7.4 Hard starting at times

M

Michael Marcello

New Member
Jan 9, 2022
7
Boat Info
1993 290 Dancer
Engines
7.4 454
Hi i have a 7.4 That is hard to start at times, here is what happens. When it starts it runs and idels fine.
If i start it aprox. 1-3 days apart it starts and runs OK, after waiting over 4 days (aprox) it starts getting harder and i have to pump the trottle repeatatly. The longer i wait between starts the harder it gets.
1993 290 Dancer 7.4 454 Gen V Brovo 2 OD839053 Quadrojet The choke is not electric.
The Carb has never been rebuilt, i am the second owner and my marina has maintained this boat since it was new.
Does anyone think it would be a good idea to get the Carb rebuilt while the boat is layed up for the winter. All of the ignition parts have been replaced, the fuel seperator is replaced every fall and the fuel pump was rebuilt last season.
Thanks Mike










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The gas in the carb is evaporating over the course of a few days. It takes a bit of cranking to get the mechanical fuel pump to push enough fuel back into the bowls so you have enough to fire up the engines. To my knowledge, nothing you can do except start it up a bit more often. For me, I advance the throttle all the way once - to set the manual choke. Then crank (maybe 10sec) STBD for a bit, than PORT, then back to STBD and PORT again. I then pump the throttle once (now that there is fuel in the carb) and set the throttle open a bit to help with the initial start. As soon as it fires back it down quickly. Getting the carbs rebuilt/cleaned is always a good idea - but wont solve this particular issue that I am aware of. Just the nature of the beast given the age/era of the carb.
 
Michael Marcello said:
Hi i have a 7.4 That is hard to start at times, here is what happens. When it starts it runs and idels fine.
If i start it aprox. 1-3 days apart it starts and runs OK, after waiting over 4 days (aprox) it starts getting harder and i have to pump the trottle repeatatly. The longer i wait between starts the harder it gets.
1993 290 Dancer 7.4 454 Gen V Brovo 2 OD839053 Quadrojet The choke is not electric.
The Carb has never been rebuilt, i am the second owner and my marina has maintained this boat since it was new.
Does anyone think it would be a good idea to get the Carb rebuilt while the boat is layed up for the winter. All of the ignition parts have been replaced, the fuel seperator is replaced every fall and the fuel pump was rebuilt last season.
Thanks Mike
Click to expand...
This is a known problem with the quadrajet carbs. Its the float bowl well plugs leaking. They are at the bottom of the float bowl and I guess the plugs somehow corrode and allow the fuel in the bowl to slowly leak out into the intake manifold. Its not a fast leak, which is why it takes days for the bowls to drain down and the longer since last start, the more you have to crank the engine to get it to fire. On mine, it takes a bit over 3 days of non use before it is noticeable on a start.

That is why you need to turn over the engine to get the mechanical fuel pump to refill the bowl before it can start. Its annoying, but not a huge problem. There is a fix, but I have not bothered. Google "Quadrajet well plug leak" and you will find a bunch of information about it.
 
I see nothing wrong with having to crank an engine 4-5 revolutions before it starts. Gives the oil pump a change to built up some pressure before it fires off. That said if I were you I'd rebuild the carb and convert to electric choke. Did both of mine 12 years ago and they start and run great.
 
Thank you for the repleys. I think i will have it rebuilt but will not know the result till its recommisioned in the spring.
Mike
 
@Creekwood nailed it. For whomever does the rebuild, if they're not familiar with this malady, the two large and three small well plugs need to be properly cleaned and epoxied over with a compatible epoxy.
Q_jet_well_plugs.jpg
 
I also have a '93 290 DA with a 7.4 and Quadrajet. The well plug problem is well known and can be easily remedied as others have noted. Gas can still evaporate from the float bowl if left for a few days. I installed an inline, electric fuel pump that I only use to prime the carb, using a momentary switch. The mechanical pump still does the heavy lifting. End of slow starting and easier on the starter, too. The electric choke is more reliable.

Older carbs do have wear points that will allow leaking and fuel mixtures to go off calibration. Float levels can also go wrong. Tiny passages, rods and jets can all suffer with time, wear and corrosion effects. A remanufactured carb can more than pay off in fuel savings. Correct carb tuning is very important so find an old tech that knows how to do it. A well tuned Quadrajet is as good as it gets.
 
Last edited:
Definitely agree that your issue is likely the "well" plugs (actually called "Welch" plugs). Fuel in the bowl will not evaporate over the course of a few days. A MONTH maybe, but not a few days or even a couple weeks.

You should not have to pump the throttle more than ONCE. This resets the choke and squirts a little bit of fuel into the carb via the accelerator pump mechanism. If you need to move the throttle more than once then either your bowl is going dry (the plug issue) or your choke is not set properly.

A mechanical choke is fine, but if you have a divorced choke (where the thermostat element is mounted on the manifold), then you might want to check if the attachment in the center is loose. That will cause a bunch of "slop" in the mechanism and make it impossible to set the linkage correctly for consistent application. If you take the unit off, you can see if there is "slop" inside and you can re-stake the center to stop any errant movement.
 
My Crusader 454s with Qjets start without touching the throttle. With the electric chokes and the "fast idle cam" removed from the choke linkage the choke sets fully when the engine cools off therefore no need to pump the throttle to "set" the choke as it sets itself. The engine start on the first revolution if less than 3-4 days idle. After a week or more it takes 3-4 revolutions which is fine by me as it gets engine oil pressure built up prior to starting.
 
I have this exact same problem. After 3 days it’s pump pump pump pump the throttle, then flooded, wait 5 mins finally stumbles and starts.
Very frustrating.
 
Pirate Lady said:
I have this exact same problem. After 3 days it’s pump pump pump pump the throttle, then flooded, wait 5 mins finally stumbles and starts.
Very frustrating.
Click to expand...

Try leaving the throttle alone, crank engine 3-4 revolutions, pump throttle once and then turn the key to start.
 
km1125 said:
Definitely agree that your issue is likely the "well" plugs (actually called "Welch" plugs). stings.
Click to expand...

Variously termed Welch plugs, well plugs and Welsh plugs, the correct term is "carburetor metering block plugs" if we are being so technical about it. Welch plug is generic, also applying to so-called "frost plugs" in engine block castings.
 
Juliery said:
Variously termed Welch plugs, well plugs and Welsh plugs, the correct term is "carburetor metering block plugs" if we are being so technical about it. Welch plug is generic, also applying to so-called "frost plugs" in engine block castings.
Click to expand...
It's only "Welsh" if you're English (or, I guess, Canadian!) :D

They were invented and patented by Welch Motor Car company about 20 miles from where I grew up. (queue Paul Harvey to say "...and that's the rest of the story!") :D
 
Thanks again for the reply. There is a local guy about 1/2 hour from me County Carb. in Poughkeepsie NY that the local Mariners use, That is the plan as of now, Thanks
 
Please let us know if that cures your problem. We all love to know if our input helped, and can then be a data point for future searches.
 
Had the same issue with my twin carbureted 7.4's on my 95 330DA. Once you figure out when to pump the throttles, how much to pump etc, they start right up. If I recall correctly I would turn the engines over a few times, then full pump once, then set it to half throttle and they'd fire right up. Or maybe the other way around, I can't remember, but after figuring it out they started right up each time.
 
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