engine and drivetrain My rebuild won't stay running; carb or timing?

[chance.hughes]

I just rebuilt my '76 M10 engine and can't get everything set for it to keep running.  I have a E12 head, Weber 32/36 DGAV carb with electric choke, and electronic ignition vice the original points.  I also have a new battery, just to note.  The head and the carb and distributor are the same from before the rebuild and ran relatively okay then.  I put in larger pistons and switched to the IE shorty header.

 

It took me quite a while to get the timing set close enough for it run at all.  1-3-4-2 on the firing order, clockwise on the distributor.  

 

If I push the gas pedal for a moment before turning the starter it will fire off and run for about 2-3 seconds; initially being around 2-3K rpms.  If I hold the gas pedal in slightly while starting it will run for about 5 seconds (it doesn't sound rough or knocking like it is eating itself up so that's good).  Now, if I give it a little more gas and pump the pedal slightly in and out once it starts it will continue to run but only if I continue to work the gas pedal.  During this time it is not backfiring or sputtering or making other random noises.

 

*I couldn't get a spanner wrench in to set the #1 at TDC so I had to bracket the distributor in to get it aligned where it is supposed to be (that is it doesn't run at all at any other setting).  I also worked with adjusting the timing back and forth, but where it is set now is giving me the best performance, which as noted isn't great.  I do have the vacuum advance line connected to the carb.

 

There are a couple big no-nos I have broke up to this point, a big one related to starting is that I currently has regular gas in the gas tank.  I will now and forever more run premium, but at the moment it's regular.

 

 

 

Please help me out if you can.  Ask me any more questions for amplifying information.  Thanks for all the help so far!

[Buckeye]

Is the fan shroud in your way to set cylinder #1 @ TDC?

Your issues are most likely with timing not carburtor.

http://www.bmw2002faq.com/topic/108155-top-dead-center/

[Hans]

put the car in top gear, push car forward to rotate engine. Either watch for timing mark on front pulley or pull valve cover and watch cam lobes on #1. Pull some plugs if necessary. That gets you tdc. At that point, the rotor should be lined up with #1 pin on the dist cap. From there you can do rough timing with test lamp method. One engine is running, set max timing advance (plenty of instructions on FAQ)

Then I'd look at choke operation. If choke is working you shouldnt have to pump the gas, etc. Plenty of choke threads on FAQ

[jimk]

Since it now runs sort of, advance the dist (turning anti-clockwise) about 10 deg, tighten it to the head and restart.  Get out the timing light and set the timing. It can be advanced by hand under no load without huring anything.

The regular gas is not your problem.  If it runs before the timing light set, let it rev a bit, it's a new engine.  Prolonged idling while messing with the timing doesn't do it any good, not enough oil being thrown on the cyl walls.

[Mike Self]

FYI unless you're running 10:1 pistons, you don't need premium gas.  I have Euro 9.5 pistons in my '73 and use mid-grade (89 octane) and it's just fine unless I really lug it uphill, which I don't.

 

Agree--problem is most likely timing vs carburetion.

 

cheers

mike 

[TobyB]

This is why I like to do a carb cleanout before doing a new engine.

 

Get a timing light on it, and get timing dialled in first, doing as Jim says and NOT letting it idle.

Goosing it, revving it at 2500, etc, is all good, but a prolonged idle below about 2000 will not

do it any favors.  Probably won't KILL it, but it's less than ideal.

 

Then, when timing's in the ballpark, see if there is crap in the carb bowl.

 

If the timing's right and it's not running well, I'd suspect your primary jets are sucking gunge

and not delivering fuel...

 

hth

 

t

[chance.hughes]

Thanks! It was a lot easier than anticipated to hand turn the engine to set TDC. With that done, I set the distributor to line up with the notch on the top rim of the distributor for the #1 piston. I didn't pull the valve cover to check the cam shaft, but the notch on the crank pulley was lined up with the pointer on the timing chain cover.

Here is a quick video. Now that I have more confidence in the timing being within a few degrees, I think the carb can't keep up, either because it's dirty, not tuned properly or the jets are too small. I even tried giving the distributor about 10degrees counterclockwise advance but it didn't keep it going.

The first run in the video a depressed the gas pedal a little before turning the starter. The second run I pumped the gas pedal in and out while it was running.

trim.EFD80D51-6892-4E33-B519-FF44AB803640.MOV

Edited February 8, 2015 by chance.hughes

[Buckeye]

You stated engine ran relatively ok befor rebuild, therefore leave carb and jets alone for now.

Go back and set cylinder #1 @ TDC along with dizzy and this time take valve cover off. Confirm cam indicator is lined up accordingly.

[chance.hughes]

I got it all set at tdc, confirmed by removing the valve cover, matched up the markings on the crankshaft pulley and matched up the distributor for timing. I haven't been able to use the timing light to set the advance because it won't stay running long enough and the starter doesn't spin the engine fast enough.

I had trouble with the carb before in regards to starting and idle but it would run at normal speeds fine, and idle once warmed up. It would stay running today if I continually fed a small amount of fuel into the primary carb barrel with the air filter removed. I'm still using the mechanical fuel pump. It pumps but I'm not sure at what PSI. All the jets are the same as before and are smaller than the prescriptions found on here.

I'm exploring a couple different options but not confident in any of them

1. Converting to an electric fuel pump

2. Upgrading the jets and doing a rebuild

3. Replacing the carb all together maybe with a 38/38

4. Taking it in to a carb specialist to set everything.

Advice?

[chance.hughes]

I checked the bowl and cleaned the jets but stopped short of a full break down and dip into carb cleaner. Any recommendations for a pressure regulator or gauge to see what the pump is putting out?

[Buckeye]

I read it should be about 4psi. search "mechanical fuel pump pressure" in the search box above and then select Google

[DRedman]

If the car will run after pumping the gas pedal that means the float bowl has gas and the fuel pump was strong enough to fill it.  If you can pour gas in the throat and it runs then your timing is in the ball park.  After starting, if the engine will run at a higher throttle opening above idle then there may be a vacuum leak.  A worn throttle shaft, carb base gasket, or intake manifold gasket may be leaking.  You can use carb cleaner spray to isolate where the leak is since the engine will speed will increase after spraying around the suspected areas.  You may need another person to help with this.  Another possibility is clogged low speed idle circuits in the carb which can be cleaned.

['76mintgrün'02]

Does your Weber have the electric idle cut-off solenoid?

If so, that needs 12V+ with the key on or the car will not idle, due to a little pin inside that blocks the idle jet.

In my '76 it is fed with a green wire/white stripe.

My car recently - suddenly - decided not to idle and that was my problem.

Since your carburetor may not even have one, I will spare the details of what I learned, for now... but thought I would ask.

 

Here is what one looks like, next to a 'normal' idle jet.