Weber 38 Carb + DUI + unknown = excellent full throttle but no idle...

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J

jdog35

10 Year 15 Year
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Feb 6, 2010
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57
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Hey all. I'm at an impasse with my pig's engine. Here's the latest...but please, don't flame me on the 38. I've seen the hundreds of pages of arguments regarding OEM vs. 38. When I can afford it and they are in stock, I'll snag one of those highly recommended Troll-carbs. Until then, I have to get this figured out with the Weber so I can at least drive the danged thing!

The Weber was brand new in a box with the rig and came with it when I bought it. There was NO carb on the rig at that time. The stock carb was in pieces in a box. After attempting to get that carb rolling, we finally ditched it (for now) and went with the 38 so I could get the dang rig moving. The rig also had a DUI distributor (stock was not with the rig). I've ensured the DUI is installed/aimed properly according to the Toyota 2F engine manual (supposed to point at a particular bolt). There is also no emission device on the truck either. All vacuum ports have been capped, and the only vacuum running right now is the advance from the dizzy to the Weber.

The pig is (I believe) properly timed at this point. Went through the checklist (flywheel BB, TDC, cylinder 1 under pressure, etc). I'm pretty certain (and my well-versed mechanic friend is as well), that we are timed correctly.

When I crank the motor, it won't idle. We can open the throttle up, though, and it will run like a champ. Sounds fantastic actually! No signals of a miss-fire, timing issue, etc. It sounds fantastic...when wide open:/

As we let off the throttle, and the RPMs drop, we've got issues. It flat out won't idle and just dies. I'm pretty certain it's getting too much fuel at the low end. This has been reinforced a couple of times when the motor has started to sputter, and every once in a while (after various adjustment sessions) it will spurt/squirt/shoot fuel out the top of the carburetor.

My thoughts are that it is obviously getting plenty of fuel at WOT, and the timing is in line as it is running clean. My only thought for the idle issue is that it is getting roughly the same amount of fuel at the bottom end as it is when full-throttle, and flooding itself out. With the fuel shooting up like Old Faithful, it appears to me to be a fuel pressure issue (i.e. too much pressure at idle-level throttle and just right when we open it up).

I have both the OEM fuel inlet and outlet lines hooked up to the 38. New fuel filter installed as well. OEM fuel pump is working well.

Could it be an issue with the DUI dizzy not 'talking' to the carb to tell it to let off the amount of fuel going into the carb?

Could it be a lack of a fuel-pressure regulator on the inlet line causing too much psi in the line at idle RPMs? This makes the most logical sense to me, but then again, I'm not extremely well-versed in carburetor/distributor technology.

Or...am I still way out of time? It feels like it should be something remarkably simple that I'm missing here...but obviously I'm lost:/

Thanks all! As usual I really appreciate the time y'all take in answering my NOOBIE questions:)
 
From what I understand the weber needs a regulator. Where is the vacuum for your dizzy coming from. If it is getting vac at idle speeds, then it may be too far advanced. Fuel spurting up???. There are some threads on tuning webers. Try the fAQs in the 40-45,55 section. FWIW, I ran the thing for a year or so, I was happy to take it off. It could be that you have manifold leaks as well. What does it do when you try to idle it w/o the dizzy hooked up(vac source capped)
 
Thanks Lamb. I've been digging through tons of Weber tuning threads, and keep thinking that one of them is the answer...but not yet:/

No idle when I unhook the dizzy either.

Thanks for the input though! I'm sure the answer is right in front of me...I just can't see it yet.
 
I have to ask....


do you have the inlet and vent switched?

not all 38's have vents....sooo...dont be allarmed if you dont have a vent on yours
38 inlet vent.webp
 
where is your idle/air screws set? how many turns?

...there's one on each side

what altitude to you live?

is it electric or manual choke?
 
Thanks Johnny. I'm going to go double check that vent line is in the right spot. I know the inlet is, but I'm looking at that photo thinking my vent line isn't correct. And the idle/air screws are in a position I can't recall at the moment:) I started the carb tune based on what Weber instructed, and started backing out from there. Let me check that vent line and get back to you though. I'll feel pretty stupid if I walk out and see my vent line isn't in right.
 
jdog35 said:
Inlet and vent are in the proper places. I'm going to try the fuel-regulator next I guess. Still squirts out the top. Frustrating.
Click to expand...

Weird, I ran a web carb without a fuel regulator for a while with no problems. If you get a f.r. I would suggest avoiding those cheapo Mr. Gasket ones. Make sure all of your jets are correct. There is an excellent thread on this subject in the 40 tech FAQ on this subject.
 
I had the same setup on my 76 fj40. Mine would stall coming back to idle as well but would scream nicely when I stomped on the gas. It ended up being the ignition module in the DUI. I wouldn't neccesarily assume it's a carb issue particularly since it's brand new. Run down to pep boys and grab a new coil and module for a gm hei and give it a try, pretty cheap way to find out if it's the dist. If not bring em back.
Good luck.
 
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Thanks rsb. That's where I've been living the last 2 days reading EVERY FRIGGIN' WEBER THREAD!!! Going to attempt the regulator in the morning.

Thanks for the tip as well jeff. I will grab a new coil and module in the morning too. Not sure if I have a Pep Boys near me or not, so I'll get digging now.

Thanks guys!
 
jdog35 said:
Thanks for the tip as well jeff. I will grab a new coil and module in the morning too. Not sure if I have a Pep Boys near me or not, so I'll get digging now.
Click to expand...

I was just using pep boys as an example, any auto parts place will have them. I'd bring the old ones with you so the don't give you the wrong parts.
 
Well this sucks. Stuck the fuel-pressure regulator on there...and it didn't do a damn thing to stem the flow. It's still just dumping out of the fuel line. Crazy how much pressure is coming in and not going out. The ONLY thing I can think now is there is a sticky/gunked/bad valve.

Logically speaking, at wide open throttle there's enough load there to push that valve and keep the fuel pressure from building. But when the RPMs drop, that valve is getting stuck, and back-pressuring the fuel into (and out of) the carb. The fuel isn't coming out of the bowls either. It's definitely coming from the float-well and spouting out the top of the carb. Does that make sense?
 
Stuck float/clogged needle valve. Float may be stuck down causing the needle valve to stay open and fuel will just keep coming. Remove the air horn and set the float level. Remove needle valve and seat and clean/blow out. Don't over torque the cover. Prolly reuse the same gasket. Try that.
 
Thanks Lamb. Unfortunately that was one of the first few things I thought. The float was moving great. When I clamped the fuel line with my pliers, I was able to stem enough of the flow to get the damned thing to idle and stop flooding. Obviously that isn't a solution, but it did help me eliminate some other options. I was really hoping it was the float, honestly, 'cause that's at least relatively easy to fix. I hate it when a car makes me feel stupid:/
 
Felt stoopid plenty w/ my pig. It's that way to make you learn. OK on the float, what about the needle valve and seat? Missing spring between the needle and carrier? This has to be a volume metering problem. Are you still using the mech fuel pump? Is your tank pressurizing, maybe adding pressure to the supply circuit? Try running w/ the gas cap off.
 
Who's FP reg are you using ? What pressure did you set it at (3 to 3.5 hopefully), do you have an inline FP gauge post FP regulator to confirm the presure ? If it is only seeing 3 - 3.5 and it is still spewing fuel, something is wrong with your float/needle/seat assembly. Your manual clamping with pliers confirms this pretty much.
 
I'm using a Holley regulator (as that was the ONLY choice within a 20 mile distance). I did find that capping the distributor advance nozzle, and the subsequent nozzle on the carb itself, will let me idle. I cannot at that time add throttle or it will die. This tells my small brain the timing still isn't correct. In theory, then, since I can idle now but not throttle up, fixing the timing will solve all my problems when I hook that dizzy-line back up right? The joys of getting someone else's project in multiple stages of disrepair.
 
Hate to break it to you, but there is still something w/ your carb. It should NOT spit fuel like you are describing. What kind of manifold vacuum do you have. There could be an intake leak which will make it almost impossible to idle. You should have or get a vacuum gauge, a timing light, and a FSM. Check timing both static(engine off, #1 piston at 7*btdc, rotor of dizz pointing @#1terminal in dizzy) AND dynamic(engine running at idle and light pulsing in time w/ the BB mark on frywheel.) If your timing is set to 7-9*btdc, it should idle fine w/o vac advance. Having the carbs advance port capped(diz should have NO vac at idle BTW) and the diz set to proper timing(factory timing NOT DUI timing) you should be able to idle and rev w/ mechanical only advance. your timing could be off, but I am thinking you've got more going on than that. Possible intake leak, definite carb problem. The fuel delivery needs to be regulated and you need to make sure the float is operating the needle valve properly. The timing needs to be set to spec and vac advance should be capped for testing. Get it to idle and take some vacuum reading from the plug on the manifold in front of the carb. This will stem your overfueling, confirm spark timing is correct and give us an idea of how your mill is breathing. It is harder to trouble shoot things like this when so many things/ settings were changed. HTH
 
Thanks Lamb. I should have just gone down to the bare-bottom myself instead of trusting in what I was told (regarding the state of the engine when I bought it). Too trusting sometimes:/ Oh well. I guess all I've really lost is time thus far...thankfully.

Thanks again guys. I'll report back when I get a chance to crack this egg.
 
fuel pressure regulator is not needed to make it run. it helps when wheeling to keep a consistent flow of fuel so the carb doesn't starve between the pulses of the mechanical pump, most noticable on hill climbs.

have you had the vehicle up to operating temperatures and still have idle issues, or is it only when the vehicle is cold? is the choke hooked up?
 
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