Won't rev past 3000 rpm . - Hot Rod Forum : Hotrodders Bulletin Board
Hotrodders.com -- Hot Rod Forum



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

Reply
 
LinkBack Thread Tools
  #1 (permalink)  
Old 08-23-2019, 10:53 AM
boneste624's Avatar
Registered User
 
Join Date: Apr 2019
Location: Los angeles
Posts: 40
Wiki Edits: 0

Thanks: 0
Thanked 1 Time in 1 Post
Won't rev past 3000 rpm .

Vortec 350 avs2 650 carb and HeI unit off amazon..

At idle I can rev it up past 3000 just fine . But in gear if I mash the pedal the secondaries open up and it's like it hits a brick wall and wont rev past 3000. Just goes whooooooooooooooo. What could be the issue.?

    Advertisement
Reply With Quote Quick reply to this message
Sponsored Links
Advertisement
 
  #2 (permalink)  
Old 08-23-2019, 11:02 AM
dwighty390's Avatar
Registered User
 
Join Date: Mar 2013
Location: Urbandale, IA
Age: 32
Posts: 286
Wiki Edits: 0

Thanks: 0
Thanked 40 Times in 36 Posts
What's the timing doing?
Reply With Quote Quick reply to this message
  #3 (permalink)  
Old 08-23-2019, 11:04 AM
vinniekq2's Avatar
Registered User
 
Join Date: Jun 2012
Location: BC,Canada
Age: 61
Posts: 12,242
Wiki Edits: 0

Thanks: 857
Thanked 1,453 Times in 1,343 Posts
whats your whoo timing at when you rev 3000 rpm? When you look down the carb throat does everything seem to be flowing? What is your fuel pressure at when revving 3,000 rpm? At 3,000 rpm does the rpm change at 1/2 throttle? Does the Whoo change in sound level or intesity,,,?
Reply With Quote Quick reply to this message
 
  #4 (permalink)  
Old 08-23-2019, 11:53 AM
Registered User
 
Join Date: Jun 2010
Location: TX
Posts: 3,895
Wiki Edits: 0

Thanks: 37
Thanked 458 Times in 428 Posts
You need to adjust the air valve secondary (AVS2) opening rate. It is flopping wide open before the engine RPM is high enough to handle the high air flow. That is known as “bogging down” . The. Air valve secondary is one way to control the flow through the carburator. Also known as “progression”. Most carbs and multi carb set up have some form of progression.

I had two Holley 4224 Center squirt carbs on my 1962 Chevy and all eight barrels would open when I mashed the loud pedal. No progression at all. You don need progression with a drag race only car. My 55 Chevrolet had a 455 Pontiac engine.

If you want to get rid of the sudden wide open Air Valve Secondary feature, get 4.56:1 rear gears, a 454 Chevrolet engine or adjust the opening rate of the air valve secondary.

Last edited by MouseFink; 08-23-2019 at 12:04 PM.
Reply With Quote Quick reply to this message
  #5 (permalink)  
Old 08-23-2019, 12:12 PM
Registered User
 
Join Date: Apr 2012
Posts: 246
Wiki Edits: 0

Thanks: 1
Thanked 30 Times in 28 Posts
Is there enough air filter area, and is it unrestricted to the carb entrance, and/or

Is the fuel pump putting out enough volume/pressure at the carb to keep up with demand?

You can try running it with no air cleaner assembly to see if it is a restriction issue.
Reply With Quote Quick reply to this message
The Following User Says Thank You to toddalin For This Useful Post:
MouseFink (08-27-2019)
  #6 (permalink)  
Old 08-23-2019, 12:39 PM
Registered User
 
Join Date: Jun 2010
Location: TX
Posts: 3,895
Wiki Edits: 0

Thanks: 37
Thanked 458 Times in 428 Posts
The fuel pump and air cleaner has nothing to do with the AVS2 carburetor air flow rate.

The AVS opening is controlled by adjusting the linkage on the carburetor.

I had a Rochester Q-jet on my 1969 Firebird 400 and it had a secondary opening limiter tab on the linkage. I cut off the secondary adjustment tab with wire cutters so the air valve secondary would fully open after I installed 4.33:1 rear end Gears. The Edelbrock AVS2 has a more convenient linkage adjustment so you don’t have to use wire cutters.
Reply With Quote Quick reply to this message
  #7 (permalink)  
Old 08-23-2019, 01:29 PM
Registered User
 
Join Date: Jun 2010
Location: TX
Posts: 3,895
Wiki Edits: 0

Thanks: 37
Thanked 458 Times in 428 Posts
The story about the Pontiac Rochester Q-jets:

In 1967, Pontiac put the same Rochester Q-jets on the Pontiac 428, 400 GTO and Firebird 400 engines. Due to the insurance rating system of power to weight ratio, the lighter weight Firebird 400 had to have less HP than the other Pontiacs or the Firebird 400 would be in the same insurance rating category as a 1967 Corvette.

The engineers at Pontiac solved that issue by putting a AVS limit tab on the secondary air valve linkage. The limit tab would only allow the air valve to open 3/4 from vertical or from being wide open. That reduced the engine Horse power rating from 360 HP / 400 CI GTO without the limit tab to 335 HP / 400 CI Firebird 400 with the limit tab. That also reduced the insurance rate by about $100 per month.

You can raise the HP on a Firebird 400 from 335 HP to 360 HP by merely cutting off the AVS limit tab on the Rochester Q-jet carburetor secondary opening linkage.

Smart fellers, those Pontiac engineers.

Last edited by MouseFink; 08-23-2019 at 01:40 PM.
Reply With Quote Quick reply to this message
  #8 (permalink)  
Old 08-23-2019, 02:38 PM
chasracer's Avatar
True Hotrodder
 
Join Date: Oct 2018
Posts: 567
Wiki Edits: 0

Thanks: 39
Thanked 131 Times in 117 Posts
Do you have another carb or one that you can borrow? That would tell you a lot and I am guessing that you don't have a fuel pressure gauge to measure pressure but when did this start happening? Are these recent changes to the engine?
Reply With Quote Quick reply to this message
  #9 (permalink)  
Old 08-23-2019, 04:21 PM
Registered User
 
Join Date: Apr 2007
Posts: 12,399
Wiki Edits: 0

Thanks: 181
Thanked 1,142 Times in 912 Posts
Regap the plugs to .030, replace them and gap those to .030 if the plugs are old or fouled, then test again. These E bay distributors often perfer a tight plug gap. They run nice in the lower RPM's but crap out around 3000 with a lot of throttle. I've found tightening the plug gap often helps these ignitions. This is not to say there isn't a carb issue but you have to check these things out and I like to start at simple and cheap to do then work up.

Usually if the secondary air valve comes on too early it is a transitioal thing that the engine will stagger through and eventually get going.

Bogie

Last edited by BogiesAnnex1; 08-23-2019 at 04:27 PM.
Reply With Quote Quick reply to this message
  #10 (permalink)  
Old 08-23-2019, 07:11 PM
Registered User
 
Join Date: Jul 2017
Posts: 296
Wiki Edits: 0

Thanks: 0
Thanked 57 Times in 48 Posts
Is this an automatic transmission?

I had a car that would go like stink up to about 3,000 and then just nose over and accelerate slowly after about 3,000. If you held it to the wood it pull clean to the governor (in the trans) but would do it at a snails rate of acceleration. Did this in all gears. Short shift it and it would go like stink. Wouldn’t go over about 85 in third but would easily top 100+ in OD.

The final fix was to rebuild the transmission. Then it pulled hard in all gears all the way to the governor. Something in the trans was unhappy at high engine rpm.

Food for thought
Reply With Quote Quick reply to this message
  #11 (permalink)  
Old 08-24-2019, 06:58 AM
55 Tony's Avatar
Registered User
 
Join Date: Nov 2018
Location: Cocke County, TN
Posts: 1,059
Wiki Edits: 0

Thanks: 134
Thanked 181 Times in 161 Posts
You should be able to determine if it's the carb by slowly opening the throttle, easing the secondaries open slowly. If that works then for sure your carb is opening too fast. I work on Q-jets, I've never seen the edlebrock version so can't help on adjustment.
Cheap and easy to try.
__________________
Young enough to learn ... too old to remember.
Reply With Quote Quick reply to this message
  #12 (permalink)  
Old 08-24-2019, 09:15 AM
Registered User
 
Join Date: Apr 2007
Posts: 12,399
Wiki Edits: 0

Thanks: 181
Thanked 1,142 Times in 912 Posts
The Edlebrock instruction book that came with the carb gives explicit instructions as to how to adjust the secondary air valve, experience at this has taught me to follow their instructions. These instructions are also on line if you can't find the booklet.

Not that I think this is the total problem, but proper adjustment is necessary especially if you tried going off on your own, like I never did that.

But reread my earlier post, it too is bore of unpleasent experience and subsequent discovery. Always remember the old rule of carburetors; "most carburetor problems are electrical".

Bogie
Reply With Quote Quick reply to this message
  #13 (permalink)  
Old 08-24-2019, 11:55 AM
Registered User
 
Join Date: Jun 2010
Location: TX
Posts: 3,895
Wiki Edits: 0

Thanks: 37
Thanked 458 Times in 428 Posts
The so-called “anti pump up” hydraulic lifters will pump up and float the valves about 3000 RPM and the car will nose over and stop pulling. They act as a rev limiter. My associate had a 1967 GTO that would nose over at 3,000 RPM and it felt like he turned off the ignition key.

I used solid lifter camshafts in my two Pontiac motors in 1969-1970. I risked spinning rod bearings over 6,000 RPM until I rebuilt the rods using ARP bolts. I used Pontiac Ram Air IV limited travel hydraulic lifters in the three Pontiac motors I built in 1971-1980. I could spin those motors up to 7,000 RPM with a 4.33:1 rear gear ratio in my 1969 Pontiac Firebird 400.

The Pontiac limited travel lifters were discontinued in 1990. Comp Cams and other cam grinders started offering limited travel lifters in 1994 for GM engines. Those lifters set at .002” preload and have only .050” total plunger travel. You must use 7/16 rocker studs and poly locks to set the preload. Those are often called “cheater” hydraulic lifters in stock class racing that requires hydraulic lifters.
Reply With Quote Quick reply to this message
  #14 (permalink)  
Old 08-25-2019, 10:04 AM
curtis73's Avatar
Hates: Liver. Loves: Diesel
 
Last wiki edit: How to find cheap parts
Last journal entry: Found an LQ9 today
Join Date: Dec 2005
Location: Carlisle, PA
Age: 46
Posts: 5,502
Wiki Edits: 16

Thanks: 32
Thanked 59 Times in 48 Posts
When you hear that "whaaaa," it is almost always a lean condition. Fatten up the secondaries.
Reply With Quote Quick reply to this message
  #15 (permalink)  
Old 08-25-2019, 02:56 PM
Registered User
 
Join Date: Jun 2010
Location: TX
Posts: 3,895
Wiki Edits: 0

Thanks: 37
Thanked 458 Times in 428 Posts
That’s right. When you hear “woooo” means the secondaries are right.
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:
Insurance
Please select your insurance company (Optional)

Log-in



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



All times are GMT -6. The time now is 09:28 PM.


Powered by vBulletin® Version 3.8.8
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0 PL2
vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright Hotrodders.com 1999 - 2012. All Rights Reserved.