'70 Beetle runs rough on acceleration after hot startup.

[pottsrj]

Apologize for the post as I'm sure the answer is in here somewhere but I searched to no avail.

I rebuilt my engine and I'm working out the bugs. It starts great cold and runs good thereafter. My problem happens after I restart it when it's been sitting with the engine hot, like after running into a store after having just driven it there. When starting hot it fires right up, but when I accelerate it runs very rough and doesn't respond (won't accelerate). If I let off the gas it goes back to idle fine and if I just persist at accelerating it comes around to running good again in about a minute or so.

Of course I'll check valves, timing, etc (for the 3rd time), but I don't think it has to do with any of those things. It has to be tied to the car sitting hot for a while. For that reason me thinks it is likely fuel related.

Could it be that it's somehow flooding while sitting hot? If so, why does it start so well? I'm in the process of making sure the choke isn't closing when it shouldn't and initially that doesn't seem to be the case.

I'd really appreciate suggestions on trouble shooting this.

'70 1600 sp, fresh top end rebuild. Rebuilt Solex 30 pict 3. Bosch 009 w/ new points, etc. Headers w/ stinger pipe. New Coil, fuel pump, in line fuel filter, plugs/wires.

Thanks everyone!

[Agent47]

Sounds similar to vapor lock issues. Essentially the fuel in the fuel lines is getting hot and vaporizing and not pumping into the carb.

Typically the solution is to ensure that the fuel lines are up off of the cylinder tins away from the excess heat.

[Chochobeef]

Check that your metal fuel line going to your pump is routed correctly, or in my case I routed it further around (check my gallery) and wrapped it in rubber hose to protect it from heat soak.

I don't have any issues with my 34 pict 3 and 009 w/points. Show us some pictures of your engine if you can.

[zoobyshoe]

How soon after the rebuild did this start?

[pottsrj]

[pottsrj]

[pottsrj]

[zoobyshoe]

[pottsrj]

Thanks everyone for the suggestions, especially that one about the fuel pump rod binding when hot, holy cow...whoda thunk it!

I think I found the issue. I began by insulating the fuel line with 1/2 inch thick pipe insulation. I then ran the engine until hot with the aircleaner removed. I shut it down hot then restarted 5 to 10 minutes later. After restarting the issue once again presented itself and I couldn't rev over about 1200 rpm. I then looked at the choke and realized it wasn't fully open so I held it completely open and that enabled the engine to rev just fine.

So here's my theory. I'm building the car into a baja so the engine is exposed to the atmosphere. After shutting the engine down the choke module is probably cooling faster than the engine. I suspect this because the choke module is out there on it's own in the fresh air far away from the heat of the engine. Perhaps the engine cover (rear hood) minimizes the issue on a stock beetle by holding in heat and thus keeping the choke module hotter (closer to engine temp)?

What do you think of my theory? I had the choke working fine, the car runs good after cold start up. Not sure what to do now. Backing the choke off should help but the issue of the choke module cooling quicker than the engine will still exist so choking the hot engine could still happen. Also if I back it off too much it won't choke the cold engine properly creating a new problem.

Maybe I should take this over to the "offroad" forum, see what they say?

[zoobyshoe]