2.0l cu air cooled cutting out

[lefty67]

A friend's van has broken down. Was fine until stopped at a junction then engine cut out. Van now starts but revs die and cuts out immediately. I have had a quick look with my limited knowledge. Can find no air leaks and all pipe work seems fine but took air box off and got her to give it a good rev. Definite misfire with flame coming from left hand carb (solex) so thinking ignition. All leads and plugs look new and rotor arm seems ok so could this be the hall sender or vacuum advance unit?
Many thanks

[bigherb]

Actually, it does sound more like an air leak (popping back through the carb is caused by weal mixtures). Double check the air pipes especially the rubber elbows for the balance pipes and servo are not split and make sure the carbs and manifolds are still bolted down tightly.

[lefty67]

Thanks bigherb will have another check. My initial thoughts were an air leak and there is a bit of a whooshing sound on start up and cutting out.
Would it have to be a large air leak to cause it cut out immediately? Won't idle at all.

[937carrera]

You don't need much of an air leak to cause the idle to fail. As Bigherb says, check the balance pipes carefully

[lefty67]

Cheers 937 carrera
Another quick question. Would the engine still idle if the air box is removed leaving the top of the carbs exposed?

[937carrera]

Yes, removing the airbox / filter simply allows unfiltered air in before the mixture is created. An air leak means "unmetered" air gets into the inlet, causing the mixture to be weak.

My CU has neither at the moment as every time I want to move it I tend to have to fill the carb bowls with fuel No problems idling / running in that format

[bigherb]

Cheers 937 carrera
Another quick question. Would the engine still idle if the air box is removed leaving the top of the carbs exposed?

Yes as long as you plug the vacuum pipe that goes to the preheater thermostat on the air box.

[lefty67]

Thanks guys. Gives me a bit more room. Did notice a bit of damp around the right hand carb so will investigate that aswell.

[lefty67]

Still struggling with this van. Checked all the vac hoses and cant detect any air leaks, although still not ruled it out. Checked plugs, leads, distributor etc all seems fine. Bypassed idle stabilisation and no difference.

Van starts fine, revs up ok but wont idle and has a backfire in the low rev range, no noticeable backfire at high revs. The one and only time I got it to idle was when the engine was cold and I manually closed the throttle/butterfly valve.

Checked carbs and both tight, carbs do look as though they could do with a refurb, throttle plates don't seem to be opening at the same time.

Any other areas I should investigate?

[tobydog]

Blocked jet(s)?

[937carrera]

Could be a blocked idle jet, a couple of thoughts.

Why don't you synchronise the two carbs so the plates move at the same time. Then incorrectly adjust the throttle so that the butterflys are held slightly open when there is no foot on the pedal. You should then have a forced fast idle. If the fast idle is fine let the engine warm up and then adjust the cable to slow the idle down a little, bit by bit.

If the fast idle is fine until the throttle is properly adjusted so the butterfly is not open at rest, then a blocked idle jet would be a reasonable diagnosis.

Additionally, if you get it so the problem is just manifesting itself, use your hand or something else to partially cover the throat, effectively acting like a choke. If the problem disappears then it looks like you do have an air leak.

[tobydog]

Personally, I'd strip the carbs and give them a clean internally.

Could be caused by fuel hoses breaking down?

[lefty67]

Cheers guys. Agree that carbs could be a problem and do need a refuirb.
Your Idea of altering the throttle cable to give a false idle is genius Carrera, at the moment the van is parked up on a busy road so this at least gives her a chance to get it home. Can hold the revs at about 1000-1200rpm without stalling, sounds like a bag of bolts mind.

[937carrera]

only an accidental genius

[bigherb]

Check the idle valves on both carbs have 12V (ignition switched on) going to them and they click when you disconnect and reconnect the wires and check they are screwed in tight.


And check the same for the anti Dieseling valve on the left carb.