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10 mpg on complete fresh rebuild


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Hey guys im new to this forum and new to owning a carburated nissan 720 4x4 truck...It has a weber 32/36 ( pretty sure but not positive ) and all the emissions stuff has been eliminated. I just bought this pickup due to the fresh rebuild and rebuilt tranny and how clean and straight the body is. I have driven it 50 miles exactly and then refilled the tank and it was almost 5 gallons of gas (4.995 gallons)... Would the carberator needing rebuilt cause my truck to get such shitty mpg i figure this truck should at least get 18 mpg with a fresh rebuild. It does have a small vacuum leak by the throttle plate.,. Any input on this would be helpful im kinda lost 

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18 would be on a good day, 15 is more likely. 10 is very possible if short trips to work and home where the choke never shuts off.

 

 

Poor milage...

 

Driving too fast and too close to the guy ahead of you. Every time you use the brakes you just threw away the gas used to get you to that speed. Avoid braking by spacing yourself and anticipate slowing in advance. As soon as you see a red light ahead release the gas and coast up to it. Does it really make any sense maintaining your speed only to put the brakes on at the last second to wait at idle??

 

Cam timed wrong but usually the performance is very bad also.

 

Fuel leak at tank or lines.

 

Carb jetted wrong (too rick)

 

Choke stuck on or not shutting off.

 

Carb flooding. Float stuck or adjusted wrong or needle valve dirty and not closing.

 

Ignition timing wrong. (retarded)

 

Possibly T V V stuck not allowing vacuum advance when motor has warmed up, as it should. Vacuum advance on distributor stuck or vacuum advance leak in hose or hose removed by a well meaning owner.

 

Brake(s) dragging.

 

Wrong thermostat (too cold) or thermostat stuck open. Motor never reaches propper efficient working temperature.

 

Too thick of an engine/trans/trans case or differential oil

 

 

Could be any one or several of the above.

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Motor was rebuilt by Southworth machine shop here in eugene Oregon and they do awesome work I've used them many times ... I guess I'm gonna just wait a few hundred miles and see if anything changes cause the motor is still tight and not even close to being broken in . Thx datzenmike I'll check on some of those things and CPL620 800 horses....ha I wish that would make one bad ass wheeler

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I average 17 in mine. When I got it i was getting 14-15. I replaced torn fuel filler hose, opened an unnecessarily blocked breather for the gas tank, and replaced a clogged fuel filter and now 17 is the magic number. I have the stock hitachi carb though so you should probably expect less mpg and more hp than mine.

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Ok so today after talking with Weber about a diaphram on the opposite side of my accelerator pump I found out that I have a very rare Weber double pumper carb. They don't make these anymore and haven't for a while and they only get a call about once a year for one of these new diaphragms($24)... Damn kinda spendy but I'm thinking I am due to buy a new 32/36 that's up to date lol... can't do 10 mpg for too long

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I was thinking of doing some research and possibly re jetting it and using it strictly for off road... It takes 3 minutes to swap it out and the acceleration is crazy with these carbs it almost instant with no bogging but it sucks fuel down...I have definitely put in the time tuning the damn thing though

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Re jet it. Why not. Get a new one too. And I'm not sure if it is a problem on 720's but is the fuel pump regulated to webers desired pressure? My weber ran for a long while sucking down those hydrocarbons way faster than needed. Anyone want to comment on the stock 720 fuel pump pressure?

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You should be getting a minimum of 50% better mileage. If leaking fix it. If jetted and leaking fix them both. If double pumper for a six cylinder Capri or w/e get the correct carb for your application. You don't need it

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If you are indeed getting 10MPG then this isn't good for the rebuild. The unburnt gas is going to wash the lubricating oil off the cylinders and rings and dilute your oil. Plugs, combustion chambers and rings will carbon up. Rings will stick in place and can score the cylinders.

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