Coughing when pulling away - VTXOA
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post #1 of 8 (permalink) Old 09-28-2018, 12:34 PM Thread Starter
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Coughing when pulling away

Hi Guys!

I'm having a issue with my 2005 VTX 1300. When I pull away it coughs and splutters. It isn't as bad when the bike is on the side stand, worse under load. I will have to nurse the throttle gently for it to pick up and go, once it's on the main jet it pulls great. However if I pull the choke out the tiniest bit the throttle reaction is how it should be, revs up great, but then it coughs out black smoke from the pipes.

The bike is completely standard, standard pipes and filter. 55 pilot jet, 190 main jet. A/F 2 1/4 turns. 5,000 miles, fresh petrol. Carb has been cleaned, no air leaks showing when spraying easy start around the intake. Diaphragm is good with no cracks or holes. Needle is standard so no shims.

If I drip petrol into the carb it will pick up and respond as it should, meaning it is running lean. Plugs tell a different story, black around the base and tips.

I had the exact same symptoms on a Harley XL 1200 where the CKP had gone. It's that exchange of coming off the pilot and onto the main jet, it didn't know when to advance. Since the VTX doesn't have a crank sensor I thought I would disconnect the TPS to see if changed the bikes habits, hoping it would be the same and buy a new TPS. When disconnected it ran even worse so the TPS seems to be working.

Do you guys have any ideas on this? Any input would be greatly appreciated!

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post #2 of 8 (permalink) Old 10-03-2018, 07:08 PM
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Try turning the a/f screw to 1.5 to 2 turns max. If all is stock that should fix your problem.
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post #3 of 8 (permalink) Old 10-04-2018, 06:33 AM
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Welcome to the VTXOA from Daytona Beach, enjoy and ride safely. Hope you can correct the problem.
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post #4 of 8 (permalink) Old 10-04-2018, 08:17 AM
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Location: RGV. Texas, Former N.E. Ohio
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I disagree about the diaphragm... its 13 years old.... if tires are bad at 8 years... the diaphragm is shot...

holes are not the only issue with diaphragm.....

think about it.. if rubber gets harder/dryer with age.. how can it respond to a gentle change in vacuum..

also.. what about the carb to intake clamps.. are they tight
also the intake at the head and carb can CRACK over time... and leak air... remove an inspect.. are there small cracks ???

my opinion.
50 years rebuilding carbs...

2005 VTX1800 F, type II, Silver Tribal, 86,000 Miles, Purchased Feb, 2005.
MTC clutch & springs.. K&N Air Filter. Garmin 2597 GPS.

Last edited by chuck_VTX F; 10-04-2018 at 08:25 AM.
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post #5 of 8 (permalink) Old 10-04-2018, 08:47 AM
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Honda vacuum hoses split on the inside. Check/replace. Recently one VTXer had issues, said he had one hole in the slide diaphragm. I told him to look again.
His reply - 8 splits on the creases.
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2005 1300c Red, Mustang seat, HK 2.5 straights. Leds for safety-front & back. 192,882 VTX miles
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post #6 of 8 (permalink) Old 10-04-2018, 01:12 PM
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If all else is good...
"Scar Mod"......

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post #7 of 8 (permalink) Old 08-13-2019, 10:56 PM
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Had issues like that also.
My problem were the spark plugs from the second cylinder. They were black. I changed them and the coughing\backfire stopped.
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post #8 of 8 (permalink) Old 08-14-2019, 06:40 AM
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Originally Posted by Alirio View Post
Had issues like that also.
My problem were the spark plugs from the second cylinder. They were black. I changed them and the coughing\backfire stopped.

You might need to keep an eye on those. Being the bike is new to you, you donít know how old those plugs were, you could be running rich. Put some miles on the bike and check them.

Sitting on my VTX making vroom vroom sounds.

2006 Shadow Aero 750 (sold Oct 2018 )
2008 VTX1300T

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