Rough running, no idle and misfire

jimi

jimi

0
It is hard to tell from this video, but the motor was running sweet with its new carb, then one day decided it was not going to idle. I just figured the carb had junk in so cleaned it out. I might have to take it off again and double check. Pot 2 has a teeny bit less compression, but I don't think that is the issue. The van has a new fuel pump, a new glass fuel filter (and an extra plastic one as the tank is full of rust and crud).

I set tappets, checked plugs, condition of the rotor and points, then the leads. I changed the mix from lean to rich then back to somewhere in the middle - no change. I even added a new distributor cap. The distributor may have issues as when testing the timing with a strobe, it had an irregular flash at slow speed.
The coil is fairly new. The distributor is old and may need replacing.
The engine was fairly toasty when recording this video.
So if you are a good mechanic - what would you test next besides taking the engine out to check for broken piston rings?
The condenser?
 
I would guess fuel starvation. The tanks nearly always start shedding their lining (snakeskin) and even with filters in the line it seems to get through. There could be a little blockage in the jet, an old trick is to get the revs well up and stick the palm of you hand over the top. Try this a few times and hopefully the blockage will be sucked through.
 
Howdy Jimi, I am no mechanic and it could well be Panky's snakeskin if you are running on the original tank.
I had a similar misfire recently, swapped the condenser, coil, leads for known good ones (one at a time) all to no avail. I thought maybe worn distributor as well and I had cleaned the points giving slight improvement for a short time. But as it is awkward to visually check the points condition properly (without removing them), I put new points in. Cured the misfire a treat.
 
If it’s not that then could be air leak, all the vacuum advances connected and not leaking air? Carb on tight to manifold?
 
Ugh. Still struggling. It still won't run. It will just about tick over, occasionally coughing and spitting flames out the top of the carb. Fuel new and from a temporary fuel tank. Timing was perfecty OK when tested with strobe, set tappets and did a compression test, replacment coil (as one blew since last writing), new plugs, new condenser, new points, new HT leads, new rotor. I have cleaned the Weber carb in a 2 litre ultrasonic cleaner and the old Zenith carb and tested both. There is a good gasket between the carb and manifold. I have not yet inspected the centrifugal weights of the distributor and diaphragm.

I have a third carb which I may clean up and test. That is another Zenith which has seen better days but I could replace gaskets and float to see what happens. I know carbs are hard to clean. Both carbs have had 2 or 3 sessions in the ultrasonic cleaner, carb clean spray and had air blown in from a compressor.

Has anyone got any suggestions based on everything being as it should in the list above? Bear in mind that one day engine fine, no prob. Next day, rough and misfiring. So overnight it broke by magic. I will do another video if you want.
 
If it's the same as before (runs by choking the inlet) then it certainly sounds like it's running very lean that could be caused by an air leak.. Try blocking the vac line from the dizzy to eliminate that for a start, then try squirting carb cleaner around the manifold joints and see if you get a sudden increase in engine speed.
Have you checked the fuel pump to see if it delivering enough fuel?
 
THANKS
New fuel pump - and checked lots of fuel getting in.
Sorry forgot to say.
I will block the vac line tomorrow.
And spray carb cleaner round manifold.
Just loading a new video.
I am going in the garage in a minute to locate the 3rd carb and put it in the ultrasonic cleaner for a few 20 minute sessions.
I know when I put a new carb on it ran fine. Both Zeniths spit fuel from the overflow and run rubbish. The Weber ran like a dream before this problem happened and I am wondering if it is still blocked.
 
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As soon as I add throttle it fails to accelerate and violently shudders or stalls. Ticks over OK and from the video if you watch carefully you can see the difference in engine shake on tickover when HT number 1,2,3 then 4 is removed.
I want to check the condition of the distributor advance assembly and vacuum unit tomorrow.
 
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If you haven't already I think you need to strip the Webber and blow through the jets rather than put the whole thing in the cleaner - if the air leak tests turn out to be OK.
 
Have you cleaned the idle jet on the Weber? Mine used to block for fun. It's the slotted screw on top of the carb.
 
Thanks for the video. Just confused about the engine coughing out flames and unignited fuel from the top of the carb. Quite a few backfires. I was wondering if the timing chain has slipped out of line by a tooth.
 
Basic clean up instructions:
www.howacarworks.com

Checking and cleaning a fixed-jet carburettor

Fixed-jet carburettors are easily blocked by small dirt particles and chemical residues from fuel , because some of the jets are very small. Dismantle and clean them about once a year.
www.howacarworks.com www.howacarworks.com

This is a full overhaul:

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jimi said:
I was wondering if the timing chain has slipped out of line by a tooth
Click to expand...
Happened to me and I was going to suggest it next if nobody else did. In my case it wouldnt start or tickover but gave the hint that it might start:confused:. The chain tensioner had broken. Simple and cheap replacement of chain, tensioner and crank sprocket from Speedies.
 
Actually its not that simple, more like awkward to get to. Remove radiator fan, crank pulley and camchain cover and you're there to check.
 
Just joined the forum and spotted this problem listed, and it is identical to the problem I am chasing with my Daughters van. I have been trying to sort it for weeks to no avail!!!! Was your problem resolved as the timing chain having jumped a tooth? I have tried so many things with our van that I will be so glad if we can narrow it down to that having happened . Its so frustrating when everything is checked and you cant solve the problem. I realize changing the timing chain tensioner will be a pain in the derriere but at least we will know what it is!! Ta
 
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