Carburetor mods with Thumper cam - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



Register FAQ Search Today's Posts Unanswered Posts Auto Escrow Insurance Auto Loans
Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Engine
User Name
Password
lost password?   |   register now

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 06-23-2008, 07:09 PM
Registered User
 

Last journal entry: 1965/66 Impala body lines.
Join Date: Nov 2006
Location: Northern New York
Age: 63
Posts: 55
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Carburetor mods with Thumper cam

I have a 70s Chevy 350 in my 65 Impala and have installed a Comp Cams Thumper cam. My problem is that I have lost control if the idle screw adjustment. I'm reading about 5" of vacuum at idle. I also have installed an Edelbrock Performer carburetor with the factory Quad manifold using the proper adapter. I'm wondering if the idle vacuum is so low that the metering pistons are reading it a part or full throttle and allowing the metering rods to come all the way out to WOT position. Would this cause me to loose the idle screw adjust ability? Should I get the Edelbrock kit and install the lighter metering springs? It's burning so rich at idle that it burns your eyes and nose.

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 06-23-2008, 07:24 PM
n-gin's Avatar
Registered User
 
Last photo:
Join Date: May 2008
Location: Parma heights, Ohio
Posts: 148
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
There was another post in here about putting in a thumper cam and they had carb trouble . I cant seem to find it right know but I beleve he had to open the secondaries a little at idle and run the ignition 32* at idle and stop the mechanical advance in the distributor. If I happen to run across it I'll post a link.
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 06-23-2008, 07:56 PM
techinspector1's Avatar
Senior Curmudgeon
 
Last wiki edit: DynoSim combinations Last photo:
Join Date: Oct 2005
Location: Hemet, California, USA
Age: 72
Posts: 13,334
Wiki Edits: 326

Thanks: 844
Thanked 1,163 Times in 959 Posts
Copied from Edelbrock Owner's Manual......
Long Duration Camshaft
If the engine has a fairly radical camshaft it may require an excessive amount of throttle opening for idle and/or have low idle vacuum levels. Either condition can lead to poor levels of
adjustability and erratic idles.
Another fix for the above condition is to run as much spark advance as possible at idle. If the distributor is fitted with a vacuum advance unit, connect it directly to manifold
vacuum. If you are not able to employ vacuum advance for some reason, then the mechanical curve should have a low limit, which will allow you to use plenty of initial spark advance.
Measure the manifold vacuum at idle. If it is below 7" Hg, there is a good chance that the Metering Rods are in the up (rich) position. When combined with a high idle air rate this can
cause the Nozzles to discharge fuel at idle. Use a weaker Step-Up Spring (see section on Step-Up calibration) to keep the Rods down at idle. With some cams, a stiffer spring (pink or
silver) is necessary. Experimentation is the best way to determine which is best for your application.

Part #1464 will get you a complete set of springs.

Last edited by techinspector1; 06-23-2008 at 08:01 PM.
Reply With Quote Quick reply to this message
  #4 (permalink)  
Old 06-23-2008, 08:52 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: ohio
Posts: 1,615
Wiki Edits: 0

Thanks: 54
Thanked 67 Times in 64 Posts
Do you have the flat tappit thumpr or roller thumpr? I have the big mutha thumpr hydraullic roller wich is 243/257 @50 with 537/519 lift. I just paid over $600.00 plus for a new carb a q series quickfuel 650 mechanical secondary to go with it and I have a problem with it staying running after its in gear but it gets plenty of gas when you pump it. I had a 650 speed demon and it was not enough carb. I hope you can figure out how to get it running right. I did have an edelbrock and you will have to use different metering rods and spring to go with that cam with so much overlap. That is what I had to do with a 292h comp cam I use to have in one of my old motors. After i changed the rods and springs out and it idled at 1200 rpm it did fine other then the off idle stumble. Hope you get the kinks out. It seems to me a lot of people have problems with getting carbs to tune with the thumpr cams.
Eric
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 06-24-2008, 12:52 AM
SSedan64's Avatar
Registered User
 
Last photo:
Join Date: Dec 2007
Location: Macon, GA.
Age: 50
Posts: 6,016
Wiki Edits: 0

Thanks: 0
Thanked 46 Times in 46 Posts
Square Bore to Q Jet Adapter

These adapters work great for square bore carb to Quadrajet intake. They are tapered from 4-hole square to fit the Quad pattern. These line up perfectly with between the 2 different bores. The adapter in the picture needs to be flipped over.

http://cgi.ebay.com/ebaymotors/EDELB...mZ230264904939
Reply With Quote Quick reply to this message
  #6 (permalink)  
Old 02-19-2010, 11:46 PM
Registered User
 
Join Date: Feb 2010
Location: mt
Posts: 49
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
carb help w/ mutha thumper cam

i have a 351w bored .030 over and10:0:1 comp. broke cam in and i had to turn carb idol screw in alot to idol. edelbrock 600 carb. i read something about springs and vacume. the motor spits and sputters and is runni9ng rich too. can anyone walk me through this to set it up right? im new to this but not ignorent and learn fast w/a lil help. im running a mad w/b;aster 2 coil and msd street fire ignition box. also im using 45 plugs @ factory gap specs. shld i use a dif plug and @ what gap with this set up. or regap the ones i have. also i know 600 is a lil small but @ 3600 feet elev. what jet and needel shld i use too? in time i will go to a holley and is there issues with that carb i need to know about? can someone recomend which holley carb to go with. oh im running a c4 2500 stall. thx...SHAWN
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 02-20-2010, 12:06 AM
Registered User
 
Join Date: Feb 2010
Location: mt
Posts: 49
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Carb Help

Quote:
Originally Posted by F-BIRD'88
What cam shaft is in this motor?. If its a biggy size long duration cam you will need to recurve the distributor for much more initial spark timing at idle yet limit the advance travel limit so the thing is not over advanced at high rpm (that involves more than swapping advance springs) and its very likely you will need a torque converter with more than 2500 stall
What cam is in the motor?
its the mutha thumper cam for a 351w. and im running the stall it recomends. now im running a vac advance and i dont know alot about what you mentioned about the dist. i have read about the spring change in the carb but im lost after that..ill look for my cam card too.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 02-20-2010, 12:33 AM
Registered User
 
Join Date: Feb 2010
Location: mt
Posts: 49
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by 68stang73
its the mutha thumper cam for a 351w. and im running the stall it recomends. now im running a vac advance and i dont know alot about what you mentioned about the dist. i have read about the spring change in the carb but im lost after that..ill look for my cam card too.
ok dur @ .050 is 235 int and 249 exh. lobe seperation is 107.0
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 02-20-2010, 07:07 AM
Rickracer's Avatar
ASE Master Tech, Fabricator
 
Last wiki edit: Taurus 2-speed fan control wiring diagram Last photo:
Join Date: Jan 2010
Location: Kissimmee, Florida
Age: 55
Posts: 937
Wiki Edits: 8

Thanks: 0
Thanked 3 Times in 3 Posts
Quote:
Originally Posted by F-BIRD'88
The biggest mutha thumper cam requires a lot lot lot of initial spark timing at idle.
Lock out the distributor mechanical advance and set the idle timing at 34-36deg BTDC.
Install the lightest/lowest tension edelbrock metering rod/power piston step up springs.
Be sure the PCV system is hooked up to the base of the carb and is functional.
the opposite valve cover needs a breather.
Edelbrock carbs do not idle off the secondaries like a holley does. They will be closed at idle.

Once you've modified the distributor and replaced the power piston step up springs and reset the carb idle mixture and idle speed adjustment the idle will be much cleaner. The throttle response will be much better.
A 3500stall torque converter is required. (10" th350 converter) (9" th700r4)

There is no proper carb adapter for the square flanged performer carb on a factory Qjet manifold.
Change the intake manifold. A edelbrock performer RPM is what you need.
Way to much fuel distribution upset with any adapter on a Qjet manifold.
Stop fooling yourself.

If when the motor is hot, the motor is hard to start with the timing locked out, install a SPST switch on the distributor (HEI) or external spark amplifier box power switch on wire to kill the spark during cranking.
Kick it over with the spark switch off, then throw the switch and it will fire right up. Any 10A or more rated automotive grade SPST switch will work.
Mount it on/under the dash where you won't kick or knock it while driving........ Get the proper intake manifold.
This is DEAD ON info, trust it, it will get you where you need to go,
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 02-20-2010, 08:14 AM
Registered User
 

Last journal entry: 1965/66 Impala body lines.
Join Date: Nov 2006
Location: Northern New York
Age: 63
Posts: 55
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by 68stang73
i have a 351w bored .030 over and10:0:1 comp. broke cam in and i had to turn carb idol screw in alot to idol. edelbrock 600 carb. i read something about springs and vacume. the motor spits and sputters and is runni9ng rich too. can anyone walk me through this to set it up right? im new to this but not ignorent and learn fast w/a lil help. im running a mad w/b;aster 2 coil and msd street fire ignition box. also im using 45 plugs @ factory gap specs. shld i use a dif plug and @ what gap with this set up. or regap the ones i have. also i know 600 is a lil small but @ 3600 feet elev. what jet and needel shld i use too? in time i will go to a holley and is there issues with that carb i need to know about? can someone recomend which holley carb to go with. oh im running a c4 2500 stall. thx...SHAWN
[B]If you go to the Edelbrock site you can download the instrution manual. Also I know Summit carries the kit that includes the springs and metering rods you need. I never got to set mine up because i ended up having other issues with that engine and swaped it out. Good luck. That 351 sound sweet.[/B]
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 02-20-2010, 08:32 AM
Registered User
 
Join Date: Feb 2010
Location: mt
Posts: 49
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
thx

Quote:
Originally Posted by Rickracer
This is DEAD ON info, trust it, it will get you where you need to go,
first off thank you for the help. the cam is the mutha thumper NOT bg mutha. and the mutha recomends 2500 i checked and cross checked. i will check into the mods you have mentioned as well and see if it works. im sure it will. im a lil unsure how to do some of tht but i dont mind asking questions and learn fast. i am runnibg th msd pro billit...NOT the ready to run style. this one requires a ignition box. any other help wld be great. thx again guys.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 02-20-2010, 09:30 AM
Rickracer's Avatar
ASE Master Tech, Fabricator
 
Last wiki edit: Taurus 2-speed fan control wiring diagram Last photo:
Join Date: Jan 2010
Location: Kissimmee, Florida
Age: 55
Posts: 937
Wiki Edits: 8

Thanks: 0
Thanked 3 Times in 3 Posts
The Pro Billet comes with all the instructions and parts to set up the advance curve where ever you want it, right out of the box, so you're ahead of the game already,
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 02-20-2010, 01:55 PM
Registered User
 
Join Date: Feb 2010
Location: mt
Posts: 49
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
yada

Quote:
Originally Posted by F-BIRD'88
Yada Yada yada Yada...... get the 3500 stall converter.

Someone down at Comp Cams needs a ***** slap up side the head.
well i have it ideling @ 1000 rpm and already put it in and out of gear many times and it does just fine with the 2500. dont know what your issue is? im not on here for sarcasm just some help from fello hot rodders. i get enough of that plus some from my ex wife... i have yet to change the spring and do the dist and it idols just fine in and out of gear. thx again for those of you who want to help...
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 02-20-2010, 07:33 PM
Registered User
 
Last photo:
Join Date: May 2008
Location: ohio
Posts: 1,615
Wiki Edits: 0

Thanks: 54
Thanked 67 Times in 64 Posts
Well since last year I have ditched the stupid big mutha thumpr cam I used to had. It was the best thing I ever did. And to agree with Fbird you need a 3500 stall with a cam with a big amount of overlap like that. To me thumpr cams may sound nice and give some average performance for street wise but they are a pain in the rear to tune with any carburetor period.

I was able to get an edelbrock to work with a comp 292 cam but the big thumpr cam is way more radical specs wise for overlap. When you have very low vacuum like that your asking for trouble. Everything has to be up to spec from engine setup, carburetor, ignition, timing etc to make it all work right. I know some of the guys on here can be kind of rude and mean at times but they do know there stuff and have a lot of experience which I have learned a lot from them and from my elders who have done this for many years.

Look through some of the suggestions and you will have the final choice and make sure its a good one. My advice is if funds permit get a lunati voodoo cam. I got the 231/239 @ 50 with 535/550 lift and man I went from 5 to 12 inch's of vacuum and good breaks now and man did I get a nice jump in power and torque and way better throttle response.

All I have to do is have my timing at 16 initial and 34 all in by 3500 rpm. My timing curve probably is not 100 percent but its close and it runs excellent on pump gas with no issues. I am using a 3000 to 3500 stall converter and you have to have enough. Hope thing work out for you.
Eric
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 02-20-2010, 07:57 PM
Registered User
 
Join Date: Feb 2010
Location: mt
Posts: 49
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Quote:
Originally Posted by eric32
Well since last year I have ditched the stupid big mutha thumpr cam I used to had. It was the best thing I ever did. And to agree with Fbird you need a 3500 stall with a cam with a big amount of overlap like that. To me thumpr cams may sound nice and give some average performance for street wise but they are a pain in the rear to tune with any carburetor period.

I was able to get an edelbrock to work with a comp 292 cam but the big thumpr cam is way more radical specs wise for overlap. When you have very low vacuum like that your asking for trouble. Everything has to be up to spec from engine setup, carburetor, ignition, timing etc to make it all work right. I know some of the guys on here can be kind of rude and mean at times but they do know there stuff and have a lot of experience which I have learned a lot from them and from my elders who have done this for many years.

Look through some of the suggestions and you will have the final choice and make sure its a good one. My advice is if funds permit get a lunati voodoo cam. I got the 231/239 @ 50 with 535/550 lift and man I went from 5 to 12 inch's of vacuum and good breaks now and man did I get a nice jump in power and torque and way better throttle response.

All I have to do is have my timing at 16 initial and 34 all in by 3500 rpm. My timing curve probably is not 100 percent but its close and it runs excellent on pump gas with no issues. I am using a 3000 to 3500 stall converter and you have to have enough. Hope thing work out for you.
Eric
thx... i understand the rudeness at times but i have read enough on these forums that it seems tht there is more arguing and i know more attitude than what this is intended for. i dont care what ya run heck i owned 1 of everything at one point. i dont like to play games just honest answers. i dont bash anything anyone uses but give my advice as i have experianced it and nothing more. anyways....im stuck with what i built. i dont have the money to do swaps at this time so im in the RUN WHAT YA BRUNG club right now. just wanna get it running good and if its less than what i expected then i will be the first to say so. im not taking it down the track just street use and hwy. cruz nights etc. but i do like power and the occasional race but i also wanted a sound that knowone else has around here and so thts why i went with it. i may change it down the road but im stuck now...lol! NOW im looking at my msd chart and if i get this right from what is mentioned i shld use the silver stop bushing and the light silver and light blue spring. i dont know if this is right im trying to figure it out. looks like it will stop @ 2800 rpm and have about25 26 degrees??????????????? any help wold be great..thx guys..
Reply With Quote Quick reply to this message

Recent Engine posts with photos

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Hot Rod Forum : Hotrodders Bulletin Board forums, you must first register.
Please enter your desired user name (usually not your first and last name), your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.




Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
 
Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
roller cam selection for my monte ss redbandit98 Engine 37 06-21-2008 11:39 AM
Cam button length/clearance..? mrdreex Engine 1 04-12-2008 11:17 PM
Degreed the Cam -- 40 Degrees Advanced!!! JohnTN Engine 32 03-22-2006 11:40 PM
Help Me Pick A Cam Canadian Charlie Engine 2 11-16-2005 02:11 PM
More issues....lets talk cam failure TurboS10 Engine 23 09-28-2004 12:51 PM


All times are GMT -6. The time now is 08:06 PM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.