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View Full Version : Well I thought it was a fuel problem but now I'm leaning towards electrical....ughhh


dewdude007
06-27-2009, 07:30 PM
I have a 79 S&S with a 351w. So after running for a bit, oh anywhere from 10-30 mins, the engine will bog down from 4k+ to 2k and then try to surge back up repeating the process. I have tried to fix this issue by cleaning the screens, replaced the filter, blew out the lines (funny story about getting pressurized gas in the eyes...), replaced the carb (holley 4160) and the fuel pump. After nearly rebuilding the entire fuel system this problem still persists. It seems the longer I run it, the worse it gets. It finally died at one point and wouldn't start for at least 10min+. It seemed like the carb/fuel pump wasn't keeping up with the fuel need. Well that's obviously not it at this point. Now I'm suspicious of the electrical system. The ignition system was upgraded from points. I was thinking random sensors but I'm also thinking it could be the distributor. Anybody have ideas?

TMCNo1
06-27-2009, 08:15 PM
I have a 79 S&S with a 351w. So after running for a bit, oh anywhere from 10-30 mins, the engine will bog down from 4k+ to 2k and then try to surge back up repeating the process. I have tried to fix this issue by cleaning the screens, replaced the filter, blew out the lines (funny story about getting pressurized gas in the eyes...), replaced the carb (holley 4160) and the fuel pump. After nearly rebuilding the entire fuel system this problem still persists. It seems the longer I run it, the worse it gets. It finally died at one point and wouldn't start for at least 10min+. It seemed like the carb/fuel pump wasn't keeping up with the fuel need. Well that's obviously not it at this point. Now I'm suspicious of the electrical system. The ignition system was upgraded from points. I was thinking random sensors but I'm also thinking it could be the distributor. Anybody have ideas?

Check the springs and weights in the distributor and be sure they are clean and well lubricated and the timing is near 6 degrees BTDC.
48774

dewdude007
06-28-2009, 08:01 PM
Actually I'm going after the distrib tomorrow. I'm just waiting for the cap and rotor to come in. I replaced the coil and wires today plus cleaned up the cap which slightly changed the problem. Now instead of surging, it loses power and dies...

JimN
06-28-2009, 08:13 PM
I have a 79 S&S with a 351w. So after running for a bit, oh anywhere from 10-30 mins, the engine will bog down from 4k+ to 2k and then try to surge back up repeating the process. I have tried to fix this issue by cleaning the screens, replaced the filter, blew out the lines (funny story about getting pressurized gas in the eyes...), replaced the carb (holley 4160) and the fuel pump. After nearly rebuilding the entire fuel system this problem still persists. It seems the longer I run it, the worse it gets. It finally died at one point and wouldn't start for at least 10min+. It seemed like the carb/fuel pump wasn't keeping up with the fuel need. Well that's obviously not it at this point. Now I'm suspicious of the electrical system. The ignition system was upgraded from points. I was thinking random sensors but I'm also thinking it could be the distributor. Anybody have ideas?

You don't have enough sensors to call any of them 'random' and none will do anything to kill the motor, other than the tach lead grounding out. The temperature sensor is just a thermally variable resistor, just like any other temp sensor. If it bogs again, make sure you have a small bottle with gas in it so you can add some to what's already going in. If it helps, you have a lean mix issue and if it kills, it's already rich.

Make sure the pickup in the distributor isn't loose, rubbing or too far from the cam on the shaft.

stars-stripes08
06-29-2009, 04:39 PM
when it dies does it still not start for 10 minutes? if so check and see if you have spark. if there is spark It is likely then that it is not a spark problem i.e coil etc. Hard to believe that it would be a timing issue causing it to die and not restart for ten minutes, I could see it being a timing issue causing it to bog but the restart for 10 minutes is where I am having difficulty. Have you inspected the fuel line from the tank to the fuel pump? I have seen these rubber lines get old and soft and actually get collapsed under the normal fuel pump vac.

JimN
06-29-2009, 05:36 PM
Actually I'm going after the distrib tomorrow. I'm just waiting for the cap and rotor to come in. I replaced the coil and wires today plus cleaned up the cap which slightly changed the problem. Now instead of surging, it loses power and dies...

Make sure the wire from the coil to the cap is good- as I just posted in another thread, I have had many wire sets that came with a bad coil wire. I don't know why, but after 3-4 bad ones, I just started to stock extras. You can use any kind of wire to verify this, just stick it in the coil and cap and try it.

dewdude007
06-30-2009, 12:08 AM
Well I'll give ya an update. I cleaned up the contact points in the distrib, replaced the coil and plug wires, and replaced all the old fuel line. I managed to change the problem slightly. Now it no longer surges but instead it will cruise at 4k for a bit and then lose power until it kills. The cruising time before it dies is pretty consistent, roughly 5 mins or so. Then it won't start for several minutes. My best guess is that my messing with the distrib cause this change. After Orielly's messed up my distrib cap and rotor order, I'm now a couple of days behind in parts. I took apart the distrib and found that there are only 7 magnets and the lower collar of the rotor (I'm not positive but since there are 8 slots I figured 8 magnets). Also one spring on the weight system needs to be replaced (it looked pretty stretched). At the moment I'm looking for a whole new distrib kit because whoever did the conversion didn't do a very good job.

dewdude007
06-30-2009, 12:09 AM
Oh yeah, I did check to see if there was spark. When it died there still seemed to be spark. I had my buddy look because I just don't like that shock much... :)

Bellinghamster
06-30-2009, 10:08 AM
Since it runs and dies the symptom sounds like fuel starvation - next time it dies, immediately pull the carb flame arrestor and look down the throat while you open the throttle (engine not running). If you see fuel squirt in from the accelerator pump you've got fuel in the float bowls. If no fuel in the bowls: It sounds like you've been through the fuel system pretty thouroughly from tank to intake manifold... but did you check the pickup tube in the tank? I've heard several stories about a bit of rag (dirt, wood, gunk) that would get sucked into/onto the end of the pickup tube in the tank and cause fuel starvation. If you blew out lines probably blew out the pickup, but a cracked or loose pickup tube that lets air in will cause havoc and frustration as pumps and floats don't deal well with aerated fuel. Another trick I've used is to disconnect the fuel line at the carb and connect an electric pump with a clear hose on the output. Run the pump dumping into a bucket and watch for bubbles or reduced flow (*no smoking!*). A quart per minute is an est. minimum. If air or insufficient flow, move the electric pump to the other side of the next component (i.e. engine fuel pump, fuel filter, etc.) working your way toward the tank, ending with pulling directly from the tank pickup tube... process of elimination.

I think you mentioned you checked that you had spark right after it dies and before it would start again, right? (see for yourself... I've spent too much time chasing the wrong thing based on erronious information) If fuel but no spark, but spark returns after cool-down, look at a possibly faulty breakerless ignition module, or a bad coil. (I've had two coils on vehicles that would short internally after heating up, but work again after cooling down). The mention of a shorting tach wire was a good one. Disconnect the tach lead from the coil and see if the problem goes away.

Bellinghamster
06-30-2009, 10:11 AM
There are other ways to check for spark than holding the end of the wire, although that method is pretty conclusive! :shocked:

dewdude007
07-06-2009, 10:24 PM
I thought I'd give you guys an update. Originally I began this repair with blowing out the lines and replacing the filter. When that did nothing, I replaced the fuel pump, carb, lines, coil, and the distributor. The lines and distrib needed to be replaced. Whoever did the electronic conversion was an idiot that did a p*ss poor job at best. However, none of these things fixed the problem. Out of curiosity I looked at the tank again and found the check valve on the tank. There was a lot of pressure when I sucked on it (removed from the tank). I attached my buddy's fishing boat tank and it ran like a champ. Several hundred dollars later I found a bad check valve; $1.50 at Ace.