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TOPIC: Engine does not start when warm - HELP

Engine does not start when warm - HELP 04 Jun 2009 21:31 #1

  • somerbreeze
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I have a 5lt. v8 mercruiser engine, Started with muffs after the winter break on the third attempt, great start to season. Launched boat started first time. A quick trip down the river to warm her up, turned engine off, that was it! Tried several times to restart, she would not go.Had to be towed back. Last season occasionally she was reluctant to start when warm. Starts fine when cold, where do I look for the fault?

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Engine does not start when warm - HELP 04 Jun 2009 22:03 #2

  • captjmh
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somerbreeze;304565 wrote: I have a 5lt. v8 mercruiser engine, Started with muffs after the winter break on the third attempt, great start to season. Launched boat started first time. A quick trip down the river to warm her up, turned engine off, that was it! Tried several times to restart, she would not go.Had to be towed back. Last season occasionally she was reluctant to start when warm. Starts fine when cold, where do I look for the fault?


I assume you're saying it will turn over but not fire - correct??
Have you checked the choke when it wouldn't start?

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Engine does not start when warm - HELP 04 Jun 2009 22:12 #3

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The engine turns over, I have checked the choke and that is in the off position.
I have removed the flame retarder and opened the throttle and left for 5 min. in case I had flooded the engine. When I first attempt a restart it almost catches (speeded up whilst starter engaged) but subsequent attempts she does not want to know.

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Engine does not start when warm - HELP 04 Jun 2009 22:22 #4

  • captjmh
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When you say the choke is in the off position - you mean the choke plate is open(vertical)?? - And you cranked the engine with the choke open and and at full throttle?? - Sounds like flooding which could be a stuck float or ???

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Engine does not start when warm - HELP 04 Jun 2009 22:32 #5

  • somerbreeze
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Yes, choke plate is vertical. Tried starting with and without throttle.

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Engine does not start when warm - HELP 05 Jun 2009 01:51 #6

  • av8mech
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Do you have spark? You may have a bad coil.

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Engine does not start when warm - HELP 05 Jun 2009 02:16 #7

  • 2006-289
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Vapor Lock.

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Engine does not start when warm - HELP 05 Jun 2009 02:49 #8

  • Les Fischer
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If not MPI it's in your coil or distributer.

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Engine does not start when warm - HELP 05 Jun 2009 06:32 #9

  • somerbreeze
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Thanks guys, I'm sure there is a spark but will check again anyway. I fitted a new coil last season, is that likely to have failed so soon?

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Engine does not start when warm - HELP 05 Jun 2009 12:10 #10

  • dmcb
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You said it tried to start when you left the throttle open. That indicates spark.
It sure sounds like its flooded.
Open the throttle and crank it UNTIL IT STARTS. Depending on how much its flooded it may take several turns before it starts.
Don't move the throttle back and forth because that just injects more fuel in the engine.
Doug

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Engine does not start when warm - HELP 05 Jun 2009 13:49 #11

  • captjmh
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dmcb;304884 wrote: You said it tried to start when you left the throttle open. That indicates spark.
It sure sounds like its flooded.
Open the throttle and crank it UNTIL IT STARTS. Depending on how much its flooded it may take several turns before it starts.
Don't move the throttle back and forth because that just injects more fuel in the engine.
Doug


I second Doug - since you said it tried to start at full throttle, that would indicate spark but flooded - so follow Dougs advice and bet it starts. Then you will have to figure out why it floods. While it could be a stuck float in the carb, I'd still bet on a choke issue - when it's warm and off - open the engine hatch, take the flame arrestor off and check the position of the choke -open?-closed? don't advance the throttle beyond idle position and try to start, if it starts - all good, if not check the choke position to see if it closed, if it is thats probably your problem. If it's open and won't start open throttle fully and crank til it starts - if its flooded it should start in 15 sec or so, just don't lay on the starter for more than a minute max.
Another note - when you start when warm - do you advance the throttle all the way open and then back to idle position before starting?

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Engine does not start when warm - HELP 05 Jun 2009 14:16 #12

  • somerbreeze
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Yes, I move the throttle fully forward and the back to idle. I have also tried to start with out moving the throttle at all.

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Engine does not start when warm - HELP 05 Jun 2009 14:33 #13

  • dmcb
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Moving the throttle foreward and back to idle is what you do for a cold engine. Maybe 2 or 3 times.
But not on a warm engine.
You will just flood it more without leaving it at wide open throttle to clear it.
When you advance the throttle you squirt a stream of gas in the intake. You should not have to do that with a warm engine.
Doug

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Engine does not start when warm - HELP 05 Jun 2009 14:47 #14

  • captjmh
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somerbreeze;304943 wrote: Yes, I move the throttle fully forward and the back to idle. I have also tried to start with out moving the throttle at all.


OK - when warm - you should not have to advance the throttle full and back to start - all you're doing is giving the engine a big shot of gas from the accelerator pump - which the engine doesn't need and can flood it. But since you said you have tried starting when warm without "pumping" the throttle and it doesn't start, - but it does start easily when cold - we're back to the choke as the probable culprit. (Editorial Comment: Ever since the change to automatic thermostatic coil and then electric chokes from the old manual chokes, they have been the biggest single carb problem and the best incentive for fuel injection!!)
So again we're back to checking position of choke plate when starting warm to make sure it is not in the closed or nearly closed position, if closed or nearly so - open it and try starting - if it starts - choke issue, if not, see if it will start with a healthy cranking at full throttle - if it starts probable carb/float issue. Beyond that, you'll need to find an old geezer who knows carbs and can either adjust choke or rebuild carb.

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Engine does not start when warm - HELP 05 Jun 2009 16:12 #15

  • cullyJ
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2006-289;304698 wrote: Vapor Lock.


what they said.

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Engine does not start when warm - HELP 05 Jun 2009 22:49 #16

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Thanks again! Plenty food for thought, I will have another play this weekend and let you know how I get on. Have a good weekend, regards Reg

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Engine does not start when warm - HELP 06 Jun 2009 12:50 #17

  • Gilligan
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It doesn't sound like you understand what Doug and CaptJMH are saying so allow me to repeat...

When you have trouble starting give it full throttle and keep it there while you crank the engine. Once it begins to start (which may take 5-10 seconds) be ready to drop the throttle when she kicks, but don't panic and pull her down too fast or you'll kill it. A very steady, even drop to about 1/8 throttle or so will allow her to continue to run.

Then, let 'er run for a minute or so before you take off again.


I know, engine flooded... give it more gas! Very counterintuitive.

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Engine does not start when warm - HELP 06 Jun 2009 23:03 #18

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Thanks Mike, I have tried this combination of throttle positions also. As I said I will have another look this weekend weather permitting, but I will post my findings. Regards Reg.

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Engine does not start when warm - HELP 18 Jun 2009 08:59 #19

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A sticking float in the carb was the problem, thanks to every one for their advice.

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