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xs650 > > Motorcycle Systems > > Engine > > Pre-'74 carb holders?


Pre-'74 carb holders?
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TeeCat
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PostPosted: November 7, 2009, 6:03 pm    Post subject: Pre-'74 carb holders?

What are you pre-'74 owners doing for replacement carb holders? I want to replace the ones on my '73 soon to rule out an air leak there, and I don't see any mention of '73 holders at Mike's.

TC
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tacoswild
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PostPosted: November 7, 2009, 9:39 pm    Post subject: Re: Pre-'74 carb holders?

Still using the old ones. I've asked here a couple times if anyone can say the newer ones would fit an old bike but apparently nobody has tried it yet. Old ones are on eBay often but I'd prefer to use new rubber instead of 40 year old rubber, it doesn't age well.
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TeeCat
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PostPosted: November 7, 2009, 9:45 pm    Post subject: Re: Pre-'74 carb holders?

I wonder if one can recondition the existing ones with Permatex silicone sealer or something?
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JeffM
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PostPosted: November 8, 2009, 12:09 am    Post subject: Re: Pre-'74 carb holders?

No hands on exerience here but from what I have read the issue is the early ones have a different angle so the stock airbox will not line up. The carbs are the same diameter. The newer ones might work with pods.

Perhaps we need to make a group request to Mikesxs to reproduce these, I have been watching ebay for these too. Repops with vacuum barbs please Mike???

I have had good luck repairing cracks in the intake snorkel of my air-cooled VW with black automotive silicone seal. Hard to say if heat is as much an issue there though.
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JeffM
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PostPosted: November 8, 2009, 12:10 am    Post subject: Re: Pre-'74 carb holders?

Why do I get double posts???
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TeeCat
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PostPosted: November 8, 2009, 11:56 am    Post subject: Re: Pre-'74 carb holders?

Jeff... thanks much for your reply. Ditto, Mike!

I am not running airboxes, but I'm not sure if there would be other issues.

I'm getting a decel pop when at operating temp, and that goofy idle when warm, so I think replacements might be a good idea. I have to pull the existing ones and examine them when I get time.

TC
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gordo
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PostPosted: November 8, 2009, 7:38 pm    Post subject: Re: Pre-'74 carb holders?

Tee Cat, you could silicone the outside of the old rubber manifold's, but the problem will return because you've got nothing to support the carb's other than the manifold's. The airbox did offer support to the carb's, but a good set of manifold's from 650 Central might be what your looking for. Give Mike Morse a call & talk to him about your situation, I guarentee he'll have an answer for about the manifold's, whether the newer model's will work or not. He has some aluminium one's that are a bit priecy, but look like they'll hold up against almost anything.What you pay for one of the alum. one's would buy a set from Mike's XS.
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TeeCat
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PostPosted: November 8, 2009, 9:18 pm    Post subject: Re: Pre-'74 carb holders?

gordo, thanks for that suggestion! I might give Mike a call. I have spoken with him before... a true gentleman. Smile
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danno
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PostPosted: November 9, 2009, 3:29 am    Post subject: Re: Pre-'74 carb holders?

I have read on other sites that folks have repaired leaky manifolds by using sections of bicycle innertubes to cover the cracks. Just a thought.
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TeeCat
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PostPosted: November 9, 2009, 8:02 am    Post subject: Re: Pre-'74 carb holders?

That's a good idea too. I suppose one would "laminate" the innertube section over the existing rubber using Permatex or something.

Would these kinds of cracks be visible, or would they be more "microcracks" or "crazing" that admits air?
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xsjohn
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PostPosted: November 9, 2009, 9:00 am    Post subject: Re: Pre-'74 carb holders?

Mine had some cracks 5 years ago...BS34......cleaned them well and used black silicone pushing it down in the cracks.......and a liberal coating on the rest........then as it got tacky I pushed on the metal support and wiped and let it set overnight only barely tightening as to not squish out the silicone...then snugged after 24 hours...no leaks so far.........don't think they really leaked before though.....did have some cracks........

Throttle shaft seals........on my BS34's there was room for 2 seals on the left outside under the throttle arm....not sure of the rest........at least the ones from Mcmaster Carr fit double....seemed to be the same thickness as the stock seals...next time I have a leak Iwill see if 2 will fit everywhere.......maybe someone already knows........2 would surely be better if they fit.......

xsjohn
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TeeCat
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PostPosted: November 9, 2009, 10:09 am    Post subject: Re: Pre-'74 carb holders?

John, what are the symptoms you get when you have a leak?

I'm going to investigate carb holders first, before even thinking about shaft seals... one variable at a time I reckon.

TC
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xsjohn
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PostPosted: November 9, 2009, 10:26 am    Post subject: Re: Pre-'74 carb holders?

Unmetered air enters........idol thin and wandering.............lean........hard or impossible to set mix screws satisfactory........

Spray throttle shaft seal and carb holder area with brake cleaner or carb cleaner when it's running.......if engine speed changes something is leaking.......if not it is something else.........advance springs or advance rod cleaning ...mix screw settings .....advanced timing ...ect.....
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TeeCat
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PostPosted: November 9, 2009, 10:47 am    Post subject: Re: Pre-'74 carb holders?

Well, at least I know it's not my ATU and springs... brand new as of two weeks ago, and the rod was serviced late last summer.

I e-mailed Mike at 650 Central and maybe he can help out with holders.
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TeeCat
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PostPosted: November 10, 2009, 8:25 am    Post subject: Re: Pre-'74 carb holders?

Okay... I e-mailed Mike Morse. He told me that the later model holders should work with my bike as long as I don't have air boxes that need to line up, so it might be worth a try. Then, at least, I could eliminate a place for a leak.

Btw... if butterfly seals are leaking, do they leak fuel as well as air; in other words, would there be evidence of seepage (of fuel) when they're not drawing air?

TC
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xsjohn
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PostPosted: November 10, 2009, 8:30 am    Post subject: Re: Pre-'74 carb holders?

Told you.......spray some brake or carb cleaner on the seal area while it is running.............if bad they leak air and it is sucked in and leans the mix.....it will suck in the cleaner if it is leaking and change the idol speed if so............if nothing happens when you spray there is nothing wrong..........
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TeeCat
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PostPosted: November 10, 2009, 9:22 am    Post subject: Re: Pre-'74 carb holders?

Going to do that if I get time today or tomorrow and it's not raining.

Also, after some of what I have seen the PO did to this bike - some pretty terrifying stuff even to my neophyte eye - I have adopted the practice of replacing suspect or inexpensive parts as I go along. Ordered some '74^ BS38 holders from Old Bike Barn to try, and if they work on my '73 we'll have learned something as a community. I'll still spray the seals too, though, to see what happens.

My curious noggin still struggles with why a lean mix would raise the idle instead of lower it, though... decel pop makes sense, though...

TC
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gordo
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PostPosted: November 10, 2009, 5:06 pm    Post subject: Re: Pre-'74 carb holders?

If you've got a vacuum leak, the extra air(oxygen) cause's the mixture to go lean, which raises the speed. It's because your engine is above 'stoichimetric' feul ratio. That ratio is best at about 13.5- 14 to one, or the air's natural pressure at sea level. If it's too lean, you get a rough idle, a lean missfire,(not enough fuel to burn properly), and more heat, burnt piston's, valves, ect.
The seals around the shaft's can leak fuel, but only if the float level is too high, or the needle/seat is causing fuel to overflow into the carb's.
The reason's for the higher speed is now you've got a better mixture, instead of leaner.
BTW, those burnt part's are after along time of extreem leak's.

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TeeCat
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PostPosted: November 10, 2009, 6:02 pm    Post subject: Re: Pre-'74 carb holders?

Thanks, gordo! This is very helpful, all except:

Quote::
The reason's for the higher speed is now you've got a better mixture, instead of leaner.

This part seems to contradict what you said up top, unless I'm misunderstanding you. I thought you said higher idle speed may result from a leaner (worse) mixture as opposed to a more ideal one.

TC
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gordo
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PostPosted: November 11, 2009, 4:59 pm    Post subject: Re: Pre-'74 carb holders?

Well, sorry for the confusion. More oxygen, fuel burn's more complete. That's what I meant by a better mixture. Not really a better mix, because of the heat . If the leak is bigger, idle speed will go down until more fuel is added. Idle speed is determined by the amount of fuel/ air mix going past the throttle plate's. How much the plate's are open the faster it run's. A vacuum leak has more air than fuel, so when you put in more fuel by 'filling' the leak with it, idle speed goe's up because the mix is closer to correct.Hope that's a better explaination. In effect, the vacuum leak is like opening the throttle plate without adding fuel, so when fuel(carb spray) is added, speed goe's up.
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xsjohn
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PostPosted: November 11, 2009, 5:59 pm    Post subject: Re: Pre-'74 carb holders?

Here is one for ya..................

My Toyota never did idol and run just the way I wanted it to ...............Here is how I forced it to cooperate with me .......

There is a rubber pipe from the valve cover to the vacuum side of the throttle plate.........it sucks the blow-by and such from the valve cover.....on the valve cover there is a plastic fitting with a 1/8" hole in it.....the amount it draws was more than necessary to clear the crancase.....(hole was a bit larger that 1/8") so I put a wire through the plastic part and bent it on either side to reduce the size of the hole.......(coat hanger sized wire).........now there is a less un-metered fuel mixture and it idols great and runs a bit richer and better..............

This whole thing reminded me of a vacuum leak "which it was" so I just reduced it with the wire.........still plenty of vacuum to clear the crankcase and it just plain runs better.........same mileage because I don't need so much throttle to go.............and more power

Total cost = 0

xsjohn
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