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Sat Jun 22, 2013 9:08 pm

Ok so today I was riding my dune buggy on and off all day and it was acting weird all day. Usually it backfires quietly at idle but today it would randomly backfire VERY loudly at idle or at lower engine speeds. It would happen a lot for like 10 minutes then I would shut it off for like 10 minutes and start it up, and it didn't do it anymore. This would happen on and off all day. Then later on it started to sputter and backfire when I would try to accelerate. Then I lost a cylinder. What I mean by this is one of the cylinders stopped firing. I have no idea what caused this but I am certain that it is something electrical. I took a temperature gun and put it on all of the exhaust manifolds and they all read around 500 to 600 except for cylinder 1, which read about 190. I took the spark plug out of cylinder 1 and cleaned it and put it back in and it ran on all 4 cylinders and ran normally for like 30 minutes and then it started to backfire loudly again and sputter and then it only ran on 3 cylinders. I drove it home and it sounded like the 1st cylinder was turning on and off every now and then. I got home and took the spark plug out of the 1st cylinder and grounded it and cranked it over and it sparked normally but I couldn't tell if it sparked every time it was supposed to. I took the spark plug out again and cleaned it and it still ran on 3 cylinders. I know it is number 1 cylinder not firing. I took the spark plug wire off of the number 1 cylinder and it didn't change it much. When I put it back on every time, the engine would speed up for a second, then continue to run on 3 cylinders. After running it for like 5 minutes on 3 cylinders, it seemed to run on 4 cylinders on and off at idle, and when I tried to rev it up, it would become very rough and switch to 3 cylinders. I have no idea what is causing this but the only reasonable explanation is something electrical. Does anybody have any ideas on what might be causing this? I am clueless and need it fixed in 2 days because I have a big trail ride on that day. Thanks

Sat Jun 22, 2013 9:29 pm

Swap the spark plug wire for the one with the closest match in length.
If you have a problem with the cylinder that you put that wire on then the plug wire is bad. Check your points/point gap. If you have dual carbs that are two barrel units, pull the idle jet for cyl 1 and clean it. Hard to give much advice without more info.

Sat Jun 22, 2013 9:30 pm

Swap #1 and #2 ignition wires and see of problem moves....

Swap #1 and #2 spark plug and see if problem moves...

Check distributor cap for crack near #1 tower....

What is carburetor configuration.... Single, duals?.... How about checking for vacuum leak at manifold if you have DP head...

Dale

Sat Jun 22, 2013 9:41 pm

was the spark plug carbon or oil fouled? oil fouled could mean a bad ring and carbon means the engine is running rich or building up carbon. what brand plugs? i switched from bosch to NGK B5HS which helped with plug fouling. would not hurt to gauge valves (loose valves will not let out all the exhaust from the cylinder after firing and cause carbon build up), timing is next (electronic or points) electronic can fail weird and points might not be gapped correctly or loose cause bad timing on spark. could be a bad spark plug wire (grounding out) or maybe a corroded contact on the inside of the distributor cap. what carb do you have? single or dual? icing of the intake can cause the gas not to vaporize which can cause a fouling effect. a clogged jet on a dual two barrel like a weber can seam like a fouled plug but not getting correct fuel.

Sat Jun 22, 2013 11:04 pm

I have a weber progressive carb, a 009 with electronic ignition and a Pertronix high performance coil. I will try to do these things tomorrow. Does anyone think it might be the valves? To me it does not seem very likely. It always backfired through the exhaust and never the intake. There is no leak at the intake manifold and valves were adjusted 3 months ago. There is no crack on the distributor cap and it appears that all of the contacts have some corrosion which is weird because the cap is only 4 months old. So are the wires and the coil and the plugs are 6 months old.

Sun Jun 23, 2013 6:29 am

Just because you did something 3 moths ago (adjust valves) does not mean something has not changed.... You could have failed to tighten lock nut on adjuster and now adjustment has changed.... Never trust previous work even if you did it....

If you are worried about actual cylinder/valve problem a leak down test or compression test will go a long way to tell you how internals are....

Any corrosion on anything electrical (even distributor cap) is your enemy....

Dale

Sun Jun 23, 2013 11:57 am

Being that it's not a huge process, ya might try taking the valve cover off and looking it over.
Every once in a while a broken spring washer on the rocker shaft will cause exactly what you're talking about.

Sun Jun 23, 2013 1:57 pm

Well I switched the plug wires and number 1 cylinder was still not firing. I then took the distributor cap off and cleaned the corrosion off of all the contacts and still no luck. Then I took the number 1 plug wire and held it about a half inch away from its port on the distributor cap. Now this is where it gets weird. When the wire is plugged all the way in, it runs off and on on 3 cylinders, but when I hold it about a half inch away from its port, the spark arcs and the engine runs on 4 cylinders all the time and I think it even ran a little better than before when it ran on 4 cylinders. What would cause this? Then I switched the number 1 and 2 cylinder spark plugs out and then cylinder 2 wasn't firing. So now I know that it is the plugs not firing. I will have to pick up some new ones tomorrow. The plugs are only like 8 months old so I don't know why it went bad. I cleaned it off and it looks brand new. Could it just be a faulty plug? I looked at the valves and they all are ok. I couldn't adjust them or measure the gaps because the engine was hot. Also just a random question how hot should the exhaust manifold be right where it exits the cylinder when the engine is running? What I really want to know is why did the engine run perfectly when the plug wire wasn't plugged all the way in? Thanks

Sun Jun 23, 2013 2:10 pm

If one went, there's a chance that all 4 plugs are marginal... I'd just replace the cap, rotor, wires and plugs just to be on the safe side. Then again, I'm the guy that carries an extra ignition system in a box behind the seat...

Mon Jun 24, 2013 2:12 pm

Got new plugs today and runs on all 4 cylinders :D :D