Carb Problem on 1996 300 Sundancer

Bill Goetz

Bill Goetz

Member
Jun 18, 2022
37
Gloucester, Va
Boat Info
Searay Sundancer 300 1996
Engines
Twin 5.7L 350
Hurth V Drive Inboards
Just wondering if anyone has experience with Weber WBA carb. Port side engine won't start cold. Need to prime with starting fluid or gas down the throat, then it starts right up and runs fine. Checked the operation of the choke seems to be OK. Checked accelerator pump and it is suspect. Tried all 3 positions. Operating manually doesn't seem to squirt much gas. (I assume it should). Throttle position and pumping has no impact. Doesn't seem to be any information on line even from Weber. Dead ends everywhere.
 
2 or 3 barrel?
Cold after a few hours
Or a week?
weak accelerator pump most likely is low fuel bowl level (no fuel to pump)

I have 4 bbl Rochesters but otherwise similar.

After 20 years the mechanical fuel pumps get worn out and can be slow to pump fuel up. Check valves get weak and diaphragm gets brittle.

I had similar hard starts long cranking to get the carbs to refill.

new fuel pumps and rebuilt the carbs and no issues for four years now.

carb rebuild is mostly just good cleaning, follow the kit instructions. watch out for small steel check balls and get the float height set accurately.

ps
Look dor a metal tag on the carb top screws or a number stamped on top for exact carb model
 
Thanks. I suspected as much, but I'm hesitant to just dive in not knowing. Wondering if fuel pump is bad, why does it run at all?
 
Exactly what Hugh said, same as mine. If sits more than a few days, hard start. Regardless of cold engine, if started on Saturday it fires right up on Sunday. Over sitting a few days it bleeds down.
Learned a trick from my mechanic. Pump about 5 times. Pull throttle back to neutral. Then crank for about 5 secs don’t touch throttle, this fills the bowl. Now pump while cranking, fires up.
Accelerator pump but too lazy to rebuild, this start sequence works for me.
 
Hey thanks for the tip. Worked like a charm, but I didn't even have to do the whole procedure. Pumped 5 times, throttle to neutral, turn the key...Bam! started right up! It's gonna sit till Saturday. Crossing my fingers that it wasn't a fluke. Didn't want to pull stuff apart till its out for the winter.:cool:
 
If you pump the throttle and don't see squirting gas going across the the carb then your accelerator pump needs replaced. This is a mechanical plunger that shoots gas into the carb.
 
I had a similar procedure for the 330DA, carbureted 7.4s. I had to full pump the throttles 2-3 times, then something else, try it for a few seconds, stop, then stand on one leg, throw salt over my shoulder, say a prayer or two, etc. and they would fire right up. The fuel evaporates after a few days. It was annoying as my neighbors fuel injected ones always fired right up. My next 7.4s were fuel injected, never had this issue.
 
Don’t know carbs well. Thought the accelerator pump is what filled the bowls, oh well. As was explained to me some part is letting the float bowls back drain over a few days. Hence hard start when sits. Doing the pump key thing beats $300 for a carb rebuild.
 
Carbs are really simple, a novice could overhaul one in a few hours taking ones time.
As I mentioned only tricks are don't lose the check balls and set the float carefully.
Carbs like to be run, flow some gas thru them regularly no problems. Let them sit that's problems.

Injection and particularly electronic injection, only came into use because EPA and the need to run very lean.
With a carbs it is very tricky to run lean but not so lean you detonate the cylinders.
In a boat the gains of injection over carbs is maybe 2% economy gain. At 1.5 mpg does that really matter?
And yes a smoother idle and quick starts IF everything works correctly.

$75 for my fuel pump, (cool fuel $300?)
$35 for my rebuild kit, (injectors $75*8?)
No computer, idle air control valve, TPS, MAP, no codes, beeps, get home mode...

I'm good.
 
If the throttle pump thing doesn't work after a multiple day rest, I would suspect the mechanical fuel pump is allowing the fuel to work it's way back to the fuel tank.
If it is the correct "marine" pump, there will be a clear hose running from it to the carb. There should be no fuel in it. If there is, the diaphragm has ruptured, and it has to be replaced.
 
Interesting you should mention that. I believe that hose is called a carburetor vent hose and we found that it was disconnected. Put it back on, but no apparent change.
 
Still struggling...Post #5 worked twice. Boat has been sitting for 2 weeks. Today it failed. Only savior was starting fluid. Then fired right up. Accelerator pump does not appear to be pumping, but if the gas has drained back, there probably isn't any gas to get! Lots of advice from leaking diaphragm in the fuel pump to bad accelerator pump to anti-syphon valve. Not sure where to go first. Those engine access panels are heavy!
 
The mechanical fuel pump has check valves in it. They should prevent the fuel in the lines from draining back to the tank. Sounds like that is what is going on and they are not doing their job.
Techmitch suggested checking fuel supply pressure, but I am not aware of how that can easily be done on these engines. Agree it would identify faulty pump operation, but it is simpler to just try a new pump IMO. Yours is likely 26 years old.
The ruptured diaphragm was mentioned as the cause if finding fuel in the clear vent hose from the pump to carb. They are required on these marine pumps so fuel does not drain (vent) to the bilge with a failed diaphragm.
 
So now it's March and the race is on to get ready for May 1 splashdown. Decide to tackle the cold start problem head-on. Had to do some other stuff underneath so we decided to replace the fuel pump just on general principles. Tore down the carburetor today and it was pretty nasty but no apparent breakage. Got a rebuid kit so we'll change the accelerator pump, needle & seats and the floats. Question is does anyone make a direct replacement for this carb? It's the Weber 4bbl model 9781. There really isn't a whole lot of info out there other than the shop manual.
 
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