New Topic - does't run any better this year

[JPSmit]

so apparently prayer doesn't work near as well with LBC's as I figure it should. Went out to spend my first 2009 hours together. Got her started - rough and even with the throttle held wide open, still she doesn't accelerate. However when I physically lifted the piston in the carb, she started to accelerate dramatically. She did smoke like crazy though.

Here's what I know

1. I've had the carb itself in the shop (off the car) and the mechanic (who knows LBC's) said he can't find a problem.

2. There is lots of fuel flow

3. The timing is set probably 20 deg BTDC to keep it running right now (without acceleration)

any ideas?

 

[abarth69]

Dynamite works when prayers are not answered.

How about air leaks at the carb?

Smoke what shade?

Cheers

Mark

 

[aeronca65t]

Yes, torn or improperly installed carb diagphram.

Or intake manifold leak near head or carb.

If you can keep the engine running at a steady speed, spray WD-40 near the intake manifold gasket area (and carb gasket area). If it slows down, it's sucking in the WD-40 (won't hurt it a bit).

Also:

Be sure you have a decent spark and it is not fouling out beyond idle speed. Are your plugs wet or black?

And see if you are "leaking off" ignition voltage. Start the car in a dark area (no street lights)and open the bonnet and look for sparks that could indicate carbon trails "stealing" voltage from your ignition system. Sometimes you'll see nothing with this test unless you "mist" the engine with plain water using a plant sprayer.

You *sure* it's timing is roughly correct? (and not 20 degrees after TDC, right?)

And I am also curious of the colour of the smoke. More blue or black?

 

[JPSmit]

grey smoke

but why isn't the piston rising when I increase throttle

 

[aeronca65t]

If it's a ZS carb, bad diagphram (or installed wrong).
Or timing is way off.

Both of these will cause piston not to raise.

 

[JPSmit]

I'm willing to go with timing then since visually the diaphragm looks fine. How do I get it to idle well enough to set? or is that a chicken & egg question?

 

[Ed Kaler]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:]I'm willing to go with timing then since visually the diaphragm looks fine.[/QUOTE]

'Looking' fine may not be so, tho JP.

Have you verified that TDC is correct ?? Double checked that the valves are set correctly?? Is the water choke stuck on (which is what the prob sounds like)?? There IS a reason that I have averaged a couple dozen water choke to manual choke conversion kits for around the past ten years. And I am NOT including the MGB Conversion Kits sold in that number !!

If you want to chat direct please write me at:
shop@justbrits.com !!


Ed

 

[JPSmit]

I'll go look again.

Yes, TDC is correct / valves too

converted to manual choke already - ad my carb guy set it up.

the frustrating thing is that it ran perfectly in October. I changed the Alternator and then it didn't run.

I did try with the alternator disconnected - nothing.

I did mess up the timing before I realized (with help) that it seemed to be a carb issue.

timing is not correct now I do know that - but it starts which it wasn't before

 

[abarth69]

JP


Let me get this right it all went down hill after you changed the alternator?

Mark

 

[JPSmit]

maybe - it was running but not charging. Installed the new alternator but while it now charges great - can't get it right but it seems carb as I had it accelerating with the piston held up

 

[jlaird]

Can the diaphragm be upside down?

 

[JPSmit]

I still have my pre-rebuild diaphragm so I may try to swap them out later today. what is frustrating me is that it was running so well. So, for instance, I can't understand how a brand new diaphragm could go from working to not working in a month without being touched in any way. And I know we are talking LBC's here but even so it makes no sense.

Anyway, will report back

keep the suggestions coming

 

[DrEntropy]

It'd be kinda hard to set the diaphragm in there bass-ackwards. Too many alignment tab issues...

Just a WAG but, does the piston drop from being raised to full "up" with a no resistance "clunk"?

Other random thought: does it have a possible by-pass valve malfunction?

 

[aeronca65t]

Diagphram looks like assembly below, right?

Water choke could be stuck, but you'd have fouled plugs as I stated above.

Remove the piston spring (#2) on a temp basis and see if it's better without.

 

[JPSmit]

Don't know about "clunk" but it drops briskly - it doesn't seem to rise.

Once more - water choke is long gone.

 

[aeronca65t]

As I think about it, the timing is probably good enough. Otherwise, it wouldn't rev up when you raised the piston.

 

[zimmy]

it should clunk when the motor is not running...
otherwise take apart the dashpot and check it.......
if it smokes much, its getting too much gas..
check ur plugs for clues........z

 

[JPSmit]

OK - why won't it go up though?

 

[JPSmit]

haven't had the time to check yet, but now I'm freaking myself out. If I stand in front of the car facing the rear of the car and I glance down at the engine (1500) BTDC is to the left of TDC correct?

 

[DrEntropy]

eeep... slow down JP. The reason I was askin' about the piston return is: sometimes the spring in the needle "socket" can get boogered, causing the needle to be rubbing in the jet. It can sometimes be enough resistance at the bottom position to prevent the piston from rising when vacuum (running) is applied. If it doesn't rise with increased throttle the problem is VERY likely in the carb or induction someplace and NOT related to the timing.


Assemblies #5, 7 and 9a in that illustration Nial posted can ALL lead to some air bypass issues. #7 is the beastie I was referring to as the "by-pass", That can get muck on the taper'd piston in it and cause all sorts of odd running.

#5 has a dainty li'l diaphragm internally, too. You can make a gasket for THAT thingie to blank it off completely. For the purpose of testing only, of course. :smirk: