IS it Time to rebuild Rochester Quadrajet?

quote:
Originally posted by pdecat

I don't get it. It starts well cold so How could that be a leaking bowl? the bowl would be empty. The problemis after running when the bowl should be at its fullest.

Do you see fuel vapors drifting up from the warm carb? Flooding should be obvious, gas smell dark exhaust etc.

IMO there is an electrical heat related issue.

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Update: went out on the boat today and this time I had decided to cruise at low speed (i.e. 1500 rpm ) for the same amount of time as I did last weekend when cruising at 3000 rpm. I experienced the same results: after 40 minutes of 1500 rpm cruising engine will stall.
So I think to your point Bruce, that, after some time, some heat related electrical/ignition issue starts to develop.
So, we cruise back to the mooring on other engine which was about 30 minutes back. Then by that time bad engine would run again but not as smooth. Pulled out the infrared temp gun and measured coil temperature and the readings were about 153-155 degrees. By comparison, the good engine's coil temp was about 132 degrees.
So, with this observation I am starting to lean toward "not a carb" issue but indeed ( to your point Bruce) a heat related ignition problem.
150+ degrees seem a little high for a coil, no?
Will replace coil anyway with new one, hopefully tomorrow....

Stay tuned! and Thanks for the all the replies!!!
 
Good move with the temp check. You could check and compare the ohms resistance of the primary and secondary coil circuits of both good and bad engine coils. Or swap coils.
From George Van Parys' great collection of Mechanical How-to Articles forum : http://www.boatered.com/forum/topic.asp?TOPIC_ID=51465

I believe plug gap , timing, sp. plug cable condition, coil & dist. wire connections, coil input voltage, dist cap/rotor condition and, of course, coil internal resistance amongst others can all affect amp demand and heat at the coil, but Charlie and Bruce and Smitty and others here would know more about that issue than I.

I happened to remember this (non-coil) thread which might be worth a quick read due to similar delayed stalling out symptoms:
http://www.boatered.com/forum/topic.asp?TOPIC_ID=129229

And another coil-related, but a bit different:
http://www.boatered.com/forum/topic.asp?TOPIC_ID=14928
 
seems that you did some good trouble shooting. If the coil is heating internally, not from being in a hot location, then there are three possibilities. Too much voltage to the coil. Shorting coil or too long of a time when the switching circuit is closed ( what ever is the modern equivalent of too little point gap}.

Of course it could be none of the above but your temperature info is worth perusing.
 
quote:
Originally posted by pdecat

seems that you did some good trouble shooting. If the coil is heating internally, not from being in a hot location, then there are three possibilities. Too much voltage to the coil. Shorting coil or too long of a time when the switching circuit is closed ( what ever is the modern equivalent of too little point gap}.

Of course it could be none of the above but your temperature info is worth perusing.

Click to expand...


Update: Problem Resolved!!!!
Root Cause: defective ignition coil!!!
Got up early this morning, went to my local marine store, picked up a new coil and installed on engine.
From a cold start, engine fired up nicely within 2 seconds of cranking.. Wow!!!
I was amazed on how quick it started up.
Then repeated the set of troubleshooting steps (i.e. cruise at 3000 rpm for 20 minutes ) and problem disappeared!!!!
What a nice way to end up a very nice weekend of boating!!!
Guys, thank you so much for all the help and pointers in resolving this....
Lesson learned here, try the small and simple stuff first before thinking the worse...
As good practice, I will also replace coil on good to keep maintenance log in sych. These coils were 6 years old, so I'm not sure this is about their life span.

Special Thanks to Bruce for your pointer.

Very happy boater!! :)

Thanks again to all and keep on boating!!
 
There is more to rebuilding a carb than throwing in a rebuild kit. Or certainly there can be. There can be worn part that will need to be reworked or replaced that do not come in the rebuild kit.

I sent mine to Treadwell in Treadwell, NY. The guy has been working on carbs for many many years, from old tractors to marine to cars. He also rebuilt the carb for my Snowcat which has a Ford 300 straight six engine.
 
Pat- Did you check the primary and secondary circuit coil resistance on the bad one and new so you know what to look for on the other engine? Coils generally last a long time if not stressed by other factors.
 
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