3pg...loss of power/backfire

yellowhorse7 · 03-12-2011, 12:57 PM

Okay-

Some of you may have read my other thread regarding my 1989 Marathon project. Now that is close to being finished it's giving me a booger of a time. Here's what has been done:

Brand new top end (complete), new crank seals, new crank bearings, etc. Piston was installed correct with the hole towards the rear. Also converted to HEI and put on a slightly bigger carb (BV-21) as mine was cracked. The idle screw was backed out 2 turns from seated. Seemed to have good spark as well. While the cart was on jack stands I went ahead and mixed up some break-in gas and decided to fire it up. Cranked for about 20 seconds and came to life. Ran like crap but I figured that it would being recently rebuilt until it was broke in and the rings were seated. Let me also say that the muffler was "grilled" 2 seasons ago as well.

This morning I took it down and fired it up. Had to choke it a bit as it came to life but ran like crap. Put it in reverse as well and while it accelerates slightly better, it still runs awful. It seems to have a bit of popping and backfiring through the exhaust in forward, which leads me to believe something is up with the pulsar coil. I did mark the position of the coil as I disassembled the motor and thought I put it back correctly. The more that I drive it the worse that it runs. I played with the carb (the one adjustment) and it really didn't help.

Any ideas guys? Fuel pump seems to flow fine with no visible leaks. Spark seems strong. The timing is the only thing that seems left. I will say that before the overhaul it ran pretty good, just down on power from being, well, old. The pulsar and the fuel pump are original pieces that I did not replace. Anny help is appreciated.

DOOmsman · 03-12-2011, 01:05 PM

Piston was installed correct with the hole towards the rear
To the rear?? as the exhaust side??

yellowhorse7 · 03-12-2011, 01:18 PM

"F" on piston towards the flywheel side and holes in piston towards the reed assembly. Per the service manual. I assume that the motor needs to come out to replace the pulsar anyway (if thats it) and I will double check the piston. I thought the motor would barely start if the piston was in wrong??

DOOmsman · 03-12-2011, 01:24 PM

Sounds like you have it right.
After running a while((under load)) what does the spark plug
look like, is it wet?

yellowhorse7 · 03-12-2011, 01:39 PM

Plug is black and dry. Definitely fouled. I will replace and see if it helps. I imagine it will help some

Dave Box · 03-12-2011, 07:05 PM

It could be so many things but if the plug is dry, black and fouled that sounds like it is running very rich. I would try running it a short while with the air filter and assembly removed. This will lean up the mixture and indicate if it is mixture related.
Dave

yellowhorse7 · 03-12-2011, 10:05 PM

Quote:

Originally Posted by Dave Box

It could be so many things but if the plug is dry, black and fouled that sounds like it is running very rich. I would try running it a short while with the air filter and assembly removed. This will lean up the mixture and indicate if it is mixture related.
Dave

Will do. Thx Dave

madoc1 · 03-13-2011, 09:37 AM

try reversing the red and blue pulsar wires to the coil.

yellowhorse7 · 03-13-2011, 09:17 PM

Quote:

Originally Posted by madoc1

try reversing the red and blue pulsar wires to the coil.

Big thanks to you sir! This was in fact my issue. Well, kind of. I'll explain....

I looked at the diagram that is floating around on this site outlining the HEI wiring diagram. I did in fact follow it exactly as it says. The ignition coil wires were hooked up correctly. I looked at the red and blue wires coming from the pulsar to the HEI module. I then, for the hell of it, switched these wires (doing the reverse of the diagram) and presto....all systems go! Switched back to confirm and back to the same issue.

I've seen a lot of HEI modules and 95% of them are marked the same. I don't want to be quick to blame the diagram and say that it was wrong. Maybe I had an ignition module that fell in the 5%. Either way, everything seems good to go. I set the governor, checked all the throttle linkage and nut and bolted the entire cart. So far so good. It's funny how I've been building hot rods and race cars for 15 years, transmissions, motors, everything. But this damb little 2 stroker has given me more fits than I care to admit. Thanks for everyone's help

EZ-GoingJon · 03-13-2011, 10:03 PM

RIGHT ON!! Is the HEI mod a good thing to do for better performance, or is it just another way to do it other than OEM parts and prices?

03-12-2011, 12:57 PM	#1
yellowhorse7 Not Yet Wild Join Date: Apr 2009 Location: Bolingbrook, IL Posts: 68	3pg...loss of power/backfire Okay- Some of you may have read my other thread regarding my 1989 Marathon project. Now that is close to being finished it's giving me a booger of a time. Here's what has been done: Brand new top end (complete), new crank seals, new crank bearings, etc. Piston was installed correct with the hole towards the rear. Also converted to HEI and put on a slightly bigger carb (BV-21) as mine was cracked. The idle screw was backed out 2 turns from seated. Seemed to have good spark as well. While the cart was on jack stands I went ahead and mixed up some break-in gas and decided to fire it up. Cranked for about 20 seconds and came to life. Ran like crap but I figured that it would being recently rebuilt until it was broke in and the rings were seated. Let me also say that the muffler was "grilled" 2 seasons ago as well. This morning I took it down and fired it up. Had to choke it a bit as it came to life but ran like crap. Put it in reverse as well and while it accelerates slightly better, it still runs awful. It seems to have a bit of popping and backfiring through the exhaust in forward, which leads me to believe something is up with the pulsar coil. I did mark the position of the coil as I disassembled the motor and thought I put it back correctly. The more that I drive it the worse that it runs. I played with the carb (the one adjustment) and it really didn't help. Any ideas guys? Fuel pump seems to flow fine with no visible leaks. Spark seems strong. The timing is the only thing that seems left. I will say that before the overhaul it ran pretty good, just down on power from being, well, old. The pulsar and the fuel pump are original pieces that I did not replace. Anny help is appreciated.

03-12-2011, 01:05 PM	#2
DOOmsman Gone Wild Join Date: Jul 2008 Location: Reddick IL Posts: 11,220	Re: 3pg...loss of power/backfire Piston was installed correct with the hole towards the rear To the rear?? as the exhaust side??

03-12-2011, 01:18 PM	#3
yellowhorse7 Not Yet Wild Join Date: Apr 2009 Location: Bolingbrook, IL Posts: 68	Re: 3pg...loss of power/backfire "F" on piston towards the flywheel side and holes in piston towards the reed assembly. Per the service manual. I assume that the motor needs to come out to replace the pulsar anyway (if thats it) and I will double check the piston. I thought the motor would barely start if the piston was in wrong??

03-12-2011, 01:24 PM	#4
DOOmsman Gone Wild Join Date: Jul 2008 Location: Reddick IL Posts: 11,220	Re: 3pg...loss of power/backfire Sounds like you have it right. After running a while((under load)) what does the spark plug look like, is it wet?

03-12-2011, 01:39 PM	#5
yellowhorse7 Not Yet Wild Join Date: Apr 2009 Location: Bolingbrook, IL Posts: 68	Re: 3pg...loss of power/backfire Plug is black and dry. Definitely fouled. I will replace and see if it helps. I imagine it will help some

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03-12-2011, 07:05 PM	#6
Dave Box Respect the Cart Join Date: May 2010 Location: Rocky Mount, Virginia Posts: 2,190	Re: 3pg...loss of power/backfire It could be so many things but if the plug is dry, black and fouled that sounds like it is running very rich. I would try running it a short while with the air filter and assembly removed. This will lean up the mixture and indicate if it is mixture related. Dave

03-13-2011, 09:37 AM	#8
madoc1 no clue Join Date: Sep 2009 Location: spicewood, texas Posts: 3,308	Re: 3pg...loss of power/backfire try reversing the red and blue pulsar wires to the coil.

03-13-2011, 10:03 PM	#10
EZ-GoingJon Gone Wild Join Date: Nov 2010 Location: Wichita, KS Posts: 381	Re: 3pg...loss of power/backfire RIGHT ON!! Is the HEI mod a good thing to do for better performance, or is it just another way to do it other than OEM parts and prices?

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