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Weber upgrade


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Another newbie without pic's but I will have pic's soon but for now I am stumped. Beware long winded vent ahead but only to give the history so maybe there is a chance at help. Bought this wicked 1980 720 ext cab in Jan ran great (except for 2 minor things) for 3 month and the last 4 has been alot of wrench time. 1st day was new alt, second day was battery becuase I reconnected amp wire that was laying next to battery without checking to make sure was connected right (ooops). So I had the water pump go replaced that gave it a tune up while I was at it, then came carb problem's. So it would run for about 20 mins under load then sudden stall so I replaced fuel filter, then drove and it did it again so I checked for vacuum leaks found 2 and fixed but no improvement so checked fuel pressure and it was bouncing around 3 to 5 at idle so I replaced. Still having problems decided it was time to check the cat found that elbow of exhaust by my torsion bars smashed due to his crummy lowering job out came the grinder and cut off wheel now I am rocking a straight pipe while I fab up my soon to be stainless exhaust (got to love scraps from work). That of course made improvements but not what I was looking for so I rebuilt the Hatachi let the beer flow I finally got somewhere. Well at least I thought for 3 weeks of it running great then it came back but I was only getting 10 mins of run time found it was the fuel needle valve I think that is it's name. Well pop the hood take off air filter top give the carb a smack and back on the road to work and perform this over and over again until arrival at destination. Well that took about 2 days before I had enough and said its time for a Weber. Got a 32/36 DGEV from a friend that was on his shelf for 3 years and rebuilt it while waiting for adapter and linkage kit. Striped all smog off because I can in my area now it is rebuilt and installed. Again since I have gone this far new plugs, compression check, new fuel filter, and adjusted valves. So the carb is set to 2 turns out on the mixture screw and 1 1/2 on the speed screw and timing is at 12* and runs so good it gives you wood until you put it in drive the instantly falls on its face no stumble, stutter, hesitation nothing just off now like I turned the key off. Now I have been messing with the settings for 2 weeks and have not won yet the only thing that I can find is that at idle I have about 10in of vac at the dizzy unless I back the speed screw out until it is about to stall, I have check time at time again for vac leaks have had several buddies look at it and yet nothing. It will run in drive if a set the speed screw to 2800 RPM then it will not stall. hope the Ratsun gurus can get me on the road. Thanks for the help.

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for 3 weeks of it running great then it came back but I was only getting 10 mins of run time found it was the fuel needle valve


So why not just replacee the needle valve? They come in a $20 rebuild kit. The Hitachi is a great carb unless it's totally worn out, but since it ran great for 3 weeks it doesn't appear to be totally worn out.

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Doesn't the stock carb have a dashpot or something that kicks up the idle under load when in drive? that could be an issue. If you give it some fuel whilst putting it in drive will it still stall? Webers just dont have the best reputation for idling anyways.........



Not quite sure if the stock carb has a dashpot because I don't know what that it.? Yes it will not stall if I rev it up to about 2500 rpm then put it in gear or if I turn the speed screw in until it is around that RPM. The idle is perfect it is unload that I am having the problems with.

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So why not just replacee the needle valve? They come in a $20 rebuild kit. The Hitachi is a great carb unless it's totally worn out, but since it ran great for 3 weeks it doesn't appear to be totally worn out.



Whoops forgot to state that I did replace the needle vavle twice and both were sticking. I thought at first it was the float and I opened the float housing and found the float bowl moving then noticed the needle vavle was stuck.The weber was an upgrade I wanted to do anyway so it was a good time to do it. The truck always seem to lack power but it seemed to be in tuning not that I am going to get great HP out of it anyway. Even with the Weber not right I can get it on the road with a 2 foot method and long as my foot is on the gas it runs like a bat out of hell.

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the idle on load problem sounds like an air leak. You have adjusted the mixture screw to compensate, but the real solution is to find and plug the air leak. One common leak is with weber adapter plates coming loose.


I applied alot of loctite on the bolts due to all that I have read on here about the plate. I have hosed the carb down with a bottle of carb cleaner and now a bottle of starter fluid trying to find a leak and there is no change in engine speed at all. When adjusting the mixture screw I take it all the way in until litely seated then back it out 2 turns and tune from there it runs really good at about 2 1/4 turns. Reset everything this morning before I left work and found that fast idle screw was almost all the way in and was not letting the choke return. I backed it out until it was not in contact with the first cog on the fast idle cam then tuned it all up and nothing same problem will not run in gear. So I checked the dizzy and after this morning I have about 5 in of vacuum, does anyone now how much should be here at idle i thought that there should be no vac at idle and if so what other adjustments can be made other than the speed screw(it won't run if I back it out until no vac) to eliminate the vac problem?

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Ok so the problem is solved, so my buddy rubbed his magic crytal ball and told me that it sounds like I do not have 12volts all the time to the anti dieseling soleniod and to put a jumper from the battery to the soleniod. Well I did and bam just like the fortune teller said I was sitting there finally with it running in gear. So then I rembered that i disconnected the some wires next to the charcoal canister so I ohmed them out and found the is where my 12v supply came from and the connecting wire well that is where my mistake was should have put a jumper in. Thanks for all of the wisdom. I tried to add pictures to the post tbut hat seems to be more difficult than fixing the 720 so I will add them to my profile.

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