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U20 Fuel Issues


blue69

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Anyone had problems with fuel delivery on a U20 roadster? Using Nissan electric pump at rear and stock mechanical pump to SU's, Car runs good up to 60/70 mph then stumbles or struggles to get past after a few minutes. We switch tanks, lines, etc and still happens. Ran the car out of gas at Road Atlanta and stalled it coming off the track and climbing the hill. When this happens, you can typically see a very low fuel level in the filter when you stop. Tried everything but cant seem to find this one. Wonder if this could somehow be vapor lock or fuel boiling in bowls?

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We've had similar reports in every kind of Datsun. I would normally recommend a fuel pump volume test for high-speed problems.

 

In the 2000 Roadster fuel boing/vapor lock was somewhat mitigated by use of the carburetor heat shield. And careful placement of the fuel lines. Are they still in the stock location?

 

By the way, why do you run dual fuel pumps?

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*consider running one fuel pump until issue is solved

* wrap fuel line in insualtion or buy pre-wrapped insulated fuel line BIG ENOUGH for your engines delivery needs.

*as ggzilla stated heat shields are very helpful and mandatory on some rigs.

*check fuel bowl level and verify it is indeed correct.

*check routment of exhaust system and make sure fuel line is not close to exhaust

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Carb heat sheilds are in place, Stock location of lines and exhaust. I added the electric pump trying to improve the problem. Neither pump seems to make much difference. Replaced fuel line to eliminate potential problem. Several have suggested crap in the fuel tank but Ive got two, both clean, and both result in the same problem. Seems worse going up hill. Is there some inherent tank problem with dip tube,rtc that shows up in these cars? I am running a B-cam with SU's. Ive tested both pumps for flow and pressure and both seem correct. Reset float levels which appear correct. Unless these carbs just cant deliver enough gas

 

When testing the fuel line with my vacuum gun, it seems like there is back siphon pressure as the line will completely suck the reservoir on my vacuum pump dry when you release the vacuum, Maybe normal but seems odd to me, Ive tried it with no fuel cap, with recirc line attached, detached, etc. Nothing seems to make a difference,

 

Ive questioned if the feed and return were reversed, The larger line matches up with the return, which seems somewhat backwards nut based on the original fittings seems to be the only way it can be connected.

 

Any suggestions would be appreciated!

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When Datsun went to the 150HP kit for the U20, the used webers instead of the SU-type Hitachis -- if I recall correctly. However... the Hitachis won't "run out of gas", they will still have a good a/f ratio just not enough air will flow.

 

I would join s311.org and post in the forum there -- that's where U20 experts are.

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Post this question at http://311s.org/phpBB3/index.php

 

The return line was really for vapors, not fuel as on a modern fuel injected system.

 

It is not normal for a U20 to use more than the pump can provide. Only needs ~ 3.5 pounds of pressure.

 

I'd guess an air leak in the fuel system. Sounds like you eliminated the possibility of wrong gas cap - should be vented on a '69.

 

Which fuel filter do you have? '69 should be sealed white plastic filter - earlier cars had glass bowl.

 

The "comp" carb setup was Mikuni Solexes, not Webers.

 

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I have a 1600 roadster and had the problem running uphill. I switched tanks and it got better, but still seems to happen when the tank is low. I believe if the tank is old, the pickup tube in the tank could be rusted and shorter than original. When it does happen (yesterday by chance going uphill) I remove the fuel line before the filter, blow air into it until I hear it bubble in the tank, and then problem is solved.

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  • 10 months later...

Hi all, first post:  70 Datsun 2000 SRL311, owned for 25+ years, Shasta run along with many other shorter ones originating from Houston (TDROC).  Problem now I believe is fuel, do not seem to be getting the proper amount, engine runs ok at lower rpms but rats out above 3k rpm.  I've ordered a cheap electric pump just to see if this solves the problem, anyone know how much fuel should be coming out of the carb hose when just cranking?  Like x/ml per min?  Thanks for any help - Raz

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  • 2 months later...

I had a similar issue recently and it turned out to be the distributor. The centrifugal weights were sticking and not allowing the timing to advance during acceleration so the car would bog down above 2-3K rpm.

 

Might check that unless you know it's clean in there.

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Thanks, I'll double check, I've swapped distributors but will still verify advancing.  There was a time long long ago when my car did a similar thing and if I remember under a bridge in the shade I messed with the points and perhaps swapped the condenser to get her going again, it really could be a a simple thing.  Often I find myself looking for the Ogre when it's only a mouse...

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