Mercarb bogging, accelerates fine

John Poet

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Feb 27, 2014
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Bought a 1989 Celebrity Challenger with a 3.0. Hard starting but ran strong and fast. From idle it accelerated like a bat out of hell. Again, ran great even at WOT. Restarting was difficult. Saw fuel dripping in the Mercarb throat. Opened the Mercarb and noticed a ton of build up. In order to get right back on the water I bought a rebuilt Mercarb (one mixture screw). Started fine after that and still accelerated very well. However, after a short while of running WOT or anywhere down to half throttle, it felt like I was running out of gas. It bogged down and wanted to stall. Half throttle and below I could and did run for quite some time with no problems. After which I could again go WOT for a short while with the same results. Carb bowl running empty? The supplier (148 miles away) had me 1:check the float level,it was good but he said to keep adjusting it up until flooding started. Did that with the same results. 2: Replace the accelerator pump even though it never bogged during acceleration. Same results. 3: Install a new needle and seat set. Same results. 4:Install second Mercarb. Same results. I checked the fuel pressure and it was about 8.5psi the entire time from idle to acceleration to WOT and even when it bogged down to half throttle. Any ideas? Power valve? Wrong jets? Builder using the wrong top to the carb? ie Not Mercarb, resulting in restricted fuel flow regardless of pressure? Gremlins?
 

midcarolina

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Jul 16, 2013
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631
Two carbs doing the same thing means it's likely something else............. What kind of condition is the flame arrestor in? any work/upgrades done to the ignition system lately?
 

alldodge

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You mentioned that it had constant fuel pressure is the following two items should not be applicable, but going to mention them anyway. Check your anti-siphon valve at the tank, if it's hanging and restricting flow. Also check that your tank vent is clear and your not drawing a vacuum on the fuel tank. If it starts diing, shut the engine down and open the fuel cap and listen for a hiss.
 

Maclin

Admiral
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May 27, 2007
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6,761
Check for an inline filter in the fuel inlet. Make sure, if it has one, that it is not in backwards or wrong or a gasket in the way, something like that.
 

John Poet

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Feb 27, 2014
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First, Thank to each of you for your replies.
Fun Times: Copy that on the fuel pressure. As you said, manual calls for 5-6.5psi. The gauge I bought for 16 dollars at Harb** Fr**** may have a quality issue. It may be reading wrong but the steady pressure even when the motor bogs is what I was focusing on. If it really is 8.5, could that cause my issue?

MidCarolina: The flame arrestor is clean and the plates move freely. I even tried running without it on to make sure the engine could breathe. I replaced the exhaust flappers and even pulled the outdrive to check for blockage.The ignition system is the same as it was when I got it. The same as it was before the carb replacement.

AllDodge: The vent tube is clear and not kinked. The gas cap O ring seal is missing and the shop where I had the gimbal bearing replaced while I had the outdrive off said the ASV was good. I didn't have the puller for the gimbal bearing and I don't know how to check the ASV myself.

Maclin: The filter on the fuel pump is new. (Before the carb replacement and the subsequent bogging issue) The inline filter is new as well and the arrow is pointing towards the carb. And of course the fuel inlet filter was and is new on both carb replacements.

Again, I thank you all for your efforts. Do you think perhaps that the builder made the same mistake twice? Used the automotive rebuild kit instead of the marine kit? The shop in LA was an automotive shop that also sold marine carbs... Check balls, powervalve, more gremlins?
 

alldodge

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Put come clear tubing between the pump and carb and see if your getting air. Figure your HF gauge may be off at 8.5 psi. All signs show your running out of fuel, so that is either pump, fuel restriction or carb adjustment. Don't think it's the jets because you can run fine for a little while and then it starts again
 

John Poet

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Feb 27, 2014
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I have a clear inline filter between the pump and the carb (which I found out is not Coast Guard approved). No visible air. I also checked the fuel lines all the way from the tank to the pump to the filter to the carb. All clear. I agree that I am running out of fuel. From all indications it seems to be inside the carb. While I am dedicated to trying any suggestions offered, I can't help but to believe that the builder is making the same mistake over and over. Like using the top of an automotive 2g carb. More than 9 of us here in San Diego are stumped.
 
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John Poet

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Feb 27, 2014
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Found out what was wrong! The power valve was not staying open. Not sure why. I installed the new valve and a new rod and spring. Boat is running like a banshee. There is joy in San Diego! Thank you one and all for your efforts.
 
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