Hard/impossible starting

1996 5.0L mercruiser.it's got good spark,the timing is at 10 btdc,good fuel supply but it's a nightmare to start. it'll nearly flatten the battery before it fires up(if it fires up).when it does eventually go,it runs great.
The problem seems to be that the fuel isn't getting into any of the cylinders.If you look in through the carb, into the manifold, there are puddles of fuel but there seem to be no suction on the induction stroke to any of the cylinders.
the timing chain is sound,the camshaft timing appears to be fine and the valves are all moving freely
any ideas??

Re: Hard/impossible starting

What is your typical starting method? (please include as much detail as possible) Sounds like the thing is just down right major flooded. How does it start after it is warmed up, and after sitting for a couple hours?

Re: Hard/impossible starting

daleburt said:

1996 5.0L mercruiser.it's got good spark,the timing is at 10 btdc,good fuel supply but it's a nightmare to start. it'll nearly flatten the battery before it fires up(if it fires up).when it does eventually go,it runs great.
The problem seems to be that the fuel isn't getting into any of the cylinders.If you look in through the carb, into the manifold, there are puddles of fuel but there seem to be no suction on the induction stroke to any of the cylinders.
the timing chain is sound,the camshaft timing appears to be fine and the valves are all moving freely
any ideas??

Click to expand...

Ayuh,.... What Carb is on it,..??

Re: Hard/impossible starting

It's a mercarb 2 barrel carb.I cant find any ID numbers on it . If it was flooding then why is the fuel just sitting in the manifold and why are all the plugs bone dry.
Starting used to involve just turning the key and it would start,pretty much,instantly.Now it takes dozens of turns and it'll gradually speed up until it fires(or the battery flattens and I give up).It usually needs the throttle to be pumped aswell before it'll even think about firing on any cylinders.
It's had a new distributor cap and rotor arm,new plugs and the carb has been stripped,cleaned and rebuilt.
Occasionally,when i stop turning it over,it'll blow smoke back through the carb

Re: Hard/impossible starting

Do you ever watch the carb top while cranking? You want the choke plate to be nearly closed when it's cold. And pumping is normal on most carburetors. So which system do you have, is it TKS?

Re: Hard/impossible starting

You need to learn to use the throttle only position on the throttle lever. and give it some throttle and it should start easily.
Here is a copy and paste from an owners manual on how to start a carbed engine. Then it should start easily again. You may want to consider a full tuneup as well. Few carbed engines will start in neutral with no throttle or priming.


Starting And Stopping The Engine

NOTE: Only perform those functions applicable to your power package.
1. Check all items listed in Operation Chart.
2. Place the remote control handle in NEUTRAL.

CAUTION
Overheating from insufficient cooling water will cause engine and drive system
damage. Ensure that there is sufficient water always available at water inlet holes
during operation.

WARNING
Explosive gasoline fumes collect in the engine compartment. Avoid injury or
property damage, operate the bilge blower for at least five minutes prior to starting
the engine. If the boat is not equipped with a bilge blower, open the engine hatch
and leave it open while starting the engine.

3. Push THROTTLE ONLY button and position throttle setting as follows:
a. COLD ENGINE - Move control/throttle lever to full throttle, then return to about 1/4
throttle. In extreme cold it may be necessary to pump lever more than once.
b. WARM ENGINE - Move control/throttle lever to 1/4 throttle position.
c. FLOODED ENGINE - Move control/throttle lever to full throttle. Be prepared to
decrease engine speed to 1000-1500 RPM as soon as engine starts.
IMPORTANT: Do not operate starter motor continuously for more than 30 seconds.
4. Turn ignition key to START. Release key when engine starts and allow switch to return
to ON position.

5. Operate engine for 1 or 2 minutes at fast IDLE (1000-1500 rpm) or until engine temperature
reaches 140-160 degrees F (60-71 degrees C).
6. Inspect the power package for fuel, oil, water and exhaust leaks.
7. To shift into gear, move control handle with a firm, quick motion forward to shift to FORWARD
gear, or backward to shift to REVERSE. After shifting drive unit, advance throttle
to desired setting.
8. Move the remote control handle to NEUTRAL/IDLE and allow the engine to slow to IDLE
speed. If engine has been operated at high speed for a long period of time, allow the
engine to cool at IDLE speed for 3 to 5 minutes.
9. Turn ignition key to the OFF position.

Re: Hard/impossible starting

If the procedure for a flooded engine works then it may be time to look at the carb again, especially since you saw puddles of fuel.

I believe those carbs have some plugs in the bottom of the fuel bowl that epoxied in, and that stuff can dissolve over time and let fuel go directly from the fuel bowl into the intake manifold.

Re: Hard/impossible starting

I know how to use the throttle only position.I've also disconnected the remote cable and worked the carb by hand while somebody turned the ignition key.
The carb choke plate is open about 1mm while cranking.I've tried pumping the throttle while cranking,not pumping,wide open throttle,no throttle,flooded start procedure.
Would a blocked crank case breather cause this?

Re: Hard/impossible starting

No a plugged crankcase breather will not cause it.

Do you have good, bright blue spark? When you pump the throttle, does gas squirt in two good streams gas into the throttle bores?

If you have spark, pour a couple of ounces of gas into the carb and see if it starts.

Re: Hard/impossible starting

Could it be a low compression issue ?

Re: Hard/impossible starting

All cylinders are between 125-130psi

Re: Hard/impossible starting

good b
right blue spark.fuel is being squirted from carb but it just lies in the manifold.

Re: Hard/impossible starting

Sounds like a serious vacuum leak. Try covering the top of the carb with your hand or rag while someone turns the key.

Re: Hard/impossible starting

verbious said:

Sounds like a serious vacuum leak. Try covering the top of the carb with your hand or rag while someone turns the key.

Click to expand...

Be cautious of a backfire. This is a good way to solve the problem by burning the top of the motor off or going to the hospital.

Re: Hard/impossible starting

just a few observations:

If you have fuel pooling, the engine may be flooded. pull a plug, if its wet, it may not want to start without the throttle at full. if this is the case, your carb needs work.

you havent mentioned changing the plug wires.

the slow cranking speed that gradually increases that you mention would be indicative of a poor battery or poor battery connections. engines need 100-120rpm or faster cranking speed to actually fire. (Diesels just a bit higher)

with all your cylinders down to 125-130, was that taken cold? did it increase with oil being squirted in the cylinders?

Re: Hard/impossible starting

took a step back yeaterday and had a think.went throught the timing proceedure again and all was good.1 thing I did notice was that the rockers had very little lash so I adjusted them all to the correct value.Bingo!! it started after 1 turn.I've started and stopped it dozens of times since,even from cold,and it fires up straight away.
The thing I cant figure out is why,if that was the problem,was I getting a good compression reading,but if it's cured I'm not going to argue with it.

Re: Hard/impossible starting

How would that affect starting (unless the valves were tight enough to keep the engine from turning freely)?

Re: Hard/impossible starting

If you did the static valve adjustment go back and do the running type. It will make a difference and sound good too.
BTW I'm glad you found the issue.

Re: Hard/impossible starting

nola mike said:

How would that affect starting (unless the valves were tight enough to keep the engine from turning freely)?

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Tight valves wouldn't stop the engine turning.it would mean that the valves might have been held open a microscopic amount so compression & induction would be lost. .

Re: Hard/impossible starting

Valves on that engine don't have "lash". They use hydraulic lifters to maintain "zero lash".