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Diesel Tech
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Discussion Starter #1 (Edited)
I need help with these carbs.

It came with the stock 132/38. I never ran the engine with these. The left carb's jets were completely plugged.
I put in 130/35 per the manual for 4000+ft altitude. Part throttle had lean stumbling, full throttle felt okay.
I add a shim to the needles, no jet change. Runs great except for a slight hesitation 5000-6500rpm at full throttle. No problem maintaining 80mph on the highway. Plugs are slightly brown and dry.
I replaced the main jets to 132, left the pilots and shims alone, did not remove the carbs for this, just the bowls. Now above 1/3 throttle is dead in both cylinders. Won't make enough power to go above 35mph. Idles great.

What am I doing wrong? I have seen people here jet MUCH larger without complaints.
 

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Too much fuel now? I’d go back to the set up you had before swapping out the main jet, back to 130, and plug chop when it has that performance issue (that 5600rpm zone).

FWIW, I experimented with octane on my trip to South Dakota. Started out in Missouri. Bike ran like dirt on 91 octane, soon switching to 87 after my first fill up. MUCH better. When 85 became available i used that and seemed to do better in higher altitudes. At 91 octane, my bike was just gutless. At full throttle my bike topped out around 75mph or so. Haven’t figured out why, though I suspect my ignition system doesn’t have enough spark to burn the fuel, which might be why it likes lower octane.

Might check your ignition coil to see if it’s up to par.
 

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I checked my repair manual and the chart is pretty confusing. It shows the 130 main jet is for Canadian models.

Manual also states no jetting is needed for altitude since the VN meets emissions standards at all altitudes. Anyway ....

Sounds like yours is lean at the main jet. 1/3 throttle should be on the main if I'm not mistaken.

Higher octane gas: Higher octane burns slower and cooler. The VN750 is designed for 87oct and will run best on on that.
 

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Diesel Tech
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136 Posts
Discussion Starter #4
I put the old sparkplugs back into the rear cylinder to see if there would be a change and there was none. After a pull up a hill the plugs were dry.
These 132's are the original ones that had to be cleaned out. I think its just corrosion left over restricting flow to effectively less than the new 130 I had.
I have new 132's coming to try that.

While I have your attention, I need to figure out the enricher problem as well. The engine starts and idles fine cold with zero enrichment/choke. Giving it any doesn't rise RPM at all but kills the engine. Same with if I try to use it at full throttle to try and compensate for the main jet issue.
 

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That plug looks lean.

Sounds like the "choke" isn't working at all. See if the cable lifts the enrichers.
 

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Diesel Tech
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Discussion Starter #6
Right, thats why I wanted to go up a size.
The enrichers move correctly and seat fully when off.
 

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The enrichers move correctly and seat fully when off.
If they're getting full travel to open, I'd have to guess the circuits are clogged.
 

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If the jets were dirty, more than likely so are some of the internal passages in the carbs. Did you soak the carbs in Chem Dip or run them through an ultrasonic cleaner?
 

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Diesel Tech
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Discussion Starter #9
It was definitely a jet issue. It's marked 132 with the keihin star next to it, but there is a clear difference in orifice compared to the new 132.
It runs much better than before. Great power throughout the RPM range.

The choke will raise speed about 200rpm at 1/2 stroke when warm, any more and it still kills the engine.
 

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choke killing engine when warm is what mine (at sea level) always did. I think its just the nature of the choke.

If I 'needed' to increase idle rpm when warm, to use the choke, I would rev it to a 2k or so, and pull choke as I released the throttle. seemed to be able to keep running at higher idle if I did that
 

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Diesel Tech
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136 Posts
Discussion Starter #11
Okay, there is definitely something wrong with these carbs. The rear carb A/F screw makes no change and lifting it's choke alone does nothing until its almost all the way out of the barrel.

I'm just going to get a different set of carbs, go through them and do an ear shave at the same time.
If anyone reading this has a good set available, I'm on the market. None of the local breakers have 750 carbs on hand.
 

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did you ever ultrasonically or chemically clean the carb bodies? that could be a major contributing factor to those issues
 

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Diesel Tech
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Discussion Starter #13
No. I didn't want to risk melting the plastic fuel nipples.
 

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No need to worry about those, IMO. I have a jug of chem dip that I used to clean mine after completely disassembling them and removing all rubber bits, no signs of degradation on the plastic fuel inlets at all, even a year later. I'd say that's worth the shot vs buying more carbs, since whatever carbs you buy are likely dirty, too.
 

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Diesel Tech
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Discussion Starter #15
So I pulled them completely apart again. Everything looked good except I didn't realize the needles were slightly different and I had put them in the wrong carbs.
Based on lots of time searching here, I deleted the air cutoff valves, cut the excess metal from around the A/F screw holes so I can get a normal screwdriver in, and jetted it 38 pilot, 135 main and no shims.
I also deleted the plenum and put on K&N pods. I really wanted to retain the stock air system but practicality won over aesthetics. I will still retain the ears after I modify them with hinges and latches for tool and misc storage.

With a new petcock it still starves of fuel in the "on" and "reserve" positions but runs great in "prime".
It idles well, starts good hot, doesn't pop on decel (but we will see if it does in hot weather), transitions without stumbling, doesn't have the 4-5k rpm hesitation and has enough power to haul my 6'4" frame up to 100mph.
Enrichment at idle will give about 500rpm at 1/2 travel, but will still bog and kill the engine above that.
 
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