Rebuilt 7041204 issues

[ernie3]

Thanks in advance for any help. I have a 7041204 that was rebuilt by a reputable builder (not Cliff) that I cannot get completely tuned. This is going on a ’71 vette, AT, 454, automatic with a mild, unknown cam. The big issue is I cannot get the secondary’s correct, I’ve adjusted the air doors as per the book. It doesn’t have the kick that it had and for a couple of minutes after WOT it acts like it’s flooded, it does not want to stay running. It also has developed hard starting after sitting a little while, after stopping for lunch it does not want to start, it acts like it’s flooded and takes a minute or two to get back to normal – just like after WOT.

Until I go WOT it’s a pleasure to drive, it runs a little cooler, throttle response is good and no problems smoking the BF Goodrich’s with a little power braking. Prior to this carb it had a q-jet from a ’77 truck, it was running great until the float started falling apart then I started the journey of chasing the correct carb and trying to get it set up correctly.

The carb started out as a commercially re-manufactured, butchered carb with a host of issues. Here’s what I know from the build sheet:

71 jets
42B rods
.047 MAB’s
9/32” float
CV secondary rods
Idle air bleeds .066 upper, .075 lower
Idle tube .036
Down channel restriction .060
Idle bypass .096
Idle screw .089
Adjustable APT in baseplate
Secondary rod hanger height .640

I have it set up with 16 degrees initial timing, centrifugal is all in by 2500, total timing at 36, adjustable advance limited to 52 degrees. Vacuum advance is ported, total vacuum at idle is 13” and the idle is little choppy but holds steady at 675, drops 50 rpm in gear.

I also have a barely noticeable off-idle flat spot and only at light throttle, I should be able to get that right with tweaking the APT a tad more.

I purchased and have been studying Cliff’s book but am struggling with tying my symptoms to any particular fix. I’m not sure what direction I need to go. WOT issues related to the hard starting? Primary side causing the secondary issues? Any guidance is much appreciated.

Ernie

[429bbf]

welcome to chp. ernie this might be a stretch but i think the bottom plugs are leaking . ill explain . when you shut it off the gas is running into the engine and flooding it . when you go to wot they leak so bad that the gas is going straight into the intake instead of up and over and being metered correctly. might sound stupid but its worth looking into. I'm sure someone else has a better answer. fwiw

[ernie3]

Thanks for responding 429bbf, they were epoxied and plugged when it was rebuilt.

Ernie

[tayto]

i know cliff refuses to rebuild commercial "remanufactured"  units now unless they are needed for restorations. hopefully you wont need another core to rebuild.

[Ethan1]

Thanks for responding 429bbf, they were epoxied and plugged when it was rebuilt.

Ernie

 BUT, what type of epoxy was used? If JB-Weld, it could still leak after multiple heat cycles and gas erosion. If Marine-Tex, good chance it is a permanent repair.

[ernie3]

It looks to be a quality repair with black Marine-Tex. If there is a leak it doesn't appear that it would be significant.

Any thoughts on the jetting? Does the .047 MAB's with the 71/42B set up raise a flag?

Any other issues that can cause it to be flooded after WOT?

Thanks for the feedback.

Ernie

[429bbf]

ernie have you looked in carb after you shut it off to see if its overfilling the carb? needle and seat not seating good.do you know what kind of pressure you have on the fuel inlet . just a couple of things to look at.

[Ethan1]

 A few more things to check. Are the fuel transfer holes in the air horn plugged? This would also cause a off idle hesitation. Are you getting that at all? Also, a locked up accelerator pump check ball could cause the hard start. Of course, this would also cause an off idle hesitation.

 How freely is your accelerator pump moving in its bore? Is the cup still in good shape after todays ethanol fuel? What kit did you use? Cliff's? Over-the-counter?

 Ethan

[Hillbillyenginering]

I guess two things come to mind.
Since it was commercially rebuilt. Are you certain that all three sections are correct for each other?
I'm wondering if the float is sticking on the housing after wot?the float will drop down farther. Maybe stick or fuel coming in and holding it down.
Does it run good enough to jump out and look down the carb.
See if your secondary air flap is binding. I also found my secondary vacuum pot didn't let off fast enough. It was for a smaller engine with. Had to drill it out to release quicker

[ernie3]

The replies are appreciated, I should have time this week to get back on it and provide some feedback on the suggestions.

I'm not sure about the kit, it was rebuilt by someone who for whatever reason stopped providing support before I was able to get it dialed in. It was already sent back once. I'm not throwing them under the bus, I don't know their situation, they've bent over backwards prior to now.

Which is why Hillbilly's post is concerning, not sure I would know how to identify mismatched sections - and maybe they are, which is why I'm no longer getting support.

Thanks guys,
Ernie

[Ethan1]

The replies are appreciated, I should have time this week to get back on it and provide some feedback on the suggestions.

I'm not sure about the kit, it was rebuilt by someone who for whatever reason stopped providing support before I was able to get it dialed in. It was already sent back once. I'm not throwing them under the bus, I don't know their situation, they've bent over backwards prior to now.

Which is why Hillbilly's post is concerning, not sure I would know how to identify mismatched sections - and maybe they are, which is why I'm no longer getting support.

Thanks guys,
Ernie

 I bet it was an over-the-counter kit and the accelerator pump is the culprit. Just my take.

[carmantx]

I bet it was an over-the-counter kit and the accelerator pump is the culprit. Just my take.

No.  I built it and used Cliff's parts.  We have spoke again.
I have suggested a heat shield gasket under the quadrajet to offset some heat.  It could be that the fuel is heating and boiling from the heat of WOT runs.  He had reported that the tune was close after the APT installed.

[Ethan1]

No.  I built it and used Cliff's parts.  We have spoke again.
I have suggested a heat shield gasket under the quadrajet to offset some heat.  It could be that the fuel is heating and boiling from the heat of WOT runs.  He had reported that the tune was close after the APT installed.

 There you go then. Not sure what could be the problem then, as I know you built it correctly. Especially using Cliff's kit. I hope you both get it figured out!

[Cliff Ruggles]

It's difficult to offer help or advice since the carb was commercially "remanufactured" at some point.  They are the most difficult to get working correctly, and very often as mentioned they do NOT have the correct top and bottom in place, and they do a host of other things to them during the rebuilding process to make them difficult if not sometimes impossible to get working correctly.

I've pulled my hair out on enough of those units to know to avoid them......Cliff