1978 BS38 breaks up at 2500. Video included.

Ok. I fixed the leak I also found out my carb boots were very cracked. So I ordered the tour max boots and have those installed now.

The bike actually runs a little bit better now , but the main issue remains.

I still believe my issue lies within the auto advancer. So I once again removed my advance rod cleaned everything and re greased it.

I noticed that no matter which springs I use, I am unable to twist the nut to open the advancer by hand , it works easily with pliers but I've read that I should be able to twist the advancer open by hand.

I've tried different springs to see what effect it has on my advance. I've even tried different combinations of springs. With my tightest springs, I can't get the advancer to advance at all, with my loosest springs the advancer doesn't return to its closed position. When I tried the combination I managed to get it to advance however it advanced past the the mark on the rotor. Please let me know if anything seems out of place that would hinder the operation of my advancer. And if anyone here lives in the Seattle area, and you think you could solve this problem, feel free to dm me, i'd love to talk about it. (It looks like I forgot to take a photo of the advancer itself. I will report back later with a photo of that as well)


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Any ideas !? I'm about to just buy a new motor and swap it out.
 
If no rattle and no smoke .. Compression OK or good
Maybe a new electronics ignition can be a way forward Boyer Bransden -- One option among other.
Lot simpler than hauling 2 motors out and in
Yes, could change to another nearly 50 year old motor that has bigger problems. An ignition system change is probably the best idea. Everything is then new in the ignition department.
 
Yes, could change to another nearly 50 year old motor that has bigger problems. An ignition system change is probably the best idea. Everything is then new in the ignition department.
I could swap in a 1981 43 year old engine for sale nearby for 200$ which has a pretty good electronic ignition made by Yamaha. Or get the Boyer ignition for $260.

One could argue that the task of removing the engine and swapping in a new is worth the extra money. But is the boyer ignition actually better than the TCI Yamaha ignition? If so I'd love to take that route. Are there better electronic ignitions? Or is Boyer the best ? I suppose that will my my topic of research for the the next day. And hopefully that fixes the issue.
 
I could swap in a 1981 43 year old engine for sale nearby for 200$ which has a pretty good electronic ignition made by Yamaha. Or get the Boyer ignition for $260.

One could argue that the task of removing the engine and swapping in a new is worth the extra money. But is the boyer ignition actually better than the TCI Yamaha ignition? If so I'd love to take that route. Are there better electronic ignitions? Or is Boyer the best ? I suppose that will my my topic of research for the the next day. And hopefully that fixes the issue.
There's no simple answers to those points.

Though if I could buy a good spare engine for $200 I would irrespective of anything else.
 
There's no simple answers to those points.

Though if I could buy a good spare engine for $200 I would irrespective of anything else.

Yes $ 200 for a motor is cheap but since very few under price what is up for sale
I would assume it to be more or less shot.
No chance I would install it without having heard it run .To much work put it in
Just to listen to piston slap or worse .Having to take it out again
On the other hand if the alternator rotor checks out resistance and the ignition box seems good there are parts worth the price
No mention if carbs are there also.

I would think the Yamaha ignition is better I like stock .Having said that Boyer Bransden is a company been doing this for many years.
There are better ones but more expensive
Depends on space and future plans if possibility to move a motor truck and Muscles
and have the space.

The Boyer can land in the Mail Box within days And 3 -4 hours later it can be fixed
 
Let me
Yes $ 200 for a motor is cheap but since very few under price what is up for sale
I would assume it to be more or less shot.
No chance I would install it without having heard it run .To much work put it in
Just to listen to piston slap or worse .Having to take it out again
On the other hand if the alternator rotor checks out resistance and the ignition box seems good there are parts worth the price
No mention if carbs are there also.

I would think the Yamaha ignition is better I like stock .Having said that Boyer Bransden is a company been doing this for many years.
There are better ones but more expensive
Depends on space and future plans if possibility to move a motor truck and Muscles
and have the space.

The Boyer can land in the Mail Box within days And 3 -4 hours later it can be fixed
Is the one worth getting ? Looks like it has a new advance rod , which might be helpful in this instance.
https://www.ebay.com/itm/2565617873...7mAh0lFT5a&var=&widget_ver=artemis&media=COPY
 
Let me

Is the one worth getting ? Looks like it has a new advance rod , which might be helpful in this instance.
https://www.ebay.com/itm/2565617873...7mAh0lFT5a&var=&widget_ver=artemis&media=COPY

Dont want to spend other peoples money .But I believe it is the one I have
I gave up on the stock advance unit

Dont remember what charging you are using please check if compatible

The rod is an all thread a nut on the right side and the brass rotor with 2 magnets left side
More info there
http://www.boyerbransden.com/index.html

Maybe can find it a bit cheaper if you search on line

Should work.. As mentioned the company been around for many years.
have not heard any complaints except not so solid installation plates
It don't like voltage out of Spec then strange things can happen.
If low it wont start but the same for points.

If you stand down a while before ordering others can chime in
 
Let me

Is the one worth getting ? Looks like it has a new advance rod , which might be helpful in this instance.
https://www.ebay.com/itm/2565617873...7mAh0lFT5a&var=&widget_ver=artemis&media=COPY
That is a piece of 8mm all thread. It is fitted in place of the stock advance rod. The Boyer Bransden kit has electronic advance. The stock advance/retard is removed completely.

Here is my experience from three months ago fitting a Boyer Bransden kit to my 77 XS650 -

https://www.xs650.com/threads/musings-on-boyer-bransden-electronic-ignition-kit.66824/post-849399
 
When a twin engine is misfiring, it is always useful to know if both cylinders are affected or only one , and which one.
Once you know that, it is easier to find the cause and cure it.
 
Ok. Its been a while. I bought and installed the boyer ignition to rule that out. The bike idles like a champion.

I have only uni pods and stock exhaust.1978 special bs38

I've just replaced the choke gaskets. Cleaned the carbs a few times , fully disassembled. Bench sync.

Somewhere between 50 and 100 feet above sea level.

I've increased my pilot jet to a 30. (Although it runs more or less the same as the stock 27.5)

My main jet is still the stock 135.

Float level at 24mm

Just re-did the cam chain and valves

I've replaced my carb boots with tour max boots

I've attempted to run on the middle clip position as well as the second down, as well as the 4th down from the top. I'm currently in the fourth position with an extra shim washer.

Still my throttle response is very lacking in the low rpm range. The bike idles great but I need to take off from a dead stop I either need to throttle it very slow or rev it up like crazy and dump the clutch to take off. I really can't take off quickly (as one would pulling into traffic) the bike with just die. There also seems to be a loss of power between 1500 and 2500 which I can push through pretty easily. Once I get to 3k the bike runs absolutely fine. If I am in motion the bike is perfectly rideable but there's still that slight stumble.

The carb guide would lead me to believe this is a needle clip issue.

Any advice ? Bigger main jet ?
 
@Prisondawg , you fitted new throttle shaft seals when you stripped the carbs? The seals are subjected to the low pressure of the engine intake with the throttle plates closed and near closed at low throttle. Should really be replaced when the carbs are stripped. I note the pilot jet change wasn't a noticeable difference. Does adjusting the pilot mixture screw make any difference? What you describe sounds to me like partially blocked pilot mixture holes, the small ones adjacent to the throttle butterfly plate.
 
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@Prisondawg , you fitted new throttle shaft seals when you stripped the carbs? The seals are subjected to the low pressure of the engine intake with the throttle plates closed and near closed at low throttle. Should really be replaced when the carbs are stripped. I note the pilot jet change wasn't a noticeable difference. Does adjusting the pilot mixture screw make any difference? What you describe sounds to me like partially blocked pilot mixture holes, the small ones adjacent to the throttle butterfly plate.

Howdy, I've not changed the throttle shaft seals. That is the last thing on the carb list. However, there doesn't seem to be any play in the throttle shaft. I've also sprayed starter fluid all around and it doesn't effect the idle.

The fuel mix screw , I've attempted to move it all over the place. It seems very sensitive. I have a gunson color tube which I've been using to set the base line, if I hear any popping then I richen it, and then if I notice my rpms falling below 1200 after a lot of throttle, and recovering I assume that means it's too rich, so I will lean it. All my adjustments have been very small nothing more than a quarter of a turn. Which has dramatic results. For example If I turn it a quarter of a turn in, it will start popping. If I turn them a quarter of a turn out, it the idle starts to fall.
 
Howdy, I've not changed the throttle shaft seals. That is the last thing on the carb list. However, there doesn't seem to be any play in the throttle shaft. I've also sprayed starter fluid all around and it doesn't effect the idle.

The fuel mix screw , I've attempted to move it all over the place. It seems very sensitive. I have a gunson color tube which I've been using to set the base line, if I hear any popping then I richen it, and then if I notice my rpms falling below 1200 after a lot of throttle, and recovering I assume that means it's too rich, so I will lean it. All my adjustments have been very small nothing more than a quarter of a turn. Which has dramatic results. For example If I turn it a quarter of a turn in, it will start popping. If I turn them a quarter of a turn out, it the idle starts to fall.
How does it look with the Gunson colour tune?

The mixture screw only meters part of the pilot mixture into the carburettor. The fact it's very sensitive to minor turns on the screw I think means one or more of the small pilot mixture holes not metered by the screw is blocked or partly blocked. Those with more experience than me will give you an answer too, I'm sure. But that's where I would look.
 
I use the color tune especially on my 4 cyl XJ650 and 3 other XJ650 bikes (1 I flipped). I have always set them to the point where they are primarily blue with some blips of yellow (rich) to indicate I'm on the rich side of proper mixture.
For those that don't know about color tune, white is lean, blue is good burn and yellow is rich.
Here is a vid where the mixtures were set over the edge and more yellow than blue. This bike could have stood to have the carb jetting changed, but moving to >50% yellow vs blue made it accelerate better. its symptoms were similar to yours.
Having a rich idle does help with acceleration.
I forgot how the BS38 is, but the XJ650 Hitachi carbs have 3 holes at the top of the butterfly. All going through the pilot jet. The idle mixture affects one of the holes and the other 2 are just the pilot jet. As you get to about 1/8 throttle, all 3 holes on the Hitachi carb are exposed and the idle mixture has less affect (but some). 1/4 throttle and your at the Pilot jet plus the main jet/needle.
When I was fiddling with my XS650, I took a white paint pen and marked my throttle positions (need to take up the slack to mark the 0 point) and I marked 1/4 increments so when I was tuning, I could see where I was at. I put on uni pods (oil gas coated) and then I bumped up the pilot jet, and Main jet making those richer but rasied up the needle clip (making it leaner). This change was given to me in my XS650 special thread and worked quite well.
Of course, warming the bike up is key.

For the XJ650 in the below video, I did not want to buy new jets and it would take a LONG time to warm up and it would hesitate until about 2500 rpm then go like a bat out of hell. My solution for that bike which does not have needle clips was to add washers to the needle which would be like lowering the needle clip to make it richer. That helped enough to get the bike riding to sell it. Once it rode a mile or two down the road, it was great.
Remember, when its cold out, bike runs leaner (colder more dense air) so if you adjust on a hot day, it can lean out in the colder day.

Good luck

(color tune with idle mixture just over the line to the rich side)
 
Any ideas !? I'm about to just buy a new motor and swap it out.

Haven't read through all the comments, but swapping engines isn't going to fix your problem. I listened to the video. Good idle and good above 3k revs is either carbs or ignition. Swapping the motor isn't going to help that unless you also swap iggys and carbs. Put the same carbs and ignition on a new engine and you'll likely be back to square one. But then... what's the point of swapping out a perfectly good motor? Just concentrate on the carbs and ignition.

Have you tried a new coil? You'll need to figure out which side is breaking up, but I've encountered several times in the past where I fixed a problem like yours with a coil.... good start and idle (signs of a healthy engine by the way), breaks up at low rpm and then runs fine above 3-4k (another healthy engine sign).

Cylinder dielectric (mixture and density) have a strong influence on coils. Usually that shows up at low revs and works fine at high rpm. Sounds counterintuitive I know.
 
I had a Boyer ignition system fitted on my old Triumph twin. I remember this lost spark system needs the coils to be changed to 6V items to work best.
 
I had a Boyer ignition system fitted on my old Triumph twin. I remember this lost spark system needs the coils to be changed to 6V items to work best.

The Boyer system came with its own high output coils! Hopefully they picked the right one haha

I'm going to try to really thoroughly clean the idle circuit tomorrow with the mission of blowing carb cleaner through the 3 holes in the Venturi by spraying into the pilot circuit.
 
The Boyer system came with its own high output coils! Hopefully they picked the right one haha

I'm going to try to really thoroughly clean the idle circuit tomorrow with the mission of blowing carb cleaner through the 3 holes in the Venturi by spraying into the pilot circuit.
If it's a recent system, they come with a German PVL coil. Ignition coils don't really get better than that.

I would carefully probe the pilot mixture holes too with a piece of fine but stiff wire. For this I usually pull a strand off a stiff steel wire brush. Go gently but make sure the holes aren't partly blocked. Good luck.
 
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