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Mercarb Accelerator Pump

Posted by Mike on 5/7/2013 to Mercarb
Question from a customer:

I rebuilt the carb ( my first one ever) and put it back on the boat (2005 Merc 4.3L). It started right up and ran great out of water. I took the boat out yesterday (Sunday) and again started up great ran great except for one issue. The Accelerator pump is not closing completely when I have boat in idle after running it open and is causing motor to idle to high but if I manually pull the "cable" to idle position it will idle right at the recommended 900 rpm. Is there something I need or can do to fix this? Its like the accelerator pump is hanging up right at the end.

Without it sitting in front of me, I'm at a bit of disadvantage, but let's see if I can give some clues.

1st you need to make sure there isn't something in the throttle linkage causing the problem. Isolate the carburetor by disconnecting the linkage, open the throttle wide open, then let go. Does it return to idle position? If it does, then the problem is obviously in the linkage somewhere. Lets assume it isn't and go from there. Remove the link from the accelerator pump arm. This eliminates any sticking of the throttle plate, or rod problem. Again, we will assume the accelerator pump is still sticking.

Here are some possible problems:

  • The 1st thing that comes to mind is this. Did the accelerator pump return spring get put back in the carburetor? This is the spring that resides underneath the pump and it is what returns the pump to the normal position. This is important because it is this return stroke that allows the fuel to fill up the accelerator pump well.
  • The pump could have gotten torn, or rolled up when inserting it, causing it to bind.
  • The pump cup swelled up from being contaminated by ethanol, or other chemical. This happens from time to time. Use of WD-40 would cause this, along with ethanol separating from the gasoline. Ethanol over the 10%-15% mixture can damage rubber parts in a very short amount of time.
  • The top of the accelerator pump arm was inserted into the hole at the top in the wrong direction. This would cause the pump arm to push the pump down at an angle, causing it to bind.
As suggested above it is best to isolate parts of the carburetor in order to eliminate parts until you finally get to the culprit, especially when it comes to things like the pump. Action starts inside the pump well with the return spring, the pump arm on the top of the carburetor, the rod that connects the throttle lever, the throttle lever itself, the throttle plates, all the way to the throttle cable. As you can see there are several parts that could cause sticking of the pump.



Mercarb Accelerator Pump


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20 Comments

Rich
Date: 7/8/2013
I have an OMC 3.0/Rochester 2GC(man choke)and it's 25yrs.old.It started to run rough and was hard to start(warm or cold)so I thought I would just buy another carb.Bought one with auto/choke this time and it still has the same symptoms.The new carb's choke plate can't close entirely because of an internal obstruction,but the old manual choke blade closes all the way.Maybe I should rebuild the original carb and check all the settings? Your site recommends kit K4070 for #17059053. Also, could fuel
Mike
Date: 7/8/2013
You might want to watch my rebuild video on this carburetor. You will find it here. http://www.carburetor-parts.com/Rochester-2G-2GC-2GV_ep_288.html I probably talk about the choke and what to watch for on the binding. The correct kit is here: http://www.carburetor-parts.com/Rochester-2GC-Marine-Carburetor-Kit_p_1950.html
John Summer
Date: 10/1/2013
My son has a Mercarb that fuel drips out of rear venturi. Have rebuilt the carb still has the same problem. Drips at idle and drips faster as RPMs increase. Dropped the float level to below specs and it slowed down a bit. Got any ideas?
Mike
Date: 10/2/2013
It could be a plugged idle vent. Using thin wire, clean out all of the small passages, especially on and around the venturi cluster. When the idle vent is plugged, vacuum will pull fuel out of the venturi when it isn't wanted. Hopefully you replaced the float. If not you should do that also. http://www.carburetor-parts.com/Rochester-2G-2GE-2GV-Float_p_22.html Also put your float back to specs. Adjusting the float down That would not be the solution.
Will Self
Date: 4/8/2014
I need help with a fuel problem please. Cold engine; runs great! Warm engine; runs and cranks great! Drive boat for several miles. Park the boat at the dock. Turn off engine. Let boat set for an hour or two. Cranks great! Put it in gear to go somewhere and does not run when you accelerate. It simply "chokes" out. Attempt to run boat in neutral; no problems. Put boat back in forward gear and try to go somewhere, not gonna happen. Any ideas?
Will Self
Date: 4/8/2014
I need help with a fuel problem please. Cold engine; runs great! Warm engine; runs and cranks great! Drive boat for several miles. Park the boat at the dock. Turn off engine. Let boat set for an hour or two. Cranks great! Put it in gear to go somewhere and does not run when you accelerate. It simply "chokes" out. Attempt to run boat in neutral; no problems. Put boat back in forward gear and try to go somewhere, not gonna happen. Any ideas?
Mike
Date: 4/11/2014
Will, I would narrow down the problem to the accelerator pump circuit. If you have not rebuilt the carburetor, then do that 1st., otherwise: Did your carburetor have a check ball at the bottom of the well? There would be 2 holes in the well and the one on the very bottom would hold the check ball. Not all Mercarbs used a check ball in the pump well. Clean the venturi holes by running thin wire through the small passages. Ethanol leaves residue behind that looks like corrosion and plugs up the small holes. The main discharge should have a check ball, spring, then the T to hold it all in. When pressing down on the pump fluid will be forced out of this main discharge. One other possibility is that the distributor isn't advancing on take off.
Robby Little
Date: 6/18/2014
I've watched your video's and I'm getting ready to order a mercarb 2 barrel rebuild kit. Everything in the video is the same as my carb except the accelerator pump will not come out of the hole. In your video you took the top half of the carb off and the accelerator pump came right out. I disconnected the linkage on the inside and the pump moves up and down but will not pull out. On the outside of the casting I see a very small brass pin going all the way through the pump casting is this a different type. I'd love your advice
Mike
Date: 6/18/2014
Hi, The accelerator pump should pull out. I just had one that was difficult to pull out so I applied a little heat to the outside of the carburetor. When the carburetor sits for any length of time, the gas will leave corrosion behind. I'm sure that is what is causing it to stick.
tom
Date: 6/19/2014
Mike Need to know if I ruined my carter 9000. I was removing the jets and didn't pay much attention to what I was doing when I get frustrated, I removed one jet and the others are frozen in . I guess I am going to need an E-Z out. But in the mean time I used a torx driver and removed another. Then, not looking close enough instead of going into another jet I tapped the torx into the threaded hole where the one jet was and messed up the seat. Is the jet supposed to seal when it bottoms out? It screws in ok but the bottom of the c-bore is messed up I have a machine shop and can recoutnerbore it if necessary. What do you think?
Mike
Date: 6/19/2014
If I understand correctly you ran the drill past the jet and drilled into the bottom of the carburetor. Not a problem. All that matters is that the hole in the center of the jet is in good shape. The jet is nothing more than a funnel for gas to go through. Should be smooth, but new jets are easily obtained. I get jets out by starting with a small drill, then work my way up to a size just shy of the threads. The jet usually wraps around the bit and comes out of it's own accord. Here are the new jets: http://www.carburetor-parts.com/Carter-AFB-AVS-Metering-Jets_p_160.html Hope I understood your question.
Jose Hernandez
Date: 7/16/2014
I PURCHASED A REMANUFACTURE MERCARB 2BB FROM MIKE AFTER HAVING MINE FOR 20 YEARS IT WAS THE BEST DECISION I MADE, I REBUILD MY CARB TWICE IT NEVER RAN GOOD. MY BOAT IS RUNNING GREAT LIKE NEW. THANK YOU MIKE FOR YOUR SERVICE.
Wade
Date: 7/24/2014
Mike I rebuilt my mercarb that's on a 1987 3.0 mercruiser. I was was havering idle issues and off idle acceleration issues. Top end was ok. I rebuilt it and the idle is perfect. Off idle still gave me problems but I adjusted timing to fact. Spec and it fixed off idle problem. Driving 2/3 tank of new non ethanol gas it started hesitating in upper throttle range. Checked at house and ordered new top gasket pulled top plate off rechecked float and reassembled with new gasket. Same problem but I also noticed a rough idle and rich smell. Again runs fine half the day. Get home and check and there is a fuel oil mixture on outside of carb like it's leaking. Obviously something still missing
Mike
Date: 7/24/2014
Wade, I suspect dirt is getting into the carburetor. Did you clean the gas tank when rebuilding the carburetor? Gas smell at idle tells me you are getting too much fuel. Go here for some ideas on things to check out. http://www.carburetor-parts.com/Mercarb-Marine-Troubleshooting_ep_482.html
erik
Date: 10/21/2014
Mike -- at wide open throttle should the throttle valves on my '67 Rochester 2GC carb be vertical say 6 and 12 -- thank you Erik
Gordon McColl
Date: 1/20/2015
Mike, I had similar issue as Wade with my 2GC fitted to a Mercruiser 140. Cold start and run ok. Shut down hot and difficult to restart and often stalled when engaging the prop. Have since rebuilt the Carb, after watching your very helpful videos thank you. Have just refitted the Carb today and noted no fuel was being injected into the barrels from the accelerator pump. I removed the top off the carb and noted the alluminium check ball had been washed out of its hole and was sitting in the wrong part of the pump well. I repositioned the ball inserted the pump return spring, replaced the the carb top and success. The pump worked correctly for about 4 pumps then back to square 1. pulled top off carb again and yes the ball was in the wrong position. What retains the ball in the check valve seat? Regards Gordon
Troy
Date: 5/21/2015
How do I know if my mercarb requires a check ball, filter and retainer clip under the accelerator pump? My mercarb is a 3304 9565. If it does require a check ball, filter and retainer clip which hole does the check ball go in?
Troy
Date: 5/21/2015
How do I know if my mercarb requires a check ball, filter and retainer clip under the accelerator pump? My mercarb is a 3304 9565. If it does require a check ball, filter and retainer clip which hole does the check ball go in?
Bob
Date: 9/2/2016
I was having trouble with leakage where metal fuel line enters carb. (not between the filter nut and the carb, but the fuel line and the filter nut) all is the same set up as as shown in your videos...the surfaces of both look to be in good shap. Hate to replace fuel line so I tried putting o-ring into fitting prior to inserting the fuel line and it seems to work fine with no leaks. Do you think this is an acceptable permanent fix? Do you think the Oring will hold up well to the gas? Hate to be up lake somewhere and have it start leaking. Thanks for any help on this matter It is a 3.0 Merc 2 barrel
Glenn Paganetti
Date: 5/8/2019
So, ny mercruiser 3.0 ran great all last season. this april I have trouble getting it started, It tooks dozens of crank and sometime it did turn over. Then it ran great. Still having issues starting even when cold. Spark seems to be good, Had is running or an hour and restarted it several time and was fine. Took it on a sea trial yesterday and it eventually stalled and was dead in the water. What was odd was I noticed while the boat was in neutral and off fuel was flowing into the card. when I moved the throttle 20 degrees forward or backward fuel stopped. Im now sure flooding is the issue, why is fuel flowing when stopped .
Mike
Date: 5/8/2019
You may have multiple problems. Sitting over the year, the fuel may have turned and the inside of the carburetor is varnished. That would also explain the flooding. Your main discharge is probably not sealing allowing vacuum to pull fuel through. Opening the throttle a bit drops that vacuum.

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