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Message |
    
mac99
New member
Username: mac99
Post Number: 1
Registered: 05-2016
| | Posted on Sunday, May 01, 2016 - 09:51 am: | 
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283 Holley carb boat motor 1967 Chris Craft corsair.
We are on our last leg on this problem please any information would help !!!!
Starts, runs perfect on water 20 mins , then lose power down to idle, throttle back site 5 min , then run 15 min same thing loss of power down to idle site five mins - again, and again !!!
New carb , two elect fuel pumps, pressure gauge on line etc !!!
Check electric at pumps , checked pumps sitting emptied tank running pumps to test pressure etc. No mechanical pump on motor , Line pump at carb ,
Tank at stern , inboard . |
solarrog
Senior Member
Username: solarrog
Post Number: 615
Registered: 03-2002
| | Posted on Sunday, May 01, 2016 - 10:15 am: |
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I assume you changed the fuel filter's did you check the coil to see if it's hot? change the condenser? check the ign. resister? If the pump is up near the carburetor could it be sucking air?
If there are 2 tanks check the either or valve |
ernie
Senior Member
Username: ernie
Post Number: 2273
Registered: 01-2002
| | Posted on Sunday, May 01, 2016 - 10:25 am: |
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Tanks vented properly?
Does it do it with the gas cap/s loose or off? |
bruce
Senior Member
Username: bruce
Post Number: 557
Registered: 07-2002
| | Posted on Sunday, May 01, 2016 - 10:36 am: |
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What Ernie said... Mud dauber resident in the tank vent line??? |
solarrog
Senior Member
Username: solarrog
Post Number: 616
Registered: 03-2002
| | Posted on Sunday, May 01, 2016 - 10:41 am: |
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What Ernie and Bruce said. It's always the simple things that we pass over until the aha moment. |
ernie
Senior Member
Username: ernie
Post Number: 2274
Registered: 01-2002
| | Posted on Sunday, May 01, 2016 - 05:10 pm: |
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Also pretty sure electric pumps do a better job pushing than pulling
What has changed from when it ran good last?
Assuming at one time it ran good for you.
Sitting over the winter?
New parts of some sort?
Over the years once I figured out who or what was here/done last the problem became sort of obvious.
When it goes to idle what is the fuel pressure?
How about fuel volume. Pressure is needed but so is volume.
4 to 6 PSI and the rule of thumb on a mechanical pump is crank the engine for 30 seconds with the fuel line open into a soda bottle and you should have 4 to 6 OZ. With the electric pump/s you should have the same or more but just turning the ignition on.
When it goes to idle do these checks as well as spark. Fat and blue from the coil wire to ground.
Check the spark FIRST BEFORE ANY OPEN FUEL!
Where are you getting voltage for the fuel pump? Make sure it is direct switched hot NOT from the ignition coil circuit.
When it slows down does it just slow down or does it start running rough and backfiring?
Now the stupid questions...
If it doesn't backfire and runs rough consider the following:
Is the throttle staying open or is it closing somehow?
Is the engine cover on or off? Is there a chance it is using most of the available air?
Carburetor Ice? What is the intake? Stock or some sort of performance? If it is stock are the manifold heat (center) ports on each side clean?
Hope this helps
Ernie |
jb_castagnos
Senior Member
Username: jb_castagnos
Post Number: 1155
Registered: 07-2002
| | Posted on Sunday, May 01, 2016 - 06:49 pm: |
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Carb icing brings back memories, I've only seen it once. I did service work for an oilfield supply company. One of their workboats had a Mercruiser 6 cylinder. They brought it in for service, losing power. Tuned it up and replaced filters, next rip out same problem. I went with them, it took off fine, 15 minutes later is was slowing down. By the time I got the cover open and the flame arrester off the hole through the ice in the carb was about the size of a pencil. It was below freezing and very humid. |
ernie
Senior Member
Username: ernie
Post Number: 2275
Registered: 01-2002
| | Posted on Sunday, May 01, 2016 - 07:13 pm: |
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You have to be very aware of it when flying. Use carb heat when in doubt.
I have had it happen on various vehicles over the years when the hot air pipe to the air cleaner had been removed or wasn't working correctly.
On marine stuff it was only when it was cold out and there was humidity present like you said. |
drrot
Senior Member
Username: drrot
Post Number: 197
Registered: 09-2008
| | Posted on Monday, May 02, 2016 - 09:38 am: |
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When it dies feel the ignition coil. Often times it does that before it completely fails. If it is too hot to touch replace it. |
