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Old 09-08-2013, 03:45 PM
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Rear cylinder problems

Hello, My Vulcan has run great for the 6 weeks or so since I bought it and have put over 1000 fun filled miles on it. That all ended last yesterday. I had about 130 miles on a tank of gas and it began to sputter, I switched to reserve and it continued to run like crap till it finally just died. I tried to restart it with no luck, I looked in the tank and still had a good amount. I tried again to start it on full choke and it and started. It seemed to run OK after this. I got back home and later went to the gas station to fill up thinking maybe something with the gas. Well it is running worse now, it will idle for maybe 10 seconds then RPM's drop till it dies, I can increase the throttle and it will rev up. I thought maybe I fouled a plug and not knowing when they were changed last stuck new ones in. What I noticed on the old ones were the back 2 had oil on the threads. The problem has not changed at all with the new plugs. It seemed like at higher RPMs it was running OK but a little rough. I shut it back off and wanted to look at the plugs I noticed the rear exhaust pipe was only luke warm while the front was hot. I don't know what is wrong as I didn't do anything different to bring it on. Any help will be gratly appreciated. Thanks, Cliff
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Old 09-08-2013, 04:02 PM
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it sounds close to POGS... check out this thread and see if any of the advice helps.. only thing you will be out is a couple hours of time.
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Old 09-08-2013, 05:36 PM
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OK I tried riding about 10 miles with my gas cap open and no difference in how it performed. I checked exhaust pipes mid way in my ride and the back pipe was very warm but not near as hot as the front. I will wait for the engine to cool down and recheck my plugs to see what they look like. The old plugs were all pretty dark which means it is running a little rich. I'm guessing the next step would be a compression test.
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Old 09-08-2013, 09:23 PM
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What brand of plugs were in the engine?
What brand did you replace them with?
General consensus on the board is that NGK is the best brand for Japanese bikes.
We also usually suggest changing up to NGK Iridium electrodes DPR7EIX-9 when new plugs are needed.

I have to admit though that my 1991 vn750 is still running just fine at 28,000 kilometers (17,500 miles) with (AFAIK) the original non iridium plugs.

I am not convinced yet that plugs are your problem.

Let us know what a compression test shows.
Compression needs to be between 129-199 PSI and less than 10 PSI difference between cylinders.
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Last edited by OlHossCanada; 09-08-2013 at 09:30 PM.
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Old 09-08-2013, 09:31 PM
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I replaced the plugs with NGK DP8EA-9. It is what the previous owner had in the bike.
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Old 09-08-2013, 10:35 PM
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I had a similar problem and it was carb related. The rear float was stuck and the needle valve was staying open and flooding out the rear cylinder. Check for good spark to the rear plugs and if possible check the compression if those two check out it generally is fuel related..Remeber CIF,Compression first,Ignition second an Fuel last.

We jump to the carbs first on here because they are kinda finicky.Another way to see if it is carb related try starting it with no or little choke after it has set overnight with the petcock in the off position if it fires up on the front cylinder you know you are leaking fuel through the rear carb and the bowl is draining itself overnight indicating a leaking needle valve.A little carb cleaner and seafoam may clean it out. or you may want to check wolfies method for backblowing the carb it may be a small bit of sediment hanging the needle valve off the seat.

Hope this gives you a few things to check before diving in too deep,Good luck,it doesn't sound too serious yet, Denny
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Old 09-08-2013, 10:48 PM
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Thanks for the info. I drained the carbs and have put some sea foam in the tank. I just took it for a short ride and it is running a little better, but still not properly. I didn't notice any dirt from the carbs. Something new I noticed is my headlamp idiot light is faintly lit up. My headlight has both low and high beam so could this be a voltage problem? Maybe that is why at higher RPMs it seems to run normal.
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Old 09-08-2013, 11:36 PM
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Quote:
Originally Posted by first time View Post
Thanks for the info. I drained the carbs and have put some sea foam in the tank. I just took it for a short ride and it is running a little better, but still not properly. I didn't notice any dirt from the carbs. Something new I noticed is my headlamp idiot light is faintly lit up. My headlight has both low and high beam so could this be a voltage problem? Maybe that is why at higher RPMs it seems to run normal.
That is just a corroded connector probably on the RLU or head light plug. Mine did that the whole time I owned it ,a minor nuisance at most to me.

try this http://www.vn750.com/forum/showthread.php?t=25458 it will probably clear up totally
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Click on one x and drag to the other to read between them.

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Old 09-09-2013, 04:39 PM
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Quote:
Originally Posted by first time View Post
Thanks for the info. I drained the carbs and have put some sea foam in the tank. I just took it for a short ride and it is running a little better, but still not properly. I didn't notice any dirt from the carbs. Something new I noticed is my headlamp idiot light is faintly lit up. My headlight has both low and high beam so could this be a voltage problem? Maybe that is why at higher RPMs it seems to run normal.
The dash light is always dimly lit...it usually isn't noticed during the daytime. It means the circuit is working. If you lose one of the filaments in the headlight, the idiot light will be full brightness.

nothing to see here...move along...lol

I think backblowing the carbs and then filling them with seafoam to sit overnight should help...it certainly can't hurt.

Use heavier doses until it clears up and then go ride
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Old 09-09-2013, 07:21 PM
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I rode the bike to work today and above 3500 RPMs it seems to run normal, but below that it will spit, sputter and pop like it is only running on one cylinder. Starting out from a stop is real treat as I need to rev it to get it going. I've learned it is fine line between burning out and riding a wheelie when launching at 3500 rpms.
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