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Topic Review (Newest First)
08-20-2006 08:48 AM
drewbe
Finally

Thanks to everyone's help, we finally got to the bottom of the gremlin. We replaced ever fuel item. We installed guages everywhere fuel problem ended up to be a carb flow issue. But the poping at top end was something else. My high chip was labeled 7900, the computer in the car stated we went through the traps at 7400. Well, we pulled the chip out and the poping went away and we still went through the traps at 7400. MSD states the chip is a 7400 not a 7900. Thanks everyone for your help
08-08-2006 06:25 PM
drewbe well....just when you think its fixed... we tried a full run and the car died at 1000ft. fuel pressure dropped from 8 1/2 to 4psi. voltage is fine,relays are both good, check the pump flow and that is good. what next....
07-27-2006 10:23 PM
blown36 The 8977 has a boost port on it. The unit sees boost and we set the retard using the pro data msd software. The engine runs 28deg without any boost and pulls 7 out gradually as boost comes on.
07-27-2006 05:39 PM
drewbe Gav

thanks for the information. on your MSD what are the trigger wires connected to in order to tell the unit to remove timing.

thanks
07-27-2006 04:03 PM
blown36 My controller is MSD 8977.

Good to hear you found the fuel drama.

My carbs are out of the box Holley street supercharger carbs running 98 octane pump fuel. On the dyno we found air fuel ratio was slightly rich but left it alone to be safe. Jetting was 68/76 no adjustable air bleeds on street model carbs, no 4 corner idle either, but they work fine.

I now have the innovate tuning system on the car, and we are racing at our local Nostalgia meet on Sunday and hope to get some data to look at. I have logged the air fuel last meet and went to 66/74 but picked up only a half mph. Not worth the safety factor. This weekend I have added boost, eng rpm, and driveshaft rpm channels.

As well we have added rolling pivot traction rods to replace the slapper bars, so lets hope to see the 60ft improve.

Gav
07-27-2006 11:06 AM
drewbe Blown36- what modl digital boost retard are you using?

I know this is a out of the world question but what jets do you use? We have power valves are at 96p -99s Question- when you go up on the jet do you go up or down on the air bleeds?

Okay everybody now for the fuel issue... I want to thank even=rbody for their input and help. We looked at the entire fule system one last time, and noticed after a run the tank was getting sucked in. We looked at the vent line and appeared fine. But we spent the money and replaced the line and fitting. Car went right down the track. Vent tube was closing. Now all we have to do is fine tune.



thanks everyone for the help
07-27-2006 07:04 AM
blown36 I am running an msd digital boost retard module pigybacked onto a 6AL. It works real nice. Total timing at full boost is 21 degrees. There is no need at all on a roots / 2 DP carb deal for boost ref reg. Boost ref power valves yes.
I set my 427 up on an engine dyno in less than a day, I suggest you pull it , spend the money and time to dyno, before you grenade it. Just my 2 cents worth.

Gav.
07-26-2006 10:25 AM
Infomaniac
Quote:
Originally Posted by camaroman7d
George, I have run Holley carbs for years. They will take more pressure than many think. I have run as high as 10-12psi, if you have healthy floats and needle/seat assembly, they will hold more than 6 psi.. 7- 7.5psi has been the "rule of thumb" for years. You may be right on with the fuel pressures for Edelbrocks and Carters (same carb) but, I have only used those for street rod/very mild applications. In many of those cases there is no fuel regulator or pressure gauge.

Pressure is only part of the fuel system, flow is just as important if not more important. You don't need to set the pressure all that high.

Yea Holley carbs will accept a lot of fuel pressure when the float needle assembly is already open and is flowing anyway. It's only when the float needle is trying to shut off fuel that the fuel pressure is an issue.

Some bypass regulators have a jet that lets the idle pressure stay around 8 lbs and you can set the running pressure over 10 lbs.
07-26-2006 12:32 AM
Blazin72 Just a shot here as I am not blower savvy like several of the people already posting in this thread are... Is the power valve boost referenced? Maybe it is closing on you, causing the lean condition?

This is from another thread from a few days back:
Quote:
Originally Posted by Infomaniac
Boost referencing the power valves may or may not be necessary.

Generally if you cruise under boost it is a good idea.
Boats are the prime candidate for this.

The power valve sees manifold pressure on a N/A engine. Install the carb on top of a roots blower and it sees the exact opposite.

Under high power (open throttle) on a N/A engine the manifold pressure will be high. No longer enough vacuum to keep the power valve shut and it delivers fuel. Normal operation

Install it on top of a roots blower and under high power the blower is drawing hard on the carbs. IT JUST MIGHT draw hard enough to keep enough vacuum between the blower and carb to keep the power valve shut.

So my recomendation is: If you cruise under boost then go ahead and boost ref the power valves. If not then be safe and remove the power valves and jet up to compensate.

If you dont want to block them off put a vacuum gauge between the blower and carb and make sure the vacuum is not high enough to keep the power valves shut. You'll be good to go.
It may be worth looking at...

This is the entire thread: http://www.hotrodders.com/forum/boos...lve-94364.html
07-26-2006 12:12 AM
camaroman7d George, I have run Holley carbs for years. They will take more pressure than many think. I have run as high as 10-12psi, if you have healthy floats and needle/seat assembly, they will hold more than 6 psi.. 7- 7.5psi has been the "rule of thumb" for years. You may be right on with the fuel pressures for Edelbrocks and Carters (same carb) but, I have only used those for street rod/very mild applications. In many of those cases there is no fuel regulator or pressure gauge.

Pressure is only part of the fuel system, flow is just as important if not more important. You don't need to set the pressure all that high.
07-24-2006 02:26 PM
drewbe We are using Holley 1050 carbs built by Chuck N.

As for the jetting up, the car was real fat off the line once we hit the 1000ft mark it started to pop, we shut it down and looked at the plugs. They looked like they just came out of the box. They are white with orange around the ceramic.

We have power valves in the primary, 6.5 and tried to square off the jets as well as use a 6 spread. No matter what we try we have the same issue. The motor goes lean around the 1000ft and starts to pop.

We did not flow test the fuel system yet, we are going to do this tonight. We just installed a new pump/filter and have the same results. We are thinking the carbs might have to rechecked.
07-24-2006 11:56 AM
Tech @ BG drewbe,

Have you actually flow tested the system yet to see how long it is taking to flow a gallon of fuel?
07-24-2006 11:51 AM
Tech @ BG
Quote:
Originally Posted by drewbe
Well we changed the entire fuel system and still have a problem. The 60ft are back. Shut the car down at 60ft and check the plugs they look okay, at the 1000 ft they are lean. Went up in jet sizes same issue but real fat at the line.

Did jetting up help the way the plugs looked, or the way the car ran up top at all?

Usually if you have to jet up to the point it hurts your 60' time your fuel delivery is not keeping up.
07-24-2006 11:51 AM
gdubstub
Quote:
Originally Posted by camaroman7d
The guys are telling you correctly. Your carbs can't take 19psi of fuel pressure, that's why you were getting the black smoke and poor running engine. You may want to set your fuel pressure a little higher than 6.5 psi, do a little experimenting and see what works best. No boost reference needed.
What kind of carbs? Carters and Edelbrocks will flood at pressures of 6.5 psi or greater. For these carbs, regulate to no more than 5.5 or 6.0 psi.

George
07-24-2006 11:35 AM
Infomaniac Hey when running a bypass install it as far away from the pump as possible.

I always plumb the fuel to feed the carbs then continue to the bypass valve. That way the carbs get uninterrupted fuel and the bypass is working off of pressure that is not influenced by any plumbing restrictions.

And look at the simple things like fuel tank vented well etc.
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