Another Hot Start Question

Hi Guys,

I have a 1989 Ski Nautique, with a 351W.

I recently replaced the carb with a Quickfuel M600. It runs great! I have basically only set the idle speed.

Cold starts are fine. I thought the hot starts were are also good... If I shut off, and restart relatively soon after (say within 5 minutes) it is good.

But last time I was on the river, it was a VERY hot day (around 100 to 105 F). Then after running for a long time, shutting off the engine, then trying to restart after about 20 minutes, the engine would just crank and crank, but not fire.

I opened the engine cover and removed the flame arrestor. I saw that the squirters were working if I pumped the throttle, and it wasn't flooded. If fact, when the fuel squirted down the throat, it vaporized instantly. Is that normal? Seems like the carb was very hot from standing? Heat soak perhaps?

After letting it stand for a few minutes (with the cover open), it fired up.

Any comments or suggestions would be appreciated.

I plan to check the timing soon, and also fine tune the idle mixture (it is a bit too rich).

Cheers,
Greg

TRBenj wrote: It’s not heat soak.

As I've also been having very similar hot starting issues (which I think is due to bad cables/connections - haven't quite finished troubleshooting), I'd be interested to hear why heat soak is not a potential issue? I seem to recall reading something about vapor lock potentially becoming an issue when fuel lines get very hot? Or am I mistaken?

Tim (TRBenj) gave good counsel about timing. I would check that first.

Heat Soak or "Vapor Lock" refers to fuel percolating or boiling inside the carburetor. With today's ethanol fuel blends, the boiling point of gasoline is lower and may be contributing to heat soak. While heat soak certainly can be a problem in certain applications, I really doubt that heat soak is your problem. Distributor, plugs, wires, timing, etc. are all things I would look at first. There are some fairly simple tests you can perform to see if your carburetor has fuel in the bowls or not:

Duplicate the condition by letting the engine and engine space/bilge get up to full operating temperature. Then let the carburetor sit for 20 minutes or so to duplicate the conditions.    Since you have a QuickFuel carb, you can simply look in the sight window on the side of the fuel bowl. Look to see if you can spot fuel in the float bowl. You may have to rock the engine a bit to get the fuel to slosh around. If you can see fuel in the sight window, then heat soak is likely not the problem.

If you did not see fuel in the sight window, then give your accelerator pump a couple of full squirts by manipulating the throttle control. Do this with the key OFF and the spark arrestor removed. See if there are 2 strong streams of fuel squirting from the accelerator pump nozzles. If you see fuel squirting, then heat soak is likely not your problem. If there is no fuel squirting and no fuel visible in the sight window, then your fuel MAY have boiled out due to heat soak.

There are a couple of mods you can try to help remedy heat soak. You can install a phenolic carb spacer between the intake manifold and the carburetor. This provides a good insulation and will help keep the heat from migrating up through the carburetor. The other option is to install an electric low pressure fuel pump designed for marine-based carbureted systems. With an electric fuel pump, the fuel pump starts working the instant that the ignition is switched "on". If the carburetor fuel bowls are empty, then the electric fuel pump will quickly fill the bowls up before turning the ignition from "on" to "start". This assumes that you stay at the "on" position for a few seconds before engating the starter.

JQ

Dialing in the timing implies there is a spark to time.

You have fuel but no bang, so that leads me to believe there is no spark.

Are you suggesting not to check for spark, just assume it’s there?

Hi Guys,

Thanks for all the suggestions. I plan to setup the carb properly this weekend - set idle mixture (max vacuum) and check timing. Does it matter what I do first? Mixture or timing?

Then when I'm out on the river next, I'll see home things go.

A few comments:
- The coil is the epoxy filled type (I had issues with an oil oil filled one years ago).
- I'll definitely check the spark with the hot coil... or maybe I can't put a wet cloth on the coil, to see if cooling it helps significantly when it struggles to start?
- The squirters definitely gave a good stream of fuel (IMHO)
- The fuel level in the primary sight window was looking lower than I remember. It was at the half mark when cold, but was almost at the bottom when it wouldn't start. But I'll double check that next time (cold vs hot levels).

Thanks,
Greg

When it wouldn't start hot, did you open the throttle and how much?

Beware setting idle mix to max vacuum, it dials in lean condition and stumble off -idle and impossible no-throttle starts.
you want a torquier, more resilient idle, so set to max vacuum while in gear. just be safe doing so.
Its the old auto-trans procedure of years ago,
It will also keep the rpms more consistent in and out of gear.