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Discussion Starter #1
Hello, I may need a new idea. I have an "87"Vn750 with carb problems. I still have the original exaust pipes on it, minus the baffells and crossover. Also have the K&N air filters. The carbs have 147.5 main jetts, with two spacers on the needles. I still have backfire problems and a skipping\starving at mid to upper rpm range. I ride any where from 4000ft to 6000ft. Would any body have another idea for me?
 

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The Professor
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Hello, I may need a new idea. I have an "87"Vn750 with carb problems. I still have the original exaust pipes on it, minus the baffells and crossover. Also have the K&N air filters. The carbs have 147.5 main jetts, with two spacers on the needles. I still have backfire problems and a skipping\starving at mid to upper rpm range. I ride any where from 4000ft to 6000ft. Would any body have another idea for me?
What size pilot jet and do you have K&N pod filters or K&N air filters in stock housing and where are your pilot screws set at.
Does the engine have coasters?

For your elevation with K&N pod filters:

#40 pilot jets
#140 mains
2 shims per needle "under the needle"
2-2 1/4 turns out on the pilot screws.
 

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Discussion Starter #3
Well, I think the pilot jets are stock. I Have never changed them anyway. But if you use full chock to start cold--will flood every time. I just dont go all the way with the choke. The air filters are in stock housing. Sorry to sound stupid but what are coasters? And whats an ear shave?
 

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Sparky!!!
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The earshave is where the stock air filters are removed, and pod filters are installed directly to the carbs. Coasters are flat pieces of metal that cover the reed valve. more info can be found in the verses about these mods.
 

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Discussion Starter #5
Cool, Thanks for the information. Still have stock ears. No I do not have coasters. I own a welding shop so something like that would be easy to make. Had not thought of doing that. Think that could be my problem? Probable vacume leak?
 

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Give us some background. Was the bike running good for you up to a point in time and started doing the starving for fuel all of a sudden? Has it always flooded with full choke? Did you do any mods and then the bike started running badly?

The reed valve system can be problematic on older bikes with pin holes in vacuum hoses and such. You can put a marble in each hose attached to each reed valve and shut them down, but if the vacuum hose is split or cracked, it will leak. Could also be leaking around the carb boots causing a lean condition. Have you looked at your plugs? What color are they? Black, tan or white? Just some questions to help with your diagnosis.
 

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The Professor
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Well, I think the pilot jets are stock. I Have never changed them anyway. But if you use full chock to start cold--will flood every time. I just dont go all the way with the choke. The air filters are in stock housing. Sorry to sound stupid but what are coasters? And whats an ear shave?
Now that I have the info I need, you are getting way too much fuel and not enough air , rejet as follows:

#40 pilot jets
#135 main jets
start @ 1.75 turns out on the pilot jets
one shim under the needle but you may need to go with none.

At your elevation the 2 shims and the 147.5 main jet is causing the flooding problem at start up and mid to high rpm.

I am @1000 ft. with pod filters and 147.5 would be too much
 

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Discussion Starter #8
History? Well I got the bike used and kind of tore up. what was done before was never finished. It had a bad skipp at 4000 rpm to top end. Has allways acted like it was starving. I dought any carb was ever done after they took the exaust appart,and removed the baffels.
So far I have replaced the main jetts, put a couple spacers on the needel's, replaced the air filters with the K&N's,and gave them a good cleaning. Have pulled the carbs so many times I can pull them in about 20min. As old as it is and with a couple of cracks in the emmision tubes, and no rollers. Think I have a may have a vacume prob? The bike still seems to be starving in mid and upper range. Even with huge main jett's. Baffeling.
 

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The Professor
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3,147 Posts
History? Well I got the bike used and kind of tore up. what was done before was never finished. It had a bad skipp at 4000 rpm to top end. Has allways acted like it was starving. I dought any carb was ever done after they took the exaust appart,and removed the baffels.
So far I have replaced the main jetts, put a couple spacers on the needel's, replaced the air filters with the K&N's,and gave them a good cleaning. Have pulled the carbs so many times I can pull them in about 20min. As old as it is and with a couple of cracks in the emmision tubes, and no rollers. Think I have a may have a vacume prob? The bike still seems to be starving in mid and upper range. Even with huge main jett's. Baffeling.
Refer to my post above for proper jetting. Remove ALL emission crap, plug the rear carb vacuum port and plug the hose from surge tank to air switch under the seat.

Install coasters or put 5/8 caps on the reed valve cover ports.
 

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MANIC MECHANIC
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943 Posts
does anywhere know where you can just buy the carb needle shims i already have an assortment of keihin jets thanks to a former coworker but do not know where to purchase just the shims
 
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