Engine dieselling ??

[Rasp933]

What's up.ratssons.

So I having a bit of trouble after I installed 38/38 weber on my l18.the engine is dieselling after I turn off the ignition.never had this problem with the old carb.

I only jets I swapped ,is the   idle jets from 50 to 45s.mixture screws are 1.1/4 turn out and speed screww is at 1/2-turn in.ignition timing is at 10-12deg.my question is .is it over caburated for 1800cc ? Vacuum leaks??

Any one had this type of problem before..??

Thanks

Edited October 5, 2018 by Rasp933

[distributorguy]

If you can run moore initial advance (like 14-16),  you can close the throttle plate a little more and reduce dieseling.  Lean fuel mixture also causes it, so try setting the idle mixture up more rich - with a little lope to the idle.  Also make 1000% sure there are no manifold leaks as the smallest vacuum leak can cause hot spots and run-on.  

[datzenmike]

Yes. It's made for an engine twice the size of yours, it can work but these are some of the disadvantages of over carbing your engine.

 

The Weber can be ordered with an idle cut solenoid that shuts off fuel to the idle when the key is turned off... but that isn't an option now.

 

 

There are several things you can do including nothing. Simply hold the brake on and put in 4th or 5th, let the clutch up slightly to load the engine and turn the engine off. Engine will stall normally. When fully stopped, let the clutch up fully. Practice this a half dozen times and it will become a natural thing to do every time you stop.

 

Direct cold air to the carb inlet from in front of the radiator rather than hot air from behind. Dieseling uses the heat in the compressed air to fire the cylinder. High under hood temperatures are perfect for dieseling and run on.

 

Install a fuel return line from an L20B to provide cool gas to the Weber.

 

 

 Run on or dieseling is caused by heat. In the air the engine  or the fuel.....

 

Spark plugs wrong range (too hot) or wrong maker. Must be NGK for Datsun.

Compression too high... not much you can do here.

Engine running too hot at idle.

Too rich a mixture causing carbon deposits that hold heat and glow hot.

.

[DanielC]

Turn the idle speed down a little.

 

[datzenmike]

Indeed. Over fast idle will also do this as will a carb that is flooding.

[Stoffregen Motorsports]

I'm pretty sure you can still install an idle cut solenoid or anti dieseling solenoid on a 38/38, but I am not sure if they use one or one on each side. I do know the part number for the solenoid from Pierce is 43928.060.

 

If the idle jets have the large threads, the solenoid will fit, if it has the small idle jets, then it will not.

 

I typically do not like the 38/38 on any L series 4 cylinder.

[banzai510(hainz)]

hit the gas when you shut the key off. See if that helps.

 

what was your other carb?

 

after 72 the stock carbs had a cut off valve . Adding a Weber DGV series most dont have this  cutoff. some later do. the 32/36 EV-Ic has these and the water choke . you can tell on the 32/36 by the idle jet brass screw or holder. the main side willbe beigger than the 2nd barrel side.

I forget on the 38 38 as I had one also. but forget if it had the selinoid. I believe it did but on real hot days its would still dielsel. So I rev it up right when Im shutting the key off as the vacuum will be lower as the plates open up when motor slows down. Youll figure it out.

I had a 38/38 and loved it on a Cammed L16 with match ported intake to a L20head. Hower it was over jetted as by plugs and intake was black.

I would run water thru the car on hot days(be careful) it would clean up the valves abit and clean out the carbon.

Edited October 5, 2018 by banzai510(hainz)

[Stoffregen Motorsports]

1 hour ago, banzai510(hainz) said:

you can tell on the 32/36 by the idle jet brass screw or holder. the main side willbe beigger than the 2nd barrel side.
 

I would run water thru the car on hot days(be careful) it would clean up the valves abit and clean out the carbon.

I think the 38/38 has only one idle jet, which would make sense.

 

We used to do that water cleaning too. We called in an engine douche.

[Rasp933]

It was oem  carb progressive type

[Rasp933]

I inspected the plugs .looks like its running lean.

[banzai510(hainz)]

I hardly believe a 38/38 is running lean. But if running good learn to clutch it or try what I said on shutting t down when you rev it up. Whe you rev it your buring up the accell pump gas and hopefully when key off the motor will slow down enought not to draw(suck more gas in).

 

was the old carb bad?

Edited October 5, 2018 by banzai510(hainz)

[Rasp933]

I inspected the plugs .looks like its running lean.

[Rasp933]

Idle jets are 45s.that is probably y .

I opened another 1/4 turnvof fuel mixture screw and closed the speed screww alittle

Edited October 6, 2018 by Rasp933

[datzenmike]

9 hours ago, Rasp933 said:

I inspected the plugs .looks like its running lean.

 

The plugs will read what the engine was doing when last run. So if you drove home it's not telling you how it was when canyon carving. The best way is take your plug wrench with you and pull over safely. Plugs are self cleaning, if you have the proper heat range and type so drive for 15-20 min to burn off any deposits and get a true reading for what you have been driving. There can be a big difference between high speed full throttle and highway cruise just as idling will be different.

 

Extreme rich....... very rich.................... richer <<<<<<<<<<<< about right>>>>>>>>>> leaner... very lean... dangerously lean.

Sooty dry black... black...dark brown...brown... tan (cardboard box)........... light tan........... light............. white porcelain.

 

Never run lean. Rich is bad but lean is much worse. Full throttle lean, while lacking in power can damage the pistons. 

[Rasp933]

Got the engine running good.

95% dieselling is gone.

Cultprit was lean condition and trottle open more the 1/2 turn 

Edited October 9, 2018 by Rasp933

[datzenmike]

Gas absorbs heat when it evaporates. This cools the internal parts and reduces the diesel effect. However you may simply be running too rich just to prevent dieseling. This is not really a cure for it. Removing the fuel after shut down by using an idle cut is better or just learning to stall the engine with the clutch. 

[racerx]

Why the 38/38? Bigger does not mean better...anyway juat put it in gear when you shut it off.

[distributorguy]

Most of the time, a lean condition is due to vacuum leaks from loose fitting vacuum hoses, loose hardware, bad gaskets, blown vac unit on the distributor, failed check valve on the brake master, etc...   Re-jetting lean is also a cause, along with the float height being set too low.  Good job fixing it.  What did you change?  

[Rasp933]

I even added a fuel pressure regulator.swapped the idle jets to 50s.advanced the timing to 14btdc and closed abit of speed screw.idle set at 750-800 rpm.runs good 

Edited October 9, 2018 by Rasp933

[Rasp933]

Speed screw shouldn't be more then 1/2 turn in.thats what I was told my redline weber tech

Edited October 9, 2018 by Rasp933

[Rasp933]

On 10/5/2018 at 4:54 AM, distributorguy said:

If you can run moore initial advance (like 14-16),  you can close the throttle plate a little more and reduce dieseling.  Lean fuel mixture also causes it, so try setting the idle mixture up more rich - with a little lope to the idle.  Also make 1000% sure there are no manifold leaks as the smallest vacuum leak can cause hot spots and run-on.  

Thanks for responding

Thats what exactly what I was told by redline weber tech.

Thanks

[racerx]

What you just run it on ttl advance?

[tr8er]

I just pull the choke right before shutoff.  Works well.  

[datzenmike]

On 10/5/2018 at 6:09 AM, datzenmike said:

 

 

There are several things you can do including nothing. Simply hold the brake on and put in 4th or 5th, let the clutch up slightly to load the engine and turn the engine off. Engine will stall normally. When fully stopped, let the clutch up fully. Practice this a half dozen times and it will become a natural thing to do every time you stop.

 

 

.

 

[distributorguy]

The better solution is to tune away the problem before it leaves you with burned valves.  Turning your gas motor into a diesel clearly is a sign of a problem.   

 

I find that if your idle mixture screws are set betweeen 3/4 - 1 1/2 turns out when slow idling (under 650 rpm), then you can actually tune the entire range more precisely.  Some people will push the idle up to 800+ then tune the mixture, but what you're really tuning at that point is the emulsions tubes.  This becomes problematic when you get higher in the rpm range and are trying to get your mains and air correctors properly tuned.  You'll tend to go lean more easily - in a difficult way to control - because you've been falsely bolstering the main jets with the idle jets.  The ratio is inconsistent, so you "run out" of emulsion tubes and the mixture shifts lean where it shouldn't.  

Edited October 13, 2018 by distributorguy