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4bbl Carb- 1000rpm issue

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Dpfeffer

New member
Happy 4th! I had the following issue develop yesterday on the water:

Engine won't run at 1000 rpm
Engine stalls if I try to accelerate slowly from idle through 1100-1200 rpm.
Engine idles just fine at its nominal 650 rpm.
Engine accelerates and runs fine above 1200 rpm and below 1000 rpm.

engine: 1995 5.7L Merc (Bravo drive)
carb: Weber 4bbl
electric choke
Verified accelerator pump working well
Clearly sounds (audibly) like it's starving for fuel or air around 1000rpm

any ideas? I haven't made any carb adjustments. It just stared happening.

thanks!!
 
You have picked up some trash in the main jets. the idle jets are fine however as you are asking for the fuel to begin flowing through the main jets the trash is blocking the fuel flow until the throttle plates overcome the restriction and you can actually damage the engine running lean. Get a kit clean it adjust it and go.
 
Well, sounds like you may have a slight blockage off idle, the transition from idle to power/mains. But, you might try to richen the carb up a bit by adjusting the air/fuel mixture screws. Adjust them for max idle, then re-adjust the idle speed screw back down to your 650 to 700 rpm....
 
Thanks guys! Any way I could try cleaning the blockage without installing a full new kit? I just "overhauled" with a kit 50 engine hrs ago. I can't think of a way to get in to clean the port without tearing the carb apart, but I'm by no means a carb expert.
 
Take the linkage off the carb and throttle it by hand. Rev to about 3300 rpm enough to get the primary flowing and then close the choke or cover the primary (the part with the choke plate) with your hand. It will suck the hell out of fuel as maximum vacuum is pulling fuel through the primary purposefully cleaning out any debris
 
Thanks! That makes sense and is worth a shot!

HeresJohnny said:
Take the linkage off the carb and throttle it by hand. Rev to about 3300 rpm enough to get the primary flowing and then close the choke or cover the primary (the part with the choke plate) with your hand. It will suck the hell out of fuel as maximum vacuum is pulling fuel through the primary purposefully cleaning out any debris
Click to expand...
 
Yeah, I tried to enrichen it. No luck. It helped a tiny bit, but not enough. Thanks for the idea though. Was worth a try! I ended up just pulling the carb and will take it apart/clean it out. No easy answer this time, but it's not overly difficult. Just a little time consuming.

Fastatv said:
Did you try to adjust the air/fuel mixture screws yet?
Click to expand...
 
Dpfeffer said:
Yeah, I tried to enrichen it. No luck. It helped a tiny bit, but not enough. Thanks for the idea though. Was worth a try! I ended up just pulling the carb and will take it apart/clean it out. No easy answer this time, but it's not overly difficult. Just a little time consuming.
Click to expand...

Giving the carb a good cleaning is the best thing to do, and then you will know what you have. About your prop, at WOT, trimmed up for top speed, what is your max RPM?
 
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