Jump to content


Photo
- - - - -

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


  • Please log in to reply
23 replies to this topic

#1 DirtnastyDatty

DirtnastyDatty

    Newbie

  • New Members
  • Pip
  • 9 posts
  • Location:Snohomish
  • Cars:Datsun 620 pickup

Posted 31 December 2017 - 09:32 PM

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

#2 racerx

racerx

    Senior Member

  • Senior Member
  • PipPipPipPipPip
  • 4,448 posts
  • Location:NorCal
  • Cars:71 Datsun 510 and 65 Mustang Fastback

Posted 31 December 2017 - 09:50 PM

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

#3 wayno

wayno

    Datsunahaulic

  • Senior Member
  • PipPipPipPipPipPipPipPipPipPip
  • 13,007 posts

Posted 31 December 2017 - 09:58 PM

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


 

 


#4 Roadster-ka

Roadster-ka

    Advanced Member

  • Members
  • PipPipPip
  • 106 posts
  • Location:Vallejo
  • Cars:71 510 wagon

Posted 31 December 2017 - 10:57 PM

Sounds lean, maybe dirt in primary jet.

#5 Stoffregen Motorsports

Stoffregen Motorsports

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 3,904 posts
  • Location:Cool, CA
  • Cars:http://www.4wdandsportutility.com/features/rover/0611_4wd_1957_range_rover/viewall.html

Posted 01 January 2018 - 09:39 AM

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



#6 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,346 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 01 January 2018 - 10:27 AM

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.


Posted Image

#7 DirtnastyDatty

DirtnastyDatty

    Newbie

  • New Members
  • Pip
  • 9 posts
  • Location:Snohomish
  • Cars:Datsun 620 pickup

Posted 01 January 2018 - 11:34 PM

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

#8 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,346 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 02 January 2018 - 05:44 AM

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.


Posted Image

#9 banzai510(hainz)

banzai510(hainz)

    L motor God

  • Senior Member
  • PipPipPipPipPipPipPipPipPipPip
  • 15,064 posts

Posted 02 January 2018 - 06:29 AM

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.


Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#10 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,346 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 02 January 2018 - 07:33 AM

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


Posted Image

#11 DirtnastyDatty

DirtnastyDatty

    Newbie

  • New Members
  • Pip
  • 9 posts
  • Location:Snohomish
  • Cars:Datsun 620 pickup

Posted 02 January 2018 - 05:02 PM

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

#12 DirtnastyDatty

DirtnastyDatty

    Newbie

  • New Members
  • Pip
  • 9 posts
  • Location:Snohomish
  • Cars:Datsun 620 pickup

Posted 02 January 2018 - 05:03 PM

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

#13 DirtnastyDatty

DirtnastyDatty

    Newbie

  • New Members
  • Pip
  • 9 posts
  • Location:Snohomish
  • Cars:Datsun 620 pickup

Posted 02 January 2018 - 05:04 PM

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?

#14 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,346 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 02 January 2018 - 05:32 PM

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


Posted Image

#15 distributorguy

distributorguy

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,137 posts
  • Location:Metropolis, MN
  • Cars:77 Datsun 620, 73 Datsun 620

Posted 03 January 2018 - 05:25 AM

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.  



#16 banzai510(hainz)

banzai510(hainz)

    L motor God

  • Senior Member
  • PipPipPipPipPipPipPipPipPipPip
  • 15,064 posts

Posted 03 January 2018 - 06:12 AM

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


Throw on some Weber sidedrafts, Rising Sun hood.... call it good

#17 Stoffregen Motorsports

Stoffregen Motorsports

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 3,904 posts
  • Location:Cool, CA
  • Cars:http://www.4wdandsportutility.com/features/rover/0611_4wd_1957_range_rover/viewall.html

Posted 03 January 2018 - 08:09 AM

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.



#18 Stoffregen Motorsports

Stoffregen Motorsports

    Datsun Mechanic

  • Senior Member
  • PipPipPipPipPip
  • 3,904 posts
  • Location:Cool, CA
  • Cars:http://www.4wdandsportutility.com/features/rover/0611_4wd_1957_range_rover/viewall.html

Posted 03 January 2018 - 08:10 AM

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.



#19 d.p

d.p

    Senior Member

  • Senior Member
  • PipPipPipPip
  • 1,028 posts
  • Location:Mid-Atlantic
  • Cars:1971 521, 2015 M3

Posted 03 January 2018 - 08:34 AM

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.  



#20 datzenmike

datzenmike

    KING RAT

  • User Administrator
  • 70,346 posts
  • Location:Vancouver Island
  • Cars:'74 710 sedan, '76 710. prevoius... '78 620, '71 521, '68 510 new '76 B-210

Posted 03 January 2018 - 08:42 PM

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.


Posted Image