Engine problem

[V12T]

My recently rebuilt 512 sixpack with Al. heads and a modest cam with hydraulic followers starts from cold and runs well. However sometimes when hot the (mini) starter struggles to crank the engine and it spits back through the middle carb. Allow to cool and it starts fine. Timing is set at 35 degrees at 3000revs. Plugs a nice colour. Is it a timing issue or something else?

 

[Challenger RTA]

First thought that comes to mind. The floats might not be closeting of the fuel. After you shut it off, look to see if there is any fuel dripping. chock might be an issue.

 

[Tig]

Another thing you could try is running a good earth cable to the engine. Heat increases resistance if the connection isn't the best.

 

[V12T]

First thought that comes to mind. The floats might not be closeting of the fuel. After you shut it off, look to see if there is any fuel dripping. chock might be an issue.

Checked and can't see any. Will look again.

 

[V12T]

Another thing you could try is running a good earth cable to the engine. Heat increases resistance if the connection isn't the best.

Have direct battery to engine earth. Will double check but think it's OK.

 

[Bret Schneider]

You mentioned timing at 3000 RPM but not the base timing. That's what's going to matter during hot starts.
As has already been mentioned, check the negative and positive battery cable connections. Voltage drop tests using a multimeter works best for this check.
If that's all good, I'd want to check starter draw with the engine cold and compare it to hot. Chances are it'll be drawing noticeably more current hot as compared to cold. If that's the case and assuming the starter is OK, then you have a heat soak problem with the starter. Check out some of the starter insulating blankets/shields available.

 

[Xcudame]

All great advice so far!

Is there a header tube running next to the mini- starter? The mini- starter is great for space and weight savings, but they're more susceptible to heat. And with a 512 motor you're generating a lot of heat (power)! Invest in some kind of insulation for the mini-starter regardless so it will last!

 

[Chally]

All great advice so far!

Is there a header tube running next to the mini- starter? The mini- starter is great for space and weight savings, but they're more susceptible to heat. And with a 512 motor you're generating a lot of heat (power)! Invest in some kind of insulation for the mini-starter regardless so it will last!

I went through this issue a couple months ago with my new 440-6 build. Reused a 10-year old mini-starter which worked fine when cold but struggled with hot restart. I’m running 16 degrees base timing and tried reducing that and adding insulation to the starter but still had issues. Swapped to a new parts store mini-starter and no issues with hot start, even with 16 degrees base timing.

 

[Bret Schneider]

Good point on the mini-starter being more susceptible to heat. Smaller body therefore less material to act as a heatsink pulling heat away from the starter's electrical components.
I hate it when physics works against you..

 

[V12T]

All great advice so far!

Is there a header tube running next to the mini- starter? The mini- starter is great for space and weight savings, but they're more susceptible to heat. And with a 512 motor you're generating a lot of heat (power)! Invest in some kind of insulation for the mini-starter regardless so it will last!

Good idea . Will do that

 

[V12T]

I went through this issue a couple months ago with my new 440-6 build. Reused a 10-year old mini-starter which worked fine when cold but struggled with hot restart. I’m running 16 degrees base timing and tried reducing that and adding insulation to the starter but still had issues. Swapped to a new parts store mini-starter and no issues with hot start, even with 16 degrees base timing.

My starter is pretty new. Am going to try heat shielding.