Bingle

Yeah, always seemed to be running a bit rich but I went with a "if it ain't broke" attitude with it. Going to order some air jets and 55f9 idles. Do I need to get both or do you think 180's will be fine (for now at least)? Will tweak float and start switching jets between carbs till I find the culprit. Did my main jet and emulsion tube sound like the right size to you for the engine mods I have?

suncomb1

I would get the #180 Main Air Jets first. The 55 / F9 can be done anytime, it just gives you more latitude in adjusting your idle mixture screws. Your 36 MM Chokes, Main Fuel Jets, Emulsion Tubes, Accelerator Pumps, etc are right on the money for your motor and HP output.

Bingle

By "both" I ment 180's and 185's for air. Ordered the 180's and 55F9's yesterday so it dosen't really matter.
Last night I swapped idle jets between 1 & 4, no change. Then swapped main jets, also no change. Changed float level to 14mm (12mm is the "correct" setting, right?) still same symptoms.
Got frustrated, pulled the "defective" carb off and started doing a mid level tear down/heavy cleaning. Because I could see them clearly now, checked the idle and progression holes. All clear (or they are now). All the ports seem fine/nothing noticable. Pulled the starter jet, plugged side holes with fingers, sprayed cleaner in top and got dribble out bottom hole. O ring gasget set had no visible problems. Been cleaning it up whe best I can without complete disasemble (removed all jets/screws, left throttle spindle/butterflys/return spring in). My manual is pretty vague on how to get accel pump out. How do you get the "retaining plate/cover" off so you can pull the pump out? I don't want to force it and screw something up. Anything you'd make sure was cleaned out/pay extra attention to? Further instructions?
Also, valve stems (looking down intake) looked remarkably clean, both 3 & 4. #4 intake runner had a thin black film on some walls, no heavy deposits or anything like that, and #3 was almost completely clean. I figure it was from the poor running, but it might point to something.

suncomb1

The start system on your carb should be wired closed and never used. By wired, I mean there should be a hard wire (rod) installed to ensure the stater unit is always fully closed and never moves toward the open position. The correct float level for your carb should be set at 12 MM (bottom of gasket to top of plastic float). You stated earlier that when you moved the linkage fast the accelerator pump worked and the amount of fuel sprayed on the throttle plates was about the same on #3 and #4; so your accelerator pump works-leave it alone. Did you check the resistance of #4 plug wire and did you check your distributer cap especially at #4 position? What were you doing with the truck when the problem first appeared? Did you perform a compression check on #4 cylinder? The reason I ask this is because if you have been running as rich as what I believe you have, you could have damaged the rings. Do you have any vapor (blow-by) coming out a valve cover vent / breather?

Rusto

This may sounds dumb, but maybe you just have some bad gas? I went through a similar stretch of consternation with an old Pathfinder I had and a refill of the fuel tank with some fuel treatment cured it.

That's my one cent. I'll let the smarter people in the room talk again.

Interesting read, all the same.

Bingle

By start system, do you mean the little lever on the back of the carb that acts like a choke to enrich for cold starts? I have that hooked to a manual choke knob/wire setup and only use that on really cold (20°F ish) mornings to help get it going and even then I only open it aprox half way. I was talking about the jet that squirts when accel pump is depressed, I think my book called it the starter jet, but I may have been mistaken. I figure that cleaning the carb out won't hurt.

Haven't tried resistance in wire but had some new msd wires, swiched with my exsisting msd wires, no change. Cap and rotor looked good but am going to just change those out for new. A co-worker today mentioned "washing out" the rings as well. Am going to do a compression check this afternoon (have to get a comp checking tool, I don't have access to my dad's shop like I used to, it's on the other side of the state after I moved). Am planning on doing these steps one at a time so I can maybe figure out what the problem was.

I was just driving through town heading home when this problem started. Pulling a decent hill at 30-35 if I recall correct. Just suddenly started poping/sputtering.
Fuel system got cleaned out and sea foamed (just added to tank, didn't dump it in the intake) about 2 months ago, I only run premium, and I've been driving it regularly since I got the previous issue (fuel pump and reg) figured out.

suncomb1

The accelerarator pump supplies the Pump Jets that are located under screws just behind the float bowl and in front of the pump exhaust valves. Be careful when you pull them out, there a tiny round gaskets on the bottom of the pump jets.

Rusto

"I was just driving through town heading home when this problem started. Pulling a decent hill at 30-35 if I recall correct. Just suddenly started poping/sputtering.
Fuel system got cleaned out and sea foamed (just added to tank, didn't dump it in the intake) about 2 months ago, I only run premium, and I've been driving it regularly since I got the previous issue (fuel pump and reg) figured out."

I figured you had the bad gas scenario covered already, but thought I'd throw it out there.

Good luck.

Bingle

Suncomb,
Thank you for all your help and I will be getting back with you in a while about jetting. Looks like #3&4 pistons got washed out. # 1&2 both read 160 psi (cold engine, I know, not the "right" way to do it) and # 3&4 both read at 58 psi. Looks like I'll be tearing into it. Will let you know what I find when I get the head off. Hopefully getting the new idle and air corrector jets in will keep this from happening again. Sorry for wasting your time chasing something I should have checked a long time ago.

suncomb1

Sorry to hear that but I had the same thing happen to me with a rear Mikuni carb-it sucks. Suggestion- While you have the motor apart, really check your throttle plates on your carbs to make sure they are not bent or damaged. Rebuild your carbs and purchase a Wideband Air / Fuel Ratio system from Summit. Their system uses a Innovate sensor system which is really accurate and rugged. It will really help you to tune your carbs and help you to prevent what just happened. I constantly watch my Air / Fuel Ratio. Good luck and if you need any help let me know.

Little Elger

When you reset your valve clearance, were three and four out of spec? Maybe just stuck valves since this happened all at once. I am no expert just had similar problem with popping and no power in an old wheat truck engine, it was stuck valves on three cylinders.

Bingle

Head gasget blown out between #'s 3 & 4. I had all the spark plugs out when I was checking the compression and could hear it blowing into the other cylinder, but thought it was going past the rings. Cylinders looked good (could still see some hone marks with ~80k on bottom end rebuild) so looks like I won't need to be doing a hone/new rings!

Ordered up a new head gasget, head bolts, and a couple other goodies from LCE and with the new idle and air correct jets she should be running great. Fingers crossed.

Bingle

Well, she's running good now. Still rough till it warms up a bit, but she's always been like that, gotta warm up about 1-2min on first fire up. Throttle/engine response is different, seems better with new jets, except for there seems to be a tiny "flat spot" between the idles and mains. Not a big deal and might be mostly my imagination, just happy she's running good again. I will be waching the plugs to make sure she's not running too lean. I have to do a new exhaust in the spring and will get an O2 sensor when I do that so I can really dial this jetting in and maybe get some decent mpg numbers out of it. Not good, but decent would be nice. Thanks to all for their help/input.

Suncomb,
I'll be bugging you for jetting advice when I get an O2 hooked up, your knowledge of these carbs has been invaluable to me, thanks.

suncomb1

How many turns out are your Idle Screws and what is the temperature outside where you are located?

Bingle

I believe I'm out 2.5 or 3 turns and it's in the 30's, gonna get colder soon.