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Hitachi DCH-340 Carburetor


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Hi guys....This is crazy but I have a couple of Chevy LUV's and one has the stock engine with a DCH 340 Hitachi carb as stock on the truck. I went through some of your posts from about a year ago that dealt with the 340 and they were pretty extensive. Right now I'm having a lot of trouble with my carb not atomizing the idle fuel very well and the result is poor idling. Today I re-built the 340 and did all kinds of cleaning of the jets, orifices etc. but I'm still having the same trouble. As I look down the primary barrel I can see that the fuel is sort-of dripping/half spraying onto the top of the butterfly below. I can see beads of fuel laying on the butterfly itself too. I know the float level is good and that the vacumn lines are all hooked up correctly---according to the Haynes LUV manual and the Chevy LUV series 6 manual. I don't think I have any vacumn leaks either. I really think the problem is because the fuel spray is not well patterned or fanned well. There seems little chance of complete atomization when this happens. OK...does anyone have any ideas why the fuel is half spraying/half dripping like it is?? I allso had a Datsun210 and three Bugeye Sprites. I like these old cars/trucks and I want to keep this one running. I also think it is neat that some Datsuns and the Isuzu have the same carb. Thanks for all your help....Don

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Hi Don, welcome to Ratsun :)

Sounds like you've done some good investigating.

I also use the DCH340 and like them, but like anything else you can get the odd one with probs deeper than what's readily apparent. I too had one like yours that seemed to wanna keep the top side of the butterfly moist with fuel....turned out to be a cracked body :(

It helps to have a few spare carbs around to bolt on and rule out other probs.....if possible.

--Ray

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Don - I don't have an answer for you, but thought I'd post in hope keeping this thread alive. I noticed the other day my recently brought back to life 510 which has a rough idle seemed to be doing something similar to what you describe. At the time I didn't look too closely, but thought something didn't look quite right. Seems to smell like it is running rich at idle although it smooths out and runs fine at higher speed. I intend to take a peek down the carb on my 200SX today and see how it looks at idle.

 

Did you try spraying carb cleaner around the intake manifold and carb base when at idle? That is supposed to sometimes detect hidden vacuum leaks from a bad gasket.

 

I didn't realize LUVs used the same carb as Datsuns. When I go to Pull n Save I look at Ford and Toyotas just in case they have a Weber. I'll add Chevy to my look-at list.

 

Len

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Len....I didn't try the spray yet but will this afternoon. I'm fairly confident there are no vacumn leaks. I did notice today going to work that the power brakes don't quite feel right. I got out and checked the vacumn line to the power unit and everything looks good. But now I've decided to plug up the vacumn line in case the power unit is bad or has an internal leak. That could be a source of irratic running at low idle. Otherwise, I can feel the engine 'jerk' forward during a deceleration [like stopping at a light] and I think that is happening when the throttle is back to idle but the jet is still spitting gas and that accounts for the 'jerk'. As for the Hitachi 340, my LUV is a 1977. If you find any with a good transmission, kindly let me know. Thanks....Don

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Fuel for the idle is sucked in at or just below the throttle plate. Take a look at the location of the idle mixture screw. You should not be seeing any dripping or spray from above the plate. Certainly not from the venturi.

 

If you are, the idle may be too high and enough air is passing to draw fuel from the primary jet. This could be from a blocked idle mixture screw or your idle cut (if equipped) is not working. Without idle fuel the speed has to be turned up and it runs on the primary.

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datzenmike - Thanks once again for timely information. After posting this AM I went out and fiddled with the carb on my 510. It flashed through my mind that at idle the fuel should be coming through the idle hole down by the throttle plate, but the thing was running at low idle, and I could see fuel coming out up by the venturi, so I thought I was misremembering. You know how you look at something and think it isn't really right, but it is running so I must be wrong? I forgot about the idle cut solenoid. It isn't hooked up, so that kills fuel to the idle jet doesn't it? I took the needle out of the cut solenoid on my 200SX years ago. Actually I dropped it and the engine ran without it so I left it that way. Also could be something plugged down at the idle mixture screw. I thought about taking the mixture screw out and spraying carb cleaner and compressed air in there. I'll do that this afternoon.

 

That is if I can get my electricals back. I was trying to do a jumper wire across the plugin to the disconnected auto choke relay (unhooked it after going to IR alternator). I don't know what happened, but I have no oil or alt warning lights or starter. Headlights are working. I thought when I was fiddling around up there I could hear something clicking off and on. Does a bad starter relay kill the idiot lights on the dash? I need to get out the wiring diagram and puzzle this out. It was running so good this morning around in my driveway too. Sigh.

 

Len

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I did check the fuses with a test light before I came in for lunch, and all seemed okay. But I did it fast and whenever I hurry I miss something. I'm about to head back out and hit it again. What's odd is losing both the idiot lights AND the starting circuit at the same time. I tried wiggling the dreaded spade plugin connector down at the starter solenoid and that didn't help. I need to take the test light and start seeing where I have power and where I don't.

 

Don - I kinda of highjacked your thread here, but it does sound like we are having similar carb problems. I remember someone telling me there was a weakness in some LUV transmissions and it is tough to find a good used one. LUVs show up at Pull n Save in Spokane now and then, but no way of knowing if the trannys are good or not. It seems like buying another complete truck with bad body and good trans would be a safe way to get one. But there aren't a lot of LUVs left in the world. They used to be a common vehicle on the roads.

 

Len

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Might be more or less fixed, at least for today. When I went back out, my electrics were working, then off and on while fiddling on the carb. Tomorrow I need to do some serious checking on ground connections and all the fuses.

 

I unscrewed the fuel shutoff solenoid but someone beat me to it on removing the needle. No needle or spring left in there. I removed the idle mix screw and sprayed carb cleaner in the hole. While that was soaking I brought over a portable air tank and gave a couple of good blasts of air in the mixture screw hole at the base of the carb. Carb cleaner or gas shot out the top of the carb throat. I reinstalled the mix screw, started it up, and no more gas flowing out up at the venturi. So it seems I had a plug in the idle mixture system. I hope this works as well for Don. If he hadn't posted his question, I may never have caught this problem. It would be nice if this thread could be moved over into Engine where more people might see it. I have a feeling this is a common problem with old Hitachis.

 

Len

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Hi guys...This is great....I did remove the Vacumn line to the power assist brake booster and did not get any change. So I guess the booster is in good condition and not leaking vacumn. My leak is in the primary venturi like yours was LEN and we THOUGHT we had sprayed it out very well but I'll try your solution maybe tomorrow. The LUV is still running but doesn't idle well and I still drive it to work. I'm thinking my problem is only in the carb and not vacumn related. DatsunMike....I'm not sure of your term 'idle cut' but I did check out my anti-dieseling selenoid and it works well. Are we talking about the same thing? Anyway, I'll blow out the air/fuel port and get back with you guys. By the way, I checked out the 340 on google and a site came up from ' www620.com' that is titled "Fuel System--service instruction work sheet" that has a good blow-up and 2 pages of how to set/adjust the fast idle adjustment, the vacumn break adjustment, etc. Might be worth copying and inserting in your Datsun repair manual. It also lists 3 different Datsun engines that use the 340 carb. Thanks for your help....Don

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Don - I had the fuel up by the venturis problem re-occur, so I repeated the procedure of taking out the idle mixture screw, spraying carb cleaner in the hole, then blowing out with compressed air. After reinstalling the screw, I held the throttle butterfly open, stuck the tube of the air nozzle down the carb throat, and blew more. My idea being the air going past the idle hole under the butterfly might suck anything out of the idle circuit. Whatever I did worked and there is no gas coming out by the venturi. It also seems to be running a lot leaner at idle. I was getting really sick of the smell of unburned gas.

 

I also made good progress on my electrical gremlins. I won't say everything is fixed, cause I've thought that before and been wrong. But seems things are improving. And so far it is staying warm enough to work outside.

 

Len

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So I did another carb 'cleanout' but only the anit-dieseling and idle screw ports--also the air vents to the bowl but got no satisfactory results. I finally gave up and ordered a re-built carb from somewhere in Florida. Hope it gets here soon.

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DCH340 is more sophisticated and flows more air than a weber 32/36. But after 35 years many are worn out.

 

I would not use compressor air on a carb as there are delicate parts inside. I use spray can of carb cleaner.

 

Slow jet blocked can cause thid problem. Slow jets prevent siphoning.

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Hi guys...So, as an epilog to this subject {Hitachi  DCH-340],  I did remove the new EGR valve and I found  that I failed to insert a washer-like damper  that blocks some of the exhaust gas  and prevents a complete 'full flow'  of the gas to the carb from the egr valve.  This washer goes at the base of the valve  and restricts the passage of exhaust gas.  The washer's center holes have a range of about 1/8 inch to 5/16 of an inch to allow the egr manufacturer to apply  their product to several makes and models of engines,  The EGR manufacturer included these 'washers' in my newest box  but I think that there were none in the 'first' egr box that I installed in the car--'77 chevy LUV.   As a result I was blasting the carb's  natural venting with a heck of a lot of extra inert exhaust gas.  I think that some of the gas was even managing to enter the carb barrels and may have blown upwards  and created the 'dripping gas' problem and the incorrect fuel spray pattern I was having before.  I just wanted to get this out to you guys in case someone needed it in the future.  It sure drove me nuts for a while.    Don

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I have an 82 GMC S15 1.9l with a DCH340 on it Im rebuilding it (my first ever) and I took off all the pices that are on the stem of the throtle valve. I have them in order that they came off but not sure what direction they were. I cant find a diagram that shows this part of the carb and having trouble figuring it out so if some one could take a picture of thers and post it or send it to me it would help alot. thank you and my email is ezm420@yahoo.com And mine also was not running at idle well wich is the resound Im rebuilding. sorry if this is off topic I need to get this done and not sure were to go for help.

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Sorry the pin I pulled turned out to be the anti dieseling solenoid,I put the pin back in.What did help on mine was adjusting the electric choke.The black plastic spring housing was pinned so I could not adjust choke when I loosened the three screws.I found a pin in place in the other half of the spring housing( carb side) and pulled the pin out with a pair of vice grips.I guess some models this was a notch in the casting and you need to grind it off.Anyways after you do that it allows the choke spring housing to rotate and this helps the cold idle problem.Theres also a high idel screw adjustment thats a bitch to get too you can adjust.This kicks in when engine is cold and you hit the gas pedal once to start.After the electric choke warms up and opens the high idle cam kicks off.

 

Hope this helps

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Yeah, on the 720 carbs, the casting has a nub that fits the choke heater housing and prevents adjustment. I can see this being done by the factory to prevent owners setting it richer and spewing unburnt hydrocarbons. What the hell were they thinking.... that the choke coil inside would be stable for 30 years??? When new they are fine.  I ground mine off so I could start easier when cold and it doesn't even get that cold here.

 

The fast idle adjustment screw needn't be adjusted. It would be fine if easy to get at but it isn't. A drill bit of a certain size is set between the throttle plate and the carb casting holding it open a calibrated amount. The normal cold fast idle is between 1,800 and 2,200 depending how cold it is, how far on the choke is and what step the cam is on. I wouldn't bother opening it more, just adjust the stepped cam to come in more. Too high and it's hard to put in drive or hold  at a stop sign.

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was talking to a hot rod guy shop owner in Healdsburg a few weeks ago , he was telling me that something needs to be completely by passed in this carb.

Told me that they do multiple carb set ups with these things for v 8 stuff.

I can pm you his info maybe rebuild for you.. or pointer

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