454 bogs at WOT - ???
Thread Starter
Drifting
Joined: May 2005
Posts: 1,909
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From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
454 bogs at WOT - ???
My carb was rebuilt by Lars and my timing is set accordingly. Idles great....revs good.....but It bogs "momentarily" when I stomp it. I seriously doubt it's a carb problem. After it "catches up" its OK but I just cant get the bog out of it. This is a TOTALLY rebuilt stock spec LS4 - 454.
Any suggestions?....I hate to just start messing with stuff.
Any suggestions?....I hate to just start messing with stuff.
Thread Starter
Drifting
Joined: May 2005
Posts: 1,909
Likes: 6
From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
Le Mans Master
Joined: Oct 2006
Posts: 7,123
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From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
If Lars rebuilt that carb, $100 says it's right on and the secondary spring is set correctly. He runs his rebuilds on his car to test them. (or he used to)
Check your timing and advance systems- tons of threads about how to adjust and recurve the distributor for best performance. I'd suspect that the advance is not quite where it should be- either the weights are sticking or the vacuum advance is done.
Check your timing and advance systems- tons of threads about how to adjust and recurve the distributor for best performance. I'd suspect that the advance is not quite where it should be- either the weights are sticking or the vacuum advance is done.
Drifting
Joined: Aug 2005
Posts: 1,682
Likes: 3
From: League City TX
How long ago was the carb rebuilt?
The spring tension on the air valve is unlikely to change once set.
Since chances are very good that Lars set it properly, you might not want to adjust it just yet.
The air valve opening is also delayed by the rod that connects it to the choke pull off.
When operating correctly, the vacuum has to drop before the air valves can begin to open.
If the pull off is not working, the air valves can open too quickly causing a bog.
The spring tension on the air valve is unlikely to change once set.
Since chances are very good that Lars set it properly, you might not want to adjust it just yet.
The air valve opening is also delayed by the rod that connects it to the choke pull off.
When operating correctly, the vacuum has to drop before the air valves can begin to open.
If the pull off is not working, the air valves can open too quickly causing a bog.
Le Mans Master
Joined: Nov 2008
Posts: 5,691
Likes: 12
From: columbus oh
How long ago was the carb rebuilt?
The spring tension on the air valve is unlikely to change once set.
Since chances are very good that Lars set it properly, you might not want to adjust it just yet.
The air valve opening is also delayed by the rod that connects it to the choke pull off.
When operating correctly, the vacuum has to drop before the air valves can begin to open.
If the pull off is not working, the air valves can open too quickly causing a bog.
The spring tension on the air valve is unlikely to change once set.
Since chances are very good that Lars set it properly, you might not want to adjust it just yet.
The air valve opening is also delayed by the rod that connects it to the choke pull off.
When operating correctly, the vacuum has to drop before the air valves can begin to open.
If the pull off is not working, the air valves can open too quickly causing a bog.
Thread Starter
Drifting
Joined: May 2005
Posts: 1,909
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From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
Safety Car
Joined: Apr 2000
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From: Wichita KS
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Race Director
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From: Taylor Michigan
i`ll put my money on this reply
Racer
Joined: Feb 2009
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but It bogs "momentarily" when I stomp it.
I'm pretty sure you said you got a Q-jet on there.
Sounds exactly like a carb adjustment problem to me- air valve that is. The only thing the air valve does is give you a smooth transition into the secondaries opening. If it only bogs when you "stomp it", it's probably the air valve needs tuned. You didn't say, but I'll assume the bog started after the rebuild. If it ran fine before, unless Lars marked exactly where the air valve was set before tearing it down, he probably set it to the usual 1 full turn after the rebuild.
It's easy to adjust once you know where it is, and you can always set it back where it was to start worst case. I can probably talk you thru it if you want instructions.
"Rochester Carburetors" by Doug Roe is a great book to get. It was mostly a black box to me until someone finally talked me into getting it. Now it's no big deal to tear it apart.
I'm pretty sure you said you got a Q-jet on there.
Sounds exactly like a carb adjustment problem to me- air valve that is. The only thing the air valve does is give you a smooth transition into the secondaries opening. If it only bogs when you "stomp it", it's probably the air valve needs tuned. You didn't say, but I'll assume the bog started after the rebuild. If it ran fine before, unless Lars marked exactly where the air valve was set before tearing it down, he probably set it to the usual 1 full turn after the rebuild.
It's easy to adjust once you know where it is, and you can always set it back where it was to start worst case. I can probably talk you thru it if you want instructions.
"Rochester Carburetors" by Doug Roe is a great book to get. It was mostly a black box to me until someone finally talked me into getting it. Now it's no big deal to tear it apart.
Thread Starter
Drifting
Joined: May 2005
Posts: 1,909
Likes: 6
From: Lake Arrowhead - Georgia > 72 Base Coupe & 74 BB Roadster
Thanks Guys....I agree.....a carb rebuilt by Lars is ususlly "right on".....I think I will start with the timing. The dist probably needs rebuilt, as I can hear the tach drive gear "buzzing" which indicates the shaft is pretty worn.
Speaking of Lars......is he still around? I haven't ""seen" him here in a while. I have been absent myself with a fresh double bypass last February. Getting old sucks but beats the alternative!
Speaking of Lars......is he still around? I haven't ""seen" him here in a while. I have been absent myself with a fresh double bypass last February. Getting old sucks but beats the alternative!
Safety Car
Joined: Apr 2000
Posts: 3,802
Likes: 61
From: Wichita KS
Thanks Guys....I agree.....a carb rebuilt by Lars is ususlly "right on".....I think I will start with the timing. The dist probably needs rebuilt, as I can hear the tach drive gear "buzzing" which indicates the shaft is pretty worn.
Speaking of Lars......is he still around? I haven't ""seen" him here in a while. I have been absent myself with a fresh double bypass last February. Getting old sucks but beats the alternative!
Speaking of Lars......is he still around? I haven't ""seen" him here in a while. I have been absent myself with a fresh double bypass last February. Getting old sucks but beats the alternative!
cc
Melting Slicks
Joined: Mar 2006
Posts: 2,465
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From: Orange Park Fl
Lars set it up right. Timing is a possibility.
Now, with that said, How long ago did Lars rebuild it? You may have:
1. Accelerator pump cup deteriorated from ethanol in fuel (If it is not one of the newer ethanol resistant cups, this can happen fast).
2. Varnish in fuel passages if the car sits a lot.
God bless, Sensei
Now, with that said, How long ago did Lars rebuild it? You may have:
1. Accelerator pump cup deteriorated from ethanol in fuel (If it is not one of the newer ethanol resistant cups, this can happen fast).
2. Varnish in fuel passages if the car sits a lot.
God bless, Sensei
