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720 Weber z24 WOT dies out


Cory74700

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To start things off, I know it should go in an introductory thread, but my name is Cory, I live in Rough & Ready California and I drive a 1984 Nissan 720 4x4 King Cab on 31s

 

 

I tried to find a thread for this already but couldn't, the title is kind of generic, but my issue happens going uphill usually in 3rd or 4th gear about 3,500 to 4,000 rpms full throttle with secondaries wide open, I can go for about 10 seconds then the truck starts to bog out, like its either ocer fuelling, or running out of fuel, until I kick back down to the primaries, at which point I've already lost a lot of momentum and have to downshift. Any tips? I've tried leaning out the fuel mixture, I've tried richening it (which makes the truck diesel like crazy upon shutoff) I'm running 91 octane pump gas, and I only get fuel from shell because it's convenient.

 

Btw my setup is a nap 2.4 all stock, freshly rebuilt 500 miles ago, timing at 3* below tdc, only thing different is the Weber 32/36 dgev that's given me great overall drivability performance, just not uphill under WOT.

 

Any help is greatly appreciated.

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Hi Cory.

 

Failure to deliver enough fuel in high demand situations like what you have described can be lots of things but the simplest answer is usually the correct one. This is known as Occam's Razor. It basically states that the answer to a problem does not have to be more complicated than it needs to be.

 

Replace the fuel filter. It's cheap and easy and it's probably been more than two years since the last change. A partially plugged filter will limit how fast and how much fuel can be pumped through it. At some point the engine will empty the carb faster than it can be replaced and the engine will die.

 

 

 

There are other things to try but this is, like I said, the simplest/easiest/cheapest. It would be wrong to go right to replacing a carb or rebuilding it only to find out later that it was a $4 filter.

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I've not considered the fuel filter yet but I'll start there, thanks Mike, also the Weber carb is only 400 miles old, I discovered my vacuum secondaries on the original carb weren't working, and I had the money laying around for the Weber. I got very lucky with my truck as California DMV system says it's a diesel truck even though all the emissions parts are in tact, even has a cat on the exhaust. But I'll have my wife go get me a fuel filter and I'll install and run it up the hill tomorrow and post the results, I'd do it today but I have the kids with me till 10 pm and these king cabs don't hold car seats very well.

 

Again, thanks Mike for the snappy response.

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I'm not sure but they goofed it somehow, at any rate I'm free to do any future engine swap my heart desires now, the end result is hopefully a Mercedes om603 diesel if I have a long enough engine bay, I have a donor car I bought cheap that just needs a shift solenoid in the tranny, but that's another topic for another time and a different thread. Apparently the fuel filter for this Nissan is a hot commodity right now, the only auto parts store locally is Riebes, or NAPA Auto Parts for the folks who don't have Riebes locally and they only have one in stock so I had to have them put it on hold for me. Any tips on attacking that fuel filter? it looks like it's behind my fuel pump, I have a feeling it just pops out there's a couple hose clamps and then you replace it and pop it back in. But if there's any special technique I feel it would be worth my knowledge to know before I jump into it

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I discovered my vacuum secondaries on the original carb weren't working,

 

Just how did you determine that the vacuum secondaries weren't working ?

Was the vacuum diaphragm ruptured ?

 

The reason I ask is that those 2-barrel carbs would seldom open by just looking at them while revving the engine, due to there being quite a small orifice between the diaphragm, and the signal source.

 

I had that same set-up on a '76 Corona, and I drilled out the orifice a little at a time, until I could see the secondaries open by revving it..

Really made a difference on mid range power. So much so that the first time I went around a particular corner on my way home from work, that I had taken hundreds of times, and could floor the throttle half way through before, that the rear wheels lit up, and I looped the car.

 

Remember, car manufactures do things like that for mileage numbers, and to protect idiots that have no idea how to control a vehicle.

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When I put my rebuilt engine in, I wanted to just swap the carburetor over but I remember during the swap that previously under wide open throttle I was never able to hear nor feel the secondaries open, also it had a severe lack of power. So when I pulled the carburetor off I flipped it over and tried activating the butterflies and the one for the secondaries was stuck completely shut, I disconnected the vacuum actuator and still couldn't get the secondary butterfly to operate. So that's when I just ordered the Weber, I have previous experience with the Weber 32/36 on an old Mitsubishi Mighty Max their simplicity and adaptability is what made me just put the Weber on it instead of rebuilding the old carburetor that had almost 400,000 miles on it, and came off of an engine with a cracked block.

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It's vacuum operated and just revving rarely shows movement. A sudden very high rev with full throttle will usually cause the secondary to dump fuel showing it's open. If stuck it just needs to be loosened so the diaphragm can do it's job.

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Sounds like the secondary shaft is frozen in the base.  Remove the linkage and the secondary butter flies.  Soak with WD40 for several days and take a small brass hammer and lightly tap on the end of the shaft on both sides.  Keep trying with the WD40 and the brass hammer until you can turn it by hand.

 

I suggest that you do the bearings as this shaft will freeze up again in time and you will likely have a vacuum leak between the secondary shaft and the base where the shaft goes through.

 

I had both shafts frozen in this Weber.  Bearings on both shafts after the main shaft froze up again in less than a month.

DSC00669.jpg

 

DSC00671.jpg

 

Weber bearing install

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So I finally got around to replacing the fuel filter today, it was pretty plugged up and immediately when I replaced it I noticed that my idle dropped about 400 RPMs which would be a good indication of it richening itself. I also discovered several cracks in the fuel lines running from the tank to the filter and from the filter to the pump and from the pump to the hard line that runs to the engine bay. If anybody could enlighten me on how to post pictures from a mobile device I would share my findings with you guys. As for the tip about the Weber carburetor, mine only has 400 miles on it, it was brand new right out of the box so I don't believe it's gummed up yet or has anything malfunctioning internally, and that's based on the fact that I only run 91 octane. After work tomorrow I'll take my truck up the hill and see how it does under wide open throttle at about 4,000 RPMs, there's a stretch of highway that goes for about 3 miles so I have plenty of room to see if I can duplicate the result

 

I also took a video, there's a whining sound that wasn't present until I replace the carburetor, I don't know if it's normal with the Weber swap or not, but as stated above if anybody knows how I can post pictures and videos on here from a mobile device I'd love to share my findings.

 

Thank you everybody that has offered insight so far

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Cracked and ugly lines everywhere

https://i.imgur.com/jqtxfL9.jpg

https://i.imgur.com/GcxFaXb.jpg

 

I got curious and cut open the fuel filter after finding this silt in my hand

https://i.imgur.com/9KDduDR.jpg

https://i.imgur.com/l9vaCSF.jpg

https://i.imgur.com/yUfGJEM.jpg

 

All the shiny new stuff

https://i.imgur.com/LOrYj1u.jpg

 

And for the ones curious of the vehicle itself

https://i.imgur.com/uBfLau7.jpg

https://i.imgur.com/WvQkURi.jpg

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This is the video of the whine sound, i went to different areas of the vehicle for different sound quality and it also illustrates how far away It can be heard, also to my ears it sounds like it has a slight stutter to the idle, but if it sounds normal let me know

 

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From the other video at the very beginning there was a clicking sound that sound is coming from my fuel pump, here is a close-up video of that as well, I don't know if it is normal or if I need to replace the fuel pump but it is working it pushes fuel to the carburetor

 

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It's normal for the electric fuel pump to make a whirring sound when working. It usually slows down as the carb fills and not much gas needed.

 

 

Mike, how were you able to post the picture instead of just the link?

 

 

Go to your imgur picture and left click it and it will display by itself.  Right click it and the drop down menu will display. Left click Copy Image Location and return to your Ratsun post. Find the yellow happy face above your text and Right click on the green rectangle with the green border just below it. In the URL panel that pops up press Ctrl and V keys at the same time and then OK and your picture will display.

 

There are probably many ways to do it but this works for me. Just practice it till you don't even notice what you're doing.

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I'm using a mobile device though, not a computer, maybe I can get it to work differently if I load up the full website version or something, as for the fuel pump goes, I guess if it ain't broke don't fix it, it still gets fuel to the carburetor, I'll get an in line pressure tester one of these days and see how the fuel pressure looks

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How did your truck run after the filter and the hose change.

 

Is the fuel return still hooked up after Weber install?

 

Buy some K&N spray air filter oil and spray that air filter litely.

 

41EBM6Ce9DL.jpg

 

If that is a Weber kit from PIerce Manifolds the filter element is washable and reuseable.

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The truck runs great the first video I posted was actually after the filter and the hose replacement but that's just a title driving it around this thing still sucking down feel like it's the thing to do though I didn't get a chance to run it up a hill and see if it dies out or not as far as the fuel return line goes, that's all original so up near the carburetor the fuel lines come in at an upside down y and I'm guessing the reason for that is any excess fuel that would be pump to the carburetor just gets fed right back to the fuel tank instead of constantly sitting there putting pressure on the seals in the carburetor as for my air filter I don't believe it's a washable reusable one but it doesn't have that many miles on it yet I haven't even gotten to my first oil change yet with this new engine

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