Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
Fury Fan wrote ... The 750 Eddy has a bad rep for being a crappy carb. I had many struggles with mine, and as I ‘netsearched I found I wasn’t alone. 2 theories I found – bad casting quality on the 750, and/or when it was scaled up from the 600 some of the geometry became not-ideal. Take either of them as internet rumor.
Over the past couple of months, I've been looking deeply into Edelbrock carbs. Not just the 750, but all of them. What I can say with certainty is that neither of those rumours are correct. The problem comes from the fact that there are calibration gaps that cannot be overcome. Despite at present having identified well over 400 jet/rod combinations.
Incidentally, the intake in Krauts post does not seem to be available new anymore. Summit, plus a few other places have not had any in stock for months.
Joined: Wed Dec 21 2005, 07:34AM
Location: indiana
Posts: 791
I agree on the calibration thing. But that does not preclude there could be something else amiss wiht the 750. The calibration gaps might simply be a 3rd factor, then?
Every 600 I've ever used (only a few, but over a 15-year span) has been a peach right out of the box, and tweaking them gave little improvement. My current 800 (which I got after removing the 750) wasn't perfect, but an afternoon's work made it acceptable.
For the 750, though –
I got 2 rod/jet kits (which gave some duplicity and equals 1.5 kits) and I put all the sizes in a spreadsheet to get effective fuel-flow area for each of the rod/jet combos. Bought some individual rods and jets in areas that seemed to be the next logical tuning step. Measured/logged/tried a set of AVS rods in that 750. I do remember now that during my 'testing' that I discovered there were some rods I wanted to try that they didn't make, and couldn't get there via a different rod/jet combo. So I even modified a set of rods to a smaller dia in one section (modified my drillpress chuck so I could spin the rod against some sandpaper. (wow – I had forgotten all the effort I invested in that carb until now!)
Nothing made that carb run smooth. And by not smooth, I mean terrible drivability in either low-speed/transition from idle or in the midrange, being pig-rich in one and reduced-power-lean in the other, and I could never converge them, only swap the behavior between areas.
Now, I will concede that I only had 1 sample of a 750, so I have no statistical validity, but when I asked around and found out other people had troubles with the 750 also, that was enough info for me to towel-throw and yank the 750.
Joined: Thu Mar 22 2007, 08:13AM
Location: In the workshop
Posts: 1063
Back in '06, I was running a 750 on my old engine. Even though that engine was tuned, stock calibration worked nicely. Then, it got removed in favour of a six pack. Moving forward in time, it later got refitted. Engine spec was as previous. This time, it ran poorly. The only difference was that "before" we had gas in the pumps, and when it was refitted, it was E10.
Richening 2 steps (=+8% according to Edelbrock) got it perfect at cruise. At power it was still to lean. Richening the power stage 1 step (=+4%) was still too lean, 2 steps and it became too rich. At both cruise and power, due to the calibration gaps.
Here's the fix for the easiest out of the box carb to tune.....HANDS DOWN. It's based on the electric choke version of the TQ and now comes in black. My 800 TQ runs perfect,but if i ever have problems with it,this is going on.
Joined: Wed Dec 21 2005, 07:34AM
Location: indiana
Posts: 791
Man, I have been itching to try one of those since they first came out. But I keep thinking I should install some of the EFI stuff I have laying around instead of changing horses yet again. But if I was in the market for a carb, that's my 1st choice without a doubt.