Carb Issues

[worm4762]

I have a 1975 280 with carbs on it because at some point the wiring was completely trashed I guess. My problem is that someone put an extremely lumpy cam in it at some point (don't know the specs) and I haven't been able to get it to run correctly with DGV Webers or the japanese knock off SUs that are installed currently. I've seen some triple weber setups and was wondering if anyone has had any luck with them.
-W

[evildky]

I hate DGV's I'd stick to the SU's or the DCOE's, but if you cant get it to run well on the SU's I doubt you'll have much luck with the DCOE's, the SU's are simple, think controlled fuel leak and thats about it

your 75 came with an electric fuel pump that makes mroe pressure than any of these carbs can handle, the electric pump needs to be replaced with a low pressure unit as well as a low pressure regulator, any more than 3 psi will over power the needle valves int he su's, the DCOE's and DGV's might be able to take 5 psi but I can't verify that

if the electric pump has been replaced with a low pressure unit or a mechanical unit (if it was swapped wiht mechanical did they add the fuel pump escentric to the cam to drive the pump? ever had the tank cleaned and the linnes blown out? corrosion on the tank, pickup and lines can cause a lof of issues as well, the face that you've tried multiple sets fo carbs makes me suspect a fuel delivery issue

[worm4762]

I took the carbs off last night to clean them, so I can't check the pressure I'm getting but I want to say it's around 5. The car had a minor restoration just before I bought it- new paint, motor rebuild- and the gas from the tank seems clean. It was running okay for a little while but would spit and sputtered a little, and with the lumpy cam I had to make run pretty rich which tended to foul the plugs during warm up. It's kind of a mess and I'd rather not replace the cam if I don't have to.
-W

[evildky]

do you know which cam is in the motor?
head code?
which block?
electric or mechanical fuel pump?
who built the motor?

5 psi is too much for the su needle valves, they tend to stick and act wierd anywhere above 3 psi, you really need to run an inline gauge and verify the pressure

[worm4762]

The head is an N42, manifold is an N36, it has an inline gauge that I'm almost sure was reading right around 5psi, electric fuel pump, all I know about the cam is it's a Schneider racing cam, L28 block and absolutely no idea who built it or why there are carbs on it.
-W

[evildky]

I doubt that the cam is aggressive enough to be an issue, I hear theri stage 3 is pretty mild by some standards, does it appear that the valve springs are binding? if they run a bumpy cam with stock springs thery might not accomodate the travel of the larger cam

also is this an internally lubed cam or internally? I cant' remember for sure but I'm thinking that the N42 was external so if this is an internally lubed cam were the ports of the towers blocked? and if it's external is the spray bar installed snugly?

what are you doing for ignition? the stock 75 woudl have the electronic distributor firing the ballasted coil, you keep all this stock?

and you should definitely get a fuel pressure regulaotr and dial that pressure down to about 3

[worm4762]

You went way over my head there, but I think the cam is operating correctly. I used to work at a restoration shop and the mechanic thought the carbs were the main problem. I think the ignition is stock minus the coil. I will definitely try the fuel pressure regulator, thanks for your help.
-W

[evildky]

mechanic thought the carbs were the problem but didn't fix them?

also the ASU's are known to wear otu the bushings around the butterfly and creata a vac leak

[worm4762]

I didn't have money for parts at the time. I think I might get some actual SUs to replace these knockoffs.

[evildky]

whihc SU's are they? if they are the round top SU's you are only going to make it tougher on yourself, if they are the flat top's just find some round top su's form an earlier 240z, they tend to sell for around 150 a set