Bog when Engine is Warm
#1667982
09/06/14 10:49 AM
09/06/14 10:49 AM
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Joined: Jul 2007
Posts: 1,526 North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Guys, I may have fixed my vapor lock issue with the vapor separator and return line setup. I have noticed another tiny issue that is a little annoying now.. I notice when the engine is totally warm, maybe after 10 minutes of runtime, it has a bog when you blip the accelerator pedal. This happens right off idle or even if you're cruising. When the engine is cold/warming up it is spot-on but when it gets hot...this 1/2 second bog when you give it pedal. However, once the bog ends, the motor is strong and pulls pretty hard. The carb is a Holley 850 4150 vacuum secondaries. I have the silver (middle tension) spring installed right now. Am I right in thinking this might be an issue with secondaries opening too early maybe? If so, why only when the motor is warmed up? I have the spring kit and the quick change housing installed so if this might be my issue, what would you guys recommend as far as the spring to use? Thanks as always!
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Re: Bog when Engine is Warm
[Re: BSB67]
#1667988
09/06/14 03:30 PM
09/06/14 03:30 PM
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Joined: Jul 2007
Posts: 1,526 North Carolina
cjskotni
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OP
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Quote:
You really did not answer the key question. Will it bog/hesitate at quick part throttle?, or just WOT.
I don't ever really "floor" this car but I can tell you that it bogs at quick part throttle for about a 1/2 second or so and then picks right up and pulls hard. This feels a bit like what I had last year when I had a 32 squirter on the carburetor and I fixed it by going up to eventually settle on the 42. The 32 was the original squirter size and was confirmed to be too small on the dyno by the shop who tuned the engine originally. I tried a 38/40/42 and the 42 seemed to act the most responsive at the time....
In my fuel system troubleshooting I have swapped to a factory style hemi pump with return line/VS (from the Holley w/o return) which seems to be lower pressure according to my fuel pressure gauge. I have no idea if this is affecting anything or not.
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Re: Bog when Engine is Warm
[Re: cjskotni]
#1667989
09/06/14 04:06 PM
09/06/14 04:06 PM
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Joined: Feb 2005
Posts: 4,309 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,309
Prospect, PA
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Quote:
Quote:
You really did not answer the key question. Will it bog/hesitate at quick part throttle?, or just WOT.
I don't ever really "floor" this car but I can tell you that it bogs at quick part throttle for about a 1/2 second or so and then picks right up and pulls hard. This feels a bit like what I had last year when I had a 32 squirter on the carburetor and I fixed it by going up to eventually settle on the 42. The 32 was the original squirter size and was confirmed to be too small on the dyno by the shop who tuned the engine originally. I tried a 38/40/42 and the 42 seemed to act the most responsive at the time....
In my fuel system troubleshooting I have swapped to a factory style hemi pump with return line/VS (from the Holley w/o return) which seems to be lower pressure according to my fuel pressure gauge. I have no idea if this is affecting anything or not.
Not to sure a dyno is the best way to determine squirter size and duration. I've been to a couple of dynos, and I would also caution that a dyno guy is not necessarily a good carb tuner by default.
Your fuel pump is not the problem.
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Re: Bog when Engine is Warm
[Re: BSB67]
#1667990
09/06/14 04:25 PM
09/06/14 04:25 PM
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Joined: Aug 2006
Posts: 2,487 God's Country Maryland
GODSCOUNTRY340
top fuel
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top fuel
Joined: Aug 2006
Posts: 2,487
God's Country Maryland
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At idle, your accelerator pump arm should have NO play in it. It must start moving the instant the throttle starts moving. Look down the carb with a flashlight to confirm there is actually fuel being squirted into the carb, you can do this with the engine turned off. That 8.5 power valve may need to be replaced with a 9.5 or even a 10.5. A vacuum gauge will help here or just try the 10.5 to see if it helps. If the squirter is too big it can be confirmed with someone watching the exhaust for a puff of black smoke when you "blip" the throttle.
I love the smell of Deer guts in the morning, it smells like... VICTORY!
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Re: Bog when Engine is Warm
[Re: GODSCOUNTRY340]
#1667991
09/06/14 05:47 PM
09/06/14 05:47 PM
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Joined: Jul 2007
Posts: 1,526 North Carolina
cjskotni
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Alright. I went and inspected the adjustment on the pump arm and it seemed to be adjusted right where the arm would start to get depressed instantly when moving the throttle. Now this is something I have always wondered about but the accel pump arm has a little play in it. In other words, it can be pushed down a bit (maybe .030-.040) from its resting position before I 'feel' resistance like its pushing the diaphragm. I had the throttle arm adjusted so it was holding the accel pump arm just 'south' of that resting position but maybe .020-.030 from where it began to feel resistance. There as no gap at all between the throttle lever arm and the accel pump arm. I went ahead and backed off the adjuster nut 1/2 a turn or so which puts more tension on that arm and brings it where it will start to feel that resistance as soon as the throttle is moved. Does that sound right? Hopefully this makes sense... So anybody care to explain why if this was misadjusted, why it would be crisp while the engine was cool and get a bog when warmed up? This particular circuit should operate identically hot or cold, right? Thanks for the suggestions so far.
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Re: Bog when Engine is Warm
[Re: BSB67]
#1667993
09/06/14 07:44 PM
09/06/14 07:44 PM
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Joined: Jul 2007
Posts: 1,526 North Carolina
cjskotni
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OP
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Quote:
Does the carb have a choke? If the choke is actuated before it is warmed up, you cannot compare.
Electric choke. It starts to come off after about 20-30 seconds.
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Re: Bog when Engine is Warm
[Re: cjskotni]
#1667994
09/06/14 09:00 PM
09/06/14 09:00 PM
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Joined: Jan 2003
Posts: 5,442 Indiana
YO7_A66
master
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master
Joined: Jan 2003
Posts: 5,442
Indiana
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Your choke could be richening the idle/transfer circuit when the engine is warming up. Then when the engine is warm and the choke is open, the engine could be seeing a lean spot off idle and during tip in. I always adjust my pump cam linkage when the engine is idling and with a flash light. I lean over the engine "just enough" to see the front squirter while shining the flash light on that squirter. Then I move the linkage and watch how soon the fuel starts to pump out. If the fuel does not pump out as soon as I move the throttle, then I readjust it and check it again. I move the nut about 1/8 of a turn until I see fuel.
What pump cam color do you have? Do you have a hollow squirter screw with the 42? If not, then you won't see much of a difference in pump shot larger than a 37 squirter. Note: A 42 is a large squirter. Maybe it is time for a pump cam swap.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Bog when Engine is Warm
[Re: cjskotni]
#1667997
09/07/14 09:30 AM
09/07/14 09:30 AM
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Joined: Feb 2005
Posts: 4,309 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,309
Prospect, PA
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Quote:
What else could be wrong that the large pump shot might be compensating for?
Really?
Quote:
I had the carb jetted on the dyno with wideband O2 sensors so I am pretty sure the jetting is right...
Jetting should be very close and likely not the problem IMO. However, there is no down side to stepping up the jets in the primary side at some point just to see, but I don't think you are there yet. Curious, do you know what changes they made in jetting at the dyno?
Is this the 870 Avenger carb?
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Re: Bog when Engine is Warm
[Re: cjskotni]
#1667999
09/07/14 10:40 AM
09/07/14 10:40 AM
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Joined: Jan 2003
Posts: 5,442 Indiana
YO7_A66
master
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master
Joined: Jan 2003
Posts: 5,442
Indiana
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The PINK cam is the ""least"" aggressive off idle of the entire selection of pump cams!!!!!
I would suggest a white or red (very similar to each other and twice as aggressive off idle than the pink cam.) cam on position #1. If that helps but not all the way, then I would suggest the Orange pump cam which is more aggressive than the white or red cams and it also has more overall pump volume (which you may or may not need), But for testing purposes, I would leave the 42 in there and just swap out pump cams for now. Note: you will need to shorten the pump arm screw to install the larger pump cams. Maybe 1/2 turn before insalling the white or red cam and then once the cam is in, readjust.
1970 YO7 A66 [Canadian Export] F8 Challenger 340 (Currently in shop for stroker assy.)
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Re: Bog when Engine is Warm
[Re: cjskotni]
#1668000
09/07/14 12:02 PM
09/07/14 12:02 PM
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Joined: Feb 2005
Posts: 4,309 Prospect, PA
BSB67
master
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master
Joined: Feb 2005
Posts: 4,309
Prospect, PA
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Do you know how many turns out the idle mixture screws are?, and what the A/F ratio is at idle(from the dyno session)?
Better yet, do you have the A/F graphs?
Last edited by BSB67; 09/07/14 12:04 PM.
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Re: Bog when Engine is Warm
[Re: BSB67]
#1668001
09/07/14 01:17 PM
09/07/14 01:17 PM
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Joined: Jul 2007
Posts: 1,526 North Carolina
cjskotni
OP
pro stock
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OP
pro stock
Joined: Jul 2007
Posts: 1,526
North Carolina
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Idle mix screws are about 1.25 - 1.5 turns out from bottom. I have the graph but it only shows 3500 RPM+ so it might not be that useful here. Another thing we may be grappling with is the tune was done with a marginal fuel pump which failed totally shortly afterwards. I also later found the ignition as marginal and had to go to a lower ballast resistor to get the coil output voltage back up. At the time of tune, the output was in the 10-15kV range...new ballast...in the 45kV range. No idea if this will affect anything here or not. I have thought about experimenting with the cams but I didn't know enough to make an educated guess as to which one to try. I am appreciative of the specific suggestion on which color to try. My friend has the set of cams so I will see if I can steal his set to play with... Thanks for the help so far....
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