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post #1 of 15 (permalink) Old 03-10-2018, 03:25 AM Thread Starter
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Jetting

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.

1989 VN750
Highway blaster

2006 Honda Rebel Diesel
100mpg, low and slow

1982 Mercedes 300D
Modified engine, 4-speed manual

Last edited by DenverDiesel; 03-10-2018 at 03:28 AM.
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post #2 of 15 (permalink) Old 03-10-2018, 11:40 AM
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Too much fuel now? Iíd 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. Havenít figured out why, though I suspect my ignition system doesnít have enough spark to burn the fuel, which might be why it likes lower octane.

Might check your ignition coil to see if itís up to par.
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post #3 of 15 (permalink) Old 03-10-2018, 01:36 PM
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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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post #4 of 15 (permalink) Old 03-10-2018, 04:02 PM Thread Starter
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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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1989 VN750
Highway blaster

2006 Honda Rebel Diesel
100mpg, low and slow

1982 Mercedes 300D
Modified engine, 4-speed manual
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post #5 of 15 (permalink) Old 03-10-2018, 04:46 PM
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That plug looks lean.

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

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #6 of 15 (permalink) Old 03-10-2018, 05:59 PM Thread Starter
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Right, thats why I wanted to go up a size.
The enrichers move correctly and seat fully when off.

1989 VN750
Highway blaster

2006 Honda Rebel Diesel
100mpg, low and slow

1982 Mercedes 300D
Modified engine, 4-speed manual
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post #7 of 15 (permalink) Old 03-10-2018, 06:09 PM
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Quote:
Originally Posted by DenverDiesel View Post
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.

2003-21k mi
Shaved w/UniPK92+Stock Jets-TPE/MOSFET-Shinko Tires-AGM batt-bags-chrome-LEDs...more
__________________________________________________ ____________
Repair Manual: http://www.mediafire.com/file/mj7z81..._Catalogue.pdf

Owner's Manual: http://www.mediafire.com/file/nscb5f...ers+Manual.pdf
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post #8 of 15 (permalink) Old 03-11-2018, 09:01 AM
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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?

I'm keepin' all the left over parts. I'm gonna use 'em to build another bike!
_____________________________________________
"Black Beauty"
1989 VN750 acquired December, 2008, 6,711 miles
Currently 23,298 miles

Old Blue
2001 Honda CMX250 Rebel acquired July, 2008

1987 VN750 project bike, acquired August, 2009, 33,000 miles and balancer sticking out of the case, currently awaiting attention and parts
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post #9 of 15 (permalink) Old 03-20-2018, 10:11 PM Thread Starter
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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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1989 VN750
Highway blaster

2006 Honda Rebel Diesel
100mpg, low and slow

1982 Mercedes 300D
Modified engine, 4-speed manual
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post #10 of 15 (permalink) Old 03-21-2018, 08:29 AM
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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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