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  #1   IP: 66.245.54.164
Old 04-23-2006, 03:24 PM
JIm Purdy JIm Purdy is offline
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Post Carburetor flooding

Don, thank you for speaking with me on friday and helping me work this out. Hopefully others can learn from this, and eventually I will learn what is causing the problem and fix it. I have a 1965 Pearson Vanguard with the original early model Atomic 4, raw water cooled, mechanical fuel pump, new style carburetor. I have only owned the boat for a few months but I am familiar with the A4 from my previous boat. Up until a month ago, the engine started right up and ran well. Then one day I started it up, it ran for about 15 seconds, then died. The carburetor intake was full of fuel, and it was nasty looking. Here is what I have done: pumped out the tank, added 2 gal of fresh gas and a bit of Star Brite fuel tank cleaner, then later pumped this out and added 15 gallons of fresh gas; removed, cleaned, and replaced the fuel tank pickup tube; new Racor filter element; new shutoff valve; new fuel line; new Moyer Marine mechanical fuel pump(old mechanical pump seemed to be working, but the new one came with the boat as a spare); and I took the carb apart and cleaned it. When I try to start the engine with full choke and a tiny bit of throttle the engine will not start. After only a few secconds of cranking there is raw fuel in the carburetor intake. After this I can start the engine with no choke and full throttle: it starts right up, runs very poorly for about 30 seconds, then runs normally-smooth, plenty of power, a bit of smoke but not excessive, accelerates well. After the engine has run for a minute or an hour, it will start right up after I shut it down. After shutting it down, there is no raw fuel in the carb intake. The following day: no raw fuel in the intake before attempting to start.

Compression is 130 cold, 95 warm in all 4 cylinders. Spark is good, timing is correct (I have checked this numerous times). Spark plugs develop black soot with after only 1 hour of engine running. I bought a carburetor rebuild kit at a local shop and the parts counter person told me that there are 2 different needle and seats for mechanical and electric fuel pumps with the one for the mechanical pump designed for a higher intake pressure. Supposedly they sold me the kit for the mechanical pump. I replaced the needle and seat and sealing washer, and replaced the pickup tube sealing washer(although the old one looks fine). I still had the same cold starting problem. I had checked the float level many times and it seemed correct, but I tried bending the float down-still same problem. It seems to me that the engine is running quite rich and I have assumed that this has to do with the carb, and likely is because the float bowl level is too high. The old needle seat has the number 25 stamped on it, and the new one that I just installed has the number 35 stamped on it-this appears to have a larger apperature than the one marked 25. The needles look identical.

So thinking that either a) I had done something incorrect, or b) the carburetor had some unfixable flaw, I bought a new Zenith carburetor, and new spark plugs. I still have the same problem.

Theories-
1. I have totally overlooked something.
2. The brand new carburetor is flawed---unlikely.
3. The brand new carburetor is designed for a lower fuel pressure than my system is providing.
4. New mechanical fuel pump is providing too much pressure.
5. The new needle valve that I installed in my old carb is not designed for a mechanical pump, and the old needle valve is faulty.
6. The top of the fuel tank is 2 feet above the level of the pump, and somehow this is contributing to overwhelming the needle valve.

Eventually I will find the problem and fix it, hopefully soon. Any suggestions are most welcome.
Don, thank you for the most excellent and helpful website!

Last edited by JIm Purdy; 04-23-2006 at 03:29 PM.
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  #2   IP: 38.118.52.41
Old 04-24-2006, 07:27 AM
Don Moyer's Avatar
Don Moyer Don Moyer is offline
 
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Jim,

The most important thing to remember is that it is normal for raw fuel to puddle in the bottom of the intake throat after approximately 15 seconds of accumulated cranking with the choke closed (which would be normal during the first few seconds of cranking). What this puddle of raw fuel usually means is that the engine is not starting due to some reason other than lack of fuel (usually ignition or compression).

To clear up the subject of float valve needle and seat specifications, late model carburetors have always had seats with an index number of 25, while early models had seats with index numbers of 30. The needles were almost imperceptibly different to accommodate this slight difference in orifice size within the seats. According to Zenith, the inlet fuel pressure specification for both needle and seat combinations is 4 psi. In other words, the float valves in both carburetors were designed to accommodate fuel pump pressure up to 4 psi, which would easily accommodate both mechanical and electrical fuel pumps in normal use in the Atomic 4 fleet. Every now and then we hear of an electric pump being used with up to 7 psi with only subtle issues manifesting in terms of rich running.

I'm wondering if your ignition might be working, but weak. Can you develop 1/2" to 3/4" of secondary spark between the end of the coil lead and the head during the times when the engine is difficult to start?

Please stay in touch until we resolve your starting difficulty.

Don
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