Weber Carb Jetting/Tuning, Need some advice here (1 Viewer)

[Rock40]

I would really like some input/advice on Weber carb tuning. If your advice is to run a stock Aisin or Trollhole that's fine. I'm simply looking for input.

OK, for starters, I have spent several hours searching the forum. I have read this: ***Weber Carb*** Adjustment Thread by @JohnnyC

I've gone over the "Lean Best Idle" instructions provided by Weber multiple times.

Here's the issue, I have a 32/36 progressive carb on a freshly rebuilt F135. For tuning, all the vacuum lines have been disconnected and the timing is set at 14 BTDC. The distributor is a D.U.I HEI and the spark is very, very consistent so please don't point to an ignition problem.

The engine will NOT run unless I have the speed screw turned in over 3 turns. Per the instructions, 1.5 turns in MAX and I have verified that the enrichening circuit is activated (a no-no for curb idle) based on the fact that I have ported vacuum at the carb.

I've eliminated vacuum leaks as the issue. The base and adapter have new gaskets which I sealed with Loctite anerobic sealant.

I bought the Weber jetting kit, 701-DGV6 and I determined that the stock primary and secondary idle jets are 70 and 50 from the factory respectively. Using the kit, I maxed out the idle jets at 90/65 and overall that affected very little change in the carb idle. The speed screw is still about 3 turns in. Any less and it just dies out. I've tried to adjust the mixture screw also, any further out or in (from it's current setting) and the engine dies.

I'm frankly at a bit of a loss. I've read several times that the Weber 32/36 is "barely" adequate at feeding the "F" motor. Common sense tells me that my running issue is an idle mixture that is way too lean. Off idle, the engine seems to run great and revs up very quickly without any hesitation.

Here's a mandatory pic, any advice or current jet settings on your Weber which is correctly tuned with the speed screw no more than 1.5 turns out after touching the cam would be great.

 

[brian]

The carb is not large enough for the engine.

 

[65swb45]

Get another carburetor on the motor and figure it out later. You can’t risk the rings not seating while you’re working this out.

 

[Rock40]

Spoke with a Weber tech today and the first thing he said after I told him what motor this was on...."You need a 38/38".

 

[65swb45]

The CFM shouldn’t be an issue until you get to the top end. AF ratio is the same, regardless of CFM.

 

[Rock40]

The CFM shouldn’t be an issue until you get to the top end. AF ratio is the same, regardless of CFM.

Totally agree Mark. The issue here is only the amount of fuel the 32/36 is able to provide while operating on the idle circuit only. Think "curb idle" I guess.

I've learned a lot about Weber's over the past few days while trying to sort this out. Because I've screwed the speed screw in (idle speed) past the baseline, the enrichening circuit is cracked open and that is providing enough fuel for the engine to idle. Without that, I can't jet the idle circuit anywhere near rich enough for the engine to fire off. Does that make sense? At higher RPM, the carb runs great. Based on the Weber instructions though, you MUST have the idle circuit correct.

 

[thebigredrocker]

Any chance that 2 to 1 adapter is hindering idle fuel delivery? If so would a 2 barrel intake bolt up?

 

[RAYJON]

weber has a chart with the correct jets and bleeds/emulsion tubes based on cfm somewhere. Being that a f motor can idle at 600rpm you can do the calculation and get cfm at idle.. then use the setup as a baseline ..

My "guess" is you need a smaller air bleed, and a different emulsion tube. remember webers jets jump 5 per step 90 to 95 is one jump, air bleeds in 20's.... smaller air bleed will make it richer, look at a dgv setup for a ford inline 6-200, That may give you a closer baseline if you cant find the chart.. there are some webers where the idle air bleeds aren't replaceable..

I ran dual 32/36 dgv's on a healthy 2.8l. 240z for years, it saw twice the rpm you f motor will ever see.. (had opposite problem you are having, too rich at idle)

once you get them tuned they are great.. keep plugging away you will get there..

Do you have access to a wide band o2????

 

[RAYJON]

Was thinking, did you check the float level? and you went from 70-90 with no change??? Thats 4 steps thats huge... curious what the bleeds and emulsion tubes are in it?? Something is weird,

 

[Rock40]

Any chance that 2 to 1 adapter is hindering idle fuel delivery? If so would a 2 barrel intake bolt up?

I actually do have a 2 barrel intake for the F135 for the mount/adapter is different at the carb base

 

[Rock40]

@RAYJON, thanks for the reply and chiming in with your experience. More and more I'm thinking I may have a vac leak somewhere I have not located yet. That thought is based on the little change I saw with swapping jets and the fact that others on here have installed a 32/36 without the serious issues I'm having.

I'll look online and see if I can find that CFM chart your referenced.

 

[RAYJON]

They make kits that use a 32/36 on a 258 jeep 6 as another baseline, the 70 you started with should be close, try the carb cleaner arround all the intake ports/carb base.. propane also works,, sometimes vacuum leaks are a bitch to find.. dont forget the brake booster... also pull the idle jet and holder and carb cleaner and compressed air into where it goes , should get carb cleaner out the idle port and air bleed.. may be as simple as some crud in there...

Its been a while (im getting old) but one idle jet size was about a turn and a half.. if i remember right. so 4 steps and no change points to something else..

If it was me i would go back where you started and re baseline with new plugs. I usually miss something simple and bang my head for an hour then start over and find it real quick..


Good luck, you will figure it out just a little time...

 

[Rock40]

Thanks, I do appreciate your input. I re-torqued the manifold bolts this morning, they were all very close to the correct 37 ft/lbs.

No brake booster on the old F135 so that is out for a vac leak. I can only have a leak were the manifold meets the head and where the carb is bolted to the manifold.

Spark plugs are new and so is the Weber but I'll blow it out as you suggested. I definitely won't rule out that it could have some factory crud in it.

I'll get it started again this afternoon and go over all the connections. I plan to use soapy water first, then propane if that doesn't work followed by Gumout carb/choke cleaner.

 

[middlecalf]

Soapy water?

 

[Rock40]

Soapy water?

I was surprised too however that's what the Weber tech recommended as an alternative a flammable substance right next to the exhaust header. We'll see I guess

 

[Rock40]

Spent nearly all day fiddling with the 32/36, got nowhere.

I warmed the engine, verified the timing at 14 BTDC and checked the manifold vacuum, steady at 17", idle at 650. I did not use soapy water and instead used propane and then Gumout Carb and Choke cleaner to check for leaks. Engine bogged down if I spayed a bit of Gumout into the carb. Checked all around the base gaskets, manifold gaskets, anywhere I could potentially have a vac leak. No change in engine idle, I don't think it's a vac leak.

Pulled the spark plugs. They had black carbon on them but very, very dry. Not what I'm used to seeing on a rich/wet plug. Cleaned the plugs and reset the gap at .040 That's wider than stock but the HEI unit says to open them to .045 They had been at .045 so I closed them up a bit. No change.

Simply could not get the truck to run on the idle circuit no matter what. Smelled the exhaust while it was idling. Smelled very clean for an engine with no catalytic convertor. No soot or carbon in the exhaust pipe and no blue/black smoke. Just normal white condensation as it's warming up.

Put the original jets back in, runs the same as it ever did once the enrichening circuit starts to open. Believe me when I say that I tried adjusting the mixture screw in, out and every other way, no go. End of the day: I'm stumped and throwing in the towel at this point. Can't see what else I can do with the current 32/36. Jason is spoke to Weber and it sounds like they are going to hook him up with a 38 that is baseline turned for the "F".

For those actually running a 32/36, I'd be very, very interested to know if it's tuned correctly per the Weber instructions so that's it's only idling on the idle circuit. The F135 runs great, I just know the carb isn't right and can't live with that.

 

[Jason Reed]

All efforts appreciated Ross. Good on ya and your determination. I’m with ya, we’re moving on. Ha-

 

[RAYJON]

Just a thought, did you check at the bottom of the manifold near heat riser where the 2f manifolds crack???

 

[Rock40]

Just a thought, did you check at the bottom of the manifold near heat riser where the 2f manifolds crack???

It's the ancient F135 single barrel manifold. It's steel and has been bead blasted and repainted. I don't think those are prone to cracking at all like the later aluminum jobs and I would have caught an obvious crack during all the cleanup work.

 

[Rock40]

I just couldn’t let this go... I was thinking last night that maybe this whole issue isn't a lack of fuel delivery but rather a lack of AIR delivery at idle. As far as I can see, the 32mm butterfly on the Weber is closed during idle (if set up properly) so by opening it (by screwing the speed screw in past the max setting) I was actually adding air to the engine. I then considered that the PCV valve hose is supposed to attach to the base of the adapter however in the Weber instructions, they state that hooking it up is optional and they even provide an NPT plug for it.

With the PCV hooked up however, the engine would have quite a bit of extra air flow at idle. I assumed at least. Too bad the port is all but worthless on the adapter.

This is the carb adapter. The NPT plug is the factory location for the PCV valve. The location is HORRIBLE, essentially not usable with the way the carb is mounted on studs.

I attempted to rotate the adapter 180 to get the port away from the mounting studs. No go, it studs strike the adapter, big interference problem. I elected to drill an additional hole in the adapter 90 degrees out from the stock port and then tap it for an 1/8" NPT nipple.

Mounted back up on the intake. You can see how the factory port location is unusable