[PsychoBilly]

I have a Barry Grant 1402010VE 750 with vacuum secondaries that has a peculiar problem: once the motor has warmed up, the throttle will not return to the curb idle setting. It hangs around 1500 instead of its normal idle of 800. I've removed the entire air cleaner assembly, disconnected the throttle cable, (but left both springs attached), and even disconnected the secondary linkage trying to eliminate some sort of bind. There is no choke or choke linkage orfast idle cam or so on.

When the motor is racing at 1500, I can very gently press the primary shaft linkage home and with very little effort, and it returns to its home position at 800 rpm. Because this only occurs when the motor is fully warmed up, (180d thermostat), I suspected a heat related base plate warpage causing a bind?. (1979 Pontiac Trans AM, W72 w/ Edelbrock Performer RPM 7156 intake.) And because of the shaker hood scoop clearance, I'm not using any sort of thermal/insulator gasket, just the basic flange gasket.

I tore down the carb and removed the primary butterflies & shafts to inspect, expecting to find tattle-tale wear marks that would indicate binding but nada. BG troubleshooting guide suggests that the butterflies are not aligned, rubbing the bores but after several adjustments, nothing!

Has anybody else experienced this sort of issue on a BG carb? Solutions? Many thanks!

 

[ericnova72]

Any chance the secondary closing link length is misadjusted, and that is giving you that tiny bind??

I've had regular Holleys that have had that link too short, and it leaves the secondary blades cracked just a bit rather than pushing them closed as the primary closes.
I've also heard of the incorrect length on the vac secondary diafram rod can give a similar issue, but I've not seen it myself

 

[2001Blazer4x4]

Disconnect the vacuum advance on your distributor (temporarily) and see if that fixes the erratic idle speed issue. If so, come back and we can discuss. If not, it was an easy test.

 

[PsychoBilly]

Any chance the secondary closing link length is misadjusted, and that is giving you that tiny bind??

I've had regular Holleys that have had that link too short, and it leaves the secondary blades cracked just a bit rather than pushing them closed as the primary closes.
I've also heard of the incorrect length on the vac secondary diafram rod can give a similar issue, but I've not seen it myself

ericnova72, thanks for replying. I'll check that. When I bought this carb, new, just before BG went ****-up, I had high hopes of purchasing a superior product, especially after the stories I'd heard about Holley's quality at the time. But in addition to this issue I've found that it's a bear to tune. (In the 44 years I've owned this car I've been through several Holleys!) I'll post when I've checked this.

 

[PsychoBilly]

Disconnect the vacuum advance on your distributor (temporarily) and see if that fixes the erratic idle speed issue. If so, come back and we can discuss. If not, it was an easy test.

2001Blazer4x4, thanks for replying. I'll try. But I don't believe this is a timing snafu if that's what you're suggesting. Recall I can physically push the throttle home and it will return to the normal idle, 800 rpm, with the vacuum hose still connected. But at this point I'll try anything as I'm out of ideas. I've been working, tuning carbs since the 60's and this little gem has me stumped.
The car is on the lift right now getting fitted for new rear brakes so may be a few weeks before I'll have a chance to respond.

 

[johnsongrass1]

Sounds like the primary's are sticking to me.
Possibly the ignition advance sticking as well.

Recently I've gone as far as bolting the base plate down and loosening the throttle blade screws and resetting them, let them snap shut, several times, to help them center up.

 

[PsychoBilly]

Hmmm, I've always adjusted the butterflies on the bench but perhaps I need to try it your way, on the car and at operating temp? Gonna be a real PITA for me to reach the butterflies while mounted though. I can't recall a carb being this much grief to tune. (FWIW, Holley used to recommend never loosening the butterflies as they were preset at the factory and staked in place. But BG support has no qualms about loosening them! Whatever!) I'll post results, thanks!

 

[johnsongrass1]

You COULD use the intake manifold but I used a flat plate I had left over from a milling job I knew was flat too .001 across 15". I wondered if your base plate was warped or skewed on the bench, or flat on the bench and not when it's on the intake.

 

[PsychoBilly]

You COULD use the intake manifold but I used a flat plate I had left over from a milling job I knew was flat too .001 across 15". I wondered if your base plate was warped or skewed on the bench, or flat on the bench and not when it's on the intake.

Huh, I hadn't considered that. Or maybe even the Performer deck is warping at op temp? (EGR ports are blocked.) That could explain why my bench adjustments have not produced any remedy thus far. Man, I have work to do... Thanks.