327 with holley, bog problem...
 

Hey guys my buddy has a 327, .040 over with about 9.5:1, XE274, Dart ironj eagle 180cc 2.02 heads, airgap intake, and a 750 double pumper.. ok Now heres the problem, no matter wut he does the car bogs real bad off the line, its way to lean, Hes got #74 jets inthe front, and #80 in the back with a 50cc pumpshot and a #41 squriter with a hollow screw. Now I don't really understand how much more fuel this motor could want. He tried everything with the jets and different power valves and stuff, hes got a 6.5 in there now. Hes got alot of suspensuon work done including drag struts and shocks and he runs drag radials and hooked at 4500rpm dumpin the clutch, it will hook real hard and somtimes pull a wheel up then bog real bad then take off and only pull like a 2.2 60-foot , hes went a best of 13.4 with the car. He took it to a speed shop today that we get our parts from and the guys helped him out a little, he disconected the vacume advance and put the base timing at 16 and my buddy says it feels better but it still bogs real bad. Does any1 have any input or idea as to how to fix this problem? thanks everyone

Since it hooks real hard, it may just be too much carb in a dual pumper category for the engine to deal with when the rpm drops off.
All the jetting in the world won't fix it if that's the case.

It hooks hard then bogs? Maybe the fuel is splashing away from the jets in the secondaries? Maybe jet extentions will solve the problem? Thats one of the few possiblities

well its definatly a lean condition cause if its sitting at idle and your floor it and let rigth off it pops through the carb, so it seems like we can't give it enough fuel..

Do a search under my userID and also F-BIRD'88, and the phrase "transition slot"; both of us have discussed Holley calibration, and the exact cause of that problem, at great length recently.

An ignition issue can easily disguise itself as a fuel problem.
I just tossed an MSD box in the trash for the "pop" issue. This was after tinkering with carb and timing for months.

True dat; it is said that 90% of all difficult carb problems are in the ignition, and 90% of all hard-to-diagnose ignition problems are in the fuel system.

but the bog is just off the line and thats all. If I hook up a timing light and rev it wot and let off so it pops and watch the balencer wut would happen when it pops? cause it should just go to 36 where its set right?? He went back to the speedshop/machine shop today and the guy said how did you do and he told him how its the same and he said I have now idea, then he told him he would just tear the motor apart and start from the ground up. I kind of thought that was an obserd statement coming from someone who owns a 9 secound car. Well anyways for some reason I still think I can figure this out and get it running good but this kid refuses to give me time to help him, I mean he let me show him how to build the damn thing. Well is there any way to check and see if somthing else is causeing this??

There's an old saying, something about you can lead the horse to water but you can't make him drink.

Basically, you're not asking a car question; you're asking a human behavior question. Maybe he just has to learn the hard way.

yea thats true man, well I guess I am just a little pissed lol. Well to keep it to cars is there anyway to narrow things down here?

Seems like there's alot of "tear it all the way down" coming from people who don't own the car, to troubleshoot a driveability problem. Someone posted the other day that he had been advised to check crank end-play as part of troubleshooting a low-RPM stumble. :rolleyes:

Try a vac sec carb. If that fixes it, re-calibrate the driver.

Typically, when a carb jumps hard off idle and then bogs, it is a sign of a rich condition possibly due to wrong power valve or too much accelerator pump. A lean condition off idle will usually stumble as soon as you hit the gas, you may even have to pump the throttle to keep it from dying.

If your friend refuses help, why waste your time?

alright We put my edelbrock on his car and it did the exact same thing as the holley, so I went over the holley and the pump shots are perfect, I also uped the primary squirter from the stock 28 to a 37 and that did nothing also. I don't think this is a carb problem anymore. I figured it was lean cause it pops through the carb, but we did everything and nothing works, We changed the coil out and that didn't do a thing either. I figure it may be a faulty MSD box but wouldn't that mess up all the time and not just when u floor it real quick?? We are gonna take the box from his brothers car and try it on his to see if thats the problem but if that doesn't work that what else could it be?? maybe a messed up valve?? Should we run a compresion check? what should it be around in each cylinder also? thanks guys

Not saying that's what it is, but the ignition was crapping out on my son's Spirit for a year. Same symptom with his MSD. We went nuts with timing, pump shot, jets timing etc...
I had a new Accel 300 box sitting here and it was a day and night difference. No bog, pop or choke.

ACCELERATOR PUMP


read about it at www.holley.com

Have you pulled the spark plugs out to tell if it were extremly rich or lean? are you SURE the timing is correct? did you install the timing chain ''strait up'' with the marks? check the cam card to see where the manufacturer suggests timing to be set, to me it sounds like a ignition issue

he switched out the MSD box and that made no difference at all. The only thing I can think to do is keep changing the spring in the dist. and see if it goes away, and if not I really have no idea at all. Anybody with any type of opinion please post it cause I am lost here..

When the bog off the line was first mentioned, first thing I thought of was the typical fuel slosh up through the vent tubes which is cured with the rubber hose trick from vent to vent with a section cut out for the thing to still vent properly. But then a edelbrock was put on and same problem so that gets that cheap easy idea out. Trying not to dig too deep right off the bat:)

If your getting a pop through the carb I would tend to think it either timing is getting messed up, or possible valve hanging open. How old and what type of distributor is he running? Just last month I was running my yr old MSD billet distributor on my new motor and it did'nt run right-aka as fast I thought it should. Anyways, when I was in staging I kept hearing a non-consistent clunk/pop through the exhaust that would make the car shudder when it happened.

Ended up pulling the distributor and 1. it had too much endplay 2. was missing a plastic glide that the one weight slides on and 3. bushing was missing. So it was getting eratic timing and causing all sorts of troubles. If all the other ignition parts were swapped for testing, I'd look into trying a different dis. and see what happens.

HEs got the same dist. and its pretty much new. I was going to get one also cause I have a summit HEI with my MSD6al box and I heard bad things about the gears fallin part on them. What kind of Dist. are you running now or was it a human error thing causeing your Dist. to do wut it did?

I noticed that after I got the car out of storage sitting all winter, I pulled the cap off the dis and what a rusty crusty mess. This was the first generation of the HEI cap MSD had W/O the cap vent. So all that I can think of is the condensation from driving it in the fall then sitting all winter just provided a place for rust to grow. Before i dropped the new motor in I took off the cap/rotor and used my 3m rolocs to knock the rust off the rotor tip, and under the cap where they spark the terminals, and also off the weights and anything else I could get at without major disassembly.

Being only a yr old I was not looking for broken/missing items so it was easily overlooked by me since I took it for granted it "should" still be good to go, but .8 quicker later with the new dis. I found out different:)

What pump cam are you using and what hole is it in? I think you've got too weak of a profile on the cam. How far open is the throttle when he launches at 4,500?

Gotta run ...will get back later

he's got the big brown or black one in the back cause its the only one that fully uses the 50cc shot, in the front i don;t remember the color but it gives maximum pump travel so I know that its all the fuel possible.

The color of the pump cam is critical. While two cams can give an identical TOTAL volume, the timing of when the fuel shot is delivered varies greatly. Some have a very small initial shot, then a lot at the end. Others give a hard fast shot with just a few degrees of throttle movement. All the fuel in the world won't help if it's delivered at the wrong time. That's what nozzle and cam tuning is all about.


Please find out the following info. Front shooter size and cam used. What hole the front cam is installed in. Same with rear cam and shooter. No guessing please.

Front shooter size and pump cam are more critical than rear. In fact if he is using a single 50cc pump...it should be on the Primary side...not the Secondary!!!

I've got a very good idea what is happening....but no point in continuing unless you can supply this info.

It has to do with his 4,500rpm launch point. I believe that he has used up most of the Primary pump shot just by staging. There are ways to remedy this....in fact there are special cams used for just this purpose. Also the 50CC pump is designed to alleviate this problem....when it is installed on the Primary side.

Get back to us with the info and I'm sure that after a bit of tuning, we can have that puppy launching with the wheels up and the tires on fire!!! Cheers.

PS: in the meantime you might find these threads enlightening. Explains in greater detail accelerator cam profiles and theory. Lots of other info there as well. Tuning on Muggyjack's car ( Holley Tuning ) turned out particularily well. We PM quite often :)


Holley Tuning

I really need help with my Holley

Pay particular attention to posts in regards to color of cams and fuel delivery timing. This is what we are going to play with.

Your friends 4,500 RPM launch may require the use of a specialised pump Cam on the Primary side...but we need to do some other checks first.