How is that  trunk mounted battery grounded, Steve.  You say you  ran jumper cables to the solenoid...Positive and Negative or just positive.  Back in ought 12 Corky had poor cranking with his trunk mounted battery.  We added a 2gauge ground wire from the neg. post to a bolt on the transmission, tail shaft housing as I recall.  That fixed the problem.  grounding directly to the trunk floor, etc. is usually not a good deal.
BB1
 

Small blocks typically crank really laboriously when warm if the timing is too far advanced. Try retarding two degrees and see if that helps. A Duraspark ignition box is designed to do this automatically if both the red and white wires are connected properly.

I agree with BB, if you didn’t run a negative cable from the trunk to the engine compartment, I suggest installing one.  With my trunk mounted battery, I ran a #1AWG positive cable to the starter solenoid, and a #2AWG negative cable which I connected to the starter mounting bolt, and the frame by the starter.  The negative battery terminal is also grounded in the trunk by a #8 wire.  The engine is grounded via the OEM ground strap connected to the passenger side cylinder head.
Also, if you're running headers, the heat from it may be impacting the starter when the hot. 
 

Be wary of using some jumper cables, they are copper plated aluminum. . . not that good of a conductor.
I used 1/0 real welding cable from my trunk mounted battery to the starter, never had a cranking issue.
Also use 1/0 ground cable to the frame.

I used orange 50 mm2 welding cable, a bit smaller than 1/0, red and black heat shrink take care of any confusion. I like the higher strand count, flexibility and extra insulation.
 

Bearing Bob wrote:

Steve69 wrote:

Hey there

We finally got around to starting my 351w. Once I shut it off, it barely wants to roll over. It seems to crank fine when it's cold. I have a t5 and am using the starter with solenoid fastened to it, as well as the external mustang solenoid.. Has anyone else run into this? All grounds appear to be fine as I just wired everything.

 
I had the same symptoms and foolishly started changing everything, except the heavy wires on the inner fender mounted solenoid, cuz the looked great. After checking their resistance I found a bad wire. My bad cable looked pristine. YMMV.

   Ill check those wires out again.  Thanks
 

Bolted to Floor wrote:

The easy check is the timing. Too far advanced and a warm engine will make it hard to start. 

Wire insulation is something that needs to be looked at. I doubt the jumper cables are going to have a very high heat rating. The modern cars have a GXL or TXL type of insulations goods for somewhere around 250 degrees.  If you go with welding cable, pay attention to the insulation. A quick search shows 165 to 220 for temp ratings. 

You want larger cables with fine strands. They taught us in apprenticeship school that electrons flow along the surface of the strand, not through it. What never made since to me was how it got across the but splice of a termination lug!! 

I have 2/0 TXL on the car. So far, no issues with starting and I have plenty of under hood heat in the car. 

Were still working on figuring it out so Ill check out the cable insulation too.  

Thanks
Steve

 

RV6 wrote:

I had the same problem crop up during a bash trip. Start fine in the morning and struggle when hot to crank. It was the 30 year old starter getting old so I opted for a newer gear driven starter. While the gear reduction starter works, I like the speed of the old direct drive starters a lot more.
 

   We tried a couple of different mini starters and didn't make much difference.  Though they are cheaper Ebay starters too. 
 

Any update on this Steve?

I do agree with the MS fix of retarding the timing. What is your initial/static/base or whatever is called timing?

I'd forgotten (an increasing occurrence) about a fix I use for my 69 that starts just fine when cold, but struggles if I wait an hour or so to restart. It starts fine when warm of is a short amount of time between restarts. My car for whatever reason likes 18° or more of initial timing. I installed a coil switch for security several years ago. When my car is warm, but sat for an hour, if I turn off the coil, crank the ignition to get the motor turning, then turn on the coil, it fires right up.

My advice is to retard your timing, or install a coil cutoff switch.