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BS carbs.. I get it now!
- Thread starter jmink427
- Start date
BSS, (Bloody stupid setup), 38's.
It's the way you have set them up with those filters and intake. Do some reading/research on them and you may understand the problem is not the carbs
It's the way you have set them up with those filters and intake. Do some reading/research on them and you may understand the problem is not the carbs
jd750ace
Front Toward Enemy
Briggs & Stratton Setup? LOL. That's not gonna work well, bud. The carb has a bellmouth for a reason. You can't feed it through a tube. It needs to be able to draw air at EQUAL pressure all around the lip for it to fuel correctly. The Constant Velocity carb is dependent on proper levels of vacuum across the jets to fuel and to raise the diaphragm at the appropriate rate. the narrowing of the feed has to be at the point of fuel induction. You are effectively narrowing it way out at that filter, and you have a resonating chamber on the intake side with that long runner that invites reversion and stalling of your airflow.
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It's just one carb, it started acting up a couple weeks ago. Other than that the bike has been running pretty good.....When I start my bike it runs pretty good for a few seconds then the left cylinder quits running for a bit, then it comes back in. 
I thought it was not firing so I put a timing light on it and it's getting spark to the plug the whole time this is going on.. I'm going to put some new plugs in to rule them out. I took the carbs apart and gave them a good cleaning but they seemed pretty clean. I would like to put some new diaphragms in them while they are apart.. I also noticed the left carb had some excessive slop in the throttle shaft bushing so I'm going to replace that as we'll....
I thought it was not firing so I put a timing light on it and it's getting spark to the plug the whole time this is going on.. I'm going to put some new plugs in to rule them out. I took the carbs apart and gave them a good cleaning but they seemed pretty clean. I would like to put some new diaphragms in them while they are apart.. I also noticed the left carb had some excessive slop in the throttle shaft bushing so I'm going to replace that as we'll....Your correct, but I have run it with and with out filters and didn't notice any difference.
You won't hear it, so I won't bother.
Yeah, those ports ARE clean. Much cleaner than mine.
Reminds me of my spelunking days. I think I scraped my elbow...
Reminds me of my spelunking days. I think I scraped my elbow...
Yeah do the spray with carb cleaner while it's running thing, see how bad the throttle shaft is. Looks to me like I'm seeing a trail from fuel running from the shaft. Check both floats with a dip test, are the float valves known good? check your fuel level with the clear tube method. You can have a throttle shaft bore worn enough to be "game over" for that carb..
No carb cleaner.. That's as is after I removed the carbs.... I was really surprised.... Must be the 10% ethanol... I've been running my '65 Impala on E85 for a few years now and used a bore scope on it and it is still clean as a whistle on the inside.... As far as the slop in the throttle shaft it looks good but is loose while in the carb but I believe I can fix that with a new bushing and seals... If the non bushed side is worn as well we have a machine shop and it will get the bushing treatment also...
Spend your piss and vinegar on a liberal Democrat or are ya slipping Dick ?
The early Mikuni Solex are as good as early CV's get . They however will not tolerate even large volume individual air cleaners . It is possible to get them to work without the air box(s) but you will achieve one of two results . Wide open throttle and pull like a freight train or part throttle high vacuum cruise but not both .Even the later BS40 (Suzuki Savage) is a decent mixer if given sufficient volume behind the carburettor .
I won't spoon feed it to you unless I think you will not only use it but teach what you've learned . However...
Anything you can find on carburettors by XS John (RIP old friend)
Anything more than 34mm in a round slide Mikuni on anything less than a fire breathing 750 is silly . Find the carburettor guide and thank Dick when you're done .
EX500 carburettors are a good compromise
Keihin CR's just rock . Dialing them in is a pita
PWK's are rarely PWK's Look for Mrriggs posts
Lectron's are at best an off on switch but work very well WTFO. Even better on HOOCH
Your ports are clean but mismatched to the manifolds . They however are stock with all their faults . Do not "just clean up" the ports other than matching to the manifolds . Since the ports are marginally too large anyway removing even the slightest material from the wrong place can put port velocity into toilet . The CV carburettors cover up this too large port quite well .
~kop
Got the new diaphrams from JBM Industries today.. Also got new throttle shaft seals and butterfly screws from Mikes XS, couldn't find the throttle shaft bushings at Mikes XS... I did find them on Motions website.. $.70 each... 10mm x 8mm x 8mm, but opted to make my own....
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jmink very interested in how this works for you. I have some bushings and a long reamer but haven't had the nerve to bore into a carb body yet, getting the perfect center.... This is a bigger deal on early carbs, they have a shorter neck and no cast in bushing material, so they "oval out" on the side with the cable arm.
Nailbomb
Central New York XS650
kopcicle: good post. And it is sad to see XSjohn gone. I never spoke to the man, but his advice to others helped me and I'm sure others.
I had a set of mikuni solex 34mm carbs and could never get them to run right on my clapped out engine. I had good luck with 34mm mukini VMs untill the engine finally quit.
I'm no master at tuning carbs. I've had good luck with kehins, and S&S super Es on ironheads, super Bs on shovels, and VM round slides on XSs. Its a limited mental toolbox, but its worked for what I have.
I had a set of mikuni solex 34mm carbs and could never get them to run right on my clapped out engine. I had good luck with 34mm mukini VMs untill the engine finally quit.
I'm no master at tuning carbs. I've had good luck with kehins, and S&S super Es on ironheads, super Bs on shovels, and VM round slides on XSs. Its a limited mental toolbox, but its worked for what I have.
Gary, I got my bushing turned to size and installed looks like is gonna work great... My carbs already had a bushing on the throttle shafts on the "load" side or cable side whatever you call it. So all I had to do is remove the old ones and install the new ones... I had planned to put the carbs in the mill and install some sleeves, then I seen they already had them and they were just wore smooth out....
Thanks for that! What was involved in removing the old bushings? Yes my "early" is 70-71, I am not sure just where the change to the built in bushing occurs.
Not too much.. I removed the butterfly blade and shaft. Then just used a punch an hammer to tap it out towards the outside.. It came out very easy since it was a steel backed split bushing.
Got the carbs back together this afternoon and the slop in the throttle shaft is gone... New seals and bushing did the trick.... I did however notice that if I cover up the vent on the diaphram on one carb it will cause the engine to go fat (rich) on that cylinder and the idle speed will slow down a little but it doesn't do it on the other carb.... I guess it would be because the slide bore and bore tolerances (worn out) are to big on that one carb?????? Maybe I need to just put a Holley 4150 or 4500 series carb on it.. I'm a little more familiar with them... 
New seals and bushing did the trick.... I did however notice that if I cover up the vent on the diaphram on one carb it will cause the engine to go fat (rich) on that cylinder and the idle speed will slow down a little but it doesn't do it on the other carb.... I guess it would be because the slide bore and bore tolerances (worn out) are to big on that one carb?????? Maybe I need to just put a Holley 4150 or 4500 series carb on it.. I'm a little more familiar with them...
A leaky choke (enricher) rubber seal on the plunger will affect the diaphragm action also.
