Marine Quadrajet fresh rebuild fine yesterday, overflowing today...

[Walleye4Days]

I am at a complete loss trying to figure out this 17059298. I installed a new SBC305 that's pretty much stock except for a decent cam installed. I rebuilt my quadrajet with Cliff's marine kit around 3wks ago. Broke in the engine yesterday and broke in the cam. Then ran the engine again for around 2hrs while final tuning timing and etc. Everything ran amazing and the carb worked flawlessly.

Fast forward 24hrs, and today I go out to start the engine to fine tune the outdrive, and all of a sudden the carb is DUMPING gas out the middle tube on the rear part of the choke plate (not the overflow at the front of the carb, although it may have also been coming out of there as well). But, flooding galore.

I assumed it was a stuck needle/seat or float, so I disassemble it all and reassemble with an entirely new float measured even lower than spec (just to ensure it was shutting off the fuel) and it still was overflowing like mad.

I have a fuel regulator set at 5.5psi, mechanical fuel pump rated for 5-9psi, and for some reason the fuel is still just dumping out while trying to start the engine and during routine idle. Any ideas as to what may be going on?

Specs:
- 17059298 marine quadrajet M4ME
- orange power piston spring
- decent cam/mild cam with noticeable idle
- Stockish SBC 305/5.0
- Fresh rebuild on carb, then again another rebuild to see if that eliminated the problem.

[hiy_po]

Is it possible you have debris in the fuel/fuel line jamming up your needle seat?? Really sounds like something intermittent stopping the needle seat from sealing and debris would have to be a first thought.

[tayto]

did you retain the hook that clips onto the needle and hangs on the float? there is a service bulletin regarding that...

[Walleye4Days]

I just now took it apart, rebuilt it again, and went back to starting it. Got the clip taken care of (I had to reassure myself I hooked it right after seeing your reply) and then rechecked for debris and etc.

I have 4 filters prior to making it to the carb, so I was kinda doubting debris. But, didn't hurt to triple-check anyways.

I just started it again, it states out great and then about secs in it started overflowing again...

I'm thinking that either the fuel regulator is letting too much pressure through (it's a new regulator and was fine yesterday, but stranger things have happened) OR the needle/seat combo just happens to have went bad/not seating right.

I haven't checked the outgoing pressure in the line yet (mainly because it's a pain in the rear, because coast guard specs call fit 2 clamps at every single connection) so I may have to check there in the morning.

I may just go pickup another temp kit from my Oreillys commercial acct (they carry marine parts by us) until I can get one of Cliff's hits delivered.

- No debris
- needle was correct and hung properly. But, I'm thinking either
---- A) the needle is getting hung up somehow some way, or
---- B) Pressure is bypassing the regulator and pushing the needle up off (Its a mechanical pump pushing 9psi max, so I wouldn't think that'd be enough to unseat it would it?) Or
---- C) the float is a defunct float? (It appeared to work and etc even rebuilding again just now, but just to eliminate it I guess I should pop a new one in).

I really appreciate the help guys, it means a lot. I'll keep updating as I go so we hopefully find the culprit.

[Cliff Ruggles]

Spend some time with the "clip" on the needle as they often require some custom "tweaking" to work as intended.

The float isn't finicky but you do need to make sure it travels thru it's full range of motion without hanging up.  I very seldom see any problems with those floats and they are huge for a reason as the early design is very sensitive to fuel pressure and they will flood easily compared to later designs that used the smaller floats.

Since you are running "dead-head" with a regulator it may be something with the fuel pump.  I've seen so many issues with currently available mechanical fuel pumps I need to mention that here. 

Most are coming from Airtex and of course "off-shore" and the pressures are all over the map plus fuel flow is inconsistent and they can "spike" fuel pressure and cause all sorts of flooding and running issues.   I've helped folks trace down all sorts of carburetor issues to the mechanical fuel pump instead in the past 10 years or so........Cliff

[Walleye4Days]

Not sure exactly what it was, but I put a new float, needle, and seat in and it works as it should now. The only issue left is that the idle air screws bog out the engine when all the way in, but they don't seem to bog it out when backed all the way out. So, I'm having trouble finding the sweet spot because with the idle at 650, the primaries closed off, and engine barely chooching along, the screws work great when I screw them in/it bogs out the engine. But, when backing them back out trying to find the second bog point (to split the difference) it doesn't bog out...

[Kenth]

In my book the 17059298 is an 4MC marine Qjet.
These units have .070" upper and lower idle air bleeds and .052" idle channels with .037" idle tube restrictions.
No control on rich side of the idle screws indicates a too lean idle circuit and the idle tubes needs to be opened some. I suggest at least .038" idle tubes, maybe a couple of thousands more after test.

[Cliff Ruggles]

The upper idle airbleeds in most Marine Q-jets and really tiny and in the airhorn, not the main casting.  Common idle tube sizes are .026" to .028" and rare to see them much bigger than that.

Most will go "pig" rich if you open them up much past .032" especially on a stock engine with the correct Marine cam in it making a lot of vacuum at idle.

The exception to that are some of the Volvo Penta Marine units as being discussed here which Kenth mentions, which were built from Oldsmobile type cores and have larger upper idle bleeds in the main casting.  They are easily to ID because they will be either hot-air or electric choke, not divorced.

Just adding info here for those rebuilding or working with Marine Q-jets, but where folks really screw the pooch with Marine engines is installing cams with tight LSA and shorter seat timing.  That never works out nearly as well as a gentle cam on a wide LSA or original Marine replacement cam right to start with. 

Marine carbs don't use idle bypass air either, not even drilled for it and no reason to unless for some reason engine mods were made to lower vacuum at idle speed.

Many Marine engines have very low idle speed settings, and some even "kill" the ignition for a moment when the Morse controls are moved to engage the Marine gear or outdrive.  This is done to keep them from "slamming" into gear and damaging components.

So keep all this in mind when you make plans to "modify" your Marine engine and stay as far as you can away from most of the cams companies like Comp and others offer for them unless you have the tuning skills to get those engines to idle well at really low RPM's.....FWIW......Cliff