bs40 help please!

[vintageacat]

I just got a 76 750 and it needed much help. After freeing up the motor and boring it out I finally get to start it. After 2 seconds on the starter it fires up after 23 years! The right and middle pipe warmed up right away. The left stays cold unless I give it a little throttle. When examining the slides and I lift them up the left drops pretty quick. The center drops at the same rate but the last third of the throttle on the way down snaps. The right just drops real quick. When I lift them up only the right one acts as there is vacuum pressure as I can only lift it 80 percent of the way before the diaphragm pressure stops me. What makes me wonder is why only the left one stays cold if the center is acting similar. I can't find any holes or tears in the diaphragm and they seal well in their lip. where else can my problems be? I got around 145psi each cylinder I believe. Great spark. Point gap. Exhaust is clear. I'm really hoping I'm missing something.

[RING_DING]

Blocked pilot jet maybe?

[rngdng]

CONGRATS on getting it started!!

Probably a clogged pilot jet in the left carb. The pilot is used at idle, when you open the throttle and it fires, the slide and needle get involved. You didn't say if you were using the choke...if so, that could be clogged in the left. I'd just give the left one a good cleaning and try again.

It wouldn't hurt to clean them all again.....


Lane

[tz375]

And don't forget the tiny choke jet in the base of the float bowl. It's in the sticky on BS40 carbs.

[vintageacat]

I forgot to mention I'm very inclined with carbs. It's just I have never had a cv or bs carb before. Only the perfect mikuni vm and tm. Lol. The only thing that's worse than a cv carb is the walbro diaphragm ha. Anyway I have had them apart 3 times and all my jets appear to be clean. I can take it off choke like 2 seconds after I start it. I'll look into the carbs one last time today. would sure be funny if I got a bit of sediment in there all of a sudden and it runs perfect after. My old phone won't let me upload pictures otherwise I would. This thing is clean!

[RING_DING]

Also check the fuel supply in to the left carb. I had a similar problem a while back where everything (spark, compression, jets) checked out but the left pot would not light up. Turned out to be a blockage in the horizontal fuel supply line (i.e. after the T-junction on the carb itself)

[vintageacat]

I'll look into that. Thanks. One thing I noticed is if it's idling and I put my hand over the left carb nothing really happens. I'll get gas on my hand. But if I go it to the center or right it will almost die and I gotta nurse it to life

[pearljam724]

I'd say it's slightly out of time. Nearing completion of my 750 restoration. I could not get all cylinders to fire at the same time after dozens of attempts by static timing. I got fed up and found an original Suzuki dial gauge. First attempt using it. All 3 cylinders roared to life. I'll never rely on timing window again. Using the window in my opinion is a baseline timing method. The manual suggests not doing so, unless it's an emergency. But, I'm sure people will argue. Stating they've never had a problem doing so. The window leaves room for error. With a dual gauge it puts the timing spot on. Assuming your tank and carbs are clean and rebuilt properly.

[vintageacat]

Whoohoo! Turns out I was out of sync just enough to give me hassle. Shined a light behind the butterfly and 5 minutes of work. She popped right off. Then I had a 2 hour battle with throttle cables. My push cable was broke but the one off my old cb worked. My buddy put the cables on backwards evil knevil style haha. All I gotta do today is bleed the front brakes a bit. Airbox. And I made a chain guard that wraps around the counter shaft sprocket so I don't need to worry about a chain killing my cases. Gonna throw the wind jammer on for now till I get a good headlight bucket. Hopefully get to test it today

[Desert_75]

I videotaped the first time my Buffalo came to life after having sat for ten years, still watch it sometimes

Mine's timed using the window but I'm convinced now I need a dial indicator.....

[vintageacat]

Alright. I got to test it. It ran very well for about 200 miles. I was bombing down the highway and I realized the bike didn't have as much snap. Plugs appeared good. Got it home and it still ran. Just no guts. I throw new plugs in and the left showed no color. The center was good. Right no color. Just oily residue but for sure lean. I clean the carbs. Starts up and runs like a bat out of Hell. All 3 plugs show prefect color. I go to work and back and check my plugs. Now the left is kinda brown. The center is lean and the right is dark. I'm really getting sick of pulling these carbs. In fact I have a pinched nerve in my shoulder cause of trying to put them on myself. every time I clean them my jets are clean. I just blow out the passages and reassemble. I have new lines on it and fuel filter. What I'm wondering is where this problem is coming from. I don't even wanna touch it till I get an idea of where I went wrong. By the way when it does run good it flies and is so smooth. 90 in fourth easily. I blew past a Harley wound up in third and smoked him out at the same time. I think it's my new favorite thing to do lol.

[irish1]

Reading the post on porting and boost ports in a t500 with interest, suppose some nitwit put a couple of holes in the back of the piston that will be open to the intake at bdc, what effect will this have, more blow back, will it run like this? I don't suppose the notch in the cylinder would be a problem if a stock piston was installed, I hope. I can't imagine who do a dumb thing like that.

[rngdng]

You may have other issues like crank seals or intake leaks. If you are having trouble installing the carbs, your intake boots are stiff from age. You will love yourself for buying new ones.


Lane