Stumbling issues on hard acceleration
Thread Starter
Racer
Joined: Nov 2004
Posts: 422
Likes: 0
From: Owensboro Ky
Stumbling issues on hard acceleration
I have dealt with this issue since rebuilding the motor in March. It's now time that I put away the fears I have with carburetors and tackle the problem.
The car idles great, timming is correct(Lars paper on timming), and the engine does fine on acceleration. Its when I try and really get on the gas when the motor acts likes its missing for several seconds and then clears up. I'm told there is no smoke coming from the exhaust when this
happens so I'm assuming its the carb. Some suggestions have been catered towards the power valve and jetting? The plugs do seem to be a shade towards the white side but not bad on the comparison chart.
Listed below is the engine spec's. All parts are new and only have maybe 125 miles on the new motor. Thanks in advance for all advise.
454ci w/cast iron heads
Heads have 2.070" Int/1.720"Exh with 1.7 roller tip comp rockers and 1.440 HP springs
Hyd cam .527"Int/.533"Exh
Edlebrock Performer intake
Holly 780 Street Avenger
Edelbrock fuel pump
The car idles great, timming is correct(Lars paper on timming), and the engine does fine on acceleration. Its when I try and really get on the gas when the motor acts likes its missing for several seconds and then clears up. I'm told there is no smoke coming from the exhaust when this
happens so I'm assuming its the carb. Some suggestions have been catered towards the power valve and jetting? The plugs do seem to be a shade towards the white side but not bad on the comparison chart.
Listed below is the engine spec's. All parts are new and only have maybe 125 miles on the new motor. Thanks in advance for all advise.
454ci w/cast iron heads
Heads have 2.070" Int/1.720"Exh with 1.7 roller tip comp rockers and 1.440 HP springs
Hyd cam .527"Int/.533"Exh
Edlebrock Performer intake
Holly 780 Street Avenger
Edelbrock fuel pump
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
to solve a hesitation problem you may want to try a #330 pink accelerator pump cam with a 0.031 squirter, if the hesitation is still there put 2 or 3 - 3/32 flat washers on top of the spring on the pump arm this will make the pump more active when you hit the throttle quickly.
henry @ oles carb
henry @ oles carb
Thread Starter
Racer
Joined: Nov 2004
Posts: 422
Likes: 0
From: Owensboro Ky
Originally Posted by olescarb
to solve a hesitation problem you may want to try a #330 pink accelerator pump cam with a 0.031 squirter, if the hesitation is still there put 2 or 3 - 3/32 flat washers on top of the spring on the pump arm this will make the pump more active when you hit the throttle quickly.
henry @ oles carb
henry @ oles carb
What is a pink accelerator pump cam and a 0.031 squirter. When it comes to carbs, I'm lost. Can someone explain were these are on the carb and the function.
Henry, Thanks for your advise!
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
well, I don't know much about carbs (as has been demonstated recently....) but last night I was reading a very interesting article in the latest NCRS Restorer mag about increasing performance on your carb.
Basically, on the issue of stumble on acceleration they suggest two things:
1. increase the accelerator pump shot as is suggested by olescarb above.
They say this simply doesn't work in some cases though.
2. Another problem that can cause acceleration stumble, especially on hard acceleration, is that the fuel in the fuelbowls is moving away from the jets (slamming into the back wall of the bowl). The solution is jet extensions.
Holley advises though that when using jet extensions on a carb with a secondary power valve, the power valve must be removed and the hole pluggeg and jet size increased accordingly (approx 4-8 jet numbers).
The jet extensions may also cause interference with the floats but if so there are special floats designed to replace the stock ones that allow for the clearance needed for the jet extensions.
Basically, on the issue of stumble on acceleration they suggest two things:
1. increase the accelerator pump shot as is suggested by olescarb above.
They say this simply doesn't work in some cases though.
2. Another problem that can cause acceleration stumble, especially on hard acceleration, is that the fuel in the fuelbowls is moving away from the jets (slamming into the back wall of the bowl). The solution is jet extensions.
Holley advises though that when using jet extensions on a carb with a secondary power valve, the power valve must be removed and the hole pluggeg and jet size increased accordingly (approx 4-8 jet numbers).
The jet extensions may also cause interference with the floats but if so there are special floats designed to replace the stock ones that allow for the clearance needed for the jet extensions.
Thread Starter
Racer
Joined: Nov 2004
Posts: 422
Likes: 0
From: Owensboro Ky
Originally Posted by BarryK
well, I don't know much about carbs (as has been demonstated recently....) but last night I was reading a very interesting article in the latest NCRS Restorer mag about increasing performance on your carb.
Basically, on the issue of stumble on acceleration they suggest two things:
1. increase the accelerator pump shot as is suggested by olescarb above.
They say this simply doesn't work in some cases though.
2. Another problem that can cause acceleration stumble, especially on hard acceleration, is that the fuel in the fuelbowls is moving away from the jets (slamming into the back wall of the bowl). The solution is jet extensions.
Holley advises though that when using jet extensions on a carb with a secondary power valve, the power valve must be removed and the hole pluggeg and jet size increased accordingly (approx 4-8 jet numbers).
The jet extensions may also cause interference with the floats but if so there are special floats designed to replace the stock ones that allow for the clearance needed for the jet extensions.
Basically, on the issue of stumble on acceleration they suggest two things:
1. increase the accelerator pump shot as is suggested by olescarb above.
They say this simply doesn't work in some cases though.
2. Another problem that can cause acceleration stumble, especially on hard acceleration, is that the fuel in the fuelbowls is moving away from the jets (slamming into the back wall of the bowl). The solution is jet extensions.
Holley advises though that when using jet extensions on a carb with a secondary power valve, the power valve must be removed and the hole pluggeg and jet size increased accordingly (approx 4-8 jet numbers).
The jet extensions may also cause interference with the floats but if so there are special floats designed to replace the stock ones that allow for the clearance needed for the jet extensions.
Thanks
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
So you don't even know the names of the parts of the carburetor? The first thing you need to do is get a good carburetor manual and learn the names of the parts and how it functions. You can not tune something if you don't even know the names of the parts that people are talking about.
BigBlockk
Later.....
BigBlockk
Later.....
Thread Starter
Racer
Joined: Nov 2004
Posts: 422
Likes: 0
From: Owensboro Ky
Originally Posted by BigBlockk
So you don't even know the names of the parts of the carburetor? The first thing you need to do is get a good carburetor manual and learn the names of the parts and how it functions. You can not tune something if you don't even know the names of the parts that people are talking about.
BigBlockk
Later.....
BigBlockk
Later.....
I understand the basic functions of a carburetor and will admitt to not knowing all the part names. The point of asking these questions is for advise not for someone to respond back and belittle.
I have been a member of this forum for almost 2 years and don't ask that many questions unless absolutly needed. For the most part the members are very helpful and responsive.
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
Could you be a little bit more specific about the hesitation you are getting? Does it happen in every gear? Does it happen when you first floor it, lower rpm, or does the engine cut out only at high rpm?
I was having a problem under hard acceleration (dragstrip conditions). I would be fine through 1st gear (shifting at around 5000 rpm) but then in 2nd gear at around 5000 rpm the engine would die for a couple of seconds and then start. I am pretty sure I was running out of fuel, possibly a fuel filter problem or other constriction in the fuel line.
I was having a problem under hard acceleration (dragstrip conditions). I would be fine through 1st gear (shifting at around 5000 rpm) but then in 2nd gear at around 5000 rpm the engine would die for a couple of seconds and then start. I am pretty sure I was running out of fuel, possibly a fuel filter problem or other constriction in the fuel line.
Last edited by PRNDL; Jul 20, 2006 at 12:32 PM.
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Thread Starter
Racer
Joined: Nov 2004
Posts: 422
Likes: 0
From: Owensboro Ky
It acts as if it is missing for the first few seconds of hard acceleration. The missing and rapid cut-out comes from the exhaust. This happens in every gear and all ranges of RPM.
I forgot to mention that my ignition is MSD.
I forgot to mention that my ignition is MSD.
Racer
Joined: Jun 2002
Posts: 281
Likes: 0
From: Brookfield IL
A miss in the first few seconds would definitely make me suspect the accelerator pump circuit. Maybe for a start you could buy a Holley rebuild kit and replace the acc pump diaphragms. That's something easy to try.
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Originally Posted by BDVT69
BigBlockk,
I understand the basic functions of a carburetor and will admitt to not knowing all the part names. The point of asking these questions is for advise not for someone to respond back and belittle.
I have been a member of this forum for almost 2 years and don't ask that many questions unless absolutly needed. For the most part the members are very helpful and responsive.
I understand the basic functions of a carburetor and will admitt to not knowing all the part names. The point of asking these questions is for advise not for someone to respond back and belittle.
I have been a member of this forum for almost 2 years and don't ask that many questions unless absolutly needed. For the most part the members are very helpful and responsive.
Sense you seam unwilling to spend $20 in an attempt to farther your own knowledge I have included a link to a labeled picture of a 4150/4160 series Holley carburetor. This, alas is 2 minutes of my life I will never regain.
http://www.holley.com/data/TechServi...ded%20View.pdf
I sincerely apologize for trying to help you with this problem. Rest assured, in the future I will endeavor not to make that mistake again. Someone else can hold your hand.
BigBlockk
Later.....
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
if the car pulls in excess of 0.8G or so or has 60' times at a drag strip in the 1.5 second range, jet extensions and thier special matching floats may be a good idea. most street cars with street tires do not pull enough g-force loads to uncover the jets, but the power valve if used in the secondary does pick its fuel up at a location that is higher than the jets so it could cause problems.
I in my writing both here and as a freelance tech writer try to say things so everyone can get something from it, but i still need more practice. i hope EVERYONE can have a little patience with the others on this site and if you disagree do it civil or else do it in a private e-mail
henry @ oles carb
I in my writing both here and as a freelance tech writer try to say things so everyone can get something from it, but i still need more practice. i hope EVERYONE can have a little patience with the others on this site and if you disagree do it civil or else do it in a private e-mail
henry @ oles carb
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
Originally Posted by olescarb
if the car pulls in excess of 0.8G or so or has 60' times at a drag strip in the 1.5 second range, jet extensions and thier special matching floats may be a good idea. most street cars with street tires do not pull enough g-force loads to uncover the jets, but the power valve if used in the secondary does pick its fuel up at a location that is higher than the jets so it could cause problems.
I in my writing both here and as a freelance tech writer try to say things so everyone can get something from it, but i still need more practice. i hope EVERYONE can have a little patience with the others on this site and if you disagree do it civil or else do it in a private e-mail
henry @ oles carb
I in my writing both here and as a freelance tech writer try to say things so everyone can get something from it, but i still need more practice. i hope EVERYONE can have a little patience with the others on this site and if you disagree do it civil or else do it in a private e-mail
henry @ oles carb
as mentioned, I have TONS to learn about carbs myself. I only mentioned the jet extensions because I just saw it mentioned in an interesting article and it seemed to fit the problem the original poster asked about.
They did suggest your idea of the accelerator pump shot first though and mentioned that if that didn't fix the problem that the jet extensions were another area to consider.
BTW, in no way was I disagreeing with your suggestion - just trying to offer some additional ideas to consider if it was needed.
Your point on the jet extentions really only needed on a much higher performance car such as a drag strip car may be very valid - again I wouldn't know enough to to know so I'll take your word on it
Racer
Joined: Apr 2006
Posts: 477
Likes: 43
From: Millbrae California
Barry, in by no means was my comment directed to you (or anyone else in particular), i am in general trying to let everyone see that there are people with all levels of knowlege that are reading these posts and i want everyone to please be patient with those that are just learning what is old hat to many, I will attempt to do also. one thing that i am seeing is there may be more than one way to fix a problem. i am learning from all of you both in knowlege and the different view point and experiance each of you has. i hope my 2 cents worth of ideas are worth what you are paying for them.
henry @ oles carb
henry @ oles carb
Le Mans Master
Joined: Apr 2004
Posts: 7,106
Likes: 38
From: Newark DE
Henry, i'm like you - I think all views are good and even in areas that I THINK I've gotten comfortable with I find everyday that there is PLENTY more for me to learn 
In fact, it's one of those "the more I learn, the more I realize how much I still don't know".
In fact, it's one of those "the more I learn, the more I realize how much I still don't know".
Advanced
Joined: May 2006
Posts: 61
Likes: 0
From: NORWICH UNITED KINGDOM
I also agree with Ols. I am new here too and had a problem with my carb which Ols gave me advice on. It fixed it. I also did not know much about the carb but now when a post comes up on a carb I read with interest in order to further my knowledge. The replys and different sudgestions do help newies like me understand other elements of the carb.
Thread Starter
Racer
Joined: Nov 2004
Posts: 422
Likes: 0
From: Owensboro Ky
Thanks for everyone's advice and suggestions!!!
Although I consider myself pretty good at rebuilding engines, - carbs have always been my downfall. I knew this forum would be a great place to help start me in right direction.
Although I consider myself pretty good at rebuilding engines, - carbs have always been my downfall. I knew this forum would be a great place to help start me in right direction.
Team Owner
Joined: Jul 1999
Posts: 26,545
Likes: 46
From: Huntersville NC
Pics help. I frequently refer to objects as "thingymabobs" and "doohickys" with enough descriptive adjectives (ie, small black shiny with wires hanging off of it) to identify the part in the picture. Usually a helpful forum member will give me the proper name of the doohickey!
