Engine Judders And Splutters
Posted 12 October 2011 - 08:17 AM
Assuming you have a CO tester, i'd be looking for a 2,5 to max 3,0 at idle, 2,5 is better.
Keep revs stationary, read around 2 at each 500rpm increase.
With throttle applied you should look for about 5 CO or more.
Posted 12 October 2011 - 02:15 PM
please explain 'read around 2 at each 500 rpm increase' - do you mean 2 as 2% or 2 as make 2 readings? Or should I look for 5% or this 5% was for full throttle?
pardonnez my Spanish...
Posted 12 October 2011 - 03:34 PM
set the idle at 1500 rpm
you read 1.8%, thats perfect,
rise the idel to 2000rpm you have 1% ok stop- file down the corrispondent station until you read around 2%.
At full power you need a richer mixture, so readings will be around 5%.
Remeber that the dashpot oil has an effect on fuel enrichment under throttle, the thicket the oil, the richer the mixture.
The Spring weight affect how much the piston will raise.
The damper affect how much fast the piston will drop, if you have issues like piston not dropping completely at gearchange, you need a faster damper.
Check those three elements for fine tuning after you've profiled the correct needle for your engine.
Remeber that the tester need to reach its optimal temperature to give an accurate reading.
Dont take me as an expert on the CO tuning as i use a wideband lambda instead, which gives me the AFR making the work a lot easier
Posted 29 October 2011 - 10:30 AM
yes, the mixture at rpms higher than idle was lean. I read 0.8 to 1.1 % CO at 3000 and 4000 rpms initially. After a 20 or so seconds at these RPMs engine starts to give wrong noises. I filed down corresponding sections (and yes, I overdid them after all, haha) but the engine still reacts the same. I have another needle (ABB) what gives overall richer readings (3 - 5%) but the juddering etc still remains. When I had my needle lean, readings at the juddering went much richer. What could that mean?
I tend to think there is something completely mechanical with this setup what is wrong. My general suspect is the head. As I said, it was a cheap ebay find.
I am not familiar with these heads. I have the feeling as if valves start to stick in the head - is it possible at all?
Posted 01 November 2011 - 05:14 AM
With the mixture set to about right by polishing needle (thanks jaydee) and the noises continuing...
my suspect now is the head. Will take it off and will bring to specialist to see if valves are not sticking in their guides.
as total noobie am also quite struggling with general idea of what first - ignition or mixture? Now ignition is set using strobe light, but it seems to me engine wants it to be set far far retarded...
Posted 01 November 2011 - 07:06 PM
Can you post another short video of it?
- Check the tappets clearance, set them at 16 thou (with the engine cold) when usinga kent 266 camshaft, leaving the exhausts a little bit wider than the inlets.
- Replace points and condenser in the dizzy.
- Try a different coil.
- Check if the float bowl is dead vertical, if not it will flood the carbs choke affecting mixture badly.
- Check the the jet level it should be within 2-3 mm under the bridge or it will just flood the carb everytime the piston is raising.
- If still no avail, try an HIF44 carb..a single HS4 is too little for a modified 1275 engine.
- Remember you have to file down the needle stationsin the correct sequence. IE: if you file down the stations 4-5-6, you cant file down station 3 again. Or better, you can but you'll have to file down the successive stations too or it will missfire when passing from station 3 to station 4 and 5.
The only mechanical issues i can think of, are: worn rockers/ bent pushrods/ wrong timing/ points and condeser gone..
Worth a check on camshaft timing too, but i bet thats not your problem..
What dizzy are you using?
Also, to set the correct mixture you'll need to make some runs on open roads, and see how the engine behaves under different loads.
Expample, you'll probably notice no missfire in 2nd gear, but starts to misfire in 3rd gear at about 3krpm, that means you need a richer mixture. Once 3rd gear is fine, it will probably missfire in 4th gear, so file down again the correnspongin needle station.
Mine needed a lot of filing at about station 4-5-6 to iron out flat spots i had, expecially at cruising speed in 4th gear.
I'm not good at explaining this, but the 'rich' CO readings you have when it starts to missfire are due incorrect fuel flow out of the carbs jet, so the carb quickly passes to underfuelling-to flooding-to underfuelling again.
Edited by jaydee, 01 November 2011 - 07:09 PM.
Posted 02 November 2011 - 10:16 AM
this is my efforts at 2000 rpms
and this at 3000
the first was without any oil in dashpot, the second with thick (20W50) motor oil
will check AGAIN the valve clearances bit later
have been trying 2 coils and 2 condensers
its the dizzy from original 998 engine, D59 I believe
will see the carbs float bowl etc bit later... But all that has been fiddled with...
Edited by klivins, 02 November 2011 - 10:20 AM.
Posted 02 November 2011 - 02:30 PM
Posted 02 November 2011 - 02:41 PM
Sounds like theres something wrong with the dizzy..do you have sparks out of all 4 plugs?
Is the vacuum advance properly connected, and the mechanical advance in the dizzy fully working?
What is the number stamped on the dizzy?
Using the strobo, check the advance at about 2500 rpm with vacuum disconnected, try to reset it in the region of 16° to 20°, then apply throttle till you can see the engine reaching maximum advance. If maximum advance is no more than 25°, then you need to recourve your dizzy, if it reaches 28° or more, well we can still fiddle with timing.
Please dont accelerate by pulling the cable, use the throttle nut instead
The mixture could be too lean, the gunsons CO reader have some strange calibration to deal with, and sometimes they read 2% high..do some research on the net about it..
Try to calibrate it at 0% in the air after you warmed up the sensor..and you need to put the sensor a bit far into the exhaust.
The idle is a bit too lumpy for a 266 cam, id expect it to be a bit smoother, and this can be another symptom of wrong air/fuel mixture.
Posted 02 November 2011 - 02:46 PM
ok, now had set valve clearances to 0.4 mm instead of 0.3 mm what was prescribed by haynes...
There should be a reason why some people call it the handbook of lies LOL..
16 thou IS the reccomended tappet clearance for any camshaft of the kent range, which in metric is a wide 0,4mm.
The readings are conferming all the lean mixture suspects.
Posted 03 November 2011 - 12:51 AM
After fiddling with ignition just got inpatient and drove her up and down the street, but without MOT, insurance, bonnet and grille could not go far enough to get my juddering.
When took off vacuum advance engine started to detonate from exhaust side! Could not really test it properly as you described regarding all the angles, but advance at least works! Took dizzy off to see the numbers properly, and the points were bit too wide, again, judging from Haynes piont of view! Now have them at 0.35mm, will have couple of hours to fiddle tomorrow as well.
Posted 03 November 2011 - 09:43 AM
Its curve is about this:
Advance it to 8° or even 10° at 1000rpm, and see how it goes, look for any pinking under load.
Point should be ok at 0,35mm, i'd try replacing also the condenser, but actually what you need is a different advance curve.
Posted 03 November 2011 - 10:42 AM
Posted 03 November 2011 - 11:57 AM
What you have to do now, is to put cylinder #1 (nearest the rad of course!) at TDC - fireing stroke and see where the dizzy rotor is pointing. Thats where you put HT leads for cylinder #1, then place the other leads 3-4-2 counterclockwise as usual. No matter if cylinder #1 Lead is pointing downwards.
Take the spark plugs out, 3rd gear on, remove the rocker cover and start to pull the car slowly, until you can see both valves at cylinder #1 are closed.
Put a screwdriver in the plug hole, you should see it at TDC. Now if you're at the firing stroke, the valve #8 should be rocking (to be honest i just look at valves #1 and #2, if after pulling the car a bit more the next valve to open is the exhaust, then push it back to TDC and that is TDC firing) and you should be able to see the timing mark in the crank pulley pointing very close to the 0° in the timing marks.
Regarding dizzy type, you can send your dizzy to aldon or accuspark and they can give it a refurbish and recourve it to suit your engine spec.
Or you can play with the bobs inside the dizzy to change the mechanical advance, but personally i wouldnt bother with them..
Edited by jaydee, 03 November 2011 - 12:03 PM.
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