de-goat and popping - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 8 (permalink) Old 01-29-2012, 10:37 PM Thread Starter
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de-goat and popping

OK, so after I coastered and removed all the extra emissions stuff, I still had popping on deceleration. I decided i was going to do a temporary de-goat and see how the exhaust would sound. I also found an engine guard to install, so figured the left header had to be loosened anyway.
I pulled the left header off and was surprised to find that the crush gaskets were never installed...nothing there!
I have an 06 and never really had to pull the exhaust off for any reason, so I know they were never removed.

My question is this...has anyone else found this?

By the way, I am certain the exhaust is now air tight after bypassing the goat's belly, but am still getting some backfire and popping, so what should I be looking for besides the idle mixture being too lean? they are turned out 2 1/2 turns now and if I turn them much more, then the bike won't start when cold.

Any advice would be appreciated.
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post #2 of 8 (permalink) Old 01-30-2012, 01:43 PM
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First of all, I would put the goat back on, and make sure all 4 connections are secure and not leaking. Those graphite bushings have a habit of falling apart, and they are not cheap. When I put my stock system back on after removing the V&H Cruzers, I had to replace all 4 of them. But it was worth it to me to get the stock sound back. I also have removed both the complete air injection system and the CA evap system. I have my pilot screws out 2 1/2 turns. Make sure you have no vacuum leaks between the carbs and the heads, and I'm assuming you installed the proper gaskets at the exhaust ports. Make sure the vacuum fitting on the rear carb is plugged. Mine only makes a slight burble on deceleration, no actual backfiring and popping. Degoating completely changes the characteristics of the exhaust system, it was put there for a reason. It is one of the things on the Vulcan 750 that actually works well.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #3 of 8 (permalink) Old 01-30-2012, 03:43 PM Thread Starter
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I did install OEM crush gaskets on the header pipes when I reinstalled them. I may go with a set of the screaming eagle gasket once I return the exhaust back to original (after resolving this backfire issue).

I de-goated to ensure there were no exhaust leaks since I had constant popping from day one with this bike, and the dealer didn't have a clue.
Now that I have eliminated the crossover chamber, and basically running straight pipes to the OEM mufflers, I am now certain that the popping or backfire is coming from the rear cylinder or left side exhaust.

I do not see any air leaks on the carb boots.
Vacuum lines look good.
Coasters are sealed up and installed with air injection system removed, and the large hose from the airbox is capped.
The vacuum nipple on the right carb is capped off.
The breather tube is tucked into the right ear with the tube cut diagonally and not bottomed out.
Idle mix setting does not seem to make any difference for this particular symptom, but are both set at 2 1/2 turns out from bottom.

I have pulled the plugs to see how they look. they look fine, but to me it sounds like the rear cylinder is missing a beat and then popping once it ignites. In another thread I once described this as what sounded like a "clunk" and then a stall when it was cold. This issue has become a personal quest to resolve now and I really would like to find out exactly what is going on.
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post #4 of 8 (permalink) Old 02-03-2012, 06:56 PM Thread Starter
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OK..so I know it is the rear cylinder that is the culprit of the backfire. the exhaust is returned to stock and still popping/backfiring.

I turned the idle screws out with no change...still pops.

I talked to local guru and he suggested that the carbs are set too lean. He suggested I try to go up one size on the jets and see how it sounds and runs afterwards. He thinks the bike will run better, cooler, and eliminate the problem. I do have some blueing of the header pipes even though the plugs look ok.

I really am not looking forward to pulling the carbs unless I have to, so I would like to hear some opinions on the subject.

What would be the downside to changing the jets besides fuel efficiency?
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post #5 of 8 (permalink) Old 02-04-2012, 02:46 PM
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If you have a completely stock intake and exhaust system, no air leaks, air injection system removed and hole in airbox plugged, pilot screws turned out 2 1/2 turns, you should not have a problem. That is exactly how I have mine, and it runs fine. I have stock size jets.

Something else is wrong. If it is running lean, it is probably an air leak you haven't found, partially plugged jets, not getting sufficient fuel to the carbs, or possibly a carb venting issue. Also have you checked the spark plugs to see if they are actually working? Take another plug, remove one plug at the time, install the other plug, then connect the plug from the engine back to the wire and ground it. Start the engine. You should have a nice bright blue spark. The Vulcan engine makes this easy, because it will run with one plug per cylinder. It does not run as well though, so make sure all 4 plugs are firing correctly. It is also possible but not likely for a plug to fire fine outside the engine, but not fire right under compression. I would put that way down there on the list of things to check though. If all the plugs check out, I would be inclined to suspect the fuel system.

But before tearing into the carbs, just to eliminate the possibility, and since it is so easy, I would do a compression check on the engine. When I am trying to locate a hard to find problem, I like to know the compression is ok. That goes back decades, when I was trying to figure out why a 4 cylinder car engine wouldn't run right. I worked on it for weeks, only to find out the 2 middle cylinders had very low compression. Lesson learned. I had no reason to suspect that, as it had been running ok not too long before.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #6 of 8 (permalink) Old 02-04-2012, 05:16 PM
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I would try going out 3 turns on the rear cylinder. I'm degoated and have to have the rear cylinder a little richer than the front. If the blueing is near the engine it is running lean. If it is blueing 4 or 5 inches down the pipe it is running rich. I have stock jets and get zero backfiring. I still think you are running lean on the rear cylinder.

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" Loud Pipes Risk Rights "

2001 Vulcan 750
marbled
TOC upgrade on ACCT
Air/fuel mixture set to 2 1/2 out
rectifier relocated
splines lubed
iridiums
decals removed
upgraded mirrors
Pic up coil mod done
degoated
All LED lighting
Upgraded Mosfet rectifier
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post #7 of 8 (permalink) Old 02-07-2012, 08:46 PM Thread Starter
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Right (front) header is turning blue right at the port. I know it is running lean...it always has, but the plugs look OK.

I returned the exhaust back to stock and still get a little bit of popping on the rear exhaust port. Once again....the idle screws make no difference when backing off the throttle at higher RPM, which is when it pops.

I was told that the rear jug will run hotter than the front one, which is why it was suggested to re-jet the carbs to make it more rich.

What would be the harm in making it run more rich? Would this cause other issues if the plugs are not fouling? Would it cause any long tern problems for the engine or the life of the bike?
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post #8 of 8 (permalink) Old 02-09-2012, 05:05 PM Thread Starter
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bump

Anyone have any input on the possible down side of re-jetting the carbs to run more rich?

I will balance the cards soon and check compression once I get a gauge.
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