Vapor Lock - Danger
 

I've owned my tri-power GTO for 4 years. In that time, I've never had an issue with vapor lock. It always takes 5-7 seconds cranking on a hot start feathering the throttle to catch, but nothing too bad. Cold start no problems ever. Once I'm moving, no problems with vapor lock.

This last month, including today's cruise, it will hot start after some cranking, but will die one or two times in the first 1-2 minutes of idling/driving.

So, I was rolling out of a parking lot and trying to merge into heavy SoCal traffic and it is sputtering and dies. Not safe at all.

Again, once I'm cruising and fuel is moving, no problem. Cold, no problem. WOT, no problem.

I have a 5/16" feed fuel line to a mechanical pump. No return. The fuel line and filter are NOT in contact with the block. I have phenolic insulators under the carbs.

Using the temperature gun, the exterior of the fuel bowls is 140-160F.

The engine runs cool, <180F. The ambient temp is cool, maybe 65F. Dual electric fans, both functioning. 160F thermostat. The cooling system is beautiful.

My next move is to buy a filter with a ¼" return nipple, and run a rubber line back to the tank. I'll need a new sending unit with ⅜" feed and ¼" return, and use a reducer on a piece of rubber hose at the tank to go from ⅜" to 5/16" existing line.

Question, did something change in California gas? Anyone else suddenly having issues? I can't understand why now...

Have you checked the vent lately? Could be collapsed or plugged.

No, I have not. Good call on that. I will check it out and report back.

Fingers crossed its that simple.

From the troubleshooting section of my website:

http://www.thecarburetorshop.com/Tro...ardstarthot://

Jon.

try putting heat insulators under carbs

Richie,he has them!Tom

Spent a lot of time on this. Gas starts to boil at 95F and your fuel pump eventually is 160+f. Try the ceramic insulator that Canton sells that goes between fuel pump and timing cover. I ultimately solved my issue with a in tank electric fuel pump and a regulator at 6 psi.

Canton Racing Mechanical Fuel Pump Insulators 85-010

Installing a return line is a good idea but I'd use a reproduction A/C 1/4" steel tube instead of rubber hose all the way back. You'll have to change out the sending unit in the tank or solder in a hose nipple to accommodate the return line.

Yeah, CA gas sux. That was the main reason for installing EFI in my '66 GTO.

It may not be vapid lock, you now may have some bad rubber fuel line that's dry rotted and leaking air which the fuel pump draws in much much faster then fuel.

We use the same suppliers for gas here in Arizona, same crappy 91 octane.

As it stands right now I haven't noticed any issues on our cars. We daily 2 classics and both have been fine. One has a return line fuel system and the other does not. Temps have been hovering close to 60 up here in Prescott and 70+ in Phoenix and I've made the trip (220 round trip) with both cars recently without issues with fuel, filling up at different stations.

With that said it could be a number of different issues causing problems. Could just be you got a bad tank of gas recently. One thing I've noticed is that the ethanol content is not consistent from one station to the next. Installing a return line certainly helps and not a bad idea to do so. This fuel does not like temperature AT ALL. Sounds like you have all the other bases covered.

May have been the change from summer to winter blend fuel although that happened a few months ago.

If you didn’t have a problem before, I would think that something is failing.

I had a very similar problem on my 70 GTO and a new fuel pump took care of it. I believe the ethanol gas deteriorated the rubber seal.

The problem has been going on for 1-½ months.

The carb vent is clear.

I'm ordering the Canton fuel pump insulator from Jegs, and the fuel filter with a return provision from Pontiac Tri-Power.

https://pontiactripower.com/collecti...th-return-line

Regarding the return line, do you recommend buying a pre-bent one, or bending my own? The Right Stuff has a pre-bent one, but I have no experience with those.

Going for a test drive now... :)

I should've been more clear, I was talking about the tank vent. I assume you have the small metal line on the tank with the short section of hose. That could be rotten, or have debris in it.

I'll check the tank vent. I replaced the vent hose about 2 years ago, so I think it is OK. Also, if I had tank venting issues, I would expect the issues all the time, not just after hot starts... I will check though.

The pre-bent lines fit well and save time.

Absolutely / happens quite often years after the build one needs to go & tighten all clamps & possibly replace the rubber hose ends .

Symptoms posted remind me of a 2bbl carb that the base plate to fuel bowl screws have worked their way loose.

That or a carb that's right on the verge of loading up. Not enough to flood over but enough to cause stumble when turning or crossing unlevel pavement at idle or minimal throttle opening.

Homework before part swapping. Including basic engine tune

Clay