Carb problems

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johnscf
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Carb problems

Post by johnscf »

My 1600 had a problem cutting out when I went up the steep hill to my house. Always ran just fine everywhere else but the hill to my driveway was gravel and a little steep. I’d keep my revs up but about 3/4s of the way to the top it would start sputtering. Never did stall and was fine once I turned on to the level driveway. Hill was only about 100- 150 yards long. Thought it might be a fuel pump problem or a small hole in the line. replaced fuel pump problem remained. Put camera in the tank to see if the intake tube might have a small hole or be broken off thinking maybe the steepness of the hill dropped the fuel below the pick up tube. Tube looked fine. Unhooked the line at the fuel pump and blew air back through the line to the tank and it was clear. Hooked the line back up to the fuel pump and now the car runs rough whenever under load even on small inclines or trying to accelerate above 60 mph even on level ground. Any thoughts on what I should check next?
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Habitat.pat
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Re: Carb problems

Post by Habitat.pat »

Install a tee & pressure gauge after the fuel pump & see if the pressure drops. Put the gauge where you can see it when driving.

You can also put the tee before the fuel pump & see if you are getting a vacuum.

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RBMann
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Re: Carb problems

Post by RBMann »

My driveway is 100 yards long at 25% ave. grade. The roadster has always run bad going downhill and would sometimes die at the bottom. I installed my Color-Tune and the mixture is fine on level ground. I stopped in the driveway pointing downhill and the mixture is super lean. I didn't think to check going uphill. I need to revisit my float level.

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keith0alan
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Re: Carb problems

Post by keith0alan »

The mixture changes on hills due to the float bowl/nozzle geometry. Make sure your float level is correct. I do not know of a good fix.
johnscf
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Re: Carb problems

Post by johnscf »

Update. I by passed the fuel pump and put in an electric one. Car runs a little better and went up steep short hill in second gear without a problem but still sputtering when trying to accelerate at higher speeds even on level ground. Generally sputtering kicks in when taching around 3500 in 4th gear and trying to accelerate. Checked oil level in domes and looks fine, checked banjo filters and found them clean, floats look ok also, Any other thoughts? Have an electronic ignition Could this be a problem with the coil or the ballast? Is the something else i can check on the carbs?
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RustBucket
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Re: Carb problems

Post by RustBucket »

Sounds like maybe it is running lean or there is debris in the tube between the float bowl and nozzle (or its expanded or become brittle over the years). So when you accel hard it just cannot get enough fuel. Maybe raise the needle all the way (or pull out) and blow out the little tube.
I have a 1600 also and it is pretty common for the engine to almost quit under hard braking due to the orientation of the float bowls (in front of the carbs so the force of braking causes fuel shortage). Note, the 2000's have one in front and one in back, to mitigate this.
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Gregs672000
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Re: Carb problems

Post by Gregs672000 »

Limited recent SU experience here, but I would think that a lean condition at higher rpm would be a needle size issue or some obstruction as Rustbucket suggested, right? Fuel pressure should not make a difference if what ever pump you're using is supplying the res properly, as the pressure is to overcome the needle spring, not to pressurize the nozzle/carb (?). A wideband meter or reading plugs may be necessary to know what it's doing, rich or lean, though super rich should show up as black exhaust.

I'd also check spark. An MSD Blaster coil isn't stupid expensive...
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Re: Carb problems

Post by johnscf »

I pulled out the needle and blew out the tube from the float bowl to the nozzle and it is clear. I also changed plugs. Not sure what else to try. It runs fine at low rpms and accelerates nicely from 25 to 50 mph
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Gregs672000
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Re: Carb problems

Post by Gregs672000 »

Ya, you're going to have to read your plugs before knowing what direction. So, go out and drive it someplace safe where you can keep it in the range it's failing for some time, then shut the throttle and switch off the car as you coast to the shoulder. Pull your plugs (Hot! Bring gloves!) and see what they look like. I'd also check to make sure timing is advancing and holding normally. Timing light required.
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johnscf
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Re: Carb problems

Post by johnscf »

Took apart the return valve/pressure regulator that sets above the second carb float bowl and its guts were missing. Anyone know where I can find one to replace it?
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notoptoy
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Re: Carb problems

Post by notoptoy »

I can think of no reason being on a hill or level ground would effect spark in any way - other than MAYBE a coil that doesn't have enough oil due to a crack or leak - I would stick with looking for fuel related problem.
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Gregs672000
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Re: Carb problems

Post by Gregs672000 »

Reading plugs...
Was out tuning the EFI today. The car ran fine, all air/fuel meters etc in parameters, but something just didn't feel right. I decided to take it home and pull plugs, and this was what I found... 2 and 4 were lean (Note: The orange tinge is from Boostaine).
20210505_133145_copy_1024x768.jpg
After thinking about it, I decided to check wiring and found a weak connection that fed those injectors. A quick drive and the plugs were reading better. But if you look closely they are getting a dark black tinge. Turns out I was losing my collector bolts, allowing air into my exhaust and throwing off the wideband, which throws off the EFI computer, so it ran richer to compensate for the incorrect feedback. I found the failed gasket/bolts later, but the plugs told me beforehand. Sometimes an engine will speak to you. All the electronics said things were fine, but it wasn't...
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Greg Burrows
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Re: Carb problems

Post by unklpat »

Greg, can you talk to my hazard switch? It only wants to go left. Pat
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Re: Carb problems

Post by johnscf »

I think i identified my problem as being the fuel return valve and now just need to find one. Posted under parts wanted but no responses yet. Suggestions?
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dbrick
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Re: Carb problems

Post by dbrick »

johnscf wrote: Thu May 06, 2021 10:20 am I think i identified my problem as being the fuel return valve and now just need to find one. Posted under parts wanted but no responses yet. Suggestions?
I have late carbs, return valve and hose were capped/plugged for years. IIRC, as long as it's not a 70, the tank vents through the cap. Yours is a 70, so the venting goes throught the vapor can?
Full tank of gas would tell you if it's a fuel pickup problem. I always add a clear fuel filter before the fuel pump, if the car stumbles, shut it off immediatly and see if the filter is empty.
Last edited by dbrick on Tue May 18, 2021 10:57 pm, edited 1 time in total.

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