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Discussion Starter · #1 ·
OK, I have an angry Weber and I need suggestions. My 720 likes to sputter under heavy load. If I put it into 5th at around 45MPH and
push the accelerator down too far, it will miss pretty bad. It also does this if I have a load of wood in the bed and I try to start on an
incline, so bad in fact that I have to rev the engine pretty high and drop the clutch to get moving. Also, I can get the engine to turn
the other direction and shoot exhaust out the air filter if I give it too much gas when starting it. My primary venturi is covered in soot
now.
Here is what I've done so far so please hang with me.
-Disconnected the vacuum advance and retarded the spark but it didn't go away, so I ruled out a too advanced spark
-Disconnected ALL vacuum lines so it's not some weird vacuum leak somewhere out side of the carb
-It first started doing this when I put a smaller air corrector jet in the primary, so I thought it was getting too much fuel. I put the old
one back in but the problem still remains
-I don't think it's an electrical problem cause it consistently happens when I give it too much gas in too high a gear, that's why I
thought it was the vacuum advance. The plugs, wires, and cap aren't too old either.
-Could this be an EGR problem? I was playing around with it lately but have sense disconnected it.

I'm stumped on this one, I don't know if the missing and the backfiring through the intake are related but I really hate hearing that
"Spit..POP" sound when it backfires. Does this sound like an overly rich problem? The truck runs great under normal
conditions.

Even if you just have a small idea, fire away cause this thing is really anoying.

Bernie
'86 720 "The Stain"
 
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Discussion Starter · #2 ·
I hate to say it but when my timing chain got streched to the max after 125000 miles it did some of the same things. I played around with fuel and ignition for days until the guys at NAPA told me to replace my timing chain. How many miles do you have on your truck? Have you replaced your timing chain? the chain gets streched so much that the cam gets retarded.

 
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Discussion Starter · #3 ·
Wow...hadn't thought of that one. My truck does have 150,000 on it. So did you get a new chain from Nissan or some where else? I figure Nissan's got to charge quite a bit for it, but better quality, true? How much did the chain cost you, changing it shouldn't be too hard now that I know the block of wood trick to keep the tensioner in place. Thanks for the info.

Bernie
'86 720 "The Stain"
 
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Discussion Starter · #4 ·
I bought it form NAPA. I buy all of my important parts there. I think that nissan parts are way too expensive, but you may want to compare. Just don't buy from schucks or any other stupid places. You only want to change the timing chain once every long time. Good luck.
I paid like $100 for it
 
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Discussion Starter · #5 ·
Set the fuel pressure to 7 psi and see what happens. I don't care what the directions say. I put a weber on an '83c 720 and had the same symptoms until I turned up the fuel pressure.

 
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Discussion Starter · #6 ·
A few questions...

Mad, how do you raise the fuel pressure? I believe the pump runs about 3 to 5 psi, true?

Strider, did the chain itself cost 100 bones or did you have Nissan do it for you? Cause I just called Nissan and they wanted $40 for it. Or did you put in a new tensioner and guide rails too.

Also, is there some weird break in procedure for a new timing chain? Cause I've heard things like having to rev the engine above 2000 RPM for 15 mins once you put in a new cam or it will gride the lobs right off the shaft. Again, thanks for the info.

Bernie
'86 720 "The Stain"
 
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Discussion Starter · #7 ·
I bought the whole kit. It contained the chain, guides and the tensioner. I would recommend replacing everything while you are in there. I did it myself a few years ago and it took me a couple of days of futzing around to do it, but it was not too bad of a job, I learned a lot. As far as I know there is no break in proceedure fo the chain, I think that only cams need a break in. But I would definetly dump a bunch of oil on it and let it run for a few minutes before ripping on it.

 
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