SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: bluegoose95401 on September 03, 2012, 12:34:56 PM
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I'm helping my brother work on his boat and I'm in need of some advice. The boat is a 1986 ski centurion w/ a Ford 351, the PO put a rebuilt holley 4160 on it that by the list number, was an automotive carb that someone converted into a marine carb. So the problem is the boat wont idle with the coke off. It starts fine and runs fine but once things warm up and the choke starts to pull off it wants to die. When we took apart the carb whoever rebuilt it put the wrong jets and power valve in. Those got changed and still no better. I've heard that automotive metering blocks are different than marine blocks? Any ideas?
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ok well start with why it runs cold. and you said with the choke on right??? carb only does 2 things supplies fuel and air. id start with i think you have a vacuum leak.test my theory start it up and spray carb cleaner or something flammable around the base if the engine revs you have a leak.
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Ok I can try that tonight and report back. So do I just spray on the carb block or on the carb it self as well?
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If this is an inboard direct drive, the carburetor is installed at a horrendous angle unless it has the angled base section under the carb..
I would be willing to bet that the float levels are not even close. Do you have a way to post a picture or two?
The vacuum leak required to keep the boat from running, even like crap, would have to be enormous. Like the hold down studs being too long and the wrong base gasket being used....
You need to be sure the right bowl and block gaskets are being used. And no, there is virtually no difference in automotive metering blocks versus marine. Marine carburetors have a different throttle plate and typically have u-tubes on the bowl vents....Sometimes they will have an off road float setup that has spring loaded floats (not always).
Good luck.
GT
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Yea it is an inboard direct drive and I can take pics, what specifically would you like to see?
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Yea it is an inboard direct drive and I can take pics, what specifically would you like to see?
Looking for an angle base, they typically used a cast iron angle base with a PCV valve connection. Curious as to the model of 351 so I can get specific with you.
I worked on these for over 15 years. Sometimes actually for Fineline Industries (builder of the Centurion).
GT
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Turn up your idle on the drivers side (in a car) and remove the fast idle screw on the choke side of the carb.
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Here are some pics. Its a PCM 351W. and I looked and there doesn't seem to be a fast idle screw.[attach=1]
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more pics[attach=1][attach=2]
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You said the jet sizes were not correct....What does this mean?
Does it run at all with the choke off?
The PCM (Pleasure Craft Marine) typically had points ignition, has this been checked? Is the ignition timing even close?
There is no reason for this not to run tits LaRue unless there is a gasket match issue...Like was said earlier if the problem is just idle, give the idle screw a few turns to the right...The next thing to check would be to make sure she's trying to run on gas and not water... :sly: You can also try plugging up the PCV valve to see if that helps.
To keep it running until the problem can be located, try using a dry shop towel over the air horn to fatten things up so you can play around with it, don't forget to put the water pickup hose in a bucket with the garden hose keeping the level up....Unless of course you have a flusher.... ;)
All the correct parts are there and I believe that is the correct carburetor. 8)
GT
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I found a spec sheet saying that the stock size jets were supposed to be 65's and there were 64's in it and there was a 6.5 power valve when the spec sheet called for a 2.5.
When warmed up it'll only run with the choke off, if idled up quite a bit.
When he bought it the PO tried to add a pertronix set up but forgot to install the sending unit that replaces that cam piece that actuates the points. So we switched it back to the original points set up. And timing was done by ear (turned distributor to the highest idle point)
How would I check to make sure its not running on water exactly? I'll try plugging the pcv too.
I need to find me a good bucket. We have just been sticking hose in the pick up line and turning the water on as much as it seemed to be needed.
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Here are some pics. Its a PCM 351W. and I looked and there doesn't seem to be a fast idle screw. (Attachment Link)
You are correct sir. I didnt know it was a marine carb, they dont have fast idle screws thats why i said to remove it. Turn your idle up, turn it down as you tune it in.
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I found a spec sheet saying that the stock size jets were supposed to be 65's and there were 64's in it and there was a 6.5 power valve when the spec sheet called for a 2.5.
When warmed up it'll only run with the choke off, if idled up quite a bit.
When he bought it the PO tried to add a pertronix set up but forgot to install the sending unit that replaces that cam piece that actuates the points. So we switched it back to the original points set up. And timing was done by ear (turned distributor to the highest idle point)
How would I check to make sure its not running on water exactly? I'll try plugging the pcv too.
I need to find me a good bucket. We have just been sticking hose in the pick up line and turning the water on as much as it seemed to be needed.
Dwell needs to be between 30-32 degrees and the base timing at about 10*BTDC, this will get you in the park. ;) The 2.5" power valve is correct.
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OK got some time to work on the boat today, still nothing. Checked for leaks, covered the PVC hole, played with the air fuel screws, tried the timing, nothing really helped much. So tomorrow I'm going to take the carb back apart and go through it with a fine tooth comb. Is there a difference between auto and marine gaskets because I've seen two different metering block gaskets?
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OK got some time to work on the boat today, still nothing. Checked for leaks, covered the PVC hole, played with the air fuel screws, tried the timing, nothing really helped much. So tomorrow I'm going to take the carb back apart and go through it with a fine tooth comb. Is there a difference between auto and marine gaskets because I've seen two different metering block gaskets?
Like I said before, there are very few differences between a marine and an automotive carburetor.
If you install the incorrect plate gasket, there is an excellent chance you will completely close off the idle circuits. ;)If this is an inboard direct drive, the carburetor is installed at a horrendous angle unless it has the angled base section under the carb..
I would be willing to bet that the float levels are not even close. Do you have a way to post a picture or two?
The vacuum leak required to keep the boat from running, even like crap, would have to be enormous. Like the hold down studs being too long and the wrong base gasket being used....
You need to be sure the right bowl and block gaskets are being used. And no, there is virtually no difference in automotive metering blocks versus marine. Marine carburetors have a different throttle plate and typically have u-tubes on the bowl vents....Sometimes they will have an off road float setup that has spring loaded floats (not always).
Good luck.
GT
:sly: