fuel dilution on one engine

Guys, been a while since I've posted a question. I've been tied up with multiple car issues all winter. I wanted to get your advise on some fuel dilution readings on my 454's. Some background. I rebuilt both of my carbs about 4 years ago, approx. 250 hours of use. I used the kit from Cliff Ruggles and sent them in for bench testing and adjustment.


They have been flawless since and I have literally not touched them since they were reinstalled. I've noticed that the oil on the port engine turns dark pretty quickly and so I sent out samples from each engine to Blackstone Labs. They said the fuel percentage on the engine in question is 3.8% and the other engine is .08%. The fuel pumps on both engines were replaced around the same time so that's lower on my list of suspects. They are looking for readings of less than 2%. I also notice that when I check the oil that it drips right off the dipstick. It looks "thin" but the viscosity is fine according to Blackstone.


My real question is..... do you think it's simply running too rich?. I changed the plugs and they were black/rich looking which I know is better than too lean. I just don't know how much "range" a mixture adjustment can make or if that fuel percentage is likely beyond just an adjustment.Starting/idling/power up are flawless both sides which is why I've left them alone. I pulled the fuel vent hose off at the pump to see if any fuel poured out (although this was after sitting all winter). Good, although I smell a little fuel. Both engines are carb'd 1988's with about 1,200 hours and don't burn any oil.

Any thoughts appreciated.

thanks
Bob

Not uncommon for them to be rich at idle....the mixture screws have plenty of range as long a the throttle plates are set so the screws are effective...if the rpm is too high, the mixture screws wont have much effect....always check the primary bore to make sure the main nozzle isn't providing any fuel - if it is, the needles' setting won't matter much. If they are, try backing out the idle screw until they stop and then try the mixture screws again.

If the choke isn't opening soon enough (or all the way) that can happen.

Are the motors running the same temperature (as measured by an infrared temp gun)?

Jeff

Jeff,

You raise an interesting point. The engine in question has been super "cooled" for a while now. Even with multiple 160 degree thermostats, my readings on top of the thermostat housing were always in the 140 range. I just changed the risers and elbows this weekend due to age (5 years), no temp issues. On the hard last night, I got a reading of 157 on top of the thermostat.

I also noticed that choke never opened until it was fully vertical, more like 1/2 way. If I had a good run it might open more but I'm going to adjust it. Would you expect it to be fully open after 20 mins of running/idling?

thanks
Bob

Not if the motor is running way too cold, or if the choke is not adjusted correctly. deliberately adjust mine on the lean side, so I don't have that problem (and pump the gas a few extra times to start it).

Jeff

So I really took a close look at this last night. The choke coil was installed backwards so it wasn't pushing up away from the manifold and fully opening the choke. Ugh, I've been running for three or four seasons like this and it was my fault.

The other breakthrough is the engine temp. I changed the risers/elbows and now it's getting up to temp for the first time in multiple seasons as well. I'm getting 170 at the thermostat housing now. Any guesses as to what changed with the riser/elbow change?

I noticed the higher temp change prior to the choke fix so I can't pin it at that. My Stb engine has been fine all along but I'm going to run that today.

Bob

I know this is not a fix but I have heard of some people that actually tie the choke plate so that it is fully open all the time. Most of us are not going boating in extremely cold weather so the engine will start and run fine with it fully open even when the engine is cold...may just need a little throttle pumping initially.

glad you found a prime suspect...and hope that resolves it....as far as the elbow/riser change driving the operating temp - no idea - seen the opposite temp problem fixed by changing the iron but not that way....