Mercarb Help

[rlambert]

All,

I noticed a nice post someone had concerning a Mercarb Power Valve's function. I was wondering if this could be the source of my issue. I have taken apart the carb and noticed that the plunger above the power valve sticks a little upon pushing it up and down. Probably worn through the years. 1986 Sea Ray 140.

The issue I am having is that my boat seems to idle ok and accelerate upto a certain RPM. At 7mph or so the engine starts to bog down and stall usually with a backfire through the carb. Could this be an issue with the plunger sticking closed and the carb not supplying enough fuel to the engine?

Any ideas on how to get that plunger out? Kind of looks like it's pressed in.

Thanks for any help.

 

[Peaceful Pirate]

Re: Mercarb Help

Sounds like a great time of year to grab a rebuild kit for your carb and spend some quality time getting to know you boat on a personal level. It is not that difficult of a job but please allow me to offer a couple of recommendations. Make sure you have a good shop manual and follow it closely (Check out ?Adults Only? in this forum). It is not a difficult job, but attention to detail is a must. Recommendation: When you first open a carb rebuild kit, you will find a great deal of really small parts. Be careful. I find using a clear glass pie-baking dish to hold all that comes out of the kit works well for me. It makes it easy to find the individual small parts (springs, o-rings, ball valves, etc) and also helps keep them from rolling/flying off the workbench. A good work light is also a big plus. Good luck to you and as always ? have fun.

 

[havasuboatman]

Re: Mercarb Help

To answer your question, yes, that symptom is indicitive of a bad accellerator pump. Download you manual as the Pirate suggested. It's fairly straight forward.

 

[rlambert]

Re: Mercarb Help

Yep. Confirmed when I popped out the power valve piston. There is a very small bit of corrosion on the brass shaft where is slides through the stainless ring. It seems to catch on that bit of corrosion. Probably enough resistance to keep the power valve from lifting properly with a change in vacuum pressure. Apparently works through vacuum caused by the engine's compression stroke and how that varies with engine RPM. I have the Seloc manual and the manual from the link. I'll get a rebuild kit on it and hopefully this solves the issue. I'll let you know. Thanks.

 

[Peaceful Pirate]

Re: Mercarb Help

rlambert ? Just for what it is worth, read and follow your downloaded M/C manual (or better yet, get you a hard copy on say eBay) and use the Seloc manual as a chair cushion. You may (or may not) find the Seloc will track a shop manual in many cases; however, you will never know where it does not unless you lay them side-by-side. If you will get use to always following the M/C manuals, your chances of going wrong are greatly reduced. There really is something to why so many on this site always recommend the M/C manuals over the third party books. Once again ? good luck and enjoy!

 

[cr2k]

Re: Mercarb Help

Actually the intake stroke to be correct, since that is the stroke that creates vacuum.

Though they stick a little, my money is on the accelerator pump which is a common problem with marine carbs. That and corrosion in the bottom of the accelerator pump cavity.

If your carb kit comes with a new accelerator plunger that is equipped with a spring check the spring tension against your old one and use which ever spring has the most tension. Most of the kits are reboxed automotive kits and the pump spring is weaker as cars are not "punched" like boats are for acceleration.

 

[rlambert]

Re: Mercarb Help

Yeah, I keep hearin about the accelerator pump but I checked it and rebuilt it a year ago and it seems to work fine. Very clean in there. Pumps in gas smoothly every time it's pumped. The only thing I can really find that might be a problem is this power valve piston. Took it out and cleaned it up good. Had a bit of corrosion on the shaft. I checked it and it moves smooth with vacuum now. I'll try it and let you know how it goes.

 

[cr2k]

Re: Mercarb Help

May be some corrosion in the passages, maybe you can blow them out too.

 

[Jbrans1]

More Mercarb Help - Power Valve

More Mercarb Help - Power Valve

I'm in the process of rebuilding a mercarb. Currently dissasembled and sitting in cleaner. I'm having a huge problem getting the "power valve" assembly removed. It is a bronze piece and very solidly attached. It has a slot of a flat head screw driver in the top, but the slot starts to give before the assebmly begins to loosen. Has anyone experienced and overcome this problem. I don't mind destroing the piece to get it out, the rebuild kit included a new one. Typically, I would start thinking easy out, but not sure one would bite into the soft metal. Any thoughts or help would be appreciated.

 

[Spanky1376]

Re: Mercarb Help

Yeah, I keep hearin about the accelerator pump but I checked it and rebuilt it a year ago and it seems to work fine. Very clean in there. Pumps in gas smoothly every time it's pumped. The only thing I can really find that might be a problem is this power valve piston. Took it out and cleaned it up good. Had a bit of corrosion on the shaft. I checked it and it moves smooth with vacuum now. I'll try it and let you know how it goes.

Did it work I’m having the same exact issue??

 

[Eric 3.7LX Alpha 1]

Did it work I’m having the same exact issue??

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