Blower idle hunting, cycling, surging, annoying...

Discussion in 'Manton Push Rods Top Alcohol Tech Questions' started by Kendrick Roberts, Mar 7, 2011.

  1. Kendrick Roberts

    Kendrick Roberts New Member

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    I have been plagued with this problem for a while (idle surge, hunt, etc.) sometimes I can get rid of it, and other times it's right there. I thought I had a handle on it, but it showed up in round three of eliminations (hard surge) making staging difficult and breaking my drivers concentration. If I raise the idle speed to about 2000-2200 I can keep it gone but the driver doesn't like how hard he has to hold the brake against it. If I go way rich (90+% bv leak) sometimes that will fix it but it can make it stumble after extended idle time. Would really prefer to idle at 1500 or so.
    Specs are:
    545 BBC
    1471 conventional (BDS Airlock) 20% over (18 lbs boost)
    .812 lift cam with 114 LSA
    12.5:1 CR
    Brodix 2x heads
    Glide 6200 stall 10" FTI
    Talked to one of the Top Alky crew cheif's this last weekend and he gave some pointers, but I am taking any advice I can get.
    Other people seem to get rid of it.
    Thank you.
     
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  2. Mike Canter

    Mike Canter Top Dragster

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    What is your idle return poppet set at?
     
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  3. Kendrick Roberts

    Kendrick Roberts New Member

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    12 psi on Idle bypass (secondary bypass)
    More info: Waterman sprint 1000 pump (10 gal)
    95 Main jet (currently)Nozzle and jetting set to return approximately 30%
    Port poppet open at 10 PSI
    Old Black square type BV
     
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  4. TADHemiracer

    TADHemiracer Member

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    Surge Problems

    I could be wrong but it sounds to me more like a fuel delivery problem. Either the pump does not flow enough fuel because it may just be too small or has enough wear internally that it is not flowing what it was rated. Sounds like it goes lean and raises the idle speed enough to make the pump flow more then goes rich and slows down into the surge condition. You might temporarily install a 0-30 psi fuel pressure gauge on the pump side of the BV and see if the engine idling fuel pressure stays constant or drops below the 12 psi you have the idle circuit set for and/or try a smaller main pill. If it were mine, I think I would increase the port check to at least 30 psi or so to keep them dry at idle whether surging or not. Just another .02 worth.
     
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  5. Mike Canter

    Mike Canter Top Dragster

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    Kendrick, a couple of things to try. First is to drop your idle bypass down to 8 psi crack pressure and try it. The other thing is as TADHemiracer talked about is your port poppet. It maybe too low. What one normally wants is the port poppet to be closed while staging then to pop right on the launch. I believe yours is probably opening during stage or maybe even at idle. One way to do that is to start the data logger and come up to stage and see were the fuel pressure stables out at. Lets say it is at 30 lbs so now set your port poppet at 25-28 psi crack. With the idle poppet at 12 and the port at 10 you maybe opening and closing the port poppet at idle vice the idle poppet so it is hunting. I would first check the idle and the port poppet crack pressure and write them down so you can go back to them then change one the both and see what happens.

    If that doesn't fix it then the other thing to try is to set the idle and port poppets and then adjust the BV idle mixture a little and see if that helps.
     
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  6. Kendrick Roberts

    Kendrick Roberts New Member

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    I went back and looked at the datalogger, and the fuel pressure at the nozzles is between 0 and 1 psi. I think if I actually had much more than that (at the nozzles) at idle the motor would drown. I did not think to check the pressure before the BV as TADHemiracer suggested and he could be on to something there. More information is always better when trying to isolate a problem. We leave at WOT on a 2-step (set at 3200 rpm) and at that point the nozzle pressure is about 24 psi and the ports are all in.
    I have tried the idle poppet setting all the way down to 3 psi Mike, but that was years ago, and maybe it's time to revisit that.
    It is possible that I am not being clear about this. What I am after is the "rump-rump-rump" at a dead idle that is extremely common in blown and injected applications.
    I have even gone as far as getting guys who have successfully gotten rid of this on their cars to try in my application, and they just shrug and walk away after a while.
    I have never been clear on why they did this in the first place, and I used to think it was cool, but I'm over that and would REALLY like to get a handle on this.
     
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  7. Mike Canter

    Mike Canter Top Dragster

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    I understand what you are trying to get rid of. This is the way I understand what is happening. If I am wrong then somebody jump in here. The crux of the problem is that these alcohol motors increase RPM as they go lean. So when a poppet opens and bypasses fuel the motor goes a little leaner it speeds up. When it speeds up the pump puts out a little fuel and the motor goes a little richer and slows back down. The idea is to get that poppet that is on the verge of opening changed so it will not open and close. Sometimes what adds to this is the BV can cause it if it is adjusted too lean.
     
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  8. Ken Sitko

    Ken Sitko Super Comp

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    I think you have to keep in mind that it is very difficult to make an alky motor idle nice at low rpm's. I have always found that 1800 to 2000 is about the minimum. I know with a converter the driver likes to have it lower than that, but it is a delicate balance. All the above suggestions are good, you could also try opening the butterflies to about 2000, then richen the barrel valve until the rpm drops to the desired amount.

    Be careful about dropping the idle check too much, 3 lbs is very scary to me, I have had bad things happen back in the day with that setting.
     
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  9. Don Onimus

    Don Onimus New Member

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    idle

    It is what it is. We all live with that. loosen the converter a little, and tell your driver to suck it up. There are certain things we all have to live with. Blowers and converters are one of them.Sell that 44, put in a 12 or 20 or Mallory and run some more lead.There is no way that motor needs a 44. Also listen to Mike. Don
     
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  10. secondwindracing

    secondwindracing top alcohol

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    we now run a converter car and it will idle at 2000 to 2200 never a problem ..Dave
     
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  11. Don Onimus

    Don Onimus New Member

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    idle

    So do I Dave. around 2100 / 85 percent leave from just above idle. DMPE 14-71 Kebelco @ 42 over. Powerglide Coan Mega converter Don
     
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  12. Kendrick Roberts

    Kendrick Roberts New Member

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    I have had that attitude myself for a while Don, but Fast Eddie (Carecchia - I think) makes his digger idle around 1500 to 1800 with a nice Top Alky cakle to it. His advice is "it's in the barrel valve" but I can't find it. you must be thinking of someone else on that 44, we run a 7AL. I also found that less timing USUALLY makes the surge softer, but even that is not always. I am definitely listening to Mike, he seems well informed.
     
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  13. vwsamba

    vwsamba New Member

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    "its in the barrel valve" is correct. mine hunted just like you describe and it was handful to stage. Then Mike Halsted came over and said "i can fix that in a minute". He was right, just keep leaning out the barrel valve until it cleans up(mine took 5 flats to do it). Add some quick release plugs to the hat also for quick staging fine adjustments. My car was a dream after that. Thanks mike and all the best at the MM!:cool:
     
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  14. Kendrick Roberts

    Kendrick Roberts New Member

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    That is interesting VW, because the quick release plugs and minimizing the butterfly setting is what the Top Alky guy reccomended (I didn't get his name, he tuned the Artivinca car from Brasil). I plan on making these modifications, as well as looking into all of the other suggestions, and running a few gallons of fuel through it before we go to Charlotte, and I will post my success or failure in this matter, but I am not likely to give up until I feel I have solved it.
     
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  15. Mike Canter

    Mike Canter Top Dragster

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    What that is assuming is that your butterflies are set at a point that is too far closed so they are moving in and out based on suction caused by engine rpm. The motor tries to increase rpm and when it does it sucks the butterflies closed and the RPM drops then the suction is released and the open up a little again so the rpm increases again. If there is slack in the linkage or the stops on either side of the shaft are not adjusted right can cause that or just a worn injector hat. That pull on the butterflies tied with incorrect poppet setting can cause you to chase your tail. If you fix one problem without fixing the other then you will not see a result. My recommendation is to set up your whole system correctly and see what happens. Check your butterflies and see that there is no slack and the stops are both tight against the tabs. What is the butterfly gap at the bottom of each set at right now?
     
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    Last edited: Mar 9, 2011
  16. pete9857

    pete9857 Member

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    idling

    Is it possible you a vaccum leak under the hat? Or a crack? That will create havoc on the tune-up, especially when temps change. Our hemi with a coan converter idles smooth as glass at 1900 rpm's.

    Glenn
     
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  17. Kendrick Roberts

    Kendrick Roberts New Member

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    Right now the butterflies are at 0.011". During the time that I have been chasing this I saw the deflection you are referring to and opened the butterflies from their starting point of 0.006" and this seemed to reduce the tendency to open and shut slightly during the surge. There is no appreciable wear on the shaft, and it is the later design with the 3/8" cross shaft and the roller bearings at all of the pivots. I am very careful with the throttle and idle stops in order to avoid shaft twisting at either end of the travel. (I went out and re-checked that just to make sure I wasn't full of crap). I had not considered a vacuum leak as pete9857 suggested, but I have checked for cracks and nothing is jumping out at me. I like your advice to start fresh because chasing my tail is a good description of what I have been doing. I am going to put gauges in a few places that I haven't looked at before to see what is going on, and I am going to try and beat the fundamentals to death to see where that gets me.

    Thanks to all who threw in their $.02 (I think Ive got about a quarter now)
     
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  18. Mike Canter

    Mike Canter Top Dragster

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    Are you using silicone sealer between the hat and the blower? The norm for the butterflies is .012" on the tightess one.
     
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  19. Fuel Cars

    Fuel Cars AA/AM

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    I had a leak in my system between the hat and blower and the idle was sky high, not surging.

    Good luck
     
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  20. Kendrick Roberts

    Kendrick Roberts New Member

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    No silicone, just the green gasket with the screen that keeps rocks and small children out of the blower. When did the standard become 0.012"? I was always told 0.004" to 0.006" and that was just as a starting point. I don't have a problem with this, I am just curious.
    As Fuel Cars mentioned- when I have had leaks in the past the idle went high- but at this point everything is on the table.
     
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