General Category > Quadrajet Carb Talk and Tips

Very rich at idle

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Mla1:
Hello,
 
First time user of the forum, i just received Cliff's Jet book and I'm reading it, great book by the way!.

Vehicle is a '65 Impala 396.  Engine ran well prior to work beginning the customer just wanted to period correct Q jet on it.  We installed a 4MV on it for a customer and right out of the box it was not right as it flooded out of the vent tube.  We purchased the carb from a re builder in Los Angeles who was "highly regarded", had i known about Cliff's I would have purchased one from him and saved myself hours of time that i now have into this carb.

I pulled the top off and found they hung the needle through one of the little holes in the float and it was not closing on the seat so i hung it correctly.  I also found the power piston stuck in its bore.  I took it out and polished it up and polished up the bore and got it to slide in its bore very nicely.  Restarted the engine thinking we would be good. It did not flood any longer but was still running way to rich at idle and i could not lean it out.

Removed the carb again and started taking a closer look at things.  Pulled off the base plate and the epoxied plugs on the underside were not leaking but i found the two little air bleeds in the primary air horn right next to the two tapered  screws missing.  I took two out of another Q jet i have for parts and installed them with a little locktight, checked the float level and found it at 1/4" and left it there.  Verified the secondary throttle plates are closed

Reinstalled the Carb and it was better but still way too rich and putting my fingers over the two air bleeds i installed did not even make a difference.  Closing off the idle screws barely makes a difference in idle RPM, spark plugs are black.

I have no fuel dripping out of the primaries but it is so hard to keep it idling i only get a moment to see them before i have to raise the rpm to keep it running.

I am at a loss with were to go now.  I have no info on the correct needle and jet package and i don't know if that will really make it as rich as it is at idle.  Would like some help with were to go n

qjetsrule:
Is there fuel dripping out of the primary nozzle at idle? Throttle plates should be completely closed at idle, transfer slot barely exposed. Pull a manifold vacuum line off at idle, if idle increases there's too much fuel getting in. Check out Cliff's post on reman. carbs.

Cliff Ruggles:
"I pulled the top off and found they hung the needle through one of the little holes in the float and it was not closing on the seat so i hung it correctly.  I also found the power piston stuck in its bore.  I took it out and polished it up and polished up the bore and got it to slide in its bore very nicely."

Sounds like you discovered 2 of the 15-20 problems typically found on commercially "remanufactured" carburetors.  Instead of polishing a turd the carb should have went back to where it came from for a refund....IMHO.

It is IMPOSSIBLE to help in any area with the information supplied.  What is the part number on the fine piece of bovine excrement they sold to you?  You simply mentioned "period correct".  The list of people skilled enough to supply you with a correctly working early Chevy Q-jet for the 396 would be a short one for sure. 

The original 1965 Q-jets used on the Olds and Chevy engines were by far the WORST Q-jets every made.  They had too many issues to list here without writing another book, but good news is that the factory moved quickly and by 1967 they fixed most of them except the leaking bottom plugs and the corrected that issue by 1969. 

Sadly it was a little too late and they Quadrajet had a pretty bad reputation by then.  It was so bad that to this day folks still regurgitate old/outdated/inaccurate/incorrect information about them.  Leaking bottom plugs is at the top of the list.  I say that because every single one that comes in here will have a ton of "monkey chit" dabbed over plugs that weren't leaking in the first place.  8 out of 10 have so much glue on them it's holding the baseplate away from the main casting too far and causing either a vacuum leak, binding of the secondary shaft or a little of both.

Anyhow, without knowing all the parameters it's impossible to help.  All I know at this point is that you pulled some sort of Q-jet someone supplied out of a box and put it on a 396 and it doesn't work well.

To help I would need to know the engine specs if other than completely stock (which is rare these days).  What is the carburetor part number, and exactly what has been done to it?  I you are dealing with some sort of "frankencarb" which is highly likely I may not be able to help unless you go into my book and measure every hole in it mentioned in the chapter on modifying them, plus pictures of exactly what you are working on.

It already appears that you noticed "missing airbleeds" in the airhorn.  Most likely those were the upper Main Air Bleeds.  What else doesn't appear correct or has been altered or modified?  What jets, metering rods, idle tubes, DCR's, upper/lower IAB's, upper/lower MAB's are used.  Where are the upper IAB's located? Bypass air?  Hole size under the mixture screws?

Do you at least have any pics of the carb to put up here?.......Cliff

Mla1:
Thanks for the replies and i understand the need for more info.  I uploaded photos and i am waiting on a set of numbered drill bits to get you some sizes. The primary metering rods are number 44.  Sorry but that is all i have for now.  Thank you in advance. 

Cliff Ruggles:
Couple of quick observations.

The float is too small for that type of carburetor.  I would replace it with the correct large float for improved fuel control and less potential for flooding.

The secondary divider is in backwards.

It appears that you are missing the stainless steel plate above the gasket to seal off the exhaust crossover passage under the carburetor.

I also see a nipple in the filter housing, which means rubber hose/clamps are being used.  That is very dangerous on the pressure side of the pump.  Best to run a solid steel line between the pump and carburetor instead of rubber hose and clamps.

It appears that you have a very early carburetor, round tag and it may be the bypass type that doesn't use a threaded fuel inlet seat.  Those are the worst of the Q-jets and the most difficult as they had many flaws and fundamental issues in several areas.

Can you put up a pic of the accl pump.  Also a closer pic of the N/S assembly with the float removed.......

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