need carb tuning help

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quickd100
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need carb tuning help

Post by quickd100 » Sat Aug 27, 2005 1:43 pm

I've got a 850 holley double pumper that I'm running on E85,(15% gas,85% alcohol). I've jetted it up 35% over the gas baseline, 88's&86's. I've opened up the idle feed restrictions .004, installed the 50cc accelerator pump kit on the primarys with the brown cam supplied. I also installed the large cream colored cam on the secondaries. I've tried #37 squirters, #40's and a set I drilled to .055. The motor idles with 12" of vacuum and am running 6.5 power valves front and back.
I've got a bog or stumble when I nail the throttle from idle or low speed. The #40 squirters so far cause the least stumble. Need some ideas on pump cams and or squirter sizes to try.
The rest of the motor is as follows, dodge 440, 11.2-1 compression, 452 home ported iron heads, small solid cam, .496I, .518E, duration @.50 is 239/246, 110 center. M1 single plane, 1-3/4" headers. Timing is 38 degrees at 650rpm along with 10 degrees in the vacuum advance can. 4000rpm stall, 4.10 gears.
It idles and drives as good as any gas motor I've run, just the stumble when I stab it. Is it squirters& pump cams that need attention or am I overlooking something else? Dave
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Post by oldhead » Sat Aug 27, 2005 2:43 pm

I have never tryed what you are doing,but,What about your power valve channels...If you need bigger jets you would need bigger channels too....Look the eazy way is try a mix like 50/50 see if it gets better...call Holley at 1-270-781-9741 Ask them thats in there alco. carbs. for sizes.Good Luck.OLDHEAD :D :D :D :D
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Post by bill jones » Sat Aug 27, 2005 6:16 pm

-why did you stop at .004 larger on the idle restrictions?
-When you state you jetted it up 35%, what is 35% up? the square inch area of the jets or the diameter-what?
-I have seen some 850's that had .093" power valve orifices.
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-Does this stumble only happen when the secondaries are quickly opened at low rpm or will the stumble happen just on the primaries?
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-I would:

1-do a 100 rpm increment test from idle and see when the primaries venturis start to flow, note that rpm, then change the float level up two flats and see what that does to the start rpm of the venturi flow, then go down two flats get those numbers.
-once you get that start point figured out and what the float level does to it you can try raising the float level to get the venturi flow sooner and see if that helps.
-then maybe try the same thing on the secondaries unhooking the secondary linkage or just try raising the secondary float if raising the front float had done something positive.

2-I don't think the idle restrictions are large enough to properly feed the transition slots---maybe they are OK for idle but those orifices also affect the transition slot fuel.
-if the primary blades are nice and low on the slots like within .025" of closing the slots off and the idle screws are adjusted out close to or more than 2 turns I'd enlarge the idle restrictions a thou at a time to about .044" considering that the stock idle restrictions were .038".

3-I made a pair of dial indicater mounts and a degree wheel that allows me to measure the throttle position starting at idle---in degrees to wide open throttle---and the indicators show me the pump lever movement out on the lever right below the spring/bolt that pushed the lever.
-This allows you to tweak the cams and to get the max squirt out of the existing pump component combinations---and at least you can then graph out the pump shot and SEE what you have.

4-I'd install a vacuum gauge and note the vacuum right when the stumble occurs---and I'd also note what happens in relation to the vacuum advance dropping away---and you can then also correlate the power valve opening point.
-If the vacuum advance drops off too quick you can get a delay valve like the older Fords used to slow down the drop off rate.

5-if you have room to install a 2" tall spacer I'd try a 4 holer that is flared out from the throttle bores to match the manifold and to get the 4 holes blened in the center to reduce as much turbulence as possible---and it will help to get the venturis to start to flow quicker.

6-If you can do something to cause this to happen while the car is stopped I'd check the timing as see if something is happening with the ignition timng that directly corresponds to the stumble.

7-If your squirter nozzles are the short ones I'd try the extended tube type.

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Post by quickd100 » Sat Aug 27, 2005 7:45 pm

Bill; Thankyou for the suggestions, to answer your questions.
I jetted up by using the mean flow numbers supplied by holley. The 80's mean flow is 703cc's , 703x1.35=949, a #88flows 952cc's.
I opened the idle feed restrictions .004 because my holley book said a .001 increase represents an 8-10% fuel delivery increase. My idle screws are now 1/2-5/8 of a turn out from seated.
I've tryed the extended tube squirters and it didn't make a difference. I believe the ignition timing is fine, I also tryed it with the vacuum advance plugged.
I'll try unhooking the secondaries and see what happens and try the venturi/rpm flow/ float level test and see what happens
Dave
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Post by putztastics » Sat Aug 27, 2005 8:30 pm

Sounds to me like you need cams with more initial movement and larger shooters to go with them.

I would pay attention to the power valve channel restrictors too, they probably should be opened up. The power valve channel restrictors work with the main jets. The two conditions they cover are;

cruise condition when the manifold vacuum has not opened up the power valves and only the main jets are flowing fuel

and power conditions when the manifold vacuum is low enough for the power valves to open and both the power valve channel restrictors (PVCRs) and main jets are flowing fuel.

So it's possible to be jetted right for cruise conditions but when you go to power conditions be lean if the PVCRs haven't been opened up.

The way this tuning should be done is set the cruise mixture first using the main jets and then set the power mixture with the PVCRs.

Most people get by setting cruise and power mixtures with the main jets only but you probably have to mess with both main jets and PVCRs since you are using E85 and the mixture is quite different from gasoline. E85 stoich A/F ratio is about 9.6 and its power ratio is more like 6.5 - 7.

Are you going to be in Bismarck with the vehicle anytime soon? We could tune it with the LM-1 wide band A/F meter I have. That meter is fast enough to log A/F ratios during acc pump operation.

LM-1 log of a 360 Dodge accelerating under no load
Last edited by putztastics on Sat Aug 27, 2005 8:32 pm, edited 1 time in total.

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Post by quickd100 » Sat Aug 27, 2005 8:59 pm

Bill and Jesse; I unhooked the secondaries and took a spin in it on my semi-private drag strip,(440 Street SW,Really). It bogs, stumbles when you quickly flat foot it. I tryed the #40 squirter and a #55. The #55 does more of a stutter and then catches rather than almost die before it picks up. The 55 was a long tube squirter, tryed it again with and without the vacuum advance, no difference. The venturi/float/rpm test will have to wait until tommorrow, it ran out of fuel in the garage.
Jesse; I've got 50cc pumps on both front and back, the cams are the biggest most aggressive ones, big brown cam in front, big cream colored one on the secondary. I tried the smaller ones and kept going up. The idle and cruise I believe are on the money.
I'm pretty sure I have to open the PVCR's up, but how much? I have to go back in it to be sure but I think they are .051 now.
I wish you didn't live half way across North Dakota you'd have a tough time getting rid of me when you had the dyno fired up. And you and the wife and kids would be getting fat on spuds. Dave :D
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Post by putztastics » Sat Aug 27, 2005 9:28 pm

Dave, that is the beauty of using a wide band meter, you would just creep up on the correct PVCR size according to what the meter is telling you.

Did you click on the link on my post and look at the LM-1 log?

This is the 21st century man!!

I've used a lot of pink cams for the most agressive initial pump shot but I'm not sure it is a 50cc cam. Some cams are linear, and some more exponential, that is they deliver more initial shot and taper off with increasing throttle position. You want one with more initial shot. Also you can change the acc pump cam screw position to change the pump action. What I would look for is the cam/screw postition that moves the acc pump lever most agressively right off idle. Just look how the acc pump lever lays on the acc pump cam at idle and watch how the cam moves the lever right off idle. Of course you have to have big shooters to take advantage of agressive initial cam action.

It's possible too small PVCRs is contributing to the condition you describe with the 55 shooters.

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Post by quickd100 » Sat Aug 27, 2005 10:22 pm

Jesse; I've looked at your link, pretty nice curve! I know it's 2005 but I'm still working with 19th century equipment. My 850 had the pink cam to begin with. I figured I'd give the cam/50cc pump a try first before I started hacking a metering block. The cams I've got in it now are the most aggressive one.
I'm going to contact Holley Monday morning and see what size PVCR they recomend with this before I start hacking. Dave
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Post by bill jones » Sat Aug 27, 2005 10:36 pm

-if you tried this wide open throttle deal at 1000, 1500, 2000, 2500, rpm etc does it act exactly the same when testing just the primaries or does the stumble become less as you get closer to 2500rpm?
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-Personally I do not feel the power valve restrictions would have a lot ot do with the stumble at low rpm.
-It is my thinking that the power valve restrictions work on a sliding scale meaning the higher the rpm the more they work and if the problem is under 2000rpm I really don't think power valve orifices will make as much difference as working with the transfer slots and the pump shot, but the pump shot may not be able to fix the problem by itself.

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Post by quickd100 » Sun Aug 28, 2005 3:35 pm

I unhooked the secondaries and ended up raising the primary float 6 flats which seemed to help a little. I tryed drilling the PVCR .003, no noticeable improvement there. It will stutter or bog when you flat foot it under 2700-2800rpm. It works fine if you quickly roll into the throttle. Dave
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Post by bill jones » Sun Aug 28, 2005 5:47 pm

-explain what you have on this engine for the ignition system components and sparkplug gaps etc..
-Is it an automatic trans? if what is the stall speed?
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-six flats higher is about 1/8" inch and that should make a significant difference in when the fuel starts to flow from the boosters---a lot sooner.
-I'd like to know what the float levels are set at if you measured them with the bowls off and inverted, using a set of dial calipers.

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Post by putztastics » Sun Aug 28, 2005 6:09 pm

Dave, do you still have the vacuum advance hooked up? If so are you sure it's hooked to ported vacuum? Also what is the initial advance amount?

Is this 850 the carb you were using before E85? If so was it working good?

Have you tried a smaller carb?

Have you tried a 1" four hole spacer or like Bill suggested a 2" four hole flaired to open spacer?

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Post by quickd100 » Sun Aug 28, 2005 6:36 pm

Ignition is a MSD 6C, 8mm Taylors , plugs gapped at .040. Torqueflite, with a TA 10", stalls about 4000 behind my junk. The 850 has been on the truck for the last 4-5 years and has always worked real well. Last spring on gasoline the truck, (3550lbs.) ran a 1.595 60ft. and 7.621 in the 1/8 and was picking the front wheel 8" off the ground leaving the line. (truck has 67% of the weight over the front axle too).
I tryed 8 flats on the float and it was pushing fuel out the vent. The spark advance is 38 degrees at 650rpm. I've usually run without the vacuum advance but thought I'd try to improve mileage on the street. I've tryed it without the advance hooked up and that wasn't the problem. I haven't tryed a 4 hole spacer as yet because I don't have one laying around the garage. On gasoline I've used a 2" and a 4" open spacer with good results. Dave
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Post by putztastics » Sun Aug 28, 2005 6:36 pm

Is this an older carb with the ball check in the fuel bowl for the acc pump? Or does it have the rubber check valve? I've seen the ball check valve retainer break and then you don't get a full pump shot because part of the pump shot flows back into the fuel bowl. This is an unusual problem though and it would have been obvious when you put the 50cc pumps on.

The reason I'm asking is I would think that with 55 shooters and aggressive cams you should be getting plenty of pump shot.

Does fuel flow out of the shooters with the very slightest throttle movement?

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Post by quickd100 » Sun Aug 28, 2005 8:38 pm

Check ball is OK, fuel comes out at the slightest touch of the throttle.
After talking with you on the phone this afternoon Jesse I went out and jetted up 4 sizes and tryed it, no improvement. I then went up another 4 sizes to 96's and it started coming around, just a little hesitation. I went back and jetted it up to 98's pri, 96's sec. and hooked up the secondaries and installed #40 squirters front and back. It still stumbled a bit but I haven't touched the rear metering block. I think it would have worked nicely if I had. I guess this means open up the PVCR's. I'll call Holley in the morning about it.
On a side note, when I stood on it at 40mph on warm clean blacktop the rearend wanted to come around on me, it just Roasted the tires. Dave :twisted:
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