Avffva24

Hi I'm new to offshore only and have heard there's a lot of knowledge on here for the power boat owner so I thought I would give it a shot...

I have a 1999 hustler slingshot with twin 502 naturally aspirated engines with Holley carburators. For the last few months I have been having an issue that I can't seem to figure out. The boat runs great for about 20-30 minutes. Keeping the engines around 3200 rpm not touching the throttles the rpm gauge after 20-30 minutes will go down to 2800 back up to 3200 and won't stay stable. The more throttle I give it the rpm gauges go backwards like its getting choked out. So I back off the throttles completely and the engines will not idle the both shut off immediately. Putting the boat back into neutral and trying to power it back up again after its been ran for 20-30 minutes it will not start. Moving the throttle up little less than half throttle the motor will finally turn over and run up around 3500 or higher then fall down to the rpm it should be at with the throttle still being a little less than half throttle. After getting the engines started putting them back at idle which is around 1k rpm I go to put it in gear which then the engine falls down around 600 rpm and dies out and still won't stay started. The only way the boat will run after its been ran for 20-30 minutes is to wait around 3-4 hours and by that time it again will start and both engines will run again for another 20-30 minutes.

Dealing with this problem for the past few weeks I have tried and thought of the different things that could be going wrong to make both these engines do what I have just explained. What I have done is check the pressure coming from the fuel pumps and the tested out good. Checked the coils to make sure they weren't getting hott and causing it not to start. Checked for fuel lines that may be sucking in air causing them not to get proper fuel. Looked inside of tank to make sure nothing is inside it stopping the pumps from seeking fuel. All these problems still haven't fixed the issue. If you have experienced this or have any advice I'd greatly appreciate it as I'm ready to go boating!

Pantera24

This happens to both motors simultaneously?

Avffva24

Yes, at this time. Three weeks ago it was just the one engine now both are doing the exact same thing. Changed fuel filters checked to make sure no water in fuel. I'm wondering if my carbs could be gummed up? Float sticking dumping too much fuel for the 20-30 minutes then flooding engines out to where the die off? Idk?? Should I try rebuilding them next or does that not make sense? I'm not a mechanic so again I'm just guessing

KAAMA

iTrader: (1)

I know you already said you checked the coils, but I would take a second look at the coils....Sounds a lot like a coil problem. They will usually die within 20/30 minutes until they heat up and then shut down out of the blue until they cool off again and then they will allow you to restart again and keep repeating the failure----but hey, what do I know??? I just kill bugs for a living!!!

I'm sure a good trouble shooter will come along and have the answer for you.

pitmitch910

+1 on an ignition problem, coils dont cost too much it may be a good idea to just replace them to rule it out. Could also be bad wires. Sounds ignition related. Just my $.02

demonmaestro

hmm well i would say being they are both holly carbs i would go ahead and rebuild them they both will cost under $50 bucks to rebuild and fairly easy. just wondering but has the boat sit for any amount of time recently? how long have you been experencing this issue?

Avffva24

This has been going on the past five weeks. Started with one motor now they both are doing the same thing. The reason I believe it's a fuel related problem instead of ignition is because again when it dies off and won't idle I'm able to position the throttle a little less than half throttle and get both engines to fire up and run and slowly back off the gas until they idle at 1k. If it was something getting hott such as a coil or ignition it seems to me it wouldn't matter where the throttle is placed at it wouldn't start until it sit long enough to cool down.

Young Performance

Is it really hot where you boat? Sounds like a possible vapor lock problem. It runs when it cools down and doesn't after running a while. Do you have a fuel pressure gauge in the dash? I see you checked pressure, but was it with a temp. gauge or one in the dash? If it's vapor locking, the pressure will drop. You will need to monitor the pressure right near the carb.
Eddie

wannabe

This is definitely a fuel issue. Either vapor lock or inadequate supply from the tanks. Check your fuel filters and I would put a thermometer in the engine room, even a digital one with a remote reading at the dash. Coils don't act like that in synchronous actions. One would fail befor the other.

Wannabe

inthetundra

iTrader: (1)

Do you have electric fuel pumps? When I was stationed in the gulf we had a problem like this and it was a bad run of fuel pumps that would quit after they got warm. Got new ones from a different manufacturer and the problem disappeared.