Engine runs for 2 or 3 seconds but then

iwantacobra427 · #1 (**permalink**) 11-12-2008, 07:50 PM

stops. This is a new build (seasoned 302 block- 331 stroker, MSD 6AL ignition, AFR 185 heads, 4 barrel Holly carb). The gas pressure at the carb is 7 psi. Does it sound like the carb is not getting enough gas once the engine is running? I guess my timing is good enough since the engine is starting. I pump the pedal 3 times then hold the pedal half way down and turn the key. It'll run for 2 or 3 seconds then die... I tried putting the pedal all the way down and then starting it but that didn't help.. I think I've found the best location for the distributor through trail and error. The best result is the 2 to 3 seconds of engine run time. The initial distributor installation was done after putting the engine at TDC for No. 1 cyclinder. Then positioning the rotor to point at the No. 1 spark plug wire at the rotor cap. Any tips?? Thanks.

Tim Brewer · #2 (**permalink**) 11-12-2008, 08:54 PM

Well, first off, I'll take it that you have a chokeless carb. If so, the best starting method is to give the engine two full pumps, then try starting it with NO gas. If you try pumping or giving it gas while starting, after the first initial two good pumps, it's not going to want to start. As far as enough fuel, with the engine off and your pump on, (I'm guessing you have an electric pump), pump the carb by hand and watch to see fuel squrting into the carb. You should clearly see it squirt.

Jac Mac · #3 (**permalink**) 11-12-2008, 09:05 PM

Have you got power for ignition with the key in the on/run position, sounds like it could be running only while the key is in the start position.

payaso25 · #4 (**permalink**) 11-12-2008, 10:19 PM

I agree with Jac Mac. You have the wrong wire running from the switch to the MSD box.

Payaso25

trularin · #5 (**permalink**) 11-13-2008, 05:12 AM

I think Jac Mac has it. But it could be you have the "only while starting" side of the solinoid connected to the box. If you have a two stud solinoid, one side allows you to by-pass the coil resistor for hotter starts. The problem is it turns off once you let go of the key.

May I suggest a check of the solinoid wiring before you get deeper in.

Additionally, grounds are a big issue. Make sure yours are all making good contact.

Just my $0.02 worth.

iwantacobra427 · #6 (**permalink**) 11-13-2008, 05:30 AM

Thanks guys. I'll double check the solenoid wiring. By the way I have a mechanical fuel pump. I can see the fuel squirt in when the throttle is moved.

Clois Harlan · #7 (**permalink**) 11-13-2008, 07:44 AM

Check your wiring on your ignition key. I bet you have your red wire to the msd wired to an accessory post. Pull your ignition switch out and Turn your key on and see if the wire going to your msd box has power. I bet it doesn't.

Clois

iwantacobra427 · #8 (**permalink**) 11-13-2008, 05:53 PM

Success! You guys were right. I double checked the solenoid and neglected to connect a wire. After about two dozen tries.. she FIRED! I let it warm up then checked the timing. It was only about 4 or 6 degrees BTDC so I increased it to about 12 degrees BTDC. The MSD distributor I'm using has the blue bushing installed (21 degrees). So I figure a total timing of 33 deg (21 + 12) should work well. Also I'm using the two blue MSD springs in the rotor and the Comp Cam I'm using is a 351W based one. I had a little engine run on after I turned it off. Does that mean I have too much static timing? The rpm increased from around 900 to 1000 after I changed the timing. What do you guys think?

Dwight · #9 (**permalink**) 11-13-2008, 06:34 PM

fuel pressure should be 4.5 to 5.5 psi. I think 7 is to much.

Dwight

FWB · #10 (**permalink**) 11-14-2008, 06:49 PM

set your timing at total, meaning set timing for 36deg at some where around
2500 rpm if drivability is good and no detonation, pinging, bump up the timing
one or two more. run on could be a fuel issue. excess fuel dumping into
plenum during shut off. the 7 psi fuel pressure could be the culprit, that pressure could over power the needle and seat. put a regulator on the line
keep it under 6 psi.

Fred

Gaz64 · #11 (**permalink**) 11-15-2008, 03:33 AM

All of the above, and add an anti-dieseling solenoid to the carb, set the idle speed at whatever speed you want with the solenoid screw.
Then with the solenoid unplugged, set the idle speed with the carb speed screw to 100-150 less than with the solenoid connected.

The engine will run at the speed you choose, then the butterflys will close to the lower setting when the ignition is turned off.

Some engines are more prone than others to run-on.
Compression ratio, cam timing, chamber/piston shape are more influencing factors than base timing or fuel octane.

Too much base timing can cause slow cranking/starter kickback.