Car will run great and then bog and stutter

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superstock2
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Car will run great and then bog and stutter

Post by superstock2 »

So I've gotten my 1970 2000 swapped roadster running. The car runs great and the engine seems to have good power and be very healthy. However, about half the time during short drives it will bog and feel like it's being fuel starved. It's never left me stranded but I've had to limp it home several times seemingly on two cylinders. The fuel filter has quite a bit of debris in it so my first thought was to pull the gas tank and have it boiled out. Any other recs? I gave the car a full tune-up but am not sure everything is sett 100% with the distributor. Any help is greatly appreciated!

Cheers,

Tony
1970 1600/2000 Datsun Roadster
1989 Nissan 240sx/Silvia
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Bwk2000
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Re: Car will run great and then bog and stutter

Post by Bwk2000 »

+1 on cleaning out the tank. With the amount of debris you mentioned, this should be rectified first or trouble-shooting any additional symptoms becomes problematic at best. Once done, I would be looking closely at the condenser & coil to start.
Kai
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Re: Car will run great and then bog and stutter

Post by Habitat.pat »

Decades ago I was on a road trip with my 240z & had that problem. I bought a vacuum/fuel pressure gauge & some fittings. I put the gauge in the bottom of the windshield & tied it into the manifold vacuum & drove. When the car started getting sluggish the gauge showed normal vacuum so I moved it to the output of the Engine fuel pump & drove. Sure enough, fuel pressure dropped. I moved it to inlet of the fuel pump for one final test. In several miles it started pulling a vacuum. Turned out I’d picked up a tank of crappy gas & K was plugging filter in the electric pump @ the tank.

Peace,
Pat
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rwmann
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Re: Car will run great and then bog and stutter

Post by rwmann »

Yep. A lifetime of crud. Clean the fuel tank, (carefully) blow out the hard and soft fuel lines from tank to carbs and and return lines, inspect/replace any filters including any fitted upstream of the fuel pump, any banjo fitting ring filters on the carb lines, and while you're there, inspect the float bowls for crud.
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Re: Car will run great and then bog and stutter

Post by The Neck »

Does it seem to be vapor locking? Sounds pretty similar to what I was tackling for many many months up until recently. I'd definitely suggest what others have mentioned about cleaning the entire system out very very well.

I ended up replacing the heat shield, making extra double and triple sure the coolant system was burped, rerouted the fuel lines not running over the engine, and retuned the carbs that were probably about 1-2 full turns way too rich. Now it's running like a top for long drives and sitting in traffic.
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rwmann
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Re: Car will run great and then bog and stutter

Post by rwmann »

If vapor lock is suspected, is the fuel return line functioning?
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superstock2
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Re: Car will run great and then bog and stutter

Post by superstock2 »

Hello all! Started on the gas tank removal and am struggling slightly getting the fuel lines removed from the tank.
I've been following this post - http://www.311s.org/pmwiki-311/pmwiki.p ... ankRemoval
I can't tell if there just stuck or I'm doing something wrong. Definitely don't want to break something haha. They're currently sitting with some PB blaster on them.
1970 1600/2000 Datsun Roadster
1989 Nissan 240sx/Silvia
1993 Mazda RX-7
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Re: Car will run great and then bog and stutter

Post by greydog »

It's been some time but it seems like I lowered the tank a little to get a bit more room to access the feed and return lines. I remember the return line was especially tigh.Luckily I have a fitting wrench that fits the return fitting.
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superstock2
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Re: Car will run great and then bog and stutter

Post by superstock2 »

Tank came out with some wrestling and has been boiled out at a radiator shop. Should I coat the inside? Or just run it as is?
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Bwk2000
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Re: Car will run great and then bog and stutter

Post by Bwk2000 »

What do you want to do?
Opinions will likely be split based on the pros & cons of both approaches and what has previously worked, or not worked, for them (or someone they know).
That being said, if it was mine, no inside coating.
Kai
Halifax, N.S.
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Classic Cars - Because clean fingernails, free weekends, intact knuckles and financial stability are totally overrated.
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superstock2
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Re: Car will run great and then bog and stutter

Post by superstock2 »

Tank went back in, still having similar issues, wondering if I should the pump next? What else can I check, spark is good, carbs looked clean when I had them open... Stumped on this. Does anyone have a good diagram of the correct fuel line routing?
1970 1600/2000 Datsun Roadster
1989 Nissan 240sx/Silvia
1993 Mazda RX-7
2001 Toyota 4Runner
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Re: Car will run great and then bog and stutter

Post by rwmann »

You blew out the lines and checked the return line? Checked carb float bowls and needle valves?
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Re: Car will run great and then bog and stutter

Post by Gregs672000 »

Yep, what rwmann said... go through the system end to end... only way to be sure.
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Bwk2000
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Re: Car will run great and then bog and stutter

Post by Bwk2000 »

In addition to what is recommended above (recheck the installation plumbing), we could use some more info:
What’s it doing now after the tank cleaning and new fuel filter?
**Does it still run good sometimes and not so good other times?**
Is the problem only when the engine is cold/hot or both?
Does it start easily?
How does it idle once warmed up and off choke? (Does it want to stall, is it loping a lot, more or less steady?)
Any visual signs of gas leaking around the pump, filter or lines, strong fuel smell once warmed up?
Kai
Halifax, N.S.
‘69 SPL311 Sports 1600

Classic Cars - Because clean fingernails, free weekends, intact knuckles and financial stability are totally overrated.
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Re: Car will run great and then bog and stutter

Post by redroadster »

Mine the S bend in the line out of the tank wasn't plugged but was down to a 1/8 " and the fuel pump will not pull that I installed a new line with sock filter
Sure the carb slides are both moving free
Old gas , that gets thicker , possibly
Spark plugs fuel fowled , high comp.engs easy to do

I don't like sidedrafts for the trouble they cause