Same truck; new problem. Now my carb isn't working right. (1 Viewer)

[Random Dan]

I posted a thread a few days ago trying to diagnose why I wasn't getting a spark at my spark plugs. I wound up replacing my points dizzy with a large cap electronic ignition from a USA 60 and now my spark plugs are sparking happily. But it still won't start. I double and triple checked that timing was right, and it was. So then I tried spraying carb cleaner in the top of the carb and lo and behold it tried to fire. So that tells me that my issue is fuel delivery. I checked and the carb glass is half way full just like it should be.
Anybody have any idea whats going on?

 

[Random Dan]

Ok, so I asked my brother to help crank it over while I watched the carb jets to see what was going on. After about 15sec of cranking and it fired right up! No idea what made it work now, but hey I'm not complaining.

 

[Slow Left]

Ok, so I asked my brother to help crank it over while I watched the carb jets to see what was going on. After about 15sec of cranking and it fired right up! No idea what made it work now, but hey I'm not complaining.

Nice!

Might want to make sure that choke plate is making a nice tight seal over the throat of the carb...for cold starts...

 

[Random Dan]

Well, seems it was a little too good to be true. Carb is acting up again. Took the truck out on the road and it ran great for a little while then died, started back up, died again. Got it back home now. It'll start up, run nice and smooth for maybe 5-10sec, then die. One of these times right when it started to die I sprayed carb cleaner in the top of the carb and that kept it going a bit longer, so I'm pretty sure that the carb is the problem.

 

[Slow Left]

Well, seems it was a little too good to be true. Carb is acting up again. Took the truck out on the road and it ran great for a little while then died, started back up, died again. Got it back home now. It'll start up, run nice and smooth for maybe 5-10sec, then die. One of these times right when it started to die I sprayed carb cleaner in the top of the carb and that kept it going a bit longer, so I'm pretty sure that the carb is the problem.

Huh. What's the story on the carb? Do you know if it has been rebuilt recently or did it come off a running truck and if not, has it been sitting for a long time...?

Either Jim or
@Pin_Head is going to have good insight on the carb...

 

[Random Dan]

I think is was rebuilt a few years ago. It was running fine up until recently.

 

[Slow Left]

Even if the ignition timing advance requirements do vary between the FJ61 and FJ60, you would still expect the engine to idle since there is no timing advance at idle...

If it were me, I'd get a can of that Seafoam with the crazy u-shaped red straw, cut off part of the straw down near the u so that you can insert it into the holes in the sides of the carb barrels and blast those circuits clean with Seafoam. Give as many circuits a nice little bath of Seafoam...and wait for expert advice from Jim and/or Pin Head...

 

[Slow Left]

After it dies, is there fuel half way up the viewing glass of the fuel bowl? I'm thinking fuel pump problems...

 

[Random Dan]

Kinda hard to tell because the glass is old and dirty but I'm pretty sure it was keeping it steady at half full.

 

[Slow Left]

Have you adjusted the idle mixture and idle speed screws? You should be able to get it to idle (even if the slow jets in the idle circuit are clogged) by backing out the idle screws so it draws fuel through the main circuit...I think?

 

[Slow Left]

Also, according the FSM, the pump plunger 'travel distance' is spec'd at 9.5 mm...so if you twist the accelerator torque rod all the way, the top of the plunger should drop down 9.5mm in vertical distance...

And if I understand correctly, when you twist that torque rod, you should see fuel spray out of the pump jet (high up in the primary barrel). If no fuel sprays out, then it could mean that you have blockage in the pump circuit...there are two ball check valves in there that might be stuck...

 

[Random Dan]

Yeah I dunno. It idles great for a little while.