low speed miss

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May 4, 2006
hello norton friends, it has been a long idaho winter and my season is starting off abit frustrating. 73 850 boyer duel 932 carbs. had my carbs re-sleeved over the winter, put them on, re-checked the sync of the slides, checked needles, (replaced about 3000 miles ago) bike has 19,000 miles, ran good before i removed the carbs. had some surging at low speed, the usual worn slide symtoms. so, now it idles abit rough. accelerates rough at low throttle, runs very eratic in 1st and 2nd gear at low rpms, surges, feels like a miss, some popping with deceleration. once i goose it and it gets going, runs strong and smooth at half throttle and more. needle is on top groove, air screws out about 1 1/2 turns and then turned abit for optimum idle. when idleing, if i blip the throttle severe i can almost kill it, big hesitation, kind of a sucking sound. is this rich running? is this air leak? i replaced the plugs and they look okay. the machinist who re-sleeved assurred me all passages are clear. i have sucessfully set up these carbs before? as usual, any suggestions appreciated. thanks, jerome
I would have thought you might be running a little richer with newly sleeved carbs, but that hesitation could be weakness. What happens if you give it a little choke? Slide chokes are a great tool for setting up carbs.

slow speed miss

Jerome,I had similar symptoms on my '74 850,resleeved carbs. Boyer,after some frustration I changed the plugs, problem solved. I use Champion plugs and have had some quality isues,they seem to go bad very easily,an over rich mixture will "poison" a plug,just because it shows a spark don't assume that the plug is good. Good luck. James.
Jerome -

I had very similar symptoms with my Mark 3 a couple of months back. I had done a few things to the bike (valve job, etc.) and kept trouble shooting the things that had been touched.

A couple of forum members had been very adamant that i should check every inch of the wiring from the Boyer unit up to the black box and to the coils. I did a visual inspection a couple of times, and kept focusing on everything else.

I changed plugs, plug wires, swapped a spare coil in and out a couple of times, kept checking carb (single Mikuni), etc.

Finally, after being told for the umpteenth time that i should "really" verify every bit of wiring from the Boyer unit, I pulled off the points cover (again). The crimp connectors at the leads were nicely folded over and taped very neatly, so I had "assumed" whatever was under the tape was fine.


I just touched the tape gently to unwind it and off came one of the wires. Simple fix, and never looked back since.

Moral of the story - when you check, really check. And don't trust your eyes - touch stuff!

Good luck.

The Boyer connections always have to be first suspect with a misfiring Com-an-go. Taking the tank off for access when replacing the carbs or even just pulling on the cables under the tank can be enough to cause this but a little oxidisation over a winter can cause dry connections also.

If it's not electrical, I'd check that the pilot drillings are clear (plenty of posts on here about that too !)

I had a similar low speed missfire, bad idle etc. on '74 850, It turned out to be the ignition switch worn.

The contacts to seem vibrate around at tick over and low motor speed causing missfiring etc., but when cruising faster seemed fine.

I think it's possible to dismantle and check the contacts by carefully uncrimping the alloy canister and removing the electrical part at the rear. :)
thank you forum friends, i have been away for the weekend and have not had a chance to deal. i appreciate all the input, will check the electrics, mess with the choke and will report back when i have some results. i assume a bad boyer connection could only cause a low speed miss? thanks again, jerome
I have been struggling with a left cylinder that won't fire on idle/low rpm's and trying to understand if it's my newly resleeved carbs or ignition that is the problem has been driving me nuts!

Tonight a local club member came up with an excellent method to sort out the "ignition or carb?" question.
It's easy. take your strobe and hook it up, run the engine and you'll see if the ignition works! Can't be much easier!

just wanted to get back to this post and let it be known all the boyer wire suggestions were on target! after messing with the timing, carbs, head scratching i let myself get used to the bike not running right. i had checked the leads from the plate physically many times and they felt stong. FINALLY after the new charging system did not change anything (my output was low for the boyer) i went back into the plate to undo the beautiful shrink wire, connector job. the lead fell off in my hand. the p.o. when stripping the wire took half the copper strands. so.....i kick myself for not listening better to those in the know. i figured because i had just done the carbs, it had to be related. hope this will help someone else. thanks, jerome
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