L16 stock carb: Will idle, bogs/cuts out when driven

[hessianben]

L16 with stock carb:

After doing a basic clean of the visible surfaces with carb cleaner, and removing the adjustment screw/needle and spraying carb cleaner in the opening, it will now idle when warm. I can also rev it in neutral with minimal hesitation. However, when I attempt to put it in gear and drive it, it bogs hard and won't rev at all. I can fan the clutch and limp it around, but as soon as I fully engage the clutch, it wants to die.

I have been doing searches for tutorials on carb adjustments, but perhaps someone can narrow down what I need to focus on.

Not back firing, just cuts out.

too rich?

(newb question: when I turn the screw clockwise- is that lean or rich?)

 

Thanks!

[datzenmike]

Clockwise is leaner. The idle adjustment won't affect off idle driving. It fine adjusts the idle mixture, period.

 

With engine off, remove the air filter and pump the throttle by hand while looking down the primary throttle bore (closest to the valve cover) You should see a strong squirt of raw fuel from the accelerator pump. If it is weak or not there, it will cause a bog or bad stumble as you take off in gear. This is because when the throttle is opened there isn't enough fuel provided by the idle circuit for all the extra air pulled in.

 

Because the engine is just above idle there isn't much air flowing through the primary venturi to cause enough vacuum to draw in fuel from the fuel bowl. The accelerator pump squirts gas directly into the carb and helps the transition from idle to primary running.

[hessianben]

Clockwise is leaner. The idle adjustment won't affect off idle driving. It fine adjusts the idle mixture, period.

 

With engine off, remove the air filter and pump the throttle by hand while looking down the primary throttle bore (closest to the valve cover) You should see a strong squirt of raw fuel from the accelerator pump. If it is weak or not there, it will cause a bog or bad stumble as you take off in gear. This is because when the throttle is opened there isn't enough fuel provided by the idle circuit for all the extra air pulled in.

 

Because the engine is just above idle there isn't much air flowing through the primary venturi to cause enough vacuum to draw in fuel from the fuel bowl. The accelerator pump squirts gas directly into the carb and helps the transition from idle to primary running.

 

thanks, it sounds a lot like the situation we have here.

so, if the accelerator pump is not working correctly, what needs to be done to fix it?

also,

there are two adjustment screws correct? one is toward the firewall, and physically adjusts the throttle linkage to hold the throttle at a desired level right? The other one which is closest the valve cover controls the idle mixture, not the running mixture, correct? Does that mean the the a/f ratio while driving is controlled by vacuum and the butterfly valves?

Edited December 21, 2008 by hessianben

[hessianben]

when I pump the throttle by hand, the accelerator pump does squirt a good amount of fuel. what would be the next thing to check?

 

thanks alot for you're patience with the stupid questions-

in the process of learning carb'd motors.

[datzenmike]

It would seem that the primary barrel is not supplying fuel as the butterfly opens. This could be a blockage or partial blockage in the primary jet. You could remove the carb and probably clean it out, but if you have it off maybe you should get a kit and re-build it along with a thorough internal cleaning and adjustment of the linkages? What do you think?

[hessianben]

It looks like that's the next step...

First, I'd like to take it off and clean it as is to see if I can improve things..

anything i should look out for?

[mike]

By the sounds of it you just cleaned the outside of the carb right?

Im not overly familiar with the older hitachis, the oldest Ive got is a 74... but alot of the same stuff applies

Has the truck been sitting for a while?

-is there rust in the fuel filter, if so some may have gotten past and clogged a jet in the carb.

Is your fuel level in the middle of the sight glass? Is it clean looking or rusty, if its rusty and youre mechanically inclined, get a carb kit, and rebuild it. Theyre not too complicated just take your time and go easy on tightening everything back down.

 

Do you have your vacuum advance hooked up and is it working?

-it should still be driveable without it but it could be part of the problem.

 

Have you checked for vacuum leaks?

-spray carb cleaner around the base of the carb and where the intake manifold bolts to the head. if it runns better while doing this GENTLY retighten the bolts, especially the manifold bolts.

-are there any air lines on the carb that are not hooked up? or maybe hoses that go nowhere? If so cap them off with a chunk of hose with an old bolt or something shoved in so that air can not escape. If plugging the ports fixes the problem try and find out where the lines go and fix it right, youll thank yourself in the long run. Also if you have some old cracked and dryrotted vacuum hoses on there replace them, If you go one at a time youll get them in the right place.

[mike]

Check for the vacuum leaks before anything else... Thats the problem about 90% of the time.

Good luck

[hessianben]

ok, i took the carb off, cleaned inside, the linkage, the float compartment, the idle jet, the butterfly valves, and the gaskets where it seats to the mani-

it gets fuel which looks clean, no rust (there's no rust in the float bowl) and the accelerator pump works.

it will fire up rough, and idle, but as soon as i add throttle, it chugs, skips and then races until it backfires white- out the carb, and then almost dies.

I don't find any vacuum lines, except to the air filter housing from the brake booster and a vent from the valve cover.

this is what the plugs are looking like... lean?

 

 

see the little splashes of coolant? those are from when it backfired huge-white ball, and then began this running rough business...

float bowl looks clean...

 

 

 

looks fairly clean right? now, the manual choke valve is on the left, correct?

what should be the angle of that during startup, and also at normal idle, and at WOT?

 

[Farmer Joe]

well if you said that coolant came out of the carb, then you have coolant getting sucked unto the engine making it run rough. so if that happend, the intake gasket is probably shot around water port for the intake. im pretty sure thats what goin on. heve you checked your coolant? if its low that could be another sign that coolants gettin sucked into the motor.

 

oh yeah, when its running, does the exhaust smell sweet kinda like burnt coolant?

[datzenmike]

Your distributor should have a round-ish canister thing on the side with a similar metal tube on it. Something like this:

 

I see the vacuum advance tube in the bottom picture you posted. It is just below the idle mixture screw. It should be connected to the vacuum advance canister in the picture I posted.

 

If your carb spits back it could still be lean. As soon as the engine uses up the squirt of fuel from the accelerator pump it returns to a lean condition.

 

Your valves all have some clearance right?

The cap/rotor/wires are in good shape?

Timing is set at +12 ?

Are all plugs the same as the one shown?

Edited December 22, 2008 by datzenmike

[hessianben]

I don't think it's burning coolant now- the exhaust is not white and smells normal.

the splashes were after a particularly violent backfire on the freeway, after which it wouldn't run smoothly. haven't seen any other hints of leaking coolant since then.

 

the vacuum advance is intact and connected.

 

here's a thought.... it is currently getting fuel, enough to idle, and is getting fuel at the accelerator pump when the throttle is pressed. perhaps it's just not getting enough fuel when the rpm's climb?

 

Question: I see what looks like wires for a fuel pump going to the fuel tank in the bed of the truck, but I also see what looks like a mechanical fuel pump on the right/front of the engine block- opposite the distributor. (appears to have been replaced very recently) Does this mean there is a redundant fuel system?

 

Also, how can I check the rate of fuel delivery at higher rpm's? might it be leaning out because of sluggish fuel supply? (correct me if I'm wrong, but if it backfires from the carb, that indicates a lean mixture?)

 

thanks for everyone's help!

I just want to drive her!!!!

[datzenmike]

That's one reason for a back fire, yes. I doubt it's the pump. Next time it won't rev up, immediately shut off and look at the front of the carb. Fuel should be at the line on the glass.

 

 

Where did all the anti freeze come from?????? Backfire???

 

Check the tightness of all the intake manifold bolts!!!!

 

If they are fine do a compression check.

 

No way antifreeze should backfire out the carb. What head is on this motor?

Edited December 22, 2008 by datzenmike

[hessianben]

as far as where the coolant came from... I'm at a loss. All the bolts are tight. I'll do a comp. test this week.

It was running really well for the entire 500 freeway drive home from central cali- I did notice that before it quit, it would very slightly skip, or cut out once or twice when I accelerated to pass or climb grades. it was becoming a little more pronounced at the 400 mile mark, and when I went to make a pass, it just bogged. I feathered the clutch and tried to get the rpms up, but it was just gutless! it would barely rev, and when I coaxed it up to transmission speed- it backfired pretty loud. My girlfriend, who was following me said she saw a white cloud exit the tailpipe, and after that the backfires were black.

 

any clues?

[moparvwfreak]

sounds like a maladjusted float to me. had that same issue with my Weber. now she runs like a top since i adjusted it.

[hessianben]

Do the hitachi's adjust in the same way as the Weber's float valves?

[datto510]

I don't mean to be a stick in the mud but, I had very similar symptoms to what you are describing. I adjusted valves, timing, carb everything. Check your compression, mine was very low in the 2 & 3 cylinders. I tried retorquing the head bolts but that didn't help. I took the head off and found this.

 

I hope your luck is better than mine.

 

 

 

 

 

[hessianben]

Yep, I was reading your thread! Well, i hope that is not the case, but if so- parts for the L series are pretty cheap!

 

or...

 

it's KA time! (yaay for EFI !!!)

[qwik510]

There is a great article in the Dime Quarterly about the downdraft carb.

 

http://dimequarterly.tierranet.com/articles/tech_carb_tuning_guide.html

 

and one on the weber carb too.

 

http://dimequarterly.tierranet.com/articles/tech_weber_tuning.html

 

I hope this helps.

[banzai510(hainz)]

Find the orginal box for the Hitachi carb

get it polished!

Then find the nearest body of water(lake ,river) then throw it in.

 

Get a weber DGV. or if possible a new stock hitachi)

 

that anti freeze all over mean something. Ck the rubber from the metal line to the intake manifold. its about 1/2-2inch long right near the carb.

Is your TEMP ok? Is it maybe over pressureizing then blowing out a weak spot.

 

I would try a new intake manifold GASKET(maybe drain the fluid alittle first before doing it,it keep water/antifreeze from spilling in the intake)

 

maybe ck the valve lash and points if still runiing points

Timming

Edited December 22, 2008 by banzai510(hainz)

[datzenmike]

Morning Hainz. Is that the red hose in this picture? Maybe the manifold gasket (coolant) leaking into intake?

 

[banzai510(hainz)]

yes!!!!!!

[hessianben]

Throw into lake. check.

 

I shall do more pulling and cleaning, and swearing...

 

Thanks guys, for all the insight. I will also check the DimeQuarterly articles. ahh, homework.

[datsunaholic]

First off, stop screwing with the carb until you get the coolant leak fixed. You should never have green stuff coming OUT of the carb. What everyone else said is probably on track- the manifold gasket is blown. Of course that's a one-piece gasket for both the intake and exhaust so that's going to be a real fun fix. Get yourself a 12mm U-joint socket... it'll save you a few swear words at how the intake/exhaust manifold common bolts are installed.

 

Second, pray that it IS the manifold gasket, because any other reason for green stuff coming out the carb is even less pleasant.

 

I would venture a guess that the blown manifold gasket is the root of your running problems. I say that because I've been there.

[hessianben]

Ok, so after tweaking with everything i could find...

it seems that it will idle just fine when started-

it will begin to accelerate thanks to the accelerator pump-

but, it will begin to cut out as soon as the revs climb.

I'm pretty sure that the vacuum-actuated secondary is not opening, and probably causing it to burn lean, and cause it to backfire out the carb. correct me if i'm wrong.

I found that if I manually activate the vacuum diaphragm linkage for the secondary valve, it revs very nicely!

So, to me that sounds like a vacuum leak somewhere in the intake manifold?

Or, perhaps a faulty diaphragm?

Either way, I decided to pull and change gaskets....

 

 

someone got happy with the adhesive...

 

 

 

would've been done and had results to report, had I not sheared off a stud in the exhaust manifold.

gotta find a tap or helicoil it...dont know if that will hold.

 

oh, well... at least it wasn't to the head!