Carby Issue

[HDTss1697]

To whom may know.. Have rebuilt Vk Brock SS engine bay. When tako reaches 2.5 - 3.0rpm then theres a total loss of power but then comes back on and off during 2nd gear onwards. We think the secondarys are the problems.. Any Ideas would be great!

[craigvk]

Take your carb off and inspect it. Check that the secondary throttle valves operate freely and that the top air valves aren't sticking. My old carb was a bit warped and the top air valves were sticking.

[DenchY]

does it happen when your got the throttle wide open?

secondarys only come on when ur foot is more then 3/4 on the gas..

maybe just the timing or mix?

[HDTss1697]

does it happen when your got the throttle wide open?

secondarys only come on when ur foot is more then 3/4 on the gas..

maybe just the timing or mix?

Thanks for replying Denchy, Yes it seem to cut out when foot is 1/2 to 3/4 on the gas. Do you think it might be the timing? We had the brock at 5000rpm
in neutral whilst looking under the bonnet and noticed that the secondarys did not engage at all and the car did not stall. Is it true that the secondarys only engage when the car is under load or moving? How do you if it's the mixture is incorrect?

Cheers Dan (HDTSS1697)

[HDTss1697]

Thanks Craig, I'll check out the throttle valves today...

cheers Dan (HDTSS1697)

[clixanup]

Best way to set mixture is to use a vacuum gauge.

Adjust the mixture screw(s) until you get the highest reading.

Does the car have electronic ignition? It still could be timing or a plug lead.

[HDTss1697]

Yes, it's got electrontic ignition but plug and leads are new..

[powerlite006]

had the same prob with my vh ... put a webber on it and never looked back was cheap as well only 90$ second hand from the wreckers ...

[craigvk]

The webbers are Ford carbs. Not much use and I am sure the OP is talking about a 4 barrel Quadrajet or at least a Varajet II carb.

[jake87]

the weber carbs are great, put one on my vh 2 days ago

[craigvk]

Do they bolt on without modification?

[HDTss1697]

had the same prob with my vh ... put a webber on it and never looked back was cheap as well only 90$ second hand from the wreckers ...

The Carbs a quadrajet, how did you fit a Weber? Being a VK Brock Commodore, I don't want to modify the engine bay.. But I'm curious about the weber....

Regards Dan (HDTSS1697)

[craigvk]

As far as I'm aware, the Weber's are XE/XF falcon sixes carb. In your case it wouldn't go.

Btw, go the quadrajet!

[craigvk]

Thanks Craig, I'll check out the throttle valves today...

cheers Dan (HDTSS1697)

Were the valves sticking or anything?

[HDTss1697]

Valves seem to be ok, But I notice the linkage for the secondarys is very loose. Do you think it might be jaming? It's strange because it seems to block at 3000 - 3,500rpm like clockwork...

[jake87]

Im not sure if its the same with the V8s but Yeah i think you can bolt the weber straight on after drilling holes in the inlet manifold. But i got an adapter plate from an auto shop down town for $42. The plate bolts on to the manifold and the 32/36weber bolts on to that. Im pretty sure you can get adapter from supercheep or autobarn. Pretty easy

[craigvk]

Im not sure if its the same with the V8s but Yeah i think you can bolt the weber straight on after drilling holes in the inlet manifold. But i got an adapter plate from an auto shop down town for $42. The plate bolts on to the manifold and the 32/36weber bolts on to that. Im pretty sure you can get adapter from supercheep or autobarn. Pretty easy

Man, the OP has a 4 barrel Quaddy to suit a V8. Your weber is to suit a six cylinder.

[viper1431]

Is it true that the secondarys only engage when the car is under load or moving?

Cheers Dan (HDTSS1697)

Under load yes, basically when vacuum drops to nothing.
If you push those secondary flaps open when the engine is off it shouldn't have much resistance, then start the engine and you should find them very hard to push open another way is to watch that vacuum module on the drivers side of the carb, it should be pulled closed with the engine on and if you pull the little vacuum line off it it will release.

With the power loss is it actually like you have lost all power and doesn't want to go any harder or is it like a lean surge where the car suddenly feels like you have hit the brakes hard?

[craigvk]

Under load yes, basically when vacuum drops to nothing.
If you push those secondary flaps open when the engine is off it shouldn't have much resistance, then start the engine and you should find them very hard to push open another way is to watch that vacuum module on the drivers side of the carb, it should be pulled closed with the engine on and if you pull the little vacuum line off it it will release.

Very good advise viper You seem to know your carb. That vacuum diaphragm I had replaced directly through Nardek. It cost me $63 which is heaps for a simple device and you are correct saying that it is pulled closed when the engine is running. To add to this, the diaphragm opens when you go full trottle, so it does play a role! What I don't get is that this diapragm we're talking about seems to fail the most. Maybe because it's always pulled in. But the diaphragm on the other side is one that seems to last. Oh well.

My old carb had sticking valves due to my gas mixer being done up with a socket bolt and when the thing was done up, it was too tight and after time my carb started to warp out of shape. (Previous owners). Now I have a wing nut on it and the tightness is just enough to not have it warp down the track. To add to this, I had flat spots going up hill say if I opened the throttle a lot more to drop down gear and go faster up the hill. So I'd also recommend checking out the valves. I ended up getting another carb off ebay for $130 and it was in pretty good shape and didn't end up needing to rebuild it with new gaskets.

While you're at it, check the vacuum hoses around the carb. If you feel any rock hard or cracked ones, then replace them.

[HDTss1697]

Under load yes, basically when vacuum drops to nothing.
If you push those secondary flaps open when the engine is off it shouldn't have much resistance, then start the engine and you should find them very hard to push open another way is to watch that vacuum module on the drivers side of the carb, it should be pulled closed with the engine on and if you pull the little vacuum line off it it will release.

With the power loss is it actually like you have lost all power and doesn't want to go any harder or is it like a lean surge where the car suddenly feels like you have hit the brakes hard?

Yep got it in 1 exactly!

[viper1431]

Make sure the vacuum module is working firstly, if it is then check the air valce adjustment. If the spring has become weak then the air doors wil just flop open to quickly causing a huge bog down when you hit the scondaries.
This pic should help, you will find this part on the drivers side of the carb and the rear top.
http://members.iinet.net.au/~jkaufman/roch6.gif

Have you always had this problem with the carb or did it used to be fine and has just started?

[craigvk]

If the link doesn't work, copy the URL and paste it into IE. Mozilla doesn't seem to want to know about it.

[viper1431]

Sorry about that, fixed up the link so it works now.

[brocke8]

There could be a number off issues.

Fuel pump
float levels in the carb
electrical fault ( Intermittent )

where are you ?

If in sydney the best bloke to see for these carbs is SAS in silverwater, these guys are the only ones that can rebuild and tune these carbs properly and I've been to a lot of shops over the years and these guys are the best.

[DenchY]

i'd say its the timing :|
i time my black 304 to 7 but factory setting is 6, all depends any work done to the motor and stuff try 8?

does it pick back up after 3000 rpm? if it does its not the mixture

another thing.. do the secondarys open mech or vacum?