71stingray454

Hi!

Sorry for repeating this topic but I can't seem to find the thread with solutions to my second problem. The engine has less than 400km on it since it's rebuild/upgrade. Every since we put on the Holley 850 double-pump, we've been having all sorts of annoying problems. First off, the air filter currently on the car is too small. The hood is an L88 style but there still isn't enough room for a 3" element but that will be fixed soon. Our mechanic says the small air filter is the source of all our engine problems. Somehow, I think the carb is just not set up properly. We have 31,32 squirters. The stuttering happens at about 1500-1700rpm (on every shift). If we keep the revs above 2000rpm, the car runs fine. Before the car is warmed up, the stuttering is really bad, the car almost stalls. Once it is warmed up, the stuttering reduces to a small hiccup but it's still there. As far as the stalling under heavy braking, the carb was cleaned but had no effect. I lost my power brakes once and ended up in the middle of the intersection. :eek:
BTW, we have a 71 454 punched to 461, Hooker Headers, fully ported, Edelbrock Performance intake, roller rockers, Comp Cam (0.595/0.595 0.294), 2.75" exhausts.
I'd like to take it to a local drag strip this Friday(in St. Eustache for fellow Quebecers) but it looks like it won't be ready.
Any help or links to threads would be greatly appreciated.

71stingray454

Chuck Harmon

It's hard to diagnose without being there; but, you have a similar motor to my L88. With that cam you will probably be best setting the idle speed to 1000-1200 rpm. The float level may be too low causing the carb to starve out under braking. Gas is sloshing to the front of the carb and uncovering the jets. Make sure that you have power valves that are not opening prematurely because of your low vacuum. I just barely get away with a 65 front and back. If you have 85 power valves (opens when manifold vacuum drops to 8.5") and your vacuum level is only 7-8", it is opening additional fuel flow too early which may cause your stuttering.

I am assuming they have properly adjusted the idle screws. Is your engine properly vented. Mine ran rough without good crankcase venting. A lot of pressure can build up, ring flutter, etc. Just open or loosen the valve cap to see if there is a difference.

Hope this helps,

Chuck



[Modified by Chuck Harmon, 9:34 AM 8/15/2001]

robzr

The stalling under braking has in my experience been a real pain to fix. I've had it with a Holley 6210 (650 double pumper) and a Speed Demon 750. I tried air vent and float levels all over the place on the Holley and never fixed it. When I called Barry Grant for help on th Demon, they suggested lowering the secondary float level (didn't help) and sync'ing the primary & secondary idle
speeds (didn't help). I'm still playing with it :( BTW their reasoning was that the 'air was surging' into the venturis which was why the primary & secondary idle speed was important. I don't understand what that means.

I don't see how it could be the primary bowl & starving jets becasue when you are braking you should have your foot off the accellerator and be running on the idle circuit. You could try raising your primary float level if you think this is the problem.

Usually the problem is that the secondary's fuel sloshes forward and comes out of the air vent (the little tower in the center on the back of the venturis). To overcome this, you can lower the secondary float level and put it air vent extenders (little plastic tabs that go inside your float bowl on the air vent outlet).

Finally, the BG tech said to try running it with the power brake booster unhooked & blocked off (to see if it's leaking or something, causing a lean condition). I haven't tried this yet, but it's worth a shot.

later,

Rob

gkull

I also had this problem with my 825 race Demon. How i solved it was a tube from front to rear vent with a tiny t connector venting in the middle. Lowered rear bowl float level and my secondaries are open more than the primary for idle speed. The reasoning was that maybe I was getting raw gas spewing out of vent into the secondaries. Causing a momentary flooding.

I would agree with Chuck on the power valves maybe even try a 5.5.

Set the idle mix scews with a VAC gauge. I also have .125 holes drilled in the throttle blades to help lean out the idle.

a smith

I am running a BG Silver Claw.It would stumble or die whenever I hit a bump,stopped real quick, or cornered real hard.I solved the problem by lower the primary float level.It is very sensitive to float level.Just a couple of nut flat ajustments to high and you have the problem.

Chuck Harmon

robzr,

The reason the float level is important even during the idle stage is that no fuel can get to the idle circuit either if it's all sloshed to the front of the bowl. The reverse can be a real problem under hard acceleration when g forces are pushing the fuel to the back of the carb uncovering the secondary jets. They have extension tubes, also called slosh tubes, for this. Turning the nut, not the hold down screw, one flat changes the fuel level plus or minus .031 inches. One full turn is 3/16ths of an inch. Fuel level is very critical. Too much and it can flood out, too little and it starves. You would do well to make sure the secondaries are set "right on". Going to a lean condition at full throttle is worse than stalling under braking for your engine.

You may have more than one area to adjust to correct the problems you mentioned. However, MAKE ONLY ONE CHANGE AT A TIME on your road to perfecting it. Multiple changes can counter act each other.

Chuck


[Modified by Chuck Harmon, 3:11 PM 8/15/2001]