hard starting when hot

[WLJ]

I have a 75 MGB with a stomberg carb that has a manual choke conversion. This car starts great when cold and runs good when driving. My problem is when I go to start the car after a run it takes a lot of cranking to get it going.The choke is completely off and it has recent plugs,wires,coil,condenser,dis. cap,air filter,points,and fuel filter.I have had this car for 18 years and recently rebuilt it but did not touch the carb except for the manual choke.It almost seems like a gas vaporizing problem. Any ideas would be appreciated.
Thanks, Warren

 

[Larry Kronemeyer]

After a run and it starts hard, pull plugs and see if they are wet or dry. Adjist mix accordingly.
Larry

 

[aeronca65t]

I'd go back and check the choke cable.
Be sure that the choke is really closing off the enrichment mechanism fully. If the carb was partly disassembled anytime recently you need to be sure that everything in the choke (gaskets, the piston, levers, etc.) was put back correctly.
And be sure that the choke arm is not "creeping out" due to vibration from running...have a look at it after shutting down.
After that, I'd check the floats and needle/seat in the float chamber.
Then the main piston diagphram.
I'll assume that the air filters are clean.
Once-in-a-while it's also good to check the nuts that hold the intake manifold to the head. Since this is a side draft setup, it has a tendency to get loose with time (and cause "funny" carb-like problems).
If you still have problems, you may want to check valve adjustment...a too-tight condition can cause poor hot starting.

[ 10-02-2003: Message edited by: aeronca65t ]</p>

 

[tony barnhill]

also check to see if your butterfly is weighted...many of us have modified our Strombergs over the years by superglueing a weight on the bottom side of the butterfly to ensure it does close completely - believe that was also a factory recall item to accomplish....I'll have to check my dealer recall/tech sheets.
...with some manual chokw setups, the choke isn't dialed in properly & closes when cold but not completely when hot...twitch the spring a bit looser & see what happens

 

[WLJ]

Thanks for the ideas I am going to check these out as soon as I can.The choke vibrating back on sounds like a possible explanation.If the diaphram was bad would the car start at all or just run badly?
Warren

 

[Larry Kronemeyer]

Still start and run badly!! The diaphragms are cheap, if they are old replace them, they originally were not made for these new fuels.
Larry

 

[Obtong]

Warren, have you changed the kind of gas or lead additive recently? Also, I was wondering if you have a case of vapor lock. Perhaps a fuel line was rerouted when you rebuilt the car and the fuel line now gets too hot.

Just a thought...

Dom

 

[WLJ]

Dom, The problem happens with all grades of gas.The fuel line is run in the same place it was before the rebuild and I only use one kind of lead additive.I did check the diaphram and made sure the choke was staying off,both are okay.The car is working really well except for this little problem.I am going to check the other suggestions as I have time.
Warren