Also check or block off the brake booster.
Carb tuning: Bog off idle.
- Thread starter Jonas Nordstrom
- Start date
Jonas Nordstrom
Well-Known Member
Stock 413. Dont know what cam specs it is, the engine came with the car and is my experiment mule while I build my 440.
Jonas Nordstrom
Well-Known Member
Todays update. Not much time to tinker in the garage today but started plugging vacuum sources and played around with the adjustable pcv.
Now things started to happen with the bog, opening up the pcv made the bog more pronounced, closing the pcv gave me a throttle response out of this world (Bog still remained but was located at a bigger throttle opening. When doing just a blip the bog was gone)
So, vacuum bog?
I have ordered an original pcv to test how the engine behaves with that one.
Then Im going to remove the intake and be really careful putting it back on, maybe use a gasket between pan and intake?
Now things started to happen with the bog, opening up the pcv made the bog more pronounced, closing the pcv gave me a throttle response out of this world (Bog still remained but was located at a bigger throttle opening. When doing just a blip the bog was gone)
So, vacuum bog?
I have ordered an original pcv to test how the engine behaves with that one.
Then Im going to remove the intake and be really careful putting it back on, maybe use a gasket between pan and intake?
Last edited:
69sunfireGTX
Well-Known Member
Wow! lots of work and you still haven't checked or played with the timing. That should be one of the first things you check before tearing into everything else. Now you are talking about taking off the intake. What makes you think that your balancer is not out of whack? Did you check it against Top dead Center?
They don't time like a Chevy... Mine likes like 45 total, It wont hardly run at 32-36. No vacuum advance necessary.
Another thought is that combo of carb parts isn't working together. Maybe try it on another engine to see.
Another thought is that combo of carb parts isn't working together. Maybe try it on another engine to see.
Jonas Nordstrom
Well-Known Member
I have a timing light on order so getting there.
I have verified my damper against TDC.
Jonas Nordstrom
Well-Known Member
The new carb works as my old tuned carb behaves the same on this "new" intake.
Geoff 2
Well-Known Member
A bog on throttle opening is nearly always going to be caused by leanness. Too much sudden air, but no fuel or not enough to stop a misfire [ bog ].
You do not know the cam specs? What is the lowest idle speed you can get & is the idle smooth?
And now you are getting bad advice like...my engine likes 45 total, hardly runs at 32-36, no vac necessary. 45 at idle or WOT?????
You do not know the cam specs? What is the lowest idle speed you can get & is the idle smooth?
And now you are getting bad advice like...my engine likes 45 total, hardly runs at 32-36, no vac necessary. 45 at idle or WOT?????
My point was that you can't tune a car without a timing light,not what to set his timing to. That's not bad advice. Thanks for sharing your experience.
Jonas Nordstrom
Well-Known Member
That's also my guess, the afr also showed values like that when the bog occurred.
No, I have not taken out the cam that came with the engine. With that said the engine still idles down to around 500 rpm and when tuned correctly it is super smooth. So it is prolly a stock cam.
This engine ran last summer with a Eddy performer intake and my Classic Holley. It ran without bogs, timing set to 14 before TDC.
So now when I put the old Holley back to test the only thing that is changed is the ch4b intake.
I will tune the car with a timing light, though haven't arrived in the post box yet and I don't want to borrow my neighbors as I did last time.
I have also bought a new timing strip that I need to put on, the last one blew of with the engine running and made one hell of a noise .and I had even used my wifes nail polish to make it stick.
And no worries about timing advice, it is coming. Lets be friends here.
Threads are more fun with pics so Ill throw in a pic of some of the carbs I tested out last summer.
Geoff 2
Well-Known Member
The best carb is bottom right in the pic.
500 rpm idle & smooth means a stock or very mild cam. It will also require a high number power valve, perhaps a 10.5, if using a Holley or clone.
500 rpm idle & smooth means a stock or very mild cam. It will also require a high number power valve, perhaps a 10.5, if using a Holley or clone.
Jonas Nordstrom
Well-Known Member
No denying that the Avs2 is a good carb, though having test/tuned them all in the pic I can say that they all behave differently in different areas. The Avs2 won in some areas while the Holleys won in others.
My self built carb takes all winning areas putting it into one carb and it has already showed that it can deliver.
For PV the Classic Holley really liked a 9.5 on my engine.
Jonas Nordstrom
Well-Known Member
Out in the sun while waiting for my timing light.
Had some fun removing all vacuum sources and testing different pcv valves.
Even tried a different ignition box.
Then I had a coffe.
Had some fun removing all vacuum sources and testing different pcv valves.
Even tried a different ignition box.
Then I had a coffe.
451Mopar
Well-Known Member
Did you ever check the idle channel restriction?
Seen a youtube video where a guy was building some hy-bred Holley where the base plate transfer slot feed holes did not line with the main body holes and he was angle drilling the base plate to fix that?
Seen a youtube video where a guy was building some hy-bred Holley where the base plate transfer slot feed holes did not line with the main body holes and he was angle drilling the base plate to fix that?
Jonas Nordstrom
Well-Known Member
Thanks, yep, tripple checked all holes when building it.
Geoff 2
Well-Known Member
Are you aware that when a 625 AFB was tested against a 600 Holley on a 350 Chev, the AFB made 17 ft/lbs more tq, 17 hp more & used less fuel doing it?
If you would like a copy of the test, PM me your email address.
If you would like a copy of the test, PM me your email address.
Wietse
Well-Known Member
Is your Wagner PCV set for dual flow mode or fixed orifice?
Try fixed orifice mode to ensure it provides a steady air flow to eliminate the possibility.
http://mewagner.com/?page_id=459
As i read from above it does make a difference after you played around with it, it could be your "vacuum leak" at light throttle.
Jonas Nordstrom
Well-Known Member
I tried both Dual and fixed. It does make a slight difference playing around with different settings, though bog is still there stalling the engine.
Wietse
Well-Known Member
It is either a lack of fuel or too much air, maybe disconnect and plug the PCV for now to eliminate it.
If you have rectified the root cause you can put it back on again.
Since it is just on idle circuit it does not have anything to do with jetting or power valves so no point checking that out.
I know my car needs a rich fuel mixture for idle, you can try fatten it up to 12.5 AFR and see what happens as you mentioned when increasing just a slight amount of more throttle the lean spot disappears which makes me think your transition slot starts feeding at that point.
This would indicate the idle circuit is ok to idle but not feeding enough to get going until the transition slot gets active.
If you have rectified the root cause you can put it back on again.
Since it is just on idle circuit it does not have anything to do with jetting or power valves so no point checking that out.
I know my car needs a rich fuel mixture for idle, you can try fatten it up to 12.5 AFR and see what happens as you mentioned when increasing just a slight amount of more throttle the lean spot disappears which makes me think your transition slot starts feeding at that point.
This would indicate the idle circuit is ok to idle but not feeding enough to get going until the transition slot gets active.
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