316, M10 not running well at all ADVICE please

[PK]

my 316 from 1983 has recently had a 32/34 DMTL weber fitted
its the direct replacement from fast road cars for the zenith carb

under mild to moderate acceleration its fine

put your foot down and it splutters and misses

investigations so far:

i can get it to no more than a lumpy idle
rotor arm, leads and plugs are all new and seem to be appropriate
choke comes all the way off

the needle valve can be screwed all the way in and i still see fuel coming in! Should this be even possible?

ive had it on a strobe, everything seems fine and then all of a sudden piston 3 starts to miss

thoughts so far:

some schools of thought say over fueling

there doesn't seem to be a return pipe to the fuel tank, haine's says there is one, i can't find it. Did th zenith carbs use a fuel return valve?
should my weber have one? there doesn't seem to be any obvious plumbing for one.

Also the exhaust gases are so rich i could sell them!

other school of thought say ignition problem

a worn distributer gear possibly???

However this doesn't seem to explain the fine driving until i put my foot down.

Please help my 316 fly, i can tell she wants to right up until she splutters)

thankyou in anticipation

pk

[e21-Mark]

Is dizzy cap new too?

[Reck]

exact same problem here. 316 w weber 32/34. Does the problem persist even at low speeds for a while after attempting to put your foot down?

[drjim]

is the electrical connection for the idle control solenoid connected, and is there an earth from the carb to the engine (rubber mount isolates it).

check plugs and leads, rotor arm and cap

Jim

[PK]

amazing some help, thanks lads...

TINKERING UPDATE

had the plugs out, all are white and clean looking, all the gaps are equal and fine. good spark to the block on all of them.

one of the leads to piston 2 has discoloured contact points both ends compared to the other three ??? errrr.

rest of the leeds, otherwise fine as are the rotor arm and cap, all these parts are new and of reasonable quality (cap could be a better fit though). the rotor arm could be a little less tight maybe.

yup the carb is earthed using the old eathclip on the accelerator cable mounting bracket doohiki, and the idle connection is on and seems to be working fine.

The dizzy is NOT new (my thinking and searching is leeding me here)

timing is as close as i could get it with a borrowed strobe gun.

Yes the problem does persist at low speeds after attempting a booting. Amazingly smooth right upto 7000rpm as long as you accelerate slowly, foot down equals splutter and a little puddle of unburnt fuel dripping from the exhaust. However this usually only happens under load

On idle (around 900rpm) you still get the occasional miss and a little extra exhaust mist

she runs slightly better with the advance and retard tubes taken off and blocked but still misses under hard acceleration.

Had a look at the fuel tank tubes. I can see the breather for the filler tube, the small metal main fuel line and another fabric clad tube that doesn't seem to be attached to anything. I can shake it and hear it rattling around in the subframe, can't see it in the engine bay either??? It might be a red herring i guess who knows.

Does the weber need a pressure regulator valve and a return tube to the tank??

I'm thinking

1 - ignition issues eminating from the dizzy = replace the dizzy

or

2 - fuel pressure regulator with return pipe = plumbing job with tiny tubes in cramped hard to reach places

Thankyou for the advice

let me know what you think

PK

[tommi_e21]

you dont need a return pipe.

have you still got all the right return springs on the webbers?

when we where tuning hannahs old car a few springs where missing and we added some for good measure, what was happeneing was the choke butterfly and other bits where moving around. would give funny starting issues and wierd idleing.

worth a look to make sure all the arms on the carbs are returning properly

[Reck]

Yes mine will drive fine all day and night but if I boot it then it'll start to miss and stall.. And this will persist at low speeds afterwards then. I'm gonna change the fuel pump when I get time and see it makes a difference.

[PK]

Personally I think our problems reside with the advance and retard. That push pull thingy on the side of the dizzy. There is no way I can generate the amount of suction required in order to test it without a vacuume cleaner and some duct tape. I'm going to try and source a new advance and retard diaphragm thingy. Wish me luck. Pk

[PK]

The weber was brand new and seems to be all sprung up well. The choke comes all the way off and is pretty solid and maintains it's posistion. I'm confidentish it's not the weber.

By the by. I flooded it today. I took the air box top off to help the fuel evaporate off. when it finally fired up a tiny little fire ball errupted from the weber. I was well impressed

[drjim]

I( have a couple of spare dizzys around if you need one to try, but it sounds to me like your carb is wrong. Was it definitely sold as being for the M10 1.8 engine. Sounds like it's way too rich so maybe it's jetted for something else.

[e21-Mark]

+1

I'd whip it off and check jet sizes with Southern carbs or someone.

[PK]

I hear you

It was sold to me as a direct replacement for the zenith that was on there. I don't have a set of guages to test the jet diameter. However one of the jets says 200 on the top of the screw, the others have no mArks on the tops of them. I purchased it direct from fast road cars. I called the guy back. He said it was jetted in the factory. Whatever that means. Do you by any chance know what jets should be on there?

Thing is she misses only after a certain pressure is applied to the accelerator. The posistion of the throttle when it goes wrong is so predictable I can drive it now without a problem. But on advance it just doesn't seem to be catching up somehow

I would have expected the plugs to be more black than they were when I pulled them out last night if it was over fueling

I would love to borrow/buy one of your dizzy's to swap in if I could though

[murran]

wasnt this the carb you bought off the guy pete that i know?

if it is, it was on a prefacelift e30 m10.

[PK]

Was writing that whilst you replied.

I'll pull the jets out soon and have a look on them for some digits or get them measured up then. Southern carbs you say. Right. I'll check with them what the diameters
should be

tell you what. I'll buy a dizzy off drjohn and research the jets. If it's the jets I'll give you my single mudflap to share/fightover.

Thanks again for the advice lads

pk

[PK]

Nope brand new from fastroad cars. To replace zenith 2be
I'm a post behind hear

my typing is weak