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Hard to start when hot

C

chris17744

Contributing Member
"Hi Guys, I am very new to thi

"Hi Guys, I am very new to this forum, and this problem may have been addressed before. I have just completed a complete restoration of a Sea Ray Weekender, could be the only one in Australia. It is powered by a Mercruiser 5.7 Bravo2 fitted with a 4 bbl Weber / Carter carb. The problem is, it is hard to start when hot. Cold, it starts first pot up. If I shut down after a run and re-start immediately, there is no problem, but if she sits for 10 / 15 min, it is almost impossible to get started but will fire at WOT but hard to keep running. I have lowered the float levels 1/8 inch but no difference. Anyone know the solution to this one ??
Chris, Hervey Bay, Australia."
 
"Hi Barry, No, the choke is no

"Hi Barry, No, the choke is not sticking, we use little choke here in the tropics. The vacuum relay opens the choke fully.
Chris."
 
"Chris...

It sounds like a

"Chris...

It sounds like a fuel delivery problem. If the choke is open all the way, maybe it shouldn't be?
Is the fuel line sitting too close to something really really hot and boiling itself dry while it sits there for 10 - 15 mins?
You said that you adjusted the float levels, but what shape is the needle/seat in. Are they leaking and the fuel is expanding while hot and spilling out into the manifold only to evaporate? Then when you go to start there is nothing there to fire. The fuel pump has to pump awhile to to fill that carb back up.
Vapour lock before the pump, or, if the line between the pump and tank empties back into the tank while sitting, it takes along time for the pump to prime itself?

Wrench"
 
"Ayuh,...

Those carbs are K

"Ayuh,...

Those carbs are Known to leak, Internally....

That's how you get the Flooded condition on restarts....
I've been told the Fix, but don't remember the procedure at this time...
I'll see if I can refind the Answer..."
 
"Chris Dauth
You may want to

"Chris Dauth
You may want to try a thicker (more insulation) throttle body to manifold gasket. It may be percolating the fuel from engine heat transfer.
I stayed in Hervey Bay for about a week, several years ago while on a holiday there. If I ever get back there it's my shout.
Bert"
 
"G-Day Bert, I think you may b

"G-Day Bert, I think you may be on the right track. I was told elsewhere that the carb was getting too hot and maybe an insulating block between the carb and manifold could fix this problem. Also the automotive guys fit an aluminium finned plate between 2 gaskets between the carb and manifold which gets rid of the heat which would go to the carb.
Other than the 'hard to start when hot' problem, the motor is perfect, plenty of power and only burns 10 gals an hour at 26 knots.
Glad you made it down here Bert ! Now is the time to come again, $US1 buys almost $AU2. Check out our web site at http://www.holidayherveybay.net . You buy the beer, I'll supply the boat ! I've just come back from a 250 NM trip up to Lady Musgrave Island on the Great Barrier Reef, you guys in the US should Google Earth this area and see what we have here !
I'll try the insulation on the carb this week and get back here and report the results.
Thanks Guys
Chris, Hervey Bay, Australia."
 
"I cant believe it is a heat i

"I cant believe it is a heat issue???

The engine barely gets above 160-170 degrees!!


First thing to check is when it WILL NOT start.
Disconnect the throttle linkage and activate the throttle and see if you get gas out of the accelerator pump circut. If you get gas then it is most likely not a lack of fuel issue.

It could be a bad adjusted float. As said above a leak internally, need more observasion......then more info/feedback."
 
What is the running temp of th

What is the running temp of the motor? What is the idle running temp of the motor.

Should be 150 idle and not much more than 170 -180 after running at speed.

The base of the carb will get hot (But not to hot)due to the exhaust crossover that is present in the intake manifold.

Again we need more info.........
 
"Temps are as above, 150 idle

"Temps are as above, 150 idle 160/70 running but will climb to 180 when coming off the plane. The carb has been rebuilt. There is fuel in the float chambers and does pump fuel from the accelerator jets. The motor will start with prolonged cranking at WOT and no pumping on the throttle lever. It appears as though the motor is flooded. Once started hot, it runs just fine."
 
OK then

when you run it th

OK then

when you run it the next time have the flame arroestor loose so you can remove it easily.

Run the boat till normal temp. SHut it down and pull the flame arrestor off and sit there and watch.

Observe to see if fuel keeps siphoning into the motor. Look to see if the choke starts to close when the linkage is moved.

The only other issue that I would be concerned with if all fuel issues are good would be a sloppy timing chain. It starts great when cold but after it stretches the timing is way off and difficult to start and it is just the method used to start it that makes it seem to be fuel related.

Just my thoughts.
 
"One more thing, Does your eng

"One more thing, Does your engine have the knock sensor on the starter side of the engine?
Is it wired in correctly? The knock sensor "could" cause the timing to retard if it is wired wrong or malfuctioning.

If it is even there........"
 
"Hard run, sits for 10-15 minu

"Hard run, sits for 10-15 minutes, won't start -
sounds like a classic case of heat soak and
vapor lock. Have seen it even affect the fuel filter if too close to the manifolds or up high
in the engine compartment. Next time you run it,
stop, raise the engine hatch, sit for 15 minutes
and see if it starts easily. If it does you have
a vapor lock problem. Could be anywhere in the
fuel delivery system."
 
"Problem solved ! I bought a

"Problem solved ! I bought a fibre block and installed it between the carb and manifold along with an aluminium finned plate. The fibre block went on first, against the manifold and the finned plate on next, then the carb. The carb is now much cooler after a hard run and the motor starts after about 2 turns of the crank. Much better than before. I got the fibre block from the local auto shop and made the finned plate. The guys at the auto shop told me that the Carter / Weber carbs don't like our tropical climate !
Thanks for all the help, I'll go and do some boating, summer here, 30c / 86F today !!"
 
"Chris
Go have fun on the boa

"Chris
Go have fun on the boat. -28C here today, winter, water's kind of hard to boat on
angry.gif

Bert"
 
I am glad you "solved"

I am glad you "solved" the issue.

I cant and dont believe that the issue is that.

There must be as suggested a segment of the fuel line to close to a hot spot.
One other thought is you could remove the intake and put the stamped steel block offs where the heated cross over is to keep the heat away from the base of the carb.

The guys at the AUTO shop may be right about the climate for a automobile but if your motor is only reaching 180' I still have a problem with the vapor lock. I personally have never seen a Marine engine (stock/factory) ever have a vapor lock issue.
 
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