Carbureted LSX forum - Hard to start when hot

Car starts fine if it has sat for a while. But if I drive it or even let it idle for 5 minutes or so it doesn't want to start back. Just spins and spins.

Any ideas? I've tried MSD grounded to block and directly to battery, no change. MSD is ran to a 50 amp Toggle switch for power. Always fires right up first time.

Almost seems carb related, but tried 2 carbs and same thing

What is your base timing set at or what is it at below 1200 rpm?

Starts 15 and ramps to 24 by 1000....

It turns over do e, just doesn't fire

What is the fuel look like? If it is too rich,you may be getting the plugs too wet to re fire.

vapor lock? how hot are your fuel lines near the carb?

Mine kinda does the same thing. Sometimes it turns right over, other times it spits back through the carb. I even went so far as buying a new cam position sensor, cause that is usually what the backfiring though the carb means.

One thing that is definitely helping is not touching the gas when hot. Just turn the key and if it doesn't fire maybe give it a half pump while cranking.

When it gets really confused then I need to hold the pedal to the floor to get it to clear.

So, would I need to let it run a bit, and when I find it not wanting to start, pull a plug and look?

Pop, that's exactly what mine's doing, sometimes I can hold it to the floor and it will fire, but not every time

If you can hold it to the floor it is getting more air and firing because of too much fuel i bet, have you checked the plugs?

Just checked a plug.

http://i172.photobucket.com/albums/w25/streetknight2/IMAG0822.jpg

I checked voltage coming into the MSD box, it has 12.28 V with switch on, but drops to 10.3 while starter is spinning. Would this have any effect or should I still be looking a carb?

What accel pump cam and nozzle size are you running? I have the pink cam and #35 nozzle with a 35 cc accel pump. It often acts like it is getting too much fuel if I pump the pedal when hot.

Do you have any type of spacer under the carb? I also wonder if it percs a bit and puts more gas in the intake when it sits while hot.

Mine does this also. Starts fine cold. But warm it up and let it sit longer than 20 minutes it starts like shit. Ive been all over with the base timing. Low and high. Just spins over. It does start after ten seconds or so. Cant figure it out.

Make sure boosters arent dripping while not running(and doing what zone is saying).

That ****** looks way rich, pull one right when it doesn't want to start as well.

The plug is not way rich the porcelain is just and I mean just on the rich sideof a good street tune. Do you have air bleeds in your idle circuit. If so maybe open them up a touch. I'd look elsewhere for your problem

are you running ethanol fuel? what carb are you running? sounds to me like you are heat soaking and dropping fuel as it sits. my elco is the same way, it fires right up when cold and sometimes has issues if its been running in the heat and sits for a while.(which is really compounded by a tired starter!)

Ok guys update time.

I had a friend come over to help, he thought by our phone conversation it was fuel related. He got there I started car, let it run 4-5 minutes and shut it off. Tried to start immediately after shutting it off and nothing.

He put screwdriver in #1 wire while I turned over and no spark. So we went back to msd. Volt meter on pink wire has 12v with switch on, but drops to 10.3 while cranking. Tried my spare 6010 box, same thing. Hooked msd directly to a separate battery so voltage couldn't drop while cranking, same thing.

He asked if I'd tried a new crank sensor, I said no. Took one out of another motor and it fired right up every time we tried it. Didn't get a chance to drive it and try start up again as my friend had came by to help trouble shoot a trans issue. Ended up having to pull the trans.

Not a definite but I think the crank sensor was it, fingers crossed anyway.

Wow, figured it would screw up every time.

Me too, I'm not saying it definitely fixed it yet, I had to pull the trans and it will take a few weeks to save to rebuild it. Won't know for sure till then

Check your float levels. Had the same issue. Turns out my carb was leaking fuel and the plugs were getting wet. Fixed the floats and haven't had an issues sense.

Just gonna update that the new crank sensor seemed to have fixed it knock on wood.

I drove the car for a while yesterday after the new rear end setup and it cranks every time.

HTH someone else and thanks for the insight guys.