Rough running when hot

norfor · Post by **norfor** » Mon Jun 20, 2005 8:03 pm

Just got my '69 2000 from the shop today with freshly rebuilt Mikuni's. I was very pleased with the job done. Went to take the wife out to dinner, and within 5 miles, the engine starts running rough. It feels like one carburator is starving for fuel. During the down time in the shop, the fuel pump was also rebuilt. Fuel tank had been cleaned previously. Have not changed the fuel filter. Any thoughts? Could the fuel line have an internal delamination or pin hole that goes bad when the engine is hot?

Phil Herring · Post by **Phil Herring** » Tue Jun 21, 2005 7:32 am

I had a similar problem after I had my fuel tank boiled out. Went through a few filters as they put a "non-reactive coating" in the tank. Could have been crud in the line, don't know. Used the clear plastic type filter. I also had a fouled plug . I would check the plugs and replace the filter and see what happens. I am in the Charlotte area and have not seen another roadster around here in years (did see Mark Dent's very nice Z-Tech conversion last Aug at the local Z-club meeting). Good luck. Phil Herring 69 2000 SU's

spyder · Post by **spyder** » Tue Jun 21, 2005 11:07 am

Perhaps fuel pressure! I have installed a throwaway in line fuel filter which I change with the oil. Even though the tank appears clean sometimes the filter would clog fast and car would run bad. So I decided to spend nineteen bucks at Summit and get a fuel pressure gauge so I could check the health of the filter. Gauge installed, and ???? No pressure. I have an electric pump at the tank which I can see flowing plenty of gas. Turns out the pressure regulator going back to the tank is wide open. So along with no pressure in the loop, the filter is seeing more gas flowing than normal. Fixed regulator and made the top end much stronger.

Possibilities?

norfor · Post by **norfor** » Tue Jun 21, 2005 7:42 pm

Thanks, I will start out by replacing the fuel filter tomorrow. Had a funny thought today. I have a replacement gas cap. Could it inhibit the ventilating, causing a "minor" vacuum problem with fuel flow

What/where is the pressure regulator

I am not familiar with that.

Phil, we are in the Raleigh area. I, too, have not seen another running roadster since Ibought these 18 months ago.

Post by **ppeters914** » Wed Jun 22, 2005 1:21 pm

I'm thinking Spyder was referring to the pressure regulator on his electric fuel pump, which is not stock and why you're not familiar with them.

However, he does bring up a good question: how much fuel pressure SHOULD there be? Or is the answer like the old Rolls Royce horsepower ratings of "adequete"?

jbush · Post by **jbush** » Wed Jun 22, 2005 4:44 pm

3-5 (iirc)

spyder · Post by **spyder** » Thu Jun 23, 2005 1:45 am

Naaaa. The regulator was on the rear su carb returning fuel back to the tank. I looked at the grainy rendering of the microfiche and it is called a "valve, fuel return assembly". The fuel pump is one of those ones that sounds like a motorboat and has no regulator. If I crimp the return hose I get around 6 lbs. of pressure on the gauge on the carbs. It runs around 4 lbs unrestricted. The carbs don't seem too fussy except at the extremes, considering I was running with no or minimal pressure for a couple of years. Top end varied sometimes

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