a little info just in case

[doublopr0]

A while ago i posted on here looking for help about my 510 which was having some trouble, i fixed the problem, and i thought i might share my experience for future reference for others.

Anyway the story goes, I was continuously having problems w/ engine(L18 w/ dual su carbs), and I couldn't seem to figure out what it was. The problem looked like this...it would start kinda slow/rough, like a lawn mower. After warming it up it idled decent, however i could hear small pops coming from the muffler, like a miniature miss inside the engine but nothing more than just a notably abnormal noise coming from a muffler.

So it idled fine, when i drove it out it would run no prob, except for a slight loss of power over all. After about 10-15 mins of driving, it would backfire and the engine felt like it locked up, it's kind of hard to describe apart from that. Then after coasting in gear for about a second(normally on the freeway) there would be a huge explosion in the pipe and the engine would start up again. Or if i was on the streets the engine would do the same thing and shut off. Then when i tried to restart it, it would turn over but there was no ignition. After letting it sit for about 30 seconds, it would start right back up again then the process would repeat again.

I went around like a chicken w/ it's head cut off changing everything i thought it would be...coil, spark plug wires, dizzy cap and rotor, fuel pump. I even tried adjusting my carburetors more lean thinking that it was the fuel mixture that was flooding the engine. all to no avail. I finally took it in to my mechanic...He tells me it could be the ignition module...i found one on ebay that fit the dizzy model i have on my engine(electronic dizzy from a 1980 720 pickup), not cheap stuff, modules are outrageously expensive, but i found one nevertheless. He did a compression check and low and behold, im running on 2 cylinders! zero compression in the 2 & 3 cylinders. Culprit?...blown head gasket because i was running a high compression head on my L18, whether because i didn't tighten the head bolts after i broke in the engine or simply because the gasket couldn't handle it.

So, I got a new normal head on the car this time, i don't want anymore problems, but turns out that it was the module that was giving me the majority of my trouble. Hopefully this may help someone to brainstorm some possible routes for someone experiencing the same problems.

[Byron510]

Thanks for sharing your experience.

I missed your first post, but I am well aware of a very old (and most often true) adage; '99% of all carburetor problems are in the ignition'.

Reading through your experience, there is one thing that comes to mind that strikes a chord – and that’s the part where the car suddenly cuts out for a few seconds and then starts to work, igniting that beautifully perfect mixed, heated mass of fuel and oxygen all sitting in the exhaust pipe – BANG!
I split two mufflers in half (the second one was one day old) with this same scenario as a teen in my very first lime green ’73 2 door. Finally found the problem; bad connection on that little metal clip bolted to the coil that the factory spade connector clips on.

I had spent a month turning the carb (likely just screwed it up worse with my total lack of knowledge as a 16 year old), changed the cap/rotor/ wires and plugs….yep back to that old adage, and now I can never forget it! A lesson well learned and I’ll bet we are not the only ones that can tell a similar story

Byron

[doublopr0]

yes now that you reminded me I had already blown off one of my mufflers about 2 months before. I was on the freeway and bang! Then i see my muffler sliding behind me in the rearview. I must say though, i was tempted to leave it like that, nothing like headers to a straight pipe.