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Power Band Understanding


Davo

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Just an update for anyone interested. I know I still have a bit more To do though.

 

New coil

New ignition to power spark electronic ignition

New distributor

New ht leads

And finally today, a new Weber dgv twin 32 36 carb

 

Timing done

Mixture set

 

Still, combustion stops just short of 3000 revs.

 

I guess the only step left before looking to the engine itself is the pressure on the fuel line with the engine running.

It’s beginning to feel like Trigger’s broom!

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So all the sparking bits replaced and a new carb fitted. You haven't yet identified the problem! Get a video up on you tube of it running and try to reproduce the hesitation. Need good sound track.

 

Bits you haven't proven. Fuel supply to the carb. Two components to this and for carbs flow is more important than pressure. Flow test first. If it passes then you don't need to pressure test! You don't say what fuel pump you are using, electric or mechanical. If mechanical pull the pipe that runs from the pump to the carb off the carb and put the end of it into a milk bottle. Now crank the engine over for 20 seconds or so. You should see fairly powerful spurts of petrol going into the bottle and a good half cupful or more in 20 seconds. If electric pump then do the same with the delivery pipe into a bottle but you just need to switch on the ignition and watch the bottle fill up.

 

Cam timing. Much less likely problem but worth checking. Need to take the belt cover off the front of the engine so you can see the cam pulley. Then just turn the engine using a spanner on the crank pulley nut (or even rock the car in 3rd gear to turn the engine) till the pointer in the cam sprocket backplate is at 6 o'clock exactly and lined up with it's dimple. Now look down at the crank pulley and the marks should show top dead centre lined up. The pics explain better. If the cam timing lines up to within 3 or 4 degrees then this is good enough for now and not your problem.

post-21-0-40105400-1525520953_thumb.jpg

post-21-0-44332700-1525520972_thumb.jpg

Edited by Longboarder
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Thanks for the reply. Its a mechanical pump powered off the side of the engine I believe.

 

I havent got round to testing the flow as you suggest, but a little while ago the fuel line did pop of the carb and was spurting everywhere so. Hardly a scientific test but it does seem like a good flow.

 

I have just take a video. Please excuse the poor shot quality but it will give you an idea. Theres a couple of shots. One shows second gear getting up to 3000 and then struggling to get beyond that. There is another shot which is more typical. Youll see that it teaters around 3000 going on an off the power. Later I then show it stationary at which point it goes way beyond 4000.

 

Interesting I did try easing back on the throttle a little and it progressed slightly more than 3000.

 

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Does the video make the problem more apparent now?

 

Is a pushrod something I can diagnose and repair or is it time to simply get an electric pump to eliminate pump issues?

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That sounds like an electrical missfire to me. Can you give details of ignition components. You haven't got any original ford bits left in the ignition system? I understood you were going to replace the distributor and you have also replaced the coil. Precisely what bits did you buy? Make and model please. Is there anything else in the ignition system?

 

If you do the pump test into a bottle you will soon know if the pump is flowing. (I made a new pushrod for the pump when I ran a pinto engine out of the stem of an old valve!)

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Ill crack on with the fuel test in the morning.

 

Nothing original ignition wise.

I replaced:

Coil

Distributor

Distributor cap

Changed points for electronic pickups

Ht leads

Spark plugs

 

Used this kit from power spark http://www.simonbbc.com/index.php?main_page=product_info&cPath=11_61&products_id=1976

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I did think that it could be the timing when the advance or retard kicks in and the spark happens so far out its completely the wrong time. Ive messed about with that so much though now I dont see how it could be. Ive sent it advanced and retarded but I didnt see any difference.

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That's excellent kit and should work very well. Money well spent and I would say a very good price too! You won't regret that as a good upgrade to the car when it is running OK. Also sensible to have no vacuum connection to fiddle with. You are sure there are no other electronic modules still connected that were associated with the original ignition system. Next suggestion when you have time for a test run is to temporarily rig a direct supply from the battery positive terminal to the coil and the new distributor. This is to rule out some wiring oddity in the cars wiring. You won't be able to switch off the engine with the ignition key so do it immediately you are about to set off on a test and disconnect it immediately you get home again.

Before you do your test run set the distributor timing to10deg before TDC as a good starting point using the strobe at tickover. Also do the pump test. Then your can wire up the temporary ignition supply and go do your drive test.

Below pics of the crank timing marks. Two types of pulley you might have. I would put a blob of white paint/tippex on the marks you want to use and the blade as shown to make life easier. The pulley is as you would see it from standing in front of the car facing the windscreen.

post-21-0-00155300-1525559622_thumb.jpg

Edited by Longboarder
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Ill get on with the line from the battery to the coil after I get some cable.

 

Here is the result of the fuel flow test. Youll see the fuel does flow but it is in spurts. Im not sure if that is a normal characteristic of the mechanical pump.

 

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That looks like a normally flowing mechanical pump. I think that removes the fuel pump from possible suspects.

Check cam timing, check ignition timing, and wire up a direct positive feed for the coil and distributor for a test run. Remove the feed from the car loom to distributor and insulate it. Don't want it dangling and shorting out by accident.

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I wouldn't for this test. The idea is to give the coil a clean supply of power. There may be a problem, intermittent short or break in the present supply from the ignition switch, a hidden ballast resistor or some other problem which is messing with the ignition currently and if you leave it connected it may still be a problem.

The whole procedure is just a way of checking the supply. If the car is fixed then you know there was a fault in the supply. If the car still won't rev above 2800 then you know ignition supply is not the fault and the search continues.

 

By the way you do have fresh petrol in the tank? Modern petrol goes off.

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Yes, actually I just filled it up yesterday with £28 worth of unleaded. Im presuming it should be unleaded for a b reg Sierra gl. It has a Vulcan rocker cover on top but Im working on the presumption that it was just for effect rather than cam or timing changes.

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The vulcan rocker is an old school upgrade to the engine looks. They do polish up nicely. I would be having it off to polish at some stage, perhaps after I checked the cam timing. The next avenue after the above tests I would do would be to check the cam to follower clearances with feeler gauge and make sure that there is no serious cam lobe wear, the gaps are about right and none of the valves is stuck open.(Rocker cover off for this so a good time to polish it!)

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