Another one about idle speed

[Dazco]

I'm not a happy bunny when it comes to carbs. When jambo is nice and warm, she starts up perfectly ok as far as the choke is concerned, she tends to stall at junctions and Andrea is non too happy about me trying to balance the throttle , foot brake and hand brake at the same time( don't know why). Runs perfectly well in all other regards. Now I remember seeing a post from Kev some time ago about setting the carb up properly , but can't seam to find it now. Could someone point me in the right direction. Thanks , Daz

[DevonMark]

Try these two threads for size...

viewtopic.php?f=37&t=112501
viewtopic.php?f=37&t=109042

Sounds like this is a fairly common problem. Neither of us seem to have sorted it yet, but neither of us have taken the plunge of replacing the carb. That's the next step for me if the stalling continues.

Like you said, it's not easy braking, revving and working the clutch at the same time, nor is it convenient having to roll around a corner on a hill at night with your lights out as you restart the engine for the 8th time in a mile

[ed_the_robot]

Good link

[Dazco]

cheers Mark

[kevtherev]

Stalling on idle is in most cases fuel related.
If it doesn't stall when the engine is cold then it's most likely mixture
Mixture is affected by an imbalance in the air/fuel ratio
Too much air (air leak, fuel delivery.. pump, filters)
Even this has quirks
The mixture adjustment only affects idle, once the engine has passed a certain rpm we're on main jets, and that mixture is set in stone and unadjustable
So a small air leak would not be so obvious at a higher rpm.
A fuel pump or filter issue would be more obvious at a higher rpm

Too much fuel (over fueling)
Is usually the choke mechanism (siezed, broken spring, badly adjusted etc)
Incorrect setting on the carb
Float height

Not so obvious at higher rpm just your wallet would be lighter
The choke mechanism is a delicate balance of springs, bi metal strips, levers, flaps, vacuum and shafts.
Usualy the mechanism will seize up, giving odd symptoms.

The choke should take 6-8 mins to open fully
When cold the choke flap should open slightly as you inrease revs
underneath all that is the fast idle mechanism.
This rotates at the same rate as the flap opens, but it's stepped, so the revs will stay up while the transition from cold to hot is performed.
once hot idle is reached, the fast idle cam should be disconnected ..and the tick over idle adjustment engaged

[DevonMark]

Stalling on idle is in most cases fuel related.
If it doesn't stall when the engine is cold then it's most likely mixture
Mixture is affected by an imbalance in the air/fuel ratio
Too much air (air leak, fuel delivery.. pump, filters)
Even this has quirks
The mixture adjustment only affects idle, once the engine has passed a certain rpm we're on main jets, and that mixture is set in stone and unadjustable
So a small air leak would not be so obvious at a higher rpm.
A fuel pump or filter issue would be more obvious at a higher rpm

Too much fuel (over fueling)
Is usually the choke mechanism (siezed, broken spring, badly adjusted etc)
Incorrect setting on the carb
Float height

Not so obvious at higher rpm just your wallet would be lighter
The choke mechanism is a delicate balance of springs, bi metal strips, levers, flaps, vacuum and shafts.
Usualy the mechanism will seize up, giving odd symptoms.

The choke should take 6-8 mins to open fully
When cold the choke flap should open slightly as you inrease revs
underneath all that is the fast idle mechanism.
This rotates at the same rate as the flap opens, but it's stepped, so the revs will stay up while the transition from cold to hot is performed.
once hot idle is reached, the fast idle cam should be disconnected ..and the tick over idle adjustment engaged

Nicely explained, even I understand all that - thanks Kev.

So, in my case, my mechanic has said that if replacing the vac piping (which would prevent air leaks adding too much air to the mixture) doesn't work he will look at the carb - does that mean the carb may just need tweaking, or might need fully replacing?

I guess my question is, does a duff old carb cause problems with the mixture?

[kevtherev]

does that mean the carb may just need tweaking, or might need fully replacing?

I guess my question is, does a duff old carb cause problems with the mixture?

I would not condemn a pierburg 2e3
There's not much to wear out to be honest.
There are a few other culprits of air
The brake servo hose
Distributor diaphragm
choke pull down (most common)
secondary throttle diaphragm
gaskets.. including the inlet manifold ones

the only place that a carb could leak are the choke & butterfly spindles...and it's gasketry of course

[Dazco]

Thanks kev.
After reeding another post in which Steve from gasure where he says the pipe from the carb to the air filter is cut and blocked to create a good vacuum for the van to run on lpg, I've disconnected the hose, blocked it and hey presto, no cutting out so far this week.

[ermie571]

Dazco - I had a really bad bout of refusing to idle, run slow, on LPG a couple of months back. Was better on petrol. Got so bad I was on the point of replacing the vapouriser. So we started from the basics...shoved super unleaded in it (its a 2.1) new leads etc, and got it running pretty much spot on on petrol - would hold an idle and would crawl in slow moving traffic.

The timing was adjusted by ear by a good mate slightly. Pick up improved. Van went from sluggish to nippy (well, as much as a T25 will). so then, back to the LPG. It was performing better. It ran. It idled. Yippee. But occassionally still after a shortish run will try and idle at 200 revs...(and generally fails!) A good kick on the pedal brings the revs back.

I have come to the conclusion that *sometimes* the engine isn't making enough vacuum to suck the gas through at idle. I am wondering if I have a sticky solenoid in there somewhere. It will be having a full gas service in the next few months.

which pipe have you blocked...the vacuum pipe?

thanks

[Dazco]

It's the pipe that goes from the back of the carb to the airbox , there's a little valve thingy in there , don't know what it's for or owt, but is running nicely as it is , hope that helps a bit .