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Old 07-25-2013, 02:42 PM   #16
_cy_
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Quote:
Originally Posted by supershaft View Post
CV carbs compensate nothing but the throttle at altitude but they do that at sea level too. Crack the throttle wide open from idle at seal level and the slide (the actual throttle) will lift only so high until the engine can actually use full throttle (the slide all the way up). Do the same thing at altitude and the same thing will happen only this time the slide won't lift as high because there isn't as much air to suck in. You can do the same thing with your wrist with a slide carb. All it takes is paying attention to your engine's needs and refraining from giving the engine too much throttle. All that does is bog it down. Jetting? CV's do not compensate jetting. What they compensate is throttle input.
sorry but you are dead wrong .. Bing CV carbs compensate to a limited amount for altitude. thickness of air changes speed piston raises, which changes fuel release profile. compensating a limited amount for altitude. this is why folks will drop Bing needles a couple of notches to lean out mixture profile for altitude.

piston going up or down controls fuel mixture on the fly, until piston reaches max opening. once full throttle has been reached, main jets takes over. diafram controlled piston then has no further effect until air velocity decreases.. allowing piston to travel downward.

above is old news and well established ..... why are you still denying this?

_cy_ screwed with this post 07-25-2013 at 03:02 PM
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Old 07-25-2013, 06:21 PM   #17
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If the PO never touched the Carbs then after 18 years it's worthwhile going thru them with the basic Bing rebuild kit and diaphragms

Doesn't take long, isn't hard and is well worth it. While you are at it get a new set of jets

Take the model # direct off of the carbs as you'll need it to make sure the right kit is ordered

http://www.bingcarburetor.com/service.html
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Old 07-25-2013, 07:15 PM   #18
supershaft
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Quote:
Originally Posted by _cy_ View Post
sorry but you are dead wrong .. Bing CV carbs compensate to a limited amount for altitude. thickness of air changes speed piston raises, which changes fuel release profile. compensating a limited amount for altitude. this is why folks will drop Bing needles a couple of notches to lean out mixture profile for altitude.

piston going up or down controls fuel mixture on the fly, until piston reaches max opening. once full throttle has been reached, main jets takes over. diafram controlled piston then has no further effect until air velocity decreases.. allowing piston to travel downward.

above is old news and well established ..... why are you still denying this?
What folks drop jet needles a couple of notches for altitude?

Why am I still denying what? A slide carb does exactly what you are describing and it isn't a CV carb. The only difference is a slide carb takes some brains to use correctly and a CV not so much. All the while the jetting remains the same in BOTH type carbs. Or put another way: OK, a CV compensates jetting at altitude but so does a slide carb if you just apply less throttle. It is the same difference.
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Old 07-25-2013, 08:06 PM   #19
Ray R OP
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Diaphragms check out ok.
Needle position....3 from top....check.
Main jet is 135...check.
Float bowls are clean...check.

Draining gas now.......
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Old 07-25-2013, 08:23 PM   #20
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When do the floats shut off the fuel flow?
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Old 07-26-2013, 12:28 PM   #21
darklight79
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Change the slide needle and the carb internal spring as well when rebuilding
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Old 07-26-2013, 02:09 PM   #22
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So far I've seen I'm supposed to change the jets, needles, diaphragms, floats, springs, o-rings, gaskets.....

What's left besides the carb shell itself and the piston?

Maybe new carbs would be cheaper?

I've verified the carbs are in their original stock condition. I'm now looking for other causes. I'll run the fresh gas test this evening, hopefully.
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Old 07-26-2013, 02:12 PM   #23
Big Bamboo
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Quote:
Originally Posted by Ray R View Post
So far I've seen I'm supposed to change the jets, needles, diaphragms, floats, springs, o-rings, gaskets.....

What's left besides the carb shell itself and the piston?

Maybe new carbs would be cheaper?

I've verified the carbs are in their original stock condition. I'm now looking for other causes. I'll run the fresh gas test this evening, hopefully.
What I would have done first (after new gas) was set the mixture screw a bit richer...
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Old 07-26-2013, 02:23 PM   #24
Mista Vern
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Can't help ya - I'm at 157 feet, so even lower than you. Good luck.
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Old 07-26-2013, 02:49 PM   #25
darklight79
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Less than 200 in parts i went thru mine including all new jets etc chamber floats et al. Easy to plug in new parts and have some spares theres a set of 32 on ebay for around 200 Worth the dollars spent runs quite nicely now
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Old 07-26-2013, 05:46 PM   #26
Ray R OP
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It's not bad gas. I ran it with some ethanol-free premium, and the problem persists.

I get it up to cruising speed at 45mph or so, and any throttle twist beyond about , and it just won’t accelerate any further. Half or less, and it seems to run fine. The issue seems to effect both cylinders.

Checked the airway, and the air filter looks like new. When I opened the petcocks to drain the fuel last night, it flowed plenty.

Must be an electrical problem. Time to get out the hammer.
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Old 07-27-2013, 07:04 PM   #27
Gripsteruser
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I still haven't seen that you've pulled the petcocks and cleaned the screens. That could limit fuel flow needed at high power. (not sure that eyeballing flow is adequate but it could be)

If it's bone-stock there are two solenoid valves in the fuel system which shut when the key goes off. If those aren't fully opening (due to gunky fuel or disuse?) you'd be starving for fuel. (Common mod is to remove those and just use simple fuel hose and Ts and the petcocks manually - I'm moving toward doing that on my '88 shortly)

Other issue could be that at full throttle you aren't getting ignition.

More air/fuel mixture in the cylinder at wide open throttle requires more of a spark to jump the gap (spark jumps easier in vacuum than in air). So plugs gapped too widely or otherwise weak spark would result in loss of power.

Just a couple more ideas to ponder.
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Old 08-02-2013, 12:27 PM   #28
Gripsteruser
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I'm posting a rebuttal to my own posting above to set the record straight.
I just removed my 25 yr old fuel plumbing, simplified the system as well as replaced with new rubber hose. I learned some things while doing the job.

The original fuel plumbing had ONE solenoid valve to turn on the gas. The second solenoid under the engine cover is a solenoid vent valve to vent the tank.

If the solenoid fuel valve is sticking part way you could have the fuel starvation symptom. One easy way to diagnose would be to jumper from petcock to carb on each side using 1/4 in hose then turn on both petcocks and ride. This would entirely bypass the original hoses and the solenoid valve and would test whether it's a fuel flow issue.

As I replaced the fuel hoses and removed the fuel solenoid from my bike I decided to leave the solenoid vent valve in place. I like the idea of sealing the tank completely when it's not in use.

Maybe the OP is long gone but maybe this writeup will help someone else.
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Old 08-02-2013, 01:02 PM   #29
Padmei
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Quote:
Originally Posted by Gripsteruser View Post

The original fuel plumbing had ONE solenoid valve to turn on the gas. The second solenoid under the engine cover is a solenoid vent valve to vent the tank.
.
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Old 08-02-2013, 02:48 PM   #30
_cy_
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Quote:
Originally Posted by Ray R View Post
Diaphragms check out ok.
Needle position....3 from top....check.
Main jet is 135...check.
Float bowls are clean...check.

Draining gas now.......
these are sea level settings for your carb ..

main jet 145
2.68 needle jet
#1 needle replace if worn ..
low speed circuit screw about one full turn out

if you have a set precision drills with digital calipers.
find a 1.45 mm drill then measure with calipers. then insert into drill index... carefully drill out main jets to 1.45mm. file off 135 marks.

the 2.68 needle jet needs to be purchased. unless you have a jeweler's lathe.
it may be easier for most to simply purchase new main jets and needle jets.




_cy_ screwed with this post 08-02-2013 at 03:07 PM
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