Quadrajet floods after turned off...

[cadunkle]

Quadrajet for '89 Merc 350/260HP. After turning engine off it doesn't want to start nicely. I can watch fuel slowly seep out of the boosters after turning off, wetting the butterflies. This is getting annoying because I have to go WOT to start every time.

I have rebuilt the carb with new needle and seat and set float level to .420" below the main body rail (as I thought all newer Quadrajets were set to). Fuel dripped out of boosters quickly like that and exhaust smelled slightly rich, so I lowered float level to .430" and now .440".

What is the correct setting for float level on this carb? Service manual gives a different measurement point from the air horn, which doesn't help. I'm measuring from the gasket surface that seals main body to air horn.

Anything besides float level that could be causing fuel to come from the boosters after shutdown?

 

[BaileysBoat]

Re: Quadrajet floods after turned off...

Either a hot soak condition, which causes the fuel to percolate out of the float bowl. This can be caused by incorrect float level.

The float level is specific to the carb number, assuming you have the correct
carb.

Once you find the correct spec you can adjust the float level to the lower end of the specified range, as the spec is usually plus or minus.

Or, the carb could be flooding slightly through the needle and seat.

I was trained on automotive engines, but you might be able to order a Delco carb kit for your carb.

 

[Evinrude Boater]

Re: Quadrajet floods after turned off...

I have rebuilt the carb with new needle and seat and set float level to .420" below the main body rail (as I thought all newer Quadrajets were set to). Fuel dripped out of boosters quickly like that and exhaust smelled slightly rich, so I lowered float level to .430" and now .440".

What is the correct setting for float level on this carb? Service manual gives a different measurement point from the air horn, which doesn't help. I'm measuring from the gasket surface that seals main body to air horn.

Measure from top of casting to top of float 3/16" from the toe of float. Need the carb no. for the measurement. Could be 5/8" or 11/16".

 

[BaileysBoat]

Re: Quadrajet floods after turned off...

After you set the float make sure you have the correct base gasket. Some are extra thick for insulating the carb from heat.

 

[hoot]

Re: Quadrajet floods after turned off...

it could be a heavy composite float or brass float with a very small hole. the float will not seal off the seat.

 

[cadunkle]

Re: Quadrajet floods after turned off...

Measure from top of casting to top of float 3/16" from the toe of float. Need the carb no. for the measurement. Could be 5/8" or 11/16".

By top of the carb casting do you mean the top of the main body casting with the air horn off and the needle seated? If so I'm way high on float level from even 5/8".

I don't have the carb number on hand but the engine SN is 0C540977. I get the carb number and post it.

 

[Evinrude Boater]

Re: Quadrajet floods after turned off...

Yes from the top of the main body casting. My Seloc manual states 15/64" to the flat top of the float, the same as my carb/engine combo.

 

[cadunkle]

Re: Quadrajet floods after turned off...

15/64" is way different than 5/8" or 11/16". It can't be only 15/64 or fuel would be pouring out the boosters. I had my float level only slightly higher than it is now (.440") and I couldn't get my idle mixture leaned out enough, smokey exhaust and burned my eyes. What year engine is that spec for? I'll check my carb numbers tomorrow afternoon.

 

[cr2k]

Re: Quadrajet floods after turned off...

There are tiny holes on each side of the primaries that are part of the accelerator pump and main jet circuits. These are visible form the throat along the main jet assy. that goes on the top in the center where the venturis attach. The purpose of these is to prevent siphoning of fuel from the bowl into the openings. We recently ran across this. Once cleaned no more fuel on the butterflies. Pull the top plate off and with a little tracing you should be able to follow the this circuit and identify the holes. Use a very fine wire to clean these if air pressure doesn't work. Don't enlarge them.

 

[cadunkle]

Re: Quadrajet floods after turned off...

There are tiny holes on each side of the primaries that are part of the accelerator pump and main jet circuits. These are visible form the throat along the main jet assy. that goes on the top in the center where the venturis attach. The purpose of these is to prevent siphoning of fuel from the bowl into the openings.

This sounds like a good possibility. I assume you are referring to the boosters when you refer to "main jet assy". I sprayed carb cleaner and compressed air through all passages I could see, but I'm still fairly new to Quadrajets so I see how I could have missed something. I'll check these passages this afternoon.

 

[Evinrude Boater]

Re: Quadrajet floods after turned off...

15/64" is way different than 5/8" or 11/16". It can't be only 15/64 or fuel would be pouring out the boosters. I had my float level only slightly higher than it is now (.440") and I couldn't get my idle mixture leaned out enough, smokey exhaust and burned my eyes. What year engine is that spec for? I'll check my carb numbers tomorrow afternoon.

The 15/64" spec is from a 1964-1991 Seloc manual. The carb number on my unit is cast in a circular formation.

 

[cadunkle]

Re: Quadrajet floods after turned off...

Carb number is 17080561, stamped in the port side of carb. There is another number on rear of carb in circular pattern that doesn't match up with any carb numbers I was looking at.

By 17080561 float level is 1/4" which I kinda believe based on watching fuel level in bowl where needle closes. If I set the level that high I get fuel dripping from boosters rapidly after shutting motor off, quickly floods and is a pain to start. Ideas?

 

[cadunkle]

Re: Quadrajet floods after turned off...

Solved... Problem was the metal gasket below the needle.

After observing fuel dripping from boosters at idle and aftershutting off I shined light into the two vents in the top of the carb and fuel level looked high but was hard to tell. Pulled the top and foul fuel bowl almost completely full to brim. Float floated, removed needlea dn seat, they were clean and sealed easily to blowing air through, so put a new metal gasket under the seat. Problem solved. Now idle withj no drip, doesn't smell rich, and can let sit for a couple minutes and start with just a tap of the key, no throttle required.