hard to start, and dieseling. timing or something else?

[beason]

merc 3.0l in a 99 sea ray.

starting:

will not start from neutral position. i have to press the throttle only button and move the throttle just to the first notch. most times it will start up from there. others it starts but chugs and dies. I have to give it even more throttle to "clear the throat". This is getting worse, and its harder to start it seems. Seems to be flooding. i can smell gas.

Shutting off:

if i let it idle a LONG time. like through the no wake zone to the ramp. It shuts right off. anything else and it diesels and chugs and finally dies.

Any other time, it runs great. Doesnt stutter when i hit the gas, WOT is good, pulls hard, and runs like a top.

ive already cleaned the spark arrester, changed the plugs (checked gap), and tried adjusting the idle down. None of these changed anything. The idle is good when in the water.

Where do i start? Timing? is the carb adjustable? tips?

 

[Don S]

Re: hard to start, and dieseling. timing or something else?

starting:
will not start from neutral position. i have to press the throttle only button and move the throttle just to the first notch. most times it will start up from there. others it starts but chugs and dies. I have to give it even more throttle to "clear the throat". This is getting worse, and its harder to start it seems. Seems to be flooding. i can smell gas.

Do a full tunup, check the timing, do a compression test, that usually takes care of 90% of them with a starting problem.

if i let it idle a LONG time. like through the no wake zone to the ramp. It shuts right off. anything else and it diesels and chugs and finally dies.

That's fairly normal, and even recommended by Merc in a service bulletin. Usually letting it idle for just a minute or two will do the job, also make sure the idle rpm are 700 or below. Timing can also affect it, as well as carb mixture adjustment. Too lean makes them hard to start and hard to shut off.

 

[beason]

Re: hard to start, and dieseling. timing or something else?

Do a full tunup, check the timing, do a compression test, that usually takes care of 90% of them with a starting problem.



That's fairly normal, and even recommended by Merc in a service bulletin. Usually letting it idle for just a minute or two will do the job, also make sure the idle rpm are 700 or below. Timing can also affect it, as well as carb mixture adjustment. Too lean makes them hard to start and hard to shut off.

I can rent/borrow a compression test setup from the auto place right?

so timing, and check compression. Should i do a seafoam run?

Ive read somewhere that on some carbs the adjustment screw is covered, and you cant adjust it.

How do i check for lean mixture? I just installed fresh plugs this season. i could look at those for clues correct? When i try to start and its hard to get it going, i smell gas. Maybe a choke?

what order should i do these?

Thanks in advance.

 

[beason]

Re: hard to start, and dieseling. timing or something else?

no one?

bueller?

 

[81 Checkmate]

Re: hard to start, and dieseling. timing or something else?

beason - Did ya do any of the things Don has recomended?

If ya did.....post up the results and im sure you will get more responces.....

 

[beason]

Re: hard to start, and dieseling. timing or something else?

bringing back an old thread since i still have not gotten this fixed.

2 weekends ago i did the following

check and adjust timing
ran an entire bottle of sea foam through the carb
put fuel system cleaner in the tank.
adjusted the idle down to around 800rpm

the boat runs better, jumps off the line better, and feels smoother.

but it still diesels.

any ideas?

 

[achris]

Re: hard to start, and dieseling. timing or something else?

bringing back an old thread since i still have not gotten this fixed.

2 weekends ago i did the following

check and adjust timing
ran an entire bottle of sea foam through the carb
put fuel system cleaner in the tank.
adjusted the idle down to around 800rpm

the boat runs better, jumps off the line better, and feels smoother.

but it still diesels.

any ideas?

Usually the only 'cure' for dieseling is to let the engine cool off for a few minutes before shutting it down...

Chris......

 

[hivoltg]

Re: hard to start, and dieseling. timing or something else?

I always wondered if it was vaporized oil gases causing this on the smaller boat motors instead of fuel. Since idling the boat for a minute or two cures the problem. Check and replace the pcv valve and clear the hose also with carb cleaner.

It may be a low octane issue or the plugs are the wrong temp range and they need togo a step cooler but with so many of these smaller engines doing it im leaning towards a buildup of crankcase gases.

 

[Bondo]

Re: hard to start, and dieseling. timing or something else?

bringing back an old thread since i still have not gotten this fixed.

2 weekends ago i did the following

check and adjust timing
ran an entire bottle of sea foam through the carb
put fuel system cleaner in the tank.
adjusted the idle down to around 800rpm

the boat runs better, jumps off the line better, and feels smoother.

but it still diesels.

any ideas?

Ayuh,..... Checked, 'n adjusted the timin' to What settin',..??

Runnin' seafoam or any other snake oil ain't the same as rebuildin' the carb, if the carb needs rebuildin',...

More snake oil in the fuel tank, at Best, causes filter pluggin' from any loosened debris,...

'n,.... 800 rpms is Too High,... it should be 650/ 700 rpms, in gear, in the water,....

 

[beason]

Re: hard to start, and dieseling. timing or something else?

Usually the only 'cure' for dieseling is to let the engine cool off for a few minutes before shutting it down...

Chris......

i try to as a much as i can, but it happens most when we are tubing. getting it shut down to recover a down rider is the problem.

 

[beason]

Re: hard to start, and dieseling. timing or something else?

I always wondered if it was vaporized oil gases causing this on the smaller boat motors instead of fuel. Since idling the boat for a minute or two cures the problem. Check and replace the pcv valve and clear the hose also with carb cleaner.

It may be a low octane issue or the plugs are the wrong temp range and they need togo a step cooler but with so many of these smaller engines doing it im leaning towards a buildup of crankcase gases.

ill check the pcv. that should be a cheap fix. How can i look up the correct plug? i replaced them last year, but just matched what was in it.

 

[beason]

Re: hard to start, and dieseling. timing or something else?

Ayuh,..... Checked, 'n adjusted the timin' to What settin',..??

Runnin' seafoam or any other snake oil ain't the same as rebuildin' the carb, if the carb needs rebuildin',...

More snake oil in the fuel tank, at Best, causes filter pluggin' from any loosened debris,...

'n,.... 800 rpms is Too High,... it should be 650/ 700 rpms, in gear, in the water,....

i guessed on the muffs and it idles about 800 in the water. ill set it lower

what part of the carb would cause this issus? im not really knowledgeable on the inner workings of them.

I installed the jumper on the dist, jumped the interupt wire together, and set it to 1deg before tdc. that is what was on the spark arrestor.

 

[hivoltg]

Re: hard to start, and dieseling. timing or something else?

ill check the pcv. that should be a cheap fix. How can i look up the correct plug? i replaced them last year, but just matched what was in it.

Post your engine serial number. One of the iboaters can verify the correct plugs.

 

[Maclin]

Re: hard to start, and dieseling. timing or something else?

If you are uncomfortable with just leaving it idling in neutral while picking up skiers and cannot let it idle for a bit before shutting it down, then you could try shutting it off while it is in gear. That may keep it loaded up just long enough to stay below the dieseling "threshold".

 

[beason]

Re: hard to start, and dieseling. timing or something else?

Post your engine serial number. One of the iboaters can verify the correct plugs.

ill swing by the garage on the way home and get that info. thanks.

 

[beason]

Re: hard to start, and dieseling. timing or something else?

If you are uncomfortable with just leaving it idling in neutral while picking up skiers and cannot let it idle for a bit before shutting it down, then you could try shutting it off while it is in gear. That may keep it loaded up just long enough to stay below the dieseling "threshold".

i tried that at the dock. still did it, even in gear. good thing i had it tied down good.

im not afraid, but the kids and SO are. i go to the back to assist the riders, so i dont want anyone flopping in the seat and hitting the throttle

 

[Maclin]

Re: hard to start, and dieseling. timing or something else?

Good for you, if there is no one at the helm then the engine needs to be off!

 

[achris]

Re: hard to start, and dieseling. timing or something else?

i tried that at the dock. still did it, even in gear. good thing i had it tied down good.

im not afraid, but the kids and SO are. i go to the back to assist the riders, so i dont want anyone flopping in the seat and hitting the throttle

As the skipper, YOU should be at the helm at all times. Get someone else to assist the person in the water....

On the dieseling... Your idle speed might be too high. Remember to check it with an accurate tacho. The dash tacho is not accurate enough. I have a friend who's tacho reads 650 revs, the engines doing 1000rpm... I set his with my advance timing light, and tell him to ignore the dash tacho....

Chris.....

 

[beason]

Re: hard to start, and dieseling. timing or something else?

As the skipper, YOU should be at the helm at all times. Get someone else to assist the person in the water....

On the dieseling... Your idle speed might be too high. Remember to check it with an accurate tacho. The dash tacho is not accurate enough. I have a friend who's tacho reads 650 revs, the engines doing 1000rpm... I set his with my advance timing light, and tell him to ignore the dash tacho....

Chris.....

its me, mama, and 2 14yr old girls normally. i have to help them in/out of the tube, connect the tube, etc.

im going to lower the idle, and see what happens. its weird that it works fine on the muffs.

 

[achris]

Re: hard to start, and dieseling. timing or something else?

its me, mama, and 2 14yr old girls normally. i have to help them in/out of the tube, connect the tube, etc.

im going to lower the idle, and see what happens. its weird that it works fine on the muffs.

Not really... On muffs the cylinder temperatures aren't anything like what they are under load.

To set the idle speed you need an accurate tacho not just a guess, or the dash tacho. Handheld tachos are not expensive, and with a lot of the features the new digital ones have, you'll be using it all the time...

Man, this one has everything, dwell, tach, all the electrical functions (V, A, Ω), transistor tester, thermocouple, capacitance... And for $26 :facepalm:...

Digital Tachometer Meter Tach Dwell Tester Multimeter Ship From USA | eBay