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someone must know driving me nuts #13047 07/07/06 8:04 pm
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Ken Offline OP
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I have a 62' BSA Star with a single 930 Concentric. The bike runs very heavy on acceleration after about 1/2 throttle. Past that and it starts to slow down and sounds as if it's choking (no backfiring though). It's fine when I back off on the throttle or upshift but I can never wind it out in any gear. It also gets worse if I use the choke and it seems to be running somewhat rich (some soot on the plugs).

I have new coils and a new Boyer with new wiring. Batter is fully charged. Bike kicks right over and idles fine. All of the carb passages are clear and no air leaks as far as I can tell.
I set the float to ~2 mm below the rim and the fuel level is ~0.230 when the float is at it max point.
I also tried larger fuel lines but it didn't make any difference. For the hell of it I also checked how long it would run with the fuel shut off at idle - 15 seconds.
When I change the slide, or the needle position it just makes it worse.

Does anyone have any ideas at all? This is driving me nuts since it has been going on for 2 years or so ever since I rebuilt the entire engine. And I think I've tried just about everything.

Thanks,

Ken
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Re: someone must know driving me nuts #13048 07/07/06 9:03 pm
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[QUOTE] ever since I rebuilt the entire engine

Assuming your carb and timing has been looked at many times and is correct, no restrictions in the ex pipe. How about the old valve springs?
Just a suggestion.


Always use the Golden Rule.
Re: someone must know driving me nuts #13049 07/07/06 9:54 pm
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pooch Offline
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15 seconds running at idle with fuel off seems quick.

Must be too rich.


56 B31 with B33 barrel
51 Golden Flash with Dusting sidecar
Re: someone must know driving me nuts #13050 07/07/06 11:51 pm
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Mike Carter R.I.P. Offline
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I really think the 930 carb is too large for this bike. I think it came with a much smaller Monobloc. you need to either change carbs (maybe a 928) or do some serious jetting, needle, slide etc changes on the 930. Have you made sure the timing is spot on for the Boyer? Just a thought ..you will get it running great..honest. :bigt:

Mike Carter

Re: someone must know driving me nuts #13051 07/08/06 12:05 am
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Bsa 23 Offline
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Hi Ken - Sounds like breather fault on tank - as it starves for air fuel mix richens. Check your cap and or breather. Easy test - after riding along and problem occurs - open fuel cap.

Re: someone must know driving me nuts #13052 07/08/06 12:17 am
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Ken Offline OP
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Thanks for the replies.
Here's what I can say in response:
-The springs are new
-The carb is a 928 (don't know why I wrote 930)
-Timing is as dead nuts as I can get it with no timing marks but it was a problem before
-Breather is completly unrestricted and taking off the cap does nothing.
-In terms of running for a short period at idle any suggestions about how long it should run and what could be causing the shortened running time?

Thanks,

Ken

Re: someone must know driving me nuts #13053 07/08/06 12:24 am
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Ken Offline OP
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Oh, almost forgot - By breather are you talking about the little hole in the cap?

Re: someone must know driving me nuts #13054 07/08/06 3:06 am
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Ken - Yes that's the hole i meant. Looks like fuel is an issue though - my A7 500 with 928 carb runs for 3 minutes after tap is turned off - checked twice,180sec & 185 secs. How about fuel taps? any blockage? I would do a flow test into a measuring cup or beaker, should give you a better idea of whether enough fuel is getting through. If there is corkseals in your taps they may have swelled.

Re: someone must know driving me nuts #13055 07/08/06 3:38 am
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Ken Offline OP
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But if my bike isn't running long enough after the taps are closed it won't have anything to do with the flow, no? Or are you suggesting that there is never enough fuel reaching the carb and that's why the idle after shutoff is so minmal?

Maybe I'll try tickling it right before I shut it down. Hell, maybe I should try tickling it right before I open the throttle and see if it still has a problem then I'll know it is a fuel volume problem.

In terms of flow rates what do you think I should be seeing in the measuring cup/beaker.

Thanks,
K

Re: someone must know driving me nuts #13056 07/08/06 5:00 am
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BONZO R.I.P. Offline
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K , A couple of questions , was the bike running well with this carb before the rebuild ? if the carb is new , is the float full of fuel ? if the carb wasnt runiing well on this bike before overhaul , what jets/needle/slide do you have in there ? Do you have stock gas tank and fuel taps? does this happen with both taps open ? do you have fuel filters inline ? When completely rebuilt , was stock '62 cam spec used ? Is this the stock '62 head and valves ? This is a lotta question with little info .
FWIW-BONZO

Re: someone must know driving me nuts #13057 07/08/06 7:37 am
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triton thrasher Online Content
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It sounds like the main jet is too big or has dropped out, but I suppose that can't be.


Amateur Loctite enthusiast.
Re: someone must know driving me nuts #13058 07/08/06 11:19 am
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If you've recently fitted a Boyer, try temporarily wiring the plug leads directly to the plugs ie. no plug caps.My Boyer did not like surpressed caps or leads. It caused misfiring and plug fouling. Worth a try.My leads are now copper wire with nil resistance caps.Bike now runs great.
Mike
bsabarmy


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Re: someone must know driving me nuts #13059 07/08/06 3:52 pm
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OK, I'll take the most recent one first:
-BSABARMY: I am running straight copper to the coils (0 ohms)
-TRITON: The main jet is firmly attached and doesn't come into play at 1/2 throttle as I understand it (it does at 3/4 to full). Anyway, I've tried larger/smaller mains and they don't make any difference
-BONZO: The bike was running OK w/ this carb prior to the rebuild but that was when I lived out west at ~7,000' above sea level (took forever to get the jetting right then, of course, I moved to sea level). The float is new (6.05 gm) but I have the an older one as well (6.25 gm)and neither is holed so I put the original one back in as it is a little sturdier. If I remember correctly (I can always open it up again for the millionth time) the main is 190, slide 2.5, needle jet .106 (cross drilled)and the needle, needle jet and jet holder are from an AMAL metering replacement kit. The needle (new) has three grooves (in middle groove) but I forget the size. Also, whenever I tried changing the needle height, cutaway, or needle/main jets it always got worse and I tried cutaways from 2 to 4 and jets from 130 to 300. Tank and taps are stock. Never tried it with only one tap open. No filter in line but a nylon filter in the banjo on the carb (both lines come in to carb at 180 degree). Cams are stock (new) as is the head (used) and the valves and springs (new but guides are old).
Maybe I'll hook up a tach to see what rev it's having trouble at cause it's probably consistent considering upshifting (too early) removes the problem.

Ken
tach

Re: someone must know driving me nuts #13060 07/08/06 7:06 pm
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Ken Offline OP
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Well I tried tickling it when it started to hesitate and it made it worse. Also, closing the air valve makes it worse. In fact, closing it all the way will make it stall. Maybe I'll plop on the tack just for the hell of it.

Ken confused

Re: someone must know driving me nuts #13061 07/08/06 8:00 pm
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Ken Offline OP
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So doesn't it seem as if the fuel supply is not a problem?

I still think it has something to do with the throttle needle I just wish there were needles with more than 3 grooves.

So anyone got any ideas?

Ken

Re: someone must know driving me nuts #13062 07/08/06 8:49 pm
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Cams are stock (new)

For giggles remove the rocker covers and look at the rockers. Do the valves seem to be opening as much as they did when you put it together?
john


Re: someone must know driving me nuts #13063 07/08/06 8:52 pm
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Ken Offline OP
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There are no rocker covers on this model. It has a rocker box and to get to it I have to remove the tank. Anyway, I recently checked the clearance and it was to spec (well as much as anything is to spec on a beesa).
Thanks,

Ken

Re: someone must know driving me nuts #13064 07/08/06 9:00 pm
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John RGS Offline
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Ken, to stop the bleeding, find someone close by and swap a carb. If this cures the problem or is markedly different, buy a new carb and put the matter to bed.


,_o
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Re: someone must know driving me nuts #13065 07/08/06 11:21 pm
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RF Whatley Offline
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IMHO it sounds like cam timing.

The last time I had this was with a T100. The owner admitted later that "the center gear once fell out so I put it back in". But he did not relate this one little fact until we had spent several hours double checking every other concievable adjustment.

You can check the cam timing easily. Roll the piston to TDC and rock the crank back and forth +/- 20 degrees. At one TDC, BOTH valves should be opening or closing (at exact TDC both should be ever so slightly open, with rocker arms tight); at the next TDC both valves should be closed (with both rockers having free-play). So you need do nothing more than remove the valve covers and sparkplugs, and then roll the bike in gear. Simple.

Hope this helps! :bigt:


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: someone must know driving me nuts #13066 07/08/06 11:32 pm
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pooch Offline
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Total guess here, as I know zilch about boyers.

But could it be failing to advance the spark, however a Boyer does it?

A manual advance left in retard position would act like you say, be Ok at low revs and upshifting early, but running out of puff at high revs.


56 B31 with B33 barrel
51 Golden Flash with Dusting sidecar
Re: someone must know driving me nuts #13067 07/08/06 11:36 pm
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Ken Offline OP
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Thanks, maybe I'll check the valves later but it's still a pain cause I have to take off the tank and the rocker box cover and at the moment I'm out of gaskets. But I really don't think the timing has changed since the rebuild. Anyway, wouldn't this problem be present at all speeds if the cam timing were off?

What I did do though was strap a tach onto the bike. It basically craps out (what it actually does is slow down the more throttle I give it) at ~ 3,200 RPM in both 1st and 2nd. I really can't get it running fast enough to check any of the other gears on residential streets and can't take it on the highway in this condition. Also, I read that max speed in 1st was ~44 mph and I can only get it to around 25 mph (and that would be at 3,200 rpm).

Ken

Re: someone must know driving me nuts #13068 07/08/06 11:51 pm
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Ken Offline OP
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Anybody know what the advance curve is on a Boyer?
From that old article by dynodave it appears that there is 10 deg of advance at 2500 (distributor) rpm plus initial advance. Anyone know different?

I should have checked it while I had the tach one the bike (it's a dual tach/dwell meter).
Anyway, too hot and and too tired to check it again tonight. Guess I'll load'er up tomorrow and check it then.

Ken

Re: someone must know driving me nuts #13069 07/09/06 1:18 am
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Ken Offline OP
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Just a quick question:
The tach I have says to double the 8 cyl scale for 4 cyl. so I double that for the bike. For example, if the 8 cyl scale was 200 RPM 4 cyl would be 400 RPM and 800 RPM for the bike (2 cyl). But since the Boyer fires twoce per revolution isn't it acting like a 4 cyl engine to the meter?

Ken

Re: someone must know driving me nuts #13070 07/09/06 3:30 am
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Ken Offline OP
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John & RF, are you talking about the camshaft in the crankcase of the overhead cams? Oh, one more thing, when I got the new cams I compared them to the old ones and they were identical. Also, when I was having trouble setting up the timing everything was exactly right: the intakes opened at 40 deg. BTDC, closed at 60 deg. ABDC and the exh opened at 65 deg. BBDC and closed at 35 deg. ATDC. and I set the lash at 0.015".

Why do you think any of this would have changed?
Thanks,

Ken

Re: someone must know driving me nuts #13071 07/09/06 10:35 pm
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Ken Offline OP
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Well I just checked it out:
dewll is 5 deg at idle between 550 & 650 rpm (I used my oscilloscope to check the idle and the corresponding scale on the meter is 8 cyl, go figure)
BTW, anyone know what the initial advance is on a Boyer?
So the problem reared it ugly head between 800 & 900 rpm at a dwell of 15 (can't get it above that cause I can't get the rpms any higher). So that comes out to around .016 deg/rpm.
I have a 930 Concentric so I'm going to throw in to see if anything changes.

Ken

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