Amal 928 on gold flash 59 cutting out with quick throttle opening

[duTch]

  Good points there (no pun intended ), and did you experiment with plug heat range, or types..?
 I had a 'not so similar' thing, and was running BP7ES, and went back to B7ES, and it made an immediate difference...so far, so good... still a touch rich, might try 6's...??

[Gerry]

Hi Richard, You may have a point there as the first plug caps I used fell apart when pulling them off the plugs so bought the NGK to fit when I fitted the Boyer so I think if I remember right that they are resistor caps. OK will see what I can replace them with. Hi WazzA, No there is no difference with the filter on or off. I'll check the slip ring, but haven't done more than 10 miles on it since fitting the overhauled mag'. Hi Morris, I did fit a Boyer system to it as a desperate attempt to solve the weak near side cylinder problem, but that didn't make any difference either although at that time I didn't have the missing with quick throttle response with either the Boyer or the various mags I tried. Hi John, When I first tried the 930 after many attempts with 356's it was the first time it ran well other than the weak left cylinder, open the throttle and immediate response, just stuck slide when hot. Hi Dutch I am using NGK BP7ES, wanted BP6ES but couldn't get hold of any locally. But I have been using them since I first got her running after the build and the problem I have now wasn't there earlier with the 930 carb. Will keep you all posted as I progress. Thanks again fellas. Much appreciate all the help. Gerry

[Gerry]

Hi John, I got it wrong!!! The last carb' I fitted was a 928 which is the same bore as the manifold. Just replaced it with the 930 and still have the problem. I also got the plugs wrong..they are BP6ES I couldn't get BK7ES but the 6's were also recommended somewhere but can't remember where. Next job is to find a set of non-resistor plug caps and check the mag' slip ring. Then if all else fails, strobe the timing. Cheers. Gerry ps getting pretty close to strip and rebuild blindfolded.

[duTch]

 Just a thought with regard to resistor caps- I've read that the spark goes 'TO' the plug on one side and 'FROM' the pug on the other side (if yea kenow whut I Mean...?), sooo,  would that mean a resistor cap on the side where the current goes TO the plug, the risistor would mess it up..??....but on the side where the current flows FROM the plug, and then through the resistor cap, it would be less affected by the resistor...??

 But then just as I finished, that little theory, I remembered that is in the case of a magneto, but you had the problem also with the Boyer....??

 Maybe move over and make room on the bench, offer up the green cone Richard....
  uhoh...
 I thought about specifying 'head cone', but am probably already in deep enough...

[RichardL]

Two good links about resistors in plug caps.


http://www.a7a10.net/forum/index.php?topic=5576.msg37955#msg37955

Make the noted selections after going to:

http://www.brightsparkmagnetos.com/faqs/

FAQ about magnetos generally
Are suppressors and resistor sparking

[chaterlea25]

HI Gerry,

Then took a 1/16" of the bottom of the slide to give the same effect as a smaller cutaway

This also has the consequences of lowereing the needle and making it leaner
to make it work you also need to bore the same amount away where the needle clip seats

I cant remember who had similar problems some time ago??? (was it you?)
As you have tried several ignition systems, ruling out ignition problems
check with a strobe on each side anyway its easy to see misfires with the strobe light

If one cylinder is lean to the point it misfires then that side is drawing air??? worn or loose valve guide??

I had a bike in with a miss on one side (after trying everything) it turned out to be a collapsed valve spring

HTH
John

[morris]

A lot of carb problems with throttle responce etc can occur if there is a step in the inlet tract
There was a link to an article on this some time ago but cannot remember where ???

Here it is again;
http://www.braigasen.com/Induction_port_obstructions__%28by_George_Templin%29.pdf

You got us all puzzled here Gerry. With the danger of being put on a stake and get burned by the international women's league, don't listen to the wife this time. Keep on looking. When you've found the solution, the reward will be great!
John might be on to something when suggesting an air leak. Hairline crack in the left side inlet tract maybe? If I'm not mistaking up until now you haven't tried another head yet?

[Gerry]

Hi Dutch, Richard, John and Morris, OK I just checked the Brightspark website as suggested by Richard, very interesting that a resistor might eventually breakdown the armature winding insulation and showing the fact that it does interfere with the spark in a minor negative way. So resistor caps are a No No!! Things have changed since I first had the non-firing near side cyl'. That side is now firing much better and besides that the other problem was the sticking slide when hot. Now I have the severe missing when blipping the throttle or on the road at about 1/4 throttle opening only the right side is combusting. If I open her up further she comes good after a lag of a second or so. What has changed? Only the magneto. I think I am going to remove the cast head and fit the alloy twin carb' head with manifold and see if that improves things, will also check porting alignment prior to fitting as suggested in the site John added (thanks John very interesting). Remember I have also tried a 376 that had been bored and resleeved with brass which was the right port size. So air finding its way around the slide wouldn't be a problem I don't think. Cheers and thanks again all. Gerry

[warmshed]

I am with "Morris", check your slip rings for carbon deposits. Had it on my Brother in law's A10. The pickup carbons can be too soft and they leave a track on the slip ring.
Try cleaning the slip ring If ok for a while get new quality pick up brushes, there are a lot of pattern pickups that are way too soft.

930 concentric carbs are renowned for distorting either when hot or when tightened. Strange some carbs never do it. other always do no matter how you prepare them, flat flange and stub etc.  Took mine off and went to Mikuni, not everybodies cup of tea but good starting, idling and running, what more do you want? and you can always revert back if you become a rivet counter.

[Gerry]

OK Guys, Took the plug caps off and wired the lead ends direct to the plugs....seemed to improve the idle but that could be wishful thinking. Checked the slip ring of the mag and absolutely clean and bright brass strip. So off came the tank.....again... and removed the rocker inspection covers and checked the tappet clearance WHATTHA!!!!! I set these with a lot of care and patience and now the right hand inlet is 0.024" should be 0.010" the exhaust is 0.020" should be 0.013" the left hand side all over the place as well....what happened here? So bugger it, took rockerbox off removed the pushrods (straight as), removed the head and placed my palm over the right hand barrel and using my other hand cranked the engine. Couldn't push the kick start too far as the suction on my hand was too much. Did the same on the left hand barrel and could turn the crank over even though there was suction on my palm it was not as much as on the right cyl'. Took the barrel off (difficult) and checked the rings and all seems good. Good clean bore in the barrels, no scoring, no visible problems with the pistons and rings are free and shiny. Looks like I shall be investing in another set of new rings and the alloy head with single casb' manifold bolted on.  Looks like a quick hone to give me the cross hatch pattern to bed in new rings. Would all these problems give me the results I have been getting? Cheers. Geriatric. I have now copied this to the engine section.

[chaterlea25]

HI Gerry,
How do the cam and followers look?
Tappet clearance increasing can be due to wear on the cam and followers
caused by lack of oil pressure bypassing the PRV 
Usual cause is worn timing side bush, or bad pump 

The current A10 in for refurb arrived with the owner saying "its not charging"
Timing cover off to reveal a v belt dyno drive full of oil and loads of up/down play on the main bush

John

[Gerry]

Hi John, See my post in engines. Cheers. Gerry

[BSA_54A10]

OK Time to go back to first principles.
Get yourself 1 ( 2 is better ) colortunes .
They are soft plugs with a window in them so you can see what is happening inside the cylinder.
This will take a lot of guess work out of your problems and save thousands of hours fixing problems you never had.
The absolute fastest way of isolating ignition problems from fuel problems particularly to the untrained ear.
You really have to go back & stop look & listen otherwisw we will happily tell you our pet problems ( the one that had us foxed forever ) and you will work through each one of our problems till one of them lines up with your particular one.

Now for starters you must have a tuffnol gasket in the inlet train and better still would be two. The thicker the better.
BSA did not fit them for the fun of it , fashion or to drive the price up

[Gerry]

Well fellas we now know what the problem was as said in another post, the bloody crankshaft timing pinion was off an A7 and one tooth out with the valve timing. Cheers. Gerry