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 4150 runs rich at light cruise 
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Joined: Tue Aug 19, 2014 3:11 pm
Posts: 33
Been fighting this for a while now on a Holley 4150 with annular boosters in a Cobra replica .... 482 FE with merged collectors and Ebrock dual plane intake . Dist. is locked at 36 degrees . Been fighting what I thought was a low speed bucking at light throttle , so I checked and I was running on transition slots . So , just playing .... dropped the transition slot restrictors to .055 " ( stock was .067 ) and surging/bucking much worse , so it looks too lean ? Went stupid rich next at .078" TSR and surging/bucking was gone , but plugs are black . So , dropping the TSR TO .067" next and IFR ( in low position ) from .036" to .033" to see what happens
I`m beginning to think the merged collectors are causing most of this . When they were put on some years ago by Calvin , my Pro Systems carb went from running ok to running rich at lower rpm range . Changed carbs and am now fighting this again .

Any suggestions on setting up a carb with merged collectors ? I do mostly street driving , but also several HPD events on road courses a year .
BTW , cam is 270 @.050 thousands at about .600" lift . 8.5 PV in primary , 88 MJ in secondary and 80 MJ in primary .


Tue Apr 11, 2017 12:11 pm
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Joined: Fri Feb 08, 2013 2:37 pm
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What venturi size is this 4150 carb? Original List # ?

Annular boosters usually (almost always) require several sizes smaller MJ than the same size venturi with a down-leg booster. Annular boosters in 1000 HP and old style 850 with 1-9/16" venturi may run well on some engines with MJ in the low 70s 72 ~ 74. I would expect #80 MJ to be rich at part throttle.

I wouldn't blame the merged collectors for this, any exhaust change will affect carb calibration, even just changing a muffler or the length of tailpipe. Engines with radical cams are more likely to be affected because there is more valve overlap time for reflected wave activity in the exhaust system to get back into the intake side of the engine. Just the nature of the beast.

I would drop the MJ in large steps, 3-4 sizes at first, until you find the lean limit for the part-throttle range with vacuum above the PV opening point, then go back in small steps to the leanest jet for good part-throttle performance, and then address whether the PVCR needs to be adjusted as a result of the jet change to maintain correct WOT A/F.


Tue Apr 11, 2017 2:59 pm
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Joined: Tue Aug 19, 2014 3:11 pm
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Tuner , thanks . Original list is 082851 . I measured the butterflies at 1.7" and the venturi at 1.6" ..... or as close as I can get with my limited measuring equipment .... i.e dial calipers . When the engine was on the dyno , the lambda ratios ranged from 13.5 at 3500rpm to 14 at 6800 rpm and hp was 671 at 6200 and torque at 647 at 4600rpm at WOT with this carb . Still pulled 601 hp at 7000 rpm .The only difference between what was dynoed and what is on the car now is I went from no PV in front and 87 primary MJ to a PV and 80 MJ .
The HSAB`s are 31 pri and sec and the LSAB are 84 sec and 90 primary . I locked the timing at at 36 degrees the other day . PVCR is .065" on primary now . E1 - .028 , E2 - .028 , ES - .031 , E4 - .032 . This is what was run on the dyno .... however , no exhaust system like I have on the Cobra .


Tue Apr 11, 2017 3:47 pm
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This 082851 came with down leg and was converted to annular? The 1-9/16" x 1-11/16" venturi x throttle bore arrangement is the combination used to make the old NASCAR legal "830 CFM" carb. A regular 850 CFM is 1-9/16" x 1-3/4". Are the bores in the base chamfered (tapered) from 1/3/4" on the top side (entry from the carb body) down to the 1-11/16" at the bottom side (exit to manifold)? If that is the case, I would replace it with a straight-through 1-3/4" base and throttle blades. The bases from BLP have the correct size slots in the correct location. The smaller throttle bore is not exactly desirable. Measure the bore diameter at the bottom of the body casting, 1.688" or 1.750" ?? With annular boosters in that body I think you need a smaller jet for part-throttle than you are using now, but the metering area you have now which you have determined to be correct for WOT should be maintained.


Tue Apr 11, 2017 5:25 pm
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Yes , carb was converted to annular boosters by someone in the past . Pulled the carb and measured the base plate and it is 1.75' with no taper and appears to be a BLP base plate ? Throttle blades are 1.75" already . Body where it mates to base plate is also 1.75" . Above 2700 rpm , carb is perfect and WOT is also good . Main problem is when running on transition slots and idle ,i.e in the pits or traffic from a stop light at very lite throttle or behind someone who has the nerve to go the speed limit and this puts me in the 2100 to 2500 rpm range in 1st or 2nd gear .
Oddly enough , the Pro Systems 950 HP made a consistent 12 to 15 hp less than this carb .


Tue Apr 11, 2017 6:44 pm
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Quote:
behind someone who has the nerve to go the speed limit and this puts me in the 2100 to 2500 rpm range in 1st or 2nd gear .
LOL, the nerve of some people.

That RPM range and steady speed level road load is in the purview of the T-slot. Sometimes, a carb with too much emulsion air, too large MAB or too large top or second E-bleed (or if the float level is too high - when is the last time the needle and seat O-rings were renewed?) will "perk" the startup of the main in blobs, like a Mr. Coffee brewing, and the blobs will cause intermittent richness with a burbling misfire that almost nods your head back and forth. Usually, it is just because the combined curb idle and T-slot is too rich because the vacuum at the 2300 RPM steady state is so much higher than the standing curb idle at 1000 RPM or lower. You should be able to tune it to run well if your patience holds out. Your cam sounds about like the old C8AX-D 330 deg. x .600" lift. That one works pretty good as I recall.


Tue Apr 11, 2017 7:36 pm
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Joined: Tue Aug 19, 2014 3:11 pm
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Tuner , got to play yesterday a little . Carb is somewhat better with the .067 TSR bleeds , but still bucks some at 2400 rpm and under when I`m at very lite throttle ( transition slots only ) . So , raising the TSR`s to 70`s today and the IFR`s from 31 to 34`s to see if that helps . Needle and seats were replaced about 2 months ago and are the BLP bottom feed units . First and second E bleeds are .028 and float levels are just under the bowl plug threads .
Any other suggestions as I`m about out of ideas ??


Thu Apr 13, 2017 9:43 am
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This is on a level road, constant speed, no acceleration at all, eh? If this is the case, you can probably hear it by just free floating the engine at the same RPM while you push some accelerator pump to it or choke it with your hand to see if it wants to be richer or leaner.

Look to see if the booster is starting up and dripping blobs of fuel right at that RPM and no load. If that isn't happening, then tune the T-slot. If it is dropping blobs of fuel then work on the main. Maybe all it needs is a lower float level.

This low speed level road area is usually the part of carb tuning that requires a lot of tinkering and patience, so don't weaken, you will get it.

Long duration and large overlap valve timing like yours results in so much exhaust dilution right in this load and RPM range the combustible A/F range is narrower, which makes the carb tuning more sensitive. Usually the A/F is too rich, the engine sort of blurbles along until adding a bit of throttle clears it up, it just won't run smooth with no load. However in this case, it sounds like you have already found the lean side by playing the T-slot jet. The idle mixture screws will affect this range of small throttle opening with no load, so a clue can be obtained sometimes by making a big change on the mixture screws (which will obviously upset the curb idle) to see if richer or leaner is the thing to do.


Thu Apr 13, 2017 1:51 pm
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Joined: Tue Aug 23, 2016 12:23 am
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2500+ RPM thru the neighborhood and parking lot in an open pipe cobra? Man, your neighbors must hate you! ;) I crawl thru those in my 408W cobra replica at about 1200. Mine surges/bucks at that speed to but I'm still working on the transition tuning.

I find I'm really only ever in the main circuit when I'm accelerating briskly or WOT. Having 500+ hp in a 2200 lb car makes for some interesting challenges. Tuning the transfer circuit to get good AFRs thru all the rpm range has been like banging my head on a wall.

What transmission do you have? What is your drive ratio in your highest gear? What RPMs are you running at 70mph on the highway?


Tue Apr 18, 2017 9:46 pm
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Joined: Tue Aug 19, 2014 3:11 pm
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Tuner , almost have it where I want it . The key was I was making big changes and needed to make them in smaller increments . Long story short , Transfer SR was originally .067" , now at .073" and bucking almost gone completely . IFR is now at .033" ( stk. was .036" ) and mixture adjust screws are at 2 1/8 turns out . I am going to try going to .076" on the TSR to see what happens ..... may make it too rich at cruise in this weather (mid to upper 80`s now and still have winter fuel at the stations ) . You can actually stay in the garage now without your eyes burning .

Texas Doc , Actually my neighbors are pretty cool . The only complaints I have had was from 3 people ..... I haven`t given them rides yet . The other day I nailed it in 1st and broke the tires loose for a good distance and the neighbor from down the street came running up ... thought he was PO`ed .... all he said was " That was so cool .... take me for a ride " .
That said , I really try to keep it down , don`t start the car after 9:00pm or earlier then 9:00am and if I`m coming in late , I coast in at idle and shut it off ASAP .
This engine dynoed at 671hp at 6400 rpm and total car weight with a full fuel load and me is 2693 lbs, so I know what you mean . Tranny is a TKO 600R with the .82 5th gear . . So with a 3.54 rear end and a .82 5th , final ratio should be 2.9 : 1. On the Interstate , 75 mph is in the 3300 rpm range , which is just where I want it . Engine ( 482 Ponds aluminum engine ) went to right at 7000rpm on the dyno , so that should be right 140 to 145 on the track ( VIR ) .
I know exactly what you mean about the transfer circuit as that`s been my whole problem .... compounded by running merged collectors on the Cobra . One other tong I did that made a difference was to change out the primary throttle blades with the holes for ones that weren`t drilled out , secondaries didn`t have the holes . Now my transfer circuit actually works .


Wed Apr 19, 2017 9:38 pm
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