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Votes: 29
I installed an Edelbrock 4 bbl intake on my '74 Fury 400 and at first tried a new Holley... The power valve was toast out of the box so I decided to do what ma Mopar felt was good and installed a newly rebuilt Thermoquad spec'd for my '74 400. It's taken me two years to finally get the choke adjusted to where it starts decent but now I have a flat spot when I let off the pedal after a WOT acceleration. It feels like it's not getting quite enough fuel but only lasts about 5-7 seconds then smooths out. I can make a hard acceleration from 0-30 or 0-75 mph no problems until I lift off of the pedal to cruise and it happens at all rpm on lift off of pedal... can this be adjusted out? Float levels? Jetting? I figured this carb would be a diect application but it's been a royal PITA. I have a '73 Road Runner 340 and I plopped an Edelbrock Performer AFB style 4 bbl carb on it last year and that things starts and runs like a 2010 Accura. SHould I just put the Thermoquad on ebay and put a Ed Performer on it? Thanks Ron S
The TQ will out perform ANY carb on the market HANDS DOWN!!!.Some might outpower it,some might more m.p.g. it.Some might even say,it's hard to adjust,...but when its running correct,it's the next best thing to EFI Did you check this adjustment as most people do not even know it's there. It's going to take a small flat screwdriver. move the small plate and adjust 1/2 turn at a time,then narrow it down to 1/4 turn once it's close. Most problems you have described are this adjustment. Most rebuild shops do not adjust the float level correct also. Brass floats should be 1 1/16" and 29/32" for nitrophyl floats
Glen <span class='smallblacktext'>[ Edited Thu Aug 12 2010, 08:35PM ]</span>
Joined: Sun Feb 26 2006, 08:46PM
Location: Kingston,Ontario
Posts: 5622
I'm with Glen. A tuned Thermoquad works awesome. The metering rod adjustment is often overlooked since the Quad is the least understood carb out there. The choke pull off shares the linkage for the secondaries and when you mess with one,you mess with the other--very tricky but it can be done without getting bog. <span class='smallblacktext'>[ Edited Thu Aug 12 2010, 10:02PM ]</span>
I'd get the Eddy-but the newer AVS (thunder series) instead of the older AFB type. While a Thermoquad is a great carb when set up right, you can't go down to the local Autozone and get parts for like you can for the new Eddy's. Also, from what the previous posts have said, nobody knows how to work on them. <span class='smallblacktext'>[ Edited Fri Aug 13 2010, 12:08AM ]</span>
Joined: Wed Dec 21 2005, 07:34AM
Location: indiana
Posts: 791
I'd vote for a TQ in your case. If you get an Eddy AFB, get a 625. Avoid the 750 - there are a few horror stories on the 'net about them (myself included). A 750 is too big for a stockish 400 anyway.
Joined: Wed Oct 12 2005, 01:10AM
Location: British Columbia, Canada
Posts: 2690
owatajrkiam wrote ... The TQ will out perform ANY carb on the market HANDS DOWN!!!.Some might outpower it,some might more m.p.g. it.Some might even say,it's hard to adjust,...but when its running correct,it's the next best thing to EFI Did you check this adjustment as most people do not even know it's there. It's going to take a small flat screwdriver. move the small plate and adjust 1/2 turn at a time,then narrow it down to 1/4 turn once it's close. Most problems you have described are this adjustment. Most rebuild shops do not adjust the float level correct also. Brass floats should be 1 1/16" and 29/32" for nitrophyl floats
Glen
Both Glen and Leaburn are correct on teh TQ's...Great carbs!! I have a TQ on both my 87 dodge ram, and my 68 T/C wagon. Both start and run like they are running throttle body injection.
As stated the biggest thing with TQ's is the initial set-up. When I redo a TQ I probably take close to 2 hours setting up all the factory crab, rod and linkage adjustments, from there you need to tune it to your engine. Time consuming but once set-up almost trouble free until the next time you have to do a carb rebuild.
I just scored a VERY rare 72' 340 AT (6139SA) Thermoquad for $40. The guy was clearing out his late fathers garage and did not know what it was. I suspect his dad put it on the shelf because he could not get it to run properly. I took it apart this afternoon and found out why! The "O" rings that are always suspect were very deteriorated and dry. And number 2 on the list,but easily corrected by cleaning and then reapplying some JB weld to reattach them,are these wells that attach on to the main body. when i put a bit of pressure on it,this is what happened,just like a loose tooth comming out. I will redo both of them and as i have tons of spare parts and kits,this one will be done soon. These are the 2 MAJOR problems with these carbs,and when you have these out of the way,it's only a matter of setting all the adjustments CORRECTLY,and this carb will give plenty of years of trouble free service for less than $50 and a bit-o-time. !thumb
Where is the vacuum port that runs the distributor advance located? I don't see it in the pics. I've read that some of them don't have this provision. <span class='smallblacktext'>[ Edited Thu Aug 19 2010, 12:40AM ]</span>