Logo

Crusader 270 vapor lock

junior4597

Contributing Member
Hey all - looking to get some information on causes and symptoms of a fuel vapor lock. I've been chasing intermittent issues - stalling at idle, RPM fluctuation underway, and starting hesitation after running for periods of time. Done a lot of troubleshooting and part replacement from fuel to electrical and haven't nailed it down! The stalling usually happens at idle when I'm pulling into a slip or maneuvering using one of the two engines and only after running the boat for a period of time. This doesn't happen if I'm running over to the fuel dock after initial start up etc. RPM gauges fluctuate and sometimes there is a loss in RPM/power when running over 2500 but it's not consistent. Restarting is a challenge after pulling up to a location for lunch or something, I have to crank her over and over and slam her with fuel a bunch of times before it kicks in. All that said I chased a lot of stuff down and finally read a post about fuel vapor lock and how the symptoms are very similar to what I'm experiencing.

I'm going to focus on this now but since it's a new thing for me I'm asking the brain trust a few questions to get me started.


  • What are the "typical" symptoms of a vapor lock? I'm sure they vary but.....
  • What can cause this?
  • What can I look for to chase this down?
  • If it's actually my issue, how can it be resolved? loaded question there depending on the outcome/cause

I'm thinking after all I have done to this point that this "might" be something to consider.

As a point of reference, I have...
Crusader 270's circa 1987
Rochester Q jets (rebuilt)
Racor fuel filters
Rubber fuel lines from anti-siphon to carb
single tank
point dizzys (changing them out this week to electronic)


Any help in understanding what causes a vapor lock, how to find it and how to fix it would be greatly appreciated!
 
This has been happening for a while, I'd say about a good 3 seasons. I've battled with various ignition issues but seem to have resolved those but am still experiencing the symptoms I mentioned in the post. It always cuts out at the worst time and only when after running for a good period of time. I also have to cross my fingers that she starts right up when I have passengers as I know it will take a lot of cranking to get her going. This only happens when we have run out for a while, stopped for lunch, and then started to head out again. I never even considered a vapor lock when I was troubleshooting as I hit everything else listed below (should help in understanding my thought process). This happens to both engines but primarily the STBD one consistently. What I don't know is if it is a vapor lock how would I verify. Is the fuel getting hot in the fuel delivery line (rubber), is it "boiling" in the float bowl? No idea how to even evaluate and check for a vapor lock or where to start, proper tools etc.

- rebuilt both carbs
- changed in-line cartridge filter
- changed plugs, cap, rotor, wires, coil, condenser, points
- re-timed engines
- adjusted mix screws
- replaced STBD mechanical fuel pump
- replaced both divorced choke springs
- replaced racor fuel filters
- replaced both anti-siphon valves
- checked, rechecked, cleaned and tightened all ignition connections
 
What we found out a while ago is that today's 'gasoline' doesn't behave like the fuel from the pre-Y2K timeframe and the engines will remind you.

What did the trick for us is as follows: after a long hard run, give the engines a cool down cycle...not so much to 'drop the temp' but to get rid of the excess heat that's present when the cooling water flow is reduced...put them in N and raise the idle to 1500 RPM for several minutes...then let them idle normally for a minute and then shut down...if it is real hot and you park, activate the blowers if not already running.

When restarting with the engines warm, slowly open the throttle at least 1/3 - no cycling the accelerator pump. work the key like normal and the engine will normally start and then increase the RPM...as the RPM increase, pull the throttle back to the stop...do it so the engine never gets over 2200-2400 and it should be fine.

As far as a positive definite test for vapor lock, I don't know a one...one usually gets to that determination going down the path you have...the one test that i do know of that will indicate you may be subjected to it is to measure the air temp inside the engine compartment...today's requirements, driven by the fuel that available) is to not exceed 150 deg F at the 'top' of the engine spaces - usually where the flame arrestor is...you be amazed how commonly it occurs and how many boat builder will try to pawn it off onto the engine OEM...
 
OK, good info! I will give this a shot this week and see if there are any differences. I was afraid that there would be no definitive diagnosis so I will keep monitoring to see if heat in the engine compartment is unusually elevated. I guess I'll go buy a thermal temp gauge to check things out, probably need one anyway for the boat!

I'll post once I figure this part of it out!

Thanks
 
Back
Top