Author Topic: Misfire under load again  (Read 1380 times)

Online Rex

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Re: Misfire under load again
« Reply #30 on: 19.12. 2018 09:31 »
My mag had been overhauled (rewound and new capacitor) relatively recently too, but the capacitor had still degraded enough over time to cause problems. Probably depends on who did the rebuild and what capacitor they used as to whether it's still good or not.

Online duTch

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Re: Misfire under load again
« Reply #31 on: 19.12. 2018 10:20 »

 I don't want to flog the horse to death, but like Rex, I had my maggie overhauled mid-90's but then it was fairly much idle until 2013 when I got the rig back on the road....was ok for 3 years, but then I a winding burned and the condensers (little modern pillow shaped orange ones), blew out....ol' mate said it'd outlast me- musta thought I looked a bit ragged.. *conf2*...Having said that, time will tell and I hope for your sake pete, that you're close to a win...(and not on a dead 'orse)  *beer*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
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Offline bsapete

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Re: Misfire under load again
« Reply #32 on: 19.12. 2018 11:57 »
I guess time’ll tell won’t it.
If it ain’t broke don’t fix it I say. *beer* to you all lads.
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Online Black Sheep

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Re: Misfire under load again
« Reply #33 on: 19.12. 2018 17:18 »
So much depends on who rebuilt your magneto. The ones on the A7 and A10 were rebuilt by the same person about 40 years ago and are still going strong. Another rebuilt one has developed massive bearing play after only 10,000 miles. I spent ages fiddling with carburation trying to sort the misfire under load before noticing the bearing play. As you say, most carb problems are the mag and vice versa.       
2 twins, 2 singles, lots of sheep

Offline bsapete

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Re: Misfire under load again
« Reply #34 on: 02.01. 2019 07:21 »
Update: I drained the tank and ended up with a leaking tap (another story) but have sorted that. Added fresh 98 octane and test rode today. With gradual acceleration it pulls ok then when opening it up a bit it has a big flat spot then picks up. If you crank the throttle open quickly it responds better - ie less hesitation. Also still pinging unless on a light throttle. I assume it’s pinging anyway. Doesn’t go away though if you retard the timing with the lever. Revving it up when stationary the engine is fairly quiet albeit a little tappety. I’m kinda struggling a bit here but I’d like to try and sort it myself. No doubt an experienced person would be able to read the symptoms better than me.
Any advise welcome.

Cheers and Happy New Year,
Pete
62 A10S Spitfire Scrambler
54 A7 Star Twin (sold on)
61 Jaguar E Type FHC Flat Floor
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Re: Misfire under load again
« Reply #35 on: 02.01. 2019 07:55 »
G'day Pete.
Put a mark on the twist grip and a corresponding mark on the housing, now twist it full on and mark the twist grip. Now mark the grip 1/2 way and 1/2 again. So now you can hold in the problem area and know which jet to change.
Timing is still too advanced.
Cheers
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Offline bsapete

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Re: Misfire under load again
« Reply #36 on: 08.02. 2019 05:24 »
Hi chaps,
Been a bit preoccupied with pulling the supercharger off my Jag to replace heater hose. Yuk.
Back to the Beeza - Musky, I did as you suggested. With markings on the throttle housing and grip, it seems to be breaking down in the mid-throttle position. I’ve just pulled the carb off to get some numbers etc.
It’s stamped 389/228 and 065 (from a 1965 A65 Lightening & Hornet according to porklips) should be 389/047.

Pilot jet is stamped 25 (correct?)

Cutaway is stamped 389 .4 should be 3?

Pilot jet is stamped 106

Main jet is stamped 400 should be 290?

Needle looks like D to my old eyes and should be in position 2.
Was originally in position 1(top groove) ran better in position 2, ran worse in position 3

Suggestions/thoughts?

Cheers,
Pete

62 A10S Spitfire Scrambler
54 A7 Star Twin (sold on)
61 Jaguar E Type FHC Flat Floor
99 Jaguar XKR Coupe

Online Klaus

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Re: Misfire under load again
« Reply #37 on: 08.02. 2019 08:08 »
Hi Pete,

yes your are right with your suggestions and the correkt set up is for the 389/047

The cutaway you have fit is to big, so the mixture is to weak.


cheers Klaus


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Online orabanda

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Re: Misfire under load again
« Reply #38 on: 08.02. 2019 08:28 »
The slide (cutaway) is richer as the number reduces. The next size down is a 3 1/2, then a 3.
Try the 3 1/2

Online duTch

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Re: Misfire under load again
« Reply #39 on: 08.02. 2019 09:32 »

 
Quote
Been a bit preoccupied with pulling the supercharger off my Jag to replace heater hose. Yuk. .....


  *bright idea*

 Try it on the Beeza while you can.... *smile* *bash*
Started building in about 1977/8 a on average '52 A10 -built from bits 'n pieces never resto intended -maybe 'personalised'
Have a '74 850T Moto Guzzi since '92-best thing I ever bought doesn't need a kickstart 'cos it bump starts sooooooooo(mostly) easy
Australia

Offline bsapete

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Re: Misfire under load again
« Reply #40 on: 08.02. 2019 10:26 »
Did cross my mind duTch. Gives the Jag an extra 100hp. Now where would I run the belt drive from...

I’ll track down the correct size jet and slide and see what gives.

Cheers
Pete
62 A10S Spitfire Scrambler
54 A7 Star Twin (sold on)
61 Jaguar E Type FHC Flat Floor
99 Jaguar XKR Coupe

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Re: Misfire under load again
« Reply #41 on: 08.02. 2019 11:07 »
G'day Pete.
Definitely need a richer slide and a smaller main jet.
As orabanda suggests a 3 1/2 would be better.
You could turn the 4 into a 3 1/2 by taking 1/32" off the bottom of the slide but you'd need to raise the needle the same amount (lower the clip 1 notch).
Also check the fuel height in the bowl. Take off the pilot jet cover and put clear tube over the pilot and bring it up beside the bowl. The fuel height should be at the pip on the cover (just under the ma of Am.al).
Cheers
'51 A7 plunger, '57 A7SS now A10CR, '76 XT500, '77 AG175 '83 CB1100F, '81 CB900F project.
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Online chaterlea25

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Re: Misfire under load again
« Reply #42 on: 08.02. 2019 21:26 »
Hi Pete,
Is the bike in question the one in your avatar ? with the twin high level open pipes?
If so you maybe check out the settings for a Spitfire Scrambler,  *????*
The second part of the number on the carb is only an indication of its original  fitment
Once the choke diameter matches the head it should work OK once properly set up

John
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Offline bsapete

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Re: Misfire under load again
« Reply #43 on: 09.02. 2019 05:32 »
Thanks fellas, I’ve found a 290 main jet and slide with 3 1/2 cutaway locally so have ordered (don’t trust myself to modify the slide I have). John, the settings I listed above are for the 389 carb fitted to 59-63 Road Rocket and Spitfire Scrambler so fingers crossed when I fit the correct size main jet & slide I’ll get a good result.

Cheers,
Pete
62 A10S Spitfire Scrambler
54 A7 Star Twin (sold on)
61 Jaguar E Type FHC Flat Floor
99 Jaguar XKR Coupe

Offline bsapete

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Re: Misfire under load again
« Reply #44 on: 15.02. 2019 05:49 »
Update: new slide and main jet arrived today. On reassembly I note the slide is tight in the bore to the point of not being able to be pushed all the way in. I have taken to it with some 1200 wet & dry and improved it somewhat, it slides but it’s still sticking open at full throttle position. Any suggestions? Keep on lightly sanding until it freely slides up and down? Perhaps a buff on the polishing wheel? The original slide moves up and down with no tight spots.
62 A10S Spitfire Scrambler
54 A7 Star Twin (sold on)
61 Jaguar E Type FHC Flat Floor
99 Jaguar XKR Coupe