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Cleaning Carbs
- Thread starter 44baluyot
- Start date
can't hurt. give it a go.
Posted via Mobile
Posted via Mobile
Too much or not enough gas. Sometimes missing or poor spark. The list of what causes backfire can be long. Like stone suggests exhaust and intake mods without adjusting carbs can do it.
first, iwant to thank you guys for replying. just got the bike, cleaned the carbs now less backfire. what i notice is when i put the petcock to pr position ( dont know what pr means but gas will pour out of the tank continousely) the rhs carb is overflowing. dont know if any modication was done.
RH float valve is leaking (not shutting off). What year is the bike, are the carb tops chromed steel or cast aluminum? depending on the carb model, it could be a leaky float, a damaged float valve or a bad float valve o-ring. I would suggest not running the bike till you fix the problem washing a cylinder down with raw gas is hard on it.
The float valve is held in place by a small screw and bracket. the body of the valve has an o-ring that seals it to the carb body it is usually toast a new one is a few cents. It sometimes is hard to remove the float valve without damaging it and the o-ring is a rather hard to find size. There is also a screen in there which can have a bunch O crap in it. The early 80 BS34's have brass floats, a simple check for a bad float is to place them in a cup of hot water and watch for bubbles.
This guy sells the float o-rings and ships fast.
http://cycleorings.com/
The page for the GS450 the simple 7.50 shipped kit would have what your carbs use.
XS John claimed he had luck wrapping the o-ring with a piece of thread to snug it up but I would fork over the big bucks and replace them both. I do that on every set of BS34s I open.
Synching the carbs is a "must do" on any old bike you have. If you haven't yet adjust the cam chain and set the valves too. both are easy on the XS650
This guy sells the float o-rings and ships fast.
http://cycleorings.com/
The page for the GS450 the simple 7.50 shipped kit would have what your carbs use.
XS John claimed he had luck wrapping the o-ring with a piece of thread to snug it up but I would fork over the big bucks and replace them both. I do that on every set of BS34s I open.
Synching the carbs is a "must do" on any old bike you have. If you haven't yet adjust the cam chain and set the valves too. both are easy on the XS650
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P.S. pri = prime, the other positions of the petcock use engine vacuum to open the valve, so prime is handy if the carbs have been drained or the bike has set for a while. But using prime has disclosed an issue with the float valve that must be fixed.
PPS a PO may have tried to stop the leak by bending the float tang so check your float level too. See the tech articles for a how to. The float height is different for the brass floats and foam floats.
bdholsin
XS Enthusiast
I found that a #5 o-ring from my local hardware fit nicely in the float body. A #6 was just a bit too tight. Just throwing it out there for you.
Float needle seat o-rings can be had from McMaster Carr. The size is 1.5mm thick X 7 or 7.5mm I.D. (either fits). You can get a 100 pack in Buna-N rubber or a 25 pack of the better Viton rubber for about $5. In fact, you can get all the o-rings used in the 650 carbs from there.
Good to know! Is it hard to order from there or does anyone do it regular and could add some to their order to "make freight" or minimum or whatever? I would be glad to get like 50 of the viton ones pay for them and send them out as needed to others. Or if someone else wants to do it that's fine too.
McMaster Carr used to sell only to industry but now anyone can order from them. It's simple to place an order on-line and pay with your credit card. Their shipping is very reasonable and they ship really fast. They use the simple "add to cart" or "add to order" system like most other web sites. Here's a link to the page for metric o-rings .....
http://www.mcmaster.com/#metric-o-rings/=9bwwhb
Yes, ordering just one item will make it not so good a deal with shipping but there's so much stuff on that site, it's easy to build a $30 or $40 order, even more, lol. With all the bikes you fix up, this place should be like Heaven for you. Here's some things to consider .....
BS38 needle jet o-rings - 1mm thick X 4mm I.D.
'78-'79 BS38 mix screw o-rings - 1.5mm thick X 3mm I.D.
BS34 mix screw o-ring - 1mm thick X 3mm I.D.
BS34 drain screw o-rings - 1.6mm thick X 4.1mm I.D.
S.S. Allens
S.S. M6 & M8 nuts
S.S. flat & lock washers
S.S. Phillips for points, advance (M6 x 20), and alternator covers (M5 x 10)
For the last item, many of the fasteners on Jap bikes are the J.I.S. standard. These are a normal metric thread but have smaller head sizes. You've probably run across the M8 bolts and nuts that take a 12mm wrench size (the standard M8 you get at the hardware store takes a 13). For some reason, Yamaha used standard screws for those covers I mentioned. They probably wanted the bigger head size to hold them better. The alternator cover specs an 8mm long screw but if you have that whole left cover off with the little alt. cover still attached and look inside, you'll see those 8's don't reach in far enough to engage all the threads. They only grab about half the threads available so it's better to switch to the longer 10mm screws.
http://www.mcmaster.com/#metric-o-rings/=9bwwhb
Yes, ordering just one item will make it not so good a deal with shipping but there's so much stuff on that site, it's easy to build a $30 or $40 order, even more, lol. With all the bikes you fix up, this place should be like Heaven for you. Here's some things to consider .....
BS38 needle jet o-rings - 1mm thick X 4mm I.D.
'78-'79 BS38 mix screw o-rings - 1.5mm thick X 3mm I.D.
BS34 mix screw o-ring - 1mm thick X 3mm I.D.
BS34 drain screw o-rings - 1.6mm thick X 4.1mm I.D.
S.S. Allens
S.S. M6 & M8 nuts
S.S. flat & lock washers
S.S. Phillips for points, advance (M6 x 20), and alternator covers (M5 x 10)
For the last item, many of the fasteners on Jap bikes are the J.I.S. standard. These are a normal metric thread but have smaller head sizes. You've probably run across the M8 bolts and nuts that take a 12mm wrench size (the standard M8 you get at the hardware store takes a 13). For some reason, Yamaha used standard screws for those covers I mentioned. They probably wanted the bigger head size to hold them better. The alternator cover specs an 8mm long screw but if you have that whole left cover off with the little alt. cover still attached and look inside, you'll see those 8's don't reach in far enough to engage all the threads. They only grab about half the threads available so it's better to switch to the longer 10mm screws.
Oh, and I almost forgot, 1/8" balls and springs for the BS34 choke rod.
Bearing grade 1/8" steel balls, 100 pack - #9528K11
And I'm thinking these springs may work .....
11" long .12" O.D. 5 pack - #9637K44
At about 8mm long, you could get 33 out of each 11" spring, 165 out of the 5 pack. Sell them to guys for a dollar per spring/ball assembly and you'll easily recoup your cost and still have tons left over for yourself.
Bearing grade 1/8" steel balls, 100 pack - #9528K11
And I'm thinking these springs may work .....
11" long .12" O.D. 5 pack - #9637K44
At about 8mm long, you could get 33 out of each 11" spring, 165 out of the 5 pack. Sell them to guys for a dollar per spring/ball assembly and you'll easily recoup your cost and still have tons left over for yourself.
Hmm good stuff 5twins. are there any off the shelf throttle shaft seals for BS38s I have not had a throttle shaft off yet to see what is in there but the set I am working on feels like it needs em. Oops sorry for the hi-jack 44Baluyot!
As a matter of fact, I have found a substitute for the throttle shaft seals, again from McMaster Carr. Wanting more than a regular round o-ring, I found they carry what's called a "Quad" cross-section o-ring. This takes the square section o-ring a step further, having 4 "lips" or points around the diameter. I thought that might work well and it seems to so far. I have them in a spare set of carbs that I've swapped in a couple times over the last few years. I only have about 3 or 400 miles on them but so far they're good.
I found these a couple years ago when Mike wanted $5 each for shaft seals. $20 seemed like a lot to do a set of carbs. Now he only gets $2.50 a seal so for $10, you can do a set. This is something that doesn't need doing very often, maybe every 20 years or so. I prefer using the real seals now since they've come down in price. I have lots of these o-rings left though so if you want to test some out, send me a P.M. and I'll send you some. Although not shown on most of the later carb parts diagrams, the same throttle shaft seal was used on all the 650 carbs, even the BS34s.
I found these a couple years ago when Mike wanted $5 each for shaft seals. $20 seemed like a lot to do a set of carbs. Now he only gets $2.50 a seal so for $10, you can do a set. This is something that doesn't need doing very often, maybe every 20 years or so. I prefer using the real seals now since they've come down in price. I have lots of these o-rings left though so if you want to test some out, send me a P.M. and I'll send you some. Although not shown on most of the later carb parts diagrams, the same throttle shaft seal was used on all the 650 carbs, even the BS34s.
