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post #1 of 15 (permalink) Old 06-08-2012, 12:41 PM Thread Starter
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Newbie with troubles

Hi,

I just bought a VN750 from 1994 with an unknown mileage. It says 20.000km but I think it may be double. It is a fine machine but it has an engine problem and I am looking for help.

The enigine stalls when I open the throttle more than about 30%. When I close the throttle you hear the bangs in the exhaust.

With the throttle slightly open I can drive nicely upto about 100 km/h at 4000 rpm. I cannot run the engine higher than 6000 rpm. When I test drived the bike I didn't notice anything strange but I probably didn't open the throttle. (stupid of course)

Idle speed is OK and the engine doesn't make any strange noises.

I check the wireing of the ignition and resistance of the ingition and pickup coils and they are all good. Als I cleaned all connections.

The spark plug are brand new and are nicely coloured and the gap is OK.

The air filters look brand new too.

The motor hasn't been used for half a year. I have driven about 100km now and used cleaner in the petrol for the last 20km.

I checked the choke cable and the free play is OK.

My first thought is that the ingition is too weak but since the measurements of the resistance are OK I doubt that now.

Can anyone advice me what to check next?

Thanks!

Frans
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post #2 of 15 (permalink) Old 06-08-2012, 12:51 PM
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The carbs probably need to be cleaned. Clogged main jet, needle, or both?

Welcome! Here's my new-owners checklist.

General
Quote:
Inspect the tires for air, age and wear. Replace if they are too old, or too worn.
Perform an oil-change.
Inspect all fluid levels. Top up where needed.
Inspect all cables. Lube and replace where needed.
Inspect the brake's wear. Replace if too worn.
Inspect the fork seals and oil. Replace as necessary.
VN750 Specific
Quote:
Inspect, and lube the drive-shaft splines. Moly 60 or better is suggested.
Replace your battery with an AGM or Gel style battery.
Replace your spark plugs with NGK Iridium Plugs #7803/DPR7EIX-9
Replace the stock Automatic Cam Chain Tensioners with Manual Cam Chain Tensioners, such as the ones manufactured by TOC.
Perform an rear-end oil-change.
Buy some SeaFoam, and use in every few tanks. If you are worried about the carbs being gummed up, you can drain some directly into the carbs via the vent hose.
Inspect the charging system on the bike. The stator is known to fail, which can cause the R/R to fail as well.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

2014 Honda VFR800F

1989 Pontiac Firebird Formula 350
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post #3 of 15 (permalink) Old 06-08-2012, 02:02 PM Thread Starter
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Where is that hose going?

Thanks for the advise!

I started to remove the carburators and then I found that a hose from the front carburator is going nowhere. It goes over the back cilinder and ends open.

It is the hose marked with the arrow on this picture:



Should that hose be connected to something? Might this be cause of the problem?
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post #4 of 15 (permalink) Old 06-08-2012, 03:29 PM Thread Starter
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I removed the carburators. That was a narrow escape!

The jets were perfectly clean. No signs of any dirt anywhere.

Tomorrow I will continue the check.
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post #5 of 15 (permalink) Old 06-08-2012, 03:40 PM
1986 VN750
 
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Nice to know they're clean. Sorry you had to take those out as they are not fun.

I would check the stator next. I know it's strange, but a grounding stator caused ignition issues on my 90. There are also tests for the coils, etc. I would run through everything that you can stick a multimeter on.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

2014 Honda VFR800F

1989 Pontiac Firebird Formula 350
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post #6 of 15 (permalink) Old 06-08-2012, 04:45 PM Thread Starter
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I posted another message about the carb vent hose not being connected. The message is waiting for an admin to approve it because I included a picture.

Anyway, the vent hose was not connected to the right ear but was left open. Could this be the problem? I am reading that it may not be left unconnected / open.

What is the function of this hose?

Tomorrow I'll reinstall the carbs. If the engine is still stalling I'll take a look at the stator. Is it enough to measure coil resistance on the that goes to the Voltage regulator?

And what about moving the pick up coils closer to the rotor. I read about a modification. Is that a good idea?
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post #7 of 15 (permalink) Old 06-08-2012, 04:55 PM
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The carb vent hose is an air vent for the carbs. You want it connected to the right ear, Cut the end at a 45 degree angle to ensure it doesn't bottom out. This may be your problem if wind is going into the tube. It can cause bogging at higher speeds.

The pickup coil gap mod helps with a few things, including hot starting.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

2014 Honda VFR800F

1989 Pontiac Firebird Formula 350
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post #8 of 15 (permalink) Old 06-16-2012, 10:56 AM Thread Starter
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Problem almost solved!

I removed the plugs after I drove about mile with the gas open and I found that the enige was running far too rich.

Then I removed one of the filter covers (I kept the filter in place) and the bike runs perfectly now.

Inside the filter boxes there are narrow silencers that is not shown in the 'VN750 manual and parts' that I downloaded. THey are narrow and make 90 degrees angle towards the filter.

Are they causing the problem and are they originally there?

BTW: It is a German model from 94, may be that makes a difference.
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post #9 of 15 (permalink) Old 06-16-2012, 01:50 PM Thread Starter
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Here is a picture of the muffler. I didn't see it on other air box pictures but then again I didn't find that many.
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post #10 of 15 (permalink) Old 06-16-2012, 01:58 PM
1986 VN750
 
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Quote:
Originally Posted by broembroem View Post


Here is a picture of the muffler. I didn't see it on other air box pictures but then again I didn't find that many.
That is something I am not familiar with. It sounds like it was indeed restricting the air too much.

I checked the 3 sets of ears I have and none have that. Weird! Maybe it was something specific for German emissions laws?

Either way, I think you found the source of your problem. You could modify those ears, replace the ears, or do an ear shave mod. Glad to hear it's running right.

Make sure the filters are clean and properly oiled as well while you're at it.

1986 Kawasaki Vulcan 750
NGK Iridium Plugs #7803/DPR7EIX-9
Duralast Gold ETX15 AGM Battery
Coastered & Shaved
TOC MCCTs
Metzeler ME880 [110/90-19, 170/80-15]
Balance Dampers Replaced
Tuxedo Mod
Rebuilt Forks w/ Progressive Springs
V&H Cruzers
VN750.com Grill Cover
Meanstreak Seat
Emgo 23-92411 Handlebars
MOSFET FH012AA R/R


1990 Kawasaki Vulcan 750

1998 Honda VFR800 FI

2014 Honda VFR800F

1989 Pontiac Firebird Formula 350
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