L16 running really rough at mid rpms but stops when under load

[DirtnastyDatty]

So I noticed this about a few weeks ago and still runs fine but around mid rpms or so, it seems like it wants to cut out, idles just fine, and high rpms are usually okay and under load it doesn't do it, but as soon as it's under no load it almost sounds like it's running out of fuel. I'm not good at diagnosing things like this, the carb I'm running is a weber 32/36 and I have a pertronix electronic ignition system. Anything helps, thanks

[racerx]

U check ur fuel filter? Is the fuel tank clean?

[wayno]

What happens when you give it pedal when it feels like it is cutting out?

[Roadster-ka]

Sounds lean, maybe dirt in primary jet.

[Stoffregen Motorsports]

Have you looked down the barrel to see if it squirts fuel?

[datzenmike]

So I noticed this about a few weeks ago and still runs fine but around mid rpms or so, it seems like it wants to cut out, idles just fine, and high rpms are usually okay and under load it doesn't do it, but as soon as it's under no load it almost sounds like it's running out of fuel. I'm not good at diagnosing things like this, the carb I'm running is a weber 32/36 and I have a pertronix electronic ignition system. Anything helps, thanks

 

First and foremost!! Are you using NGK plugs????????? BP6ES ??? Wrong make and heat ranges change everything.

 

 

Sounds like a carb problem.There's a saying that 20% of all carb problems are electrical and 20% of all electrical problems are carb. Just to be sure that it isn't an electrical problem check all electrical wires to the ballast, coil and distributor. With pertronix or points... is the distributor firmly grounded??? At idle and heavy load the engine may be twisting or positioned in it mounts such that everything works but at light throttle vibration may be causing an intermittent connection. Inspect*/clean the plugs. Both suggestions cost nothing to do.

 

*Plugs can be 'read' and are a good indication of the fuel mixtures coming from the carb.

Take your plug wrench with you and go for a drive at the speed the miss happens at. After 5 min or so pull over and remove the plugs. Plugs that ar clean and light tan or brown in color have a goos fuel/air mix and the carb is doing it's job. Black and dry sooty is over rich. This is carbon, which is a conductor that may be leaking the spark to ground and causing a miss. Black and wet/oily is... oil... and this fouling can also cause a miss fire. Very light or white porcelain is indicative of a very lean mixture. Lean mixtures are very hard to ignite. I've had a partly blocked primary jet and it runs normally until the demand for more fuel to mix with the increased air can't be supplied, and then power drops off, the engine can't rev higher and the gas pedal goes to the floor. The engine just makes a loud moaning sound.  If you can get it into the secondary it will pick up and continue to rev.

[DirtnastyDatty]

Fuel filter looks fine to me, and the carb is only a few months old but it could still be the issue, I know my first few months of driving my timing was off and for a week it was so retarded it would backfire after letting off the gas every time at 50mph, so that could've messed up the carb? But I'll check everything else, looks like there's a little nub to put a fast on for a ground on the new distributors vacuum advance and it's not hooked up. I do need new rings as there are traces of oil on my spark plugs but I didn't think that would cause this issue at a certain rpm only under no load, has been a while since I checked the plugs but I'll go through the checklist and let you guys know

[datzenmike]

Won't be the filter because under much higher fuel demand like full throttle you said it runs ok.

 

A backfire out the exhaust won't but if up through the carb most certainly it could.

 

Usually the distributor grounds through the case and mounting bolts but an extra dedicated ground is never a bad idea. It is vital that it be well grounded for the coil to ground through.

 

Plugs are normally self cleaning and light throttle may foul them up if burning oil or the mixture isn't right. Full throttle may clean them off temporarily.

[banzai510(hainz)]

buy a timming light!!!!!!!!!!!!! what the timming sert at

 

how about getting a new fuel filter anyways

 

ck the valve lash.

 

 

I assume the Pertronix still have the stock ballast resisitor and stock coil.

 

 

why you dont have th vaccum adv hooked up? Not that its the proplem.

[datzenmike]

Missed that. Vacuum advance has a huge impact on mid range throttle response.

[DirtnastyDatty]

The vacuum advance is set up, there's just that nub that looks like it could be for a ground sticming off of it, and I do have a timing light, it's set at about 9 degrees advance at idle, it ran fine for about 2 weeks after I put in the new ignition but after that is when it started acting up at mid rpms under no load. Plugs are new-ish, only a few hundred miles on them and they look healthy, valve lash though, quick rundown on what that exactly is? Heard the term but hearing it again would definitely help freshen my knowledge

[DirtnastyDatty]

Also, does the coil need to be grounded to the chassis well? Or just to the distributor

[DirtnastyDatty]

One more thing, it was backfiring out the carb when it was backfiring, shot out bits of the filter and everything so could that have messed up some stuff internally?

[datzenmike]

The '73 timing is 5 degrees so you are almost twice what you need. Dial it back before bothering with anything else.

[distributorguy]

Don't listen to Mike on timing.  Its based on how much timing is in the distributor AND the fuel quality.  8-12 BTDC is likely where it'll run its best.  Your plugs are good too.  

 

Your symptoms - popping/surging with no load is typically a vacuum leak.  I'd start with the manifold gasket and move up from there.  Do you have an open port on the manifold?  If it always happens at the same rpm AND during acceleration, it could be plugged emulsion tubes, but that's only likely at 1200-2200 rpm, and it would have a bad hesitation off idle.  

 

Did you switch to a 3 Ohm coil being fed with a full alternator voltage when you installed the Pertronix?  If not, you may be having early signs of a Pertronix failure.  

[banzai510(hainz)]

I mentioned the Pertronix needs the stock coil and ballast(3.2 ohms total is the stock set up)

 

 

Most kids buy a low ohm coil in there(LOOKS COOL) and maybe take out the ballast resisitor results the Pertronix(unilites also) will pop. 

 

 

this is a simple fix

[Stoffregen Motorsports]

One more thing, it was backfiring out the carb when it was backfiring, shot out bits of the filter and everything so could that have messed up some stuff internally?

I asked earlier if the accelerator pump was working. When you look down the barrel of the carb, can you see fuel squirting when you twist the throttle?

 

It sounds like a lean surge or miss to me.

[Stoffregen Motorsports]

The '73 timing is 5 degrees so you are almost twice what you need. Dial it back before bothering with anything else.

5 degrees is stock. Stock is no where near optimal.

[d.p]

Man I struggled with my L16 and the same weber 32/36 carb, switched the dual points to pertronix, replaced plugs, wires and coil as well.  Ran ok at first but then started having issues again.  In the end I warrantied the carb (bought it from webercarbsdirect) and haven't had any problems since then.  BUT haven't driven it all that much so who knows.  

[datzenmike]

5 degrees is stock. Stock is no where near optimal.

 

I have the '73 FSM and it specifies 5 degrees. I would have thought 12 like the L20B.

 

I've run more than the factory timing in an engine before and spun a rod bearing.

[racerx]

Prolly cab advance a couple before it pings, so maybe 7 or 8 degrees.

[banzai510(hainz)]

goes up hill in 3rd w/o pinging then its good.

 

I have never ran 5 degs my self most mine are above 10deg 12

[G8KeaPoR]

The vacuum advance is set up, there's just that nub that looks like it could be for a ground sticming off of it, and I do have a timing light, it's set at about 9 degrees advance at idle, it ran fine for about 2 weeks after I put in the new ignition but after that is when it started acting up at mid rpms under no load. Plugs are new-ish, only a few hundred miles on them and they look healthy, valve lash though, quick rundown on what that exactly is? Heard the term but hearing it again would definitely help freshen my knowledge

 

My two cents.  I would go back to the last thing you did as your source of problem.  In your case that sounds like ignition and as with all things electrical the disturbing of these connections usually only leads to problems.  The same can be said for vacuum lines too. 

 

1 cent:  Verify that you have no vacuum leaks with a gauge under.  If you do have a leak (low vacuum) then you need to find it.  Spraying starter fluid around the manifold gasket works great.  if the idle increases then there you go.  If none of the gaskets cause a surge in idle check your lines.  If you don't have a leak then pull out your multi meter set it to Ohms and check the resistance on all aspects of the ignition system.  You should be able to get acceptable resistance ranges from the manual.

If any of those are at the edge or outside the acceptable range then they need replaced.

 

 

2 cent:  That said though from your posts it sounds like you have a bunch of other issues with the engine and personally I would say take care of all of your other known issues before you start making upgrades to the engine as you're only going to end up pissing away money in the end.  It sure makes troubleshooting a lot easier (way less messy and frustrating.) when you have taken care of all your obvious problems like leaky seals etc first.

[nl320what]

It does sound like a vacuum leak in or around the carb and intake, symptom during cruise only.

 

I second trying to spray around that area carefully with Carb Cleaner, I hate the exhaust being right there for risk of fire be carefull.