hey guys, I have a 1971 521. This is the first ever car i have taken apart and put together. Had the engine rebuilt, replaced a lot of parts as well. One thing i didn't keep in mind when building was selling the stock exhaust header and replacing it with an aftermarket one i bought from Datsun Parts in Rancho Cucamonga. I have the stock Hitachi carburetor also had that rebuilt. Truck is running pretty lean now, had someone tell me to drill out the main jet in the carb one size bigger to compensate for the extra air flow? Any advice would help, I broke down the other day just started to bog out. Afterwards could turn the truck back on but as soon as i hit the gas it would just bog and shut down. Thanks for the help
Posted 19 March 2017 - 07:09 PM
Don't listen to others. A header is not going to work any better than the exhaust manifold it replaced, so...
How do you know it might be running lean???
Carb may have been rebuilt but it sounds like the primary jet is part blocked which will produce a lean condition.
Posted 19 March 2017 - 08:22 PM
Someone who worked on the truck for me prior to this happening had said it seemed to be running lean. I know very little about carbs. He told me the aftermarket header was pushing way more air than the stock header and said could possibly need to size up the primary jet because of that. If you guys have any solutions or ideas thank you. Would love to find another stock header for an L16 just havent had any luck searching for the past few weeks. stock header back on it would probably solve my problem
Posted 19 March 2017 - 10:15 PM
New to me, I've never heard of extractors causing an engine to run lean...
Sure they can improve the air flow OUT of your engine but that has no real direct effect to your fuel or airflow into the engine. The entire "back pressure" myth is just that.
Now like Mike said, it could be your jets clogged up but when was the last time you checked out the fuel filter? Start with the simple things and go from there. You're lean, okay so you don't have enough fuel... Start with that.
Posted 20 March 2017 - 05:09 AM
IF your exhaust manifold was restrictive and you removed any restriction it can sometimes alter the exchange of exhaust gasses for intake gasses. This won't be the case on the L16 manifold as you can see....
When the primary jet is blocked or partly blocked it restricts the amount of fuel available for the air drawn in by the engine. Power drops off and the engine will 'fall on it's face' when you step on the gas. If part blocked, you may be able to rev the engine sitting still but it isn't driveable under load. If badly blocked it won't even rev up in neutral.
The porcelain insulators on a lean running engine will have a very light or white color, normally they are tan or light brown. The lighter the color the leaner the mixture.
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Posted 20 March 2017 - 07:02 AM
read Olddatsuns.com the tech section. read it!!!!
If truck was running fine and then it changed then you you have to trouble shoot the carb or the distributor.
A header isnt going to change it all that much like a 2 stroke when the exhaust is swapped.
buy a timming light and just the timming.
does the truck run better when the choke on?(manual choke pull the cable. Electric just unplugg the wire)
you see gas squirted in the carb when you cycle linkage?
I would get a weber DGV myself as most carbs are just worn out by now. But if the stock carb runs fine I would still use it as a daily driver. As Im old and dont care anymore but Webers are ezer to maintain.
521s are a labor of LOVE. Mine breaks down at least once ever 2/3 months. Its just old. Now if you have limited skills it maybe a purdon on some. These are simple trucks but hard to trouble shoot on side of road soemtimes for a new guy. Most is preventative main.
You could have a rocker arm tight or dist out of time or points ignition out of adjustment. Most like a simple fix to use oldtimers.
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Posted 20 March 2017 - 12:15 PM
Have you looked at your spark plugs to make sure they are running lean? Could be something else that makes it bog down. If the carb is good why spend money to buy a 32/36 weber. Better to keep your stock exhaust manifold. Your lucky to get 5hp gain with header. Just trying to save you money, time and resources.