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Carb rebuild?


FauxRoux

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So the wife went to work in her new truck and after 5 min on the freeway reports a "chunk" noise from under the hood and a loss of acceleration followed by spluttering acceleration and limping to work then home on side streets.

I check it at home and idles fine so I drove it around the block and experience the same sputtering, lurching... broken up by the occasion normal acceleration if feathered just right.

So I figure check the fuel line and find this...

20160416_152138.jpg

Also the lines were all cracked. When I pulled the lines off the filter it completely detached on the inside.

 

I replaced the filter and lines. Unfortunately the spluttering though better....is still present.

 

So I move on thinking maybe some of that crud and rust made its way to clogging up the carb? So I take off the air cleaner and find this hidden in the back out of the corner of my eye...

20160417_194341.jpg
 

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20160417_194356.jpg

 

20160417_194415.jpg
 

I got a little leak...just to the right, halfway up the cable  there's a little puddle...also the double gasket and orange silicone?

 

 

So what do you guys think? This look like a rebuild? or worse?

 

Im new-ish to trucks and new to Datsun so any advice is appreciated.

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I would just replace the base gasket where it is leaking and see how that works out. You can get the material at any auto store to make your own gaskets. Start with the easy things first. I know first hand that a vacuum leak like that will make your truck run like shit. I hope this helps you. Good luck.

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L20Bs run hot under the hood and a thick phenolic spacer is used to insulate it from the hot intake. That does not indicate the carb was rebuilt only that it was removed and for some reason someone may have added one or lost the original and like all chevy owners they buttered it up with their favorite color RTV just to be sure.

 

 

If you have a gas puddle it isn't a leaky gasket, as intake vacuum would never allow it to get out. The filter contents have gotten into the carb and more specifically may have jammed your float needle valve and the carb is flooding. Flooding might do that. Look on the front of the carb at the small round bull's eye while the engine runs. Fuel level should be in the center at the dot.

 

The carburetor fuel inlet fitting (called a banjo fitting, you'll see why once it's removed) has a fine mesh brass screen. Might be worth removing and cleaning it?

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If any went through the engine... it went through the engine. Maybe years ago so doesn't really matter now. Probably little;e red chunks on the side of the road somewhere.

 

 

Definitely a chevy owner had this truck.

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If you decide to rebuild the carb, things to watch for - There are two tiny check balls down different holes over near the accelerator pump. They are waiting to escape and never be seen again. Study the exploded view that comes with your rebuild kit so you have an idea where they are and can catch them.

 

Three large screws come up through the bottom of the cast iron base to hold the upper carb body on. One of these 3 is hollow and needs to go back in the correct hole. When you reinstall these 3 it is strongly recommended to use Loctite on them. If you don't, they will come loose over time, cause a major vacuum leak, and the carb will have to come off again to tighten them.  I know this from experience. Best to do it right and not have to redo it in the future.

 

Autozone has the carb base gaskets individually. Not many auto parts places do.

 

Len

 

 

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If you decide to rebuild the carb, things to watch for - There are two tiny check balls down different holes over near the accelerator pump. They are waiting to escape and never be seen again. Study the exploded view that comes with your rebuild kit so you have an idea where they are and can catch them.

 

Three large screws come up through the bottom of the cast iron base to hold the upper carb body on. One of these 3 is hollow and needs to go back in the correct hole. When you reinstall these 3 it is strongly recommended to use Loctite on them. If you don't, they will come loose over time, cause a major vacuum leak, and the carb will have to come off again to tighten them.  I know this from experience. Best to do it right and not have to redo it in the future.

 

Autozone has the carb base gaskets individually. Not many auto parts places do.

 

Len

Good timing...I just finished cleaning and rebuilding the bottom....Unfortunately I didnt mark the bolts I took out the bottom though (didn't realize i needed too) ....the hollow bolt...would it be safe to assume it needs to go back in the hole that goes clear through? or is it the odd bolt?

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If you decide to rebuild the carb, things to watch for - There are two tiny check balls down different holes over near the accelerator pump. They are waiting to escape and never be seen again. Study the exploded view that comes with your rebuild kit so you have an idea where they are and can catch them.

 

Three large screws come up through the bottom of the cast iron base to hold the upper carb body on. One of these 3 is hollow and needs to go back in the correct hole. When you reinstall these 3 it is strongly recommended to use Loctite on them. If you don't, they will come loose over time, cause a major vacuum leak, and the carb will have to come off again to tighten them.  I know this from experience. Best to do it right and not have to redo it in the future.

 

Autozone has the carb base gaskets individually. Not many auto parts places do.

 

Len

What I mean to ask is, given these shots...

20160419_235107.jpg

 

20160419_235157.jpg

 

Would it be a safe bet that the hollow bolt goes in the top right? (since the top right seems to go clear through the middle of the carb).

 

and thx again for the heads up on that, it was in the ta-da nick of time.

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Fortuitously, I pulled the carby off my 510 yesterday. It has been running fine as far as idle and high speed, but has a persistent lag on acceleration. I've fiddled with, adjusted, and replaced the accelerator pump and still can't get a decent stream of gas from the A. pump nozzle. I'm wondering if the passage from the A pump to the nozzle doesn't have a partial clog. So I'm going to try a different carb. None of which is your problem, just I have two carbs to look at this morning (which may not be a good thing. Read on.).

 

The carb I removed has the hollow bolt on the float bowl side, which I think would be the upper right in your pic. As I recall two of the bolt holes are blind holes and one hole is open up into the body of the carb, so I'm reasonably sure that is where the hollow bolt goes. I think this is pretty much as you have figured out.

 

The Hitachi I plan to put onto the 510 is a different story. It has 2 hollow bolts and one solid. And as you can probably guess, the solid one is installed next to the float bowl, which seems to be wrong. I don't recall where this carb came from, it was just in my pile of carbs. But it may have ended up in my pile because it didn't run right and someone yanked it for a Weber. t has a sticker from a rebuilder on it, but I'm wondering what may be screwed up inside it, especially where the tiny check balls ended up assuming there are any in this carb.

 

Later this morning I'll go through my carb pile and do a survey for where the hollow bolt is on them. I won't be shocked to find it is totally random. I'm very curious what it does to the way the carb runs if the hollow bolt isn't in the correct hole. It is pretty major air passage so it seems like it would be important.

 

Len

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Same thing happened to me on the bolts getting loose. Massive vacuum leak that was barely drivable. I had to tighten them up but with no loctite, since I didn't have any

If you decide to rebuild the carb, things to watch for - There are two tiny check balls down different holes over near the accelerator pump. They are waiting to escape and never be seen again. Study the exploded view that comes with your rebuild kit so you have an idea where they are and can catch them.

 

Three large screws come up through the bottom of the cast iron base to hold the upper carb body on. One of these 3 is hollow and needs to go back in the correct hole. When you reinstall these 3 it is strongly recommended to use Loctite on them. If you don't, they will come loose over time, cause a major vacuum leak, and the carb will have to come off again to tighten them. I know this from experience. Best to do it right and not have to redo it in the future.

 

Autozone has the carb base gaskets individually. Not many auto parts places do.

 

Len

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I don't know anythign about those carbs, but did you look at the gaskets to see if you could tell where your leak was coming from? Inquiring minds want to know.

I did look about and didn't find any of my gaskets to be leaky (at least as far as I could tell)....

 

So mike is probably right and the Carb was flooding due to clog...although this screen is filthy and a tad bent it doesn't look covered in crap....it is rusty colored though...

 

20160419_174404.jpg

 

20160419_174354.jpg

 

P.S. I assume the blue loctite is the way to go on the 3 base bolts? Or would 1 drop of the red be OK you think?

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I'd think blue Loctite http://www.loctiteproducts.com/p/10/15/t_lkr_blue/overview/Loctite-Threadlocker-Blue-242.htm

since you may want to get it apart someday. With the location of the threads up inside the carb, being able to heat them if you use red Loctite and want to loosen it could be a problem.

 

I looked at another stray Hitachi I found out in the shed. It also has two hollow screws and one solid, but one of the hollows is on the float bowl side where I think it should be. I'm not sure where the rest of my carbs are hiding. There is one on a manifold I didn't take time to remove, but there should be 3 or 4 others loose around here.

 

Len

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2 other things.....I open up the carp and the jet(?) piece was free floating and came right out....the right side is in solidly but is super sooty compared to the loose left side. Just line it up and tighten it in with set screw on front?

20160420_124634.jpg

 

Second...You guys think I should reuse these spacers and the plate under them? (obviously not that gasket too...just hadn't removed it) Or pry them up and clean it out? I needed a 12mm open ended crowfoot to get the bottom left 1 off, closed wrench wouldn't fit in between the carb and bolt...

20160419_150641_1.jpg
 

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As to your free floating venturi, see my post #12 here:

 

http://community.ratsun.net/topic/67938-dch-340-identification-adjustment-issues-etc/

 

There may be something else in that thread relating to venturis so you should probably skim through the whole 3 pages. I'm pretty sure you need both a tiny O-ring and the spacer before you re-install the venturi. Some rebuild kits include the O-rings and some don't. I don't know if a good auto parts store would have O-rings that small available or not. The spacer you can maybe make. The screw though the side of the carb body is staked at the threads. I recall Cardinal Grammeter or someone saying they were able to turn the screw with effort. Cardinal had several carb related posts about the time of the linked one. You might want to look at his back posts. I recall there was quite a bit of detailed Hitachi info.

 

Probably a good idea to replace the gaskets under the phenolic spacer and the heat shield plate. As I said, Autozone has base gaskets if there aren't enough in your carb kit.

 

It is usually a fight to the death accessing the carb base nuts, especially if you still have the air injection tubes going into the exhaust manifold like you do. I heated a cheap 12mm wrench with a propane torch and bent the handle so I could swing it. Access to the base nuts is not one of Datsun's best designs. I always keep a small telescoping magnet handy when I do those base nuts and washers so I can retrieve the dropped ones.

 

Len

 

 

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The carb with the loose venturi is a California carb. The venturies should not be removed or an attempt to remove them made. They are each held in place by a screw on the rear side of the carb body. Non California carb venturis have two Philips screws accessed down through the top. These can be removed and the paper gasket under them replaced. The non California venturis also have an air bleed in them.

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The carb with the loose venturi is a California carb. The venturies should not be removed or an attempt to remove them made. They are each held in place by a screw on the rear side of the carb body. Non California carb venturis have two Philips screws accessed down through the top. These can be removed and the paper gasket under them replaced. The non California venturis also have an air bleed in them.

so with the loose venturi should i attempt to put it back in with the gasket and o' ring that came in my kit? and if so should I attempt to open the setscrew to tighten in place, or just do my best while being careful?

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datzenmike - I think the problem is they seem to remove themselves. I have two Cali carbs with venturis that have come loose and seen posts from other folks who have had this problem. Of course there is no way of knowing if they are loose because a previous rebuilder took them loose and didn't get them tight. But the staking on the screws on my loose ones doesn't appear to be disturbed.

 

FauxRoux - I'm going to give you a guess on what to do and hope someone else chimes in with a better idea. I'm thinking you are missing the little rectangular spacer that goes between the venturi and the screw through the carb body (I didn't see it in your picture anyway). If you have it, great, use it. If not you may be able to make one judging the thickness by looking at the spacer on the other venturi. However, I looked at the A-series Hitachi off my F10 that has a loose venturi and it appears they didn't use the spacer on that model carb. The set screw bears directly against the end of the venturi. It came loose, but so do the ones with the spacer. I don't know if you try to get by without the spacer  you will have enough threads on your set screw to get it tight. Probably, but that is something for you to think about. I don't know how easy it is to slip the venturi down into place without moving the O-ring out of place. You may need to back off the set screw to give more room to get the venturi down beside the O-ring. Is there also a paper gasket in your kit the shape of the end of the venturi? I wasn't aware of this, but my on my two with loose venturis I imagine the gasket got sucked through the engine.

 

datzenmike - Do you have anything in your bottomless notebooks on the hollow screw(s) that hold the carb base to the body? I took another carb off a manifold and it has two hollow screws. Of the four carbs I've looked at so far, three of them have two hollow screws, not just one like I thought was correct. Maybe I was wrong about there being two blind holes taking solid screws. Any opinion on number and location of hollow screws?

 

Len

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