2.0 CU timing /running issue

[bigbrother3269]

I need some guidence please...ive been working on a t25 with Aircooled 2.0 running twin solex carbs.van was a bit rough when it came in,replaced old dizzy with powerspark unit, adjusted tappets as noisy and re built carbs. Innitially ran fine and only upon test drive did a lot of popping through carbs occurr with lack of power-idle fine.so after readinv a few posts on here i redid the tappets up,checked carbs again-no joy, however by a fluke i found moving the dizzy round cured problem-however timing point now at end of scale...probably moved dizzy 10mm round.i checked lead positions etc-it was previousley at 6○ tdc as per haynes-now god knowz!. Anyone got any thoughts or ideas?

[dugcati]

sounds like either the dizzy has been moved round 180* on it's shaft (common thing esp. after rebuilds) or the vac isnt working on the dizzy - have you checked all the vac hoses are connected to the right places, there are a few of them on a std setup

[bigbrother3269]

hi-thanks for that reply,dizzy turning 180 did cross my mind but how is this possible-its an offset drive isnt it,common after rebuilds then??-has this been known to happen before?,ive fitted the powerspark dizzy set up with only 1 vac chamber,on advice from powerspark themselves i got a vac line running from manifold with t piece in-one feed to dizzy one to carb 1(master carb),vac advance appears to be working as if i remove feed to dizzy engine slows down-picks up when re-attached.Assuming something had moved with the dizzy i did a quick move the ht leads around session but to no avail-clipping timing light to any other lead makes no differance either-still shows timing point way out yet engine running fine and staring first turn-really cant work this out,when i first played with this van a few months ago with the origional dizzy on timing was at red spot on scale-which puts it at 6 degree(haynes figure)-when i replaced dizzy i re timed to this point and still no probs-just a lot of popping through carbs under load-idle fine,makes no sense to me !

[HarryMann]

Through carbs advanced usually through exhaust retarded. Did you scribe up the original dizzy position for reference?
If you aren't using the retard vac chamber you've blanked off both ends?... and depending on strobe method (whats connected and what's not) you may have to re assess the reading you're expecting.

Does it pink under load badly?

From here difficult to advise... as usual simple logic and analysis. You've maybe changed too many things at once & not kept track.

I'd back it off a bit and use eyes ears to get it running and pulling well. Then measure and record. Then fraction back fraction forward.
As always don't think a quick blast around the block is enough to detect subtleties.. can be deceiving. Settle in and really think yourself into how its running at part full and low and overrun for a while. If it pops back could be retarded or you have an airleak.
If continues to sneeze through carb then may have a couple if leads wrong way around but only you know what you have done or not done.

Good luck

[HarryMann]

Oh and plugs running too hot (too soft heatrange) or dirty or coke buildup can lead to sneezing. Don't forget it's very hot weather now so take care. Factor everything in..

[bigherb]

ive fitted the powerspark dizzy set up with only 1 vac chamber,on advice from powerspark themselves i got a vac line running from manifold with t piece in-one feed to dizzy one to carb 1(master carb),vac advance appears to be working as if i remove feed to dizzy engine slows down-picks up when re-attached.Assuming something had moved with the dizzy

If you fit a single vac distributor you only connect to to the left carb vacuum take off, not the t piece to the manifold, blank that off. Then set the timing to 7.5 deg BTDC with the vac pipe disconnected.
The idling speed should not alter with the vac pipe disconnected.

[BOXY]

Another thing to check is if the engine has got solid lifters or the original hydraulic ones. My engine has got solid lifters. Before I knew about the lifters I tried to set the tappets as per the Bentley. The result was the engine wouldn't turn over.
The only time I've had popping back through the carbs has been when a valve seat was on its way out. Have you checked the compression since you've re-set the tappets?

[HarryMann]

Good point Boxy.. I missed the tappet reference. Compression check good advice rule out valve off its seat

[bigbrother3269]

Quick update here-reset the lifter's to 1.5 turns,timing to 7.5btdc and re worked the vac lines-big change overall now.Some smoke out the exhaust but i'm checking the carbs yet again today and the autochoke settings.If this dont cure the problem i think its time to whip the heads off for a looksee....i have also checked the ignition timing dizzy driveshaft and thats ok-pulled it from block to check its condition-everthing lines up as per haynes so i'm assuming the problem is not here.
Thanks for input guys.
stu