Engine Will Not Start When Warm

[CDAHDAH]

I have a 1985 Supra Rider with an after market Holley Carb. This just happend the last few times I've taken the boat out, but the engine will not start when it is warm. It cranks, but just doesn't start up when its warm.
When the engine is cold, it starts up like a champ and runs great ALL day long...but as soon as I kill it and try to restart the engine, that's a different story. Even with some Starter Fluid (though I hate using it), it still will not start. I don't think its the battery or alternator, and the reason is, I just leave it as it is until the next morning and it'll start up fine without hesitation.

The only thing I can think of is possibly the carb somehow floods the engine when its warm (float valve??). I had the carb rebuilt last year, but i'm hoping its not the same issue.

Is there more strain or load requirements on the starter/battery or any other electrical components when the engine is warm that would keep it from starting up?

Thank you for your help in advance.
-CD

[SZEH]

I had the same issue this weekend with my '06 21V with the 340hp. Never had a problem in 2 years and then a non-start issue. It would turn over fine, but never start until the engine had cooled down.

I've been told that it's due to more stations starting to put 10% ethanol into their fuel and that ethanol vaporizes faster than fuel...that's why more boats are experiencing more problems now than in the past with vapor lock.

Here's a thread started not too long ago regarding vapor lock. Not sure if this is your problem, but it sounds very familar and is a very frustrating problem.

https://forum.supraboats.com/showthread.php?t=4304

Scott

[CDAHDAH]

Thanks Scott - That makes a lot of sense and could very well be the cause. Come to think of it, my blowers haven't been working properly, only two of the 4 vents actually blow out exhaust/heat from the engine compartment. Is vapor lock an internal engine issue or is it something that actually "fumigates" the engine compartment?

[SZEH]

Thanks Scott - That makes a lot of sense and could very well be the cause. Come to think of it, my blowers haven't been working properly, only two of the 4 vents actually blow out exhaust/heat from the engine compartment. Is vapor lock an internal engine issue or is it something that actually "fumigates" the engine compartment?

The way I understand it is that the fuel inside the fuel pump gets hot enough to vaporize...basically an air pocket in the pump so fuel wont flow. When the pump itself cools off enough the vaporized fuel turns back to its original liquid state and the engine fires right up.

That's why some guys on that thread suggest squirting cold water on the fuel pump to help cool it off and get that vaporized fuel back to liquid.

And like I said it seems to be all due to more ethanol in the fuel supply. And to pour salt in the wound I hear that they're thinking of upping the ethanol mix from 10% to 15%. The dual pump system sounds like it's going to be the future fix.

Scott

[michael hunter]

CDAHDAH
How hot is it where you run? When this happens does it smell like gas? Pull the flame arrestor off and see if the carb is dripping fuel down the barrels.

[Salty87]

is the carb new or is it the rebuild? how many hours on it?

if the carb has been running good for a while, bend your battery cables....do they pop and crackle? originals from 85 are probably done. check the ends of the cables for fraying...clean the ends too, nice and shiny...don't forget the ground on the engine block.

yes, a hot engine has more compression. it's harder to turn over. inefficient cracked, old cables don't give the starter all the juice it needs. solenoids can cause problems when hot too.

the fuel pump talk in that other thread was about a new boat, prob efi. opening the engine hatch next time would rule that out.

i'm going with cables...what could i win? lol

[CDAHDAH]

Michael -
Its pretty hot where I run the boat, down in Southeast Texas, near Houston (around 100F air temp. and water temp is about 83F). When it happens, it doesn't really smell like gas, nothing more unusual than the engine exhaust. The carb doesn't drip gas after I kill the warm engine. I'm just not too savy with carbs and troubleshooting them.

Salty -
The carb is an aftermarket Holley carb that i had rebuilt last year, and since its been rebuilt, I'd say I've probably put around 100 hours on it. How often do you think you should rebuild it?
I haven't checked the cables yet, but I also did add in a Perko switch with new cables tying the two batteries together. Should I bend the cables to test them out while the engine is running and as close to the starter as possible? I've only had the boat for a year, but I would probably think that the battery cables are stock.
haha not sure what you could win, I'd say a day of boating, but you already have a nice boat.

[Salty87]

about the carb, i just wanted to make sure it had been running before ruling it out. sounds like it's been fine.

you can bend the cables anytime. check the ends for fraying too...cleaning them might get you by for now.

[gerdy]

sometimes when ignition coils get hot they will crap out.

[CDAHDAH]

Gerdy - Does that sound like something you've experienced before with regards to an ignition coil getting too hot? It runs fine, just won't start back up.

[csuggs]

I'm with Salty and the cables. Old, frayed, brittle, corroded cables and ends will not handle the current required to start the motor when hot. I had the same problem last year and fixed it with new cables. It's an easy check and a relatively inexpensive fix.

[michael hunter]

I am confused he said it cranks fine but wont start. It sounds more like ignition? Does it still have points? The coil may be the problem also I have seen the coil wire cause no start. Next time it wont start start checking for spark at the coil wire if it has a good strong blue spark there then check the spark plug wires for spark at the plug.

[agetech]

I'm with Michael, check for spark when the engine won't start. If you still have points, change the condensor, they are cheap. If it was the coil the engine would quit while running after it gets hot.

[csuggs]

Maybe I'm confused and sorry if I read this all wrong. But, if the motor cranks over fine when hot, but just doesn't start, then it's not the cables. If it cranks very slowly only when hot, check out the cables.

[87sunsport454]

That is a good point that Hunter has. Does it still have points? If so ,I would change them out just because and the condencer too. On the other hand, when the boat wont start have you looked down the carb to see if it is squirting gas down it.

[rludtke]

I like the vapor lock theory. I think it is likely that the fuel in the float bowls and/or the inlet line is vaporizing, and will not meter. When the engine is shut down, the heat radiatiating from from the crankcase is heating the carburator enough to cause the fuel to vaporize. This is made more likely by the alchohol and other additives in today's fuels that have lower vapor pressure.

I have a 2 inch phenolic insulator block under my carburator. This helps insulate the carb from the engine crankcase heat. This is a popular automotive performance trick. These should be availible at Summit racing, or other simular performance retail outlets. You will need longer studs as well, these may be part of a kit. If you look closely at the attached picture, you can see the insulator plate beneath my carb.

You may also need to consider opening the cowl when you shut down on those extremely hot days to ventilate the heat before it radiates to the carburator.

[ngavchris]

CDAHDAH
You mentioned that your blowers arent working properly. Only two of the four vents should blow air out. The other two vents just run behind the gas tank.

[chautauquasun]

Hi guys...I ran into the same problem with mine today...and had the further humiliation of having to call my dad to come tow me home because the battery died.

I will start a new thread and give you the details about mine.