2F engine problem (1 Viewer)

[JrJoorgawt]

I haven't a clue what causes this problem, but basically if i go above 45mph the engine will lurch a bunch and then cease operation entirely
if I push in the clutch while this happens, the engine die completely (0rpm all the lights come on), and I can let the clutch back out to then restart it while rolling. Then it will work perfectly well until i'm back up to around 45 or 50 mph. I've tried spraying down the carb with carb cleaner and then putting my hand over the carburetor to choke it but that's all i've tried.

Anybody got any ideas?

 

[chichiflys]

Does the engine behave that way at similar RPMs (but different gear and speed).

 

[JrJoorgawt]

No

 

[RockDoc]

Limited fuel supply to carb? I think the way to find out would be to roll to a stop after the engine stalls out (clutched or neutral) then check the sight glass on the carb. I'm an EFI guy, so no personal experience.

 

[OSS]

Ok, this might be a stretch, but there's only one system that does something when the vehicle hits 50 mph: the air injection system. The emissions computer gets a signal from the speedometer when the vehicle hits 50 mph and the air is then diverted to the exhaust pipe.

Now I can't see in any way how that could cause engine stumbling if that system went haywire, but the Deceleration Fuel Cut System is a subsystem of that system ... and if for some crazy reason the Fuel Cut Solenoid triggered on at 50 mph, well that could explain it. But I've never heard of that scenario occurring (Probably because it's not possible).

But it would be super easy to rule it out— unscrew the speedometer cable from the transfer case and take it for a test ride (above 50). Maybe put a plug over the open speedo socket on the transfer case.

I'm thinking though that the engine stumbling isn't related to speed at all, but throttle position under load. It should do the exact same thing (stumble) in 3rd gear at the same throttle angle up a hill as 4th gear on the flats. But you never know...

If it's engine load triggered (not speed or RPM) then it's a fuel delivery problem: Carb, Fuel pump, Fuel filter, tank intake restriction.

 

[JrJoorgawt]

hm

i'm more inclined to think it's the load thing too

is the second barrel vacuum actuated?

 

[Michael Hanson]

Hi, Fuel filter, fuel pump. Check these. Mike

 

[micruz60]

Fuel pump, bucking and snorting.
Dunno about secondary. Hmm.
Are all the plug boots snug at distributor cap and plugs?

 

[JrJoorgawt]

okay i was able to repeat the problem in lower gears as well
it seems to occur after being over 2000RPM for about 2-3 minutes, then death

I checked all my plug chords and they looked good

 

[slacker24-7]

I’d go fuel pump as well.. simple to check

 

[g-man]

what about 2000 rpms at idle? very large vacuum leak would cause some lurching and stall because the fuel is not being pulled down the carb by the intake. would have to be a big leak on your intake. Probably fuel issue but listen for a hissing while you throttle it up.

 

[JrJoorgawt]

okay

 

[JrJoorgawt]

and it could easily be a huge leak

 

[micruz60]

Can you post pics of the engine bay, particularly the carburetor side, with all the vacuum spaghetti?
Try doing the 'okie carb rebuild' again, where you choke it out with a piece of cardboard over the throat, several times.
Could be a piece of FOD (foreign object debris) getting into passages at WOT (wide open throttle).

 

[chichiflys]

okay i was able to repeat the problem in lower gears as well
it seems to occur after being over 2000RPM for about 2-3 minutes, then death

I checked all my plug chords and they looked good

Ok good - while still sucky I think that helps. So an intermittent rev to 2000+ is OK but sustained time at that RPM/load is a killer, correct?

If it's a vacuum leak I'd think that would present itself as a problem at idle as well, unless it's one of the emissions systems acting up. So I'm thinking fuel delivery like others; pump, filter or float level? Also, like OSS hinted I think there is a check for the fuel cut solenoid that the FSM states something magical happens at a certain RPM? Have you gone through and checked the individual emissions systems?

 

[morganism]

Distributor pickup coil may be failing too, if vac advance is wrong. Try pulling the inside vac line, putting it on the outside diaphram, and plugging the outside line w a golf tee.

 

[JrJoorgawt]

found heavy corrosion on center plug of the distributor cap
i'm cleaning it now

 

[LAMBCRUSHER]

Sounds like when my igniter took a dirt nap

 

[JrJoorgawt]

it was bad enough that when i tried to remove the plug the actual electrode was ripped out of it
so now i have a distributor cap with half a plug stuck in it

 

[NeverGiveUpYota]

I had that happen to my beater Nissan. I was told heat and age. The rubber gets cooked and can degrade like that. Time for a new cap and wires.