the problem with the engine is the fact that the jump in vacuum from just under 1k rpm to about 780 rpm is greater than 2 inHg.
    Essentially when the car is in park idling at just under 1k rpm vacuum is 8-8.5 iinHg but when I put it into gear as rpm drops, the vacuum goes to ~ 5.5 to 6 inHg.
    The 6 inHg results in a AF ratio of over 15.5 to 16.5 but at 1k rpm in park it is at 12.8-13.4.
    Essentially the vacuum change in such a small rpm range is very big as far as I can tell. And this causes the car to be rich around 1k rpm but lean at 780 rpm. When the car is cold, it is impossible to keep it idling at 780 rpm. Even after it warms up, it wants to die if you go below 850 rpm and barely idles.
    The vacuum goes well past 15 in over 1200 rpm. Is this possibly because the carb is too small? Should there be such a big jump in AF ratio with 2 inches of change in vacuum?
    One more detail, the air/fuel screws have this plastic sleeve around them. On a number of occasions these sleeves came all the way out to the top of the screw as I keep adjusting the screws in and out. In these cases I take the screw out and reseat the sleeve into the hole close to the tip of the screw but it only goes so far deep. The a/f screws do impact the air fuel ratio based on what I see on the gauge so I think they function fine but maybe due to these sleeves coming out they are somehow defective?
    BTW I would like to try a different carb like folks suggested here but I cannot justify the ~$500 especailly if the issue does not get resolved. I do not have any one to borrow a carb either.

    Thanks for any suggestions.
     

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