Bingle

Driving the other night, truck was running great till about .5mi from home. Started poping/shaking under accel. The poping was bad enough that I thought it might be the tranny going. Pushed in the clutch and would rev fine but under load all hell breaks loose. Upon a closer inspection today, the idle is has more "lope" to it and if I give it throttle quickly it pops in the intake.

List of things I've done/checked to no avail:
changed plugs and wires (old plugs were black/brown)
checked cap and rotor (it's only got about 2000mi on it)
Checked timing (adjusted slightly)
checked rocker arms
sprayed carb cleaner to check for vac leaks at carb base and intake
Fuel pressure reg, pump, and filter are all a couple months old. Just got done with that battle and was running GREAT.
Float levels were also adjusted at that time

I really don't want to start tearing in to my carbs because getting the DCOE's off/on and synced is a PITA. Anybody got any ideas? Gotta get the old girl acting right and go get some more firewood before the snow starts flying.

Oh, in addition to info in my sig, it has msd6 ignition and coil, if that changes anything.

Bingle

Any ideas guys? I am usually pretty good at troubleshooting my truck, but this one has me stumped.

suncomb1

Check the sync on your carbs first, second check your idle jet positions (are they all close to the same number of turns out), and third check your fuel pressure at the carbs (1 Pound or no more than 1.25 Pounds). Based on what I read about your engine mods make sure your total timing is 30-32 degrees with it all in at about 2000 RPM. You can buy a Total type timing light at Sears if you do not have one. I run an LC Engineering Stage 5 Pro Cam and I have my idle set at 1100 RPM. You should be able to set your idle at 900-950 RPM.

Bingle

Thanks, all settings you mentioned were checked and/or adjusted slightly to the specs you mentioned. Idle screws are all 3 turns out, do I need bigger idle jets? I have a delay style light (dial on back, cheap but seems to function properly) and the idle is at 10° and total about 32°. When checking sync I figured out the problem is with #4 cyl. When throttle given quickly it pops/sprays some fuel mist back out, but only from #4. Re-checked for vac leaks with liberal ammounts of carb cleaner and removed and plugged vac hose for brake booster, no change.

Intake valve get gummed up and not sealing? Something with accel pump for #4? Am narowing it sown but still don't know what the cause is.

suncomb1

What size Idle Jets are you running? I run 60 and my Idle Adjustment Screws are about 2.25 turns out for warm weather and 2.5 turns out for cold weather. I am dialed in at 285 HP. I run 40 MM chokes on my 45 DCOE #152 carbs. What brand of spark plugs, what is your plug gap and what is the heat range of the spark plug? Pull #4 spark plug out and check it. Check the spark plug gap. I use a Wideband Air/Fuel Ratio controller and I run at 13.

Bingle

Idle jets are 55's. Not sure on the choke size, whatever was in the 45doce 152's that I have as well. Just put new NGK plugs gapped to .032. Oem replacement type plugs, not sure on heat range but plugs went in after problem started, didn't help, and just #4 cylander is having an issue. I checked and I have spark. She was running great after you helped me get the psi reg to where it needed to be, then this poped up suddenly, while driving. Seems like something broke loose/clogged/ect.

Carbon buildup on intake not letting is close completely? Acting like vac leak, but can't find one.

suncomb1

Take the air cleaner off of the rear carb. Use an inspection mirror, open the carb fully with the throttle linkage, look at both throttle plates and check to see if the throttle plates are in the identical position meaning that one is not bent (#4). I never had that happen to my Webers but I had it happen to a pair of Mikunis. What was the color of the old #4 spark plug? Was it a different color then the other three cylinders? Check your rear carb float level, it should be 12 MM from gasket to top of plastic float. On 45 DCOE #152 carbs there are extra air bleeds, look at a carb parts diagram to locate them. Make sure they are fully closed but do not over tighten them. Look especially at #4 cylinder barrel. Check the needle and seat on the rear carb to see that it operates smoothly, is not dirty, worn, etc. What size main fuel jets and what size main air jets are you running?

dropzone

iTrader: (6)

Sweet..


I remember from my v.w. days dual carbs being kind of a pain, but awesome when dialed in..

suncomb1

Normal HP is about 200 but I run up to 125 shot Nitrous with either "Programable Staged" or "All In" type control with twin oversized bottles. I normaly run the system at 285 Hp available, "Programable Staged" and Rev Limiter at 6500 RPM for the street. I can run up to 325 HP and Rev Limiter at 8000 RPM.

Bingle

Old plugs were all about the same color, but only drove aprox 1/2 mi with it acting up. Figure new #4 will look like crap because that one is missing or whatever it's doing.

Will check the # on the other jets tonight. I checked down the barrels and didn't notice anything but will check again. By extra air bleeds, do you mean the "idle air compensation screws"? I'll check those as well.

Found something in my weber manual that just got me thinking. If the throttle spindle dust cover on the #4 barrel side broke/cracked ect, would that give me a vac leak for that barrel and cause my problem? Going to have to remove the carb to get at that, been trying to avoid doing that.

Thanks again for all the help "suncomb". Glad there's at least one other DCOE guy on here, and he knows more than me (dosen't take much). Do you know of any others?

Dropzone, they are awesome when dialed in, and really have been pretty problem free until recently (I've been running them for ~9yrs). You should get a set for your trekker!

suncomb1

I do not think you have a vacuum leak problem. I assume you have the "O" ring type carb bases and unless you removed the carbs and reused the "O" rings you should be good. As far as the shaft dust cover / seal goes unless the carbs were used when you bought them or old they should be okay. When you checked for vacuum leaks did you notice any change in engine RPM when you sprayed around the shafts? Are your valves set to the right clearance spec for your cam? (had a dealer set mine to the wrong specs one time and it ran like crap; sounded like it was running on 2 cylinders) Soon as you get me your main fuel and air jet numbers I should get more in depth with you. Also, is your motor stock bore & stroke? Are you running a modified 22R head or a 20R head?

westjohns yota

i dont think very many people have dual side draft webbers so not many can help ya here

Bingle

Carbs were new when I got them and have been on for 8-9 yrs, never removed, plastic with 2 o-rings for carb base "gasget". Didn't spray carb cleaner at the shaft area, going to try that tonight. Rocker arms set to .008 intake and .012 exhaust (i think I have the decimal in the right place, I know it's 8 & 12 though), same as stock and that's what the data sheet for the trd stage 2 cam called for. Double checked the intake last night, better do the same with the exhaust tonight. Block is bored .020 over, stock crank (Lce stroker is on my wish list). 22R head with larger valves, will look up those #'s this evening as well. No porting or anything cool like that either. Will get a Lce stage 3 stroker someday, but that's a couple years down the road.

Westjohn, yeah, suncomb seems to be the only other guy on yotatech that runs them. I love them but I think they're "too much" for most and others just go turbo or engine swap. I feel they were well worth the money and have been very reliable, until now.

suncomb1

The #4 carb barrel is spitting back correct? That is a sign of a weak mixture. Remove the idle adustment screw from #4 barrel and inspect it with a magnifyer to make sure it is not deformed, dirty, etc. Spray carb cleaner into the #4 idle adjustment screw port. Remove the idle adjustment screw from #1 barrel and install it into #4 then install #4 idle adustment screw into #1 barrel. Turn all idle adjustment srews full closed then open them up 3 turns. Start the motor, warm it up and set your idle at 1000 RPM with the throttle adjustment screws. Sync the carbs again and make sure they are reading exactly the same. Drive the truck so it is under load to see if the engine runs normal.

Bingle

Okay, you were correct on weak mix. #4 plug has white/ashy electrode, other three are black/tan. I did the following (one at a time)with no change:
Cleaned & swapped idle screws as described above, no visable damage.
Carb cleaner around shaft, no idle change.
Throttle plates apear to be in alignment with one annother, no visible damage.
Idle air correct screws were "closed" or tightened down already.
Tripple checked valve clearances.
Sync is spot on.

So, something is making #4 run lean. Not enough fuel or too much air, right? So that means vac leak or a fuel jet or passage is plugged or restricted, just have to figure out what. Adjusting idle screw on #4 does affect the idle so it's not completely plugged. Suncomb, so you can further help with the tune (thank you so much) the jets are as follows:
Idle - 55
Main - 145
Air - 155
Emulsion tube - F16
Also, looking down the barrel the chokes apear to be stamped "36"
Any other info I am more than happy to get to you. Just looking like I'm gonna need to do a removal and full cleaning unless I can find what's gummed up and fix it on the truck.

suncomb1

How did the truck run, after performing the changes, when you drove it? Your Main Air jets are wrong, The start point (factory) is the main fuel jet size + 50, so if you have a 145 Main Fuel jet you use a 195 Main Air jet. Well that is not always true. I would get a set of 4 #180 and #185 Main Air jets. Your chokes are sized okay at 36 MM and everything else seems okay but I would change your Idle Fuel Jets to 55 / F9 (you have 55 / F8 units installed now) that will slightly enrich the idle circuit and allow you to adjust your screws a little better.

Remove #4 Idle Adjustment screw, hold open the throttle plates and spray carb cleaner down the #4 idle screw hole, cleaner should come out of the first set of holes below the throttle plates, closest to the intake manifold.

Bingle

No change, still running like crap. I will double check the air jet #, they're rather hard to read. It ran fine with the current jets but I'd be happy to change a few out and get a little better performance out of it. I will try cleaning out the idle circuit with carb cleaner again.

Any other ideas on what might be clogged/gummed up that would cause this problem? Once the truck warms up a little (temp gauge just starting to climb) the idle seems reasonably smooth, when throttle aplied (especially quickly) it pops/sprays fuel out of #4 but sounds okay at a higher rpm if held there. Holding higher rpm and letting out the clutch (in gear/applying load) yields more popping. Accel pump jet? Or something in the accel circuit plugged? Any guesses?

suncomb1

Clean the #4 Idle circuit as noted before and really look at the holes downstream of the throttle plate towards the manifold as instructed. Try blowing some compressed air through #4 idle screw port / holes. Adjust your idle RPM to 1100 and sync the carbs again. Your having a transition problem from the idle jet to the main jet circuit. When the idle is at 1100 take the throttle shaft and slowly open the carbs raising the RPM-Let me know what it does. Make sure your engine temperature is at normal position and that the thermostat is open before you do this. Also, when you sync the carbs (engine temperature normal) check each barrel and let me know what the reading is on each barrel.

Bingle

I just want to figure out what the problem is so I can fix it. I'd roll the truck off a cliff right now if I didn't love it so much. Rant over, back to it.

Last night removed idle adjust screw and the adjacent "plugs" for the progression holes? and went to town on them with carb cleaner (no compressed air available in my garage, yet). Could not really see that far back down the barrel while doing it, but held throttle plates open and could hear it spraying into the barrel and ended up with cleaner running out the intake end. Got it synced up at running temp, flow #'s with weber sync tool are all 4 reading just over 5 at 1100rpm and all at ~9 at 2000 rpm. Looked down barrel at idle and slowly opened the throttle. Accel pump squirts a little (equal on both barrels) on to throttle plate/butterfly. slowly open = no backfire/spit. Open quickly = pop/spray vapor and droplets out.

Went for a drive around the block while still warmed up. On any kind of uphill(even holding throttle stationary) or accel it pings/pops. On flats or downhill it ran/sounded fine.

Whild idleing, sprayed large amounts of carb cleaner at intake/head joint where block off plate is really close ( near back of head) I got a slight (about 150 rpm) dip in idle, but it took a few seconds (vac leake seem almost immedate) and might have been because of the vapor build up in engine bay made it to the carb intake.

suncomb1

Change your float level to 14 MM measured from bottom of gasket to top of plastic float. Check for smoothness of needle and seat operation. Your sync numbers are right on the money at 1100 RPM. Take the idle jet from #1 and install it in #4, take #4 and install it in #1. I believe you either have a fuel level problem or you are experiencing a transition problem from idle to main jet operation. I wish you had some #180-185 Main air jets just to put in #4 for a test. I know you said it always ran fine with the 155 Main Air jets but you have got to be running rich with that jet combination.