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Discussion Starter #1 (Edited)
FIXED! Hesitation at slow speed and backfiring

Hello,

I have a 2003 vtx 1800c that has a spike air filter and bub jug huggers. I have the power commander USB with fuel map loaded onto it. I did the pair valve removal with block off plates. I noticed that when riding at a slow speed at about 25-35mph I get hesitation in with the motor and occasional backfiring. I get no backfiring when I decelerate (throttle closed) and I get no hesitation at high speeds and no hesitation when accelerating hard or soft.

Any ideas as to what it could be?
 

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Sounds like the map needs to be slightly richer on the low end. I know nothing about a commander USB but the symptoms are lean operation in the range you are having problems.
 

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Mine does the same thing and I haven't been able to find the problem yet. I don't have a fuel programmer. On mine, it's the front cylinder that's doing it. The mix is a little rich. Plugs are a lot blacker than the rears when I checked them. Initially thought it was a spark issue, so I trimmed the coil wires, but that didn't help. I did the ground fix and checked my battery connections. I also tried swapping the injectors from front to rear. Didn't make any difference. I've just kind of learned to live with it.

The one thing I haven't tried is checking to see if the throttle bodies are in sync. That's the only thing I think it could be, since the front cylinder is too rich. It might not be getting enough air. I've got it torn down for a valve check, so I might give that a try while it's apart.

I've seen several threads with guys having the same issue as us, but haven't seen anyone post what fixed it.
 

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Discussion Starter #5
So remembering a problem I had previously which was sudden hard core backfiring when decelerating in gear which turned out to be that one of my rear exhaust studs came out while riding (thank you previous owner for that one). A trip to the dealership for a new gasket, stud, and nut cap fixed the solution. I didn't do much riding after I found that problem and fixed it so I don't know if it would have done the same thing at slow speeds. I think that my problem is a leaky exhaust gasket on the front cylinder.

About a month ago I checked my valves and in order to do so I had to take my front exhaust off. I was lazy and didn't put a new exhaust gasket when I put the exhaust back on the front cylinder.

To check my hypothesis I went riding 2 nights ago with a friend riding behind me and I asked him to look at which exhaust pipe he could see flames (I have no baffles on my exhaust pipes). He confirmed my suspicion that only the front cylinder was backfiring from the fact that he only saw flames come out of the bottom exhaust pipe. This makes me 99.8% sure a new exhaust gasket on the front cylinder will do the trick. The other possibility is my valves on the front cylinder because when I checked the valves the only valves I adjusted was the front cylinder exhaust valve. I found it was just slightly out of tolerance (gap slightly to big) so I adjusted it according to specifications. I don't think I tightened it to much because I rotated the engine a few times and rechecked and it was still in spec. Also, I believe that if it was to tight I would have a problem in the higher RPM range/with a load instead of this hesitation at slow speed (slower than 45mph).

If the exhaust gasket doesn't work I am going to recheck the exhaust valve on the front cylinder (might even do it when replacing the exhaust gasket) and if the valve is in tolerance then I will look at my fuel injectors to see if they are clogged. If everything seems hunky dory with the hesitation still there then I will get the bike dyno tuned (unless I can figure out what the numbers mean in the table in the dynojet program).

I ordered 2 gaskets (going to keep 1 as a spare) from online and I will post the verdict when I actually install the gasket (hopefully before the weekend).

If any more people have their own .02 to share on the matter, please do.
 

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Mine does this every now and then. Usually I have fouled plugs and simply pulling them and cleaning/re-gapping them alleviates the issue. Just do a quick inspection and see if they have a story to tell. If the problem persists, you could try running hotter plugs but I would be most interested in seeing what the plugs have to say before you start throwing money at the problem.
 

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I have read through the service manual, and it states that the throttle bodies being out of sync will cause poor operation and backfiring at idle and slow speeds. So, it seems as if that may actually be the problem. Going to have to get my hands on a vacuum pressure guage and check it out. I'll let you know what i find out.

On a side note... Hey Highroller, What pipes are those on your bike? Mine has the same ones. They were on the bike when I bought it, and I can't find pics of any pipes the look like ours on any manufacturer's websites. Closest thing I've seen to ours is Samson warlords. You have baffles in yours? Mine don't, and I love the way it sounds. Thinking about putting in some thunder baffles to increase the backpressure a little and help the engine out, but I dunno. Those things are pricey for a little 2" piece of bent tubing.
 

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Discussion Starter #8
I pulled the plugs and they were clean. There was no fouling on the plugs at all. I also replaced the front exhaust gasket and took her around the block and the issue was still present.
 

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Discussion Starter #9
Last night I checked the battery terminals and did the "ground fix". Well I will say the positive terminal on the battery was super covered in corrosion and both terminals were on tight. I cleaned the corrosion and applied dielectric grease and then went on to do the "ground fix". I have not test driven the bike yet because it was getting late last night but I will test it today to see if those things fixed my hesitation.
 

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Just curious, what map are you running?

Sent telepathically cause I can't text and ride.
 

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Discussion Starter #11
Fixed!

FIXED!!!! Yippie!!!!! I want to thank all of you for your .02 cents on my problem and also the wealth of information I was able to find on this website.

It turns out the corroded positive terminal on the battery and the "ground fix" for my bike did the trick. Which one was it exactly I don't know but it could also have also been a combination of the 2. I will say though there was not much corrosion around the ground wire and the coil bracket where it mounted to the bike but I did do exactly what the http://tech.bareasschoppers.com/ writeup said to do. BTW, Di-electric grease to my surprise was rather expensive at my local auto-zone (I can walk there from my house) but I guess it'll last me a long time.

This is now making me wonder if I should go through the entire bike and check every electrical connection and clean (if necessary) the contacts and use a little di-electric grease to prevent further headaches with electrical gremlins.

As a side note I found it noticeably changed the tone of the bike when starting her cold and at idle. But I do remember the day when I started the bike up and it had a different tone and then gave me backfiring problems and had just gotten worse and worse. I guess the front cylinder really was not operating properly while the battery terminal was getting more and more corroded.

Just curious, what map are you running?

Sent telepathically cause I can't text and ride.
I am running the fuel map for Bub "Big Willies" drag pipes w/o baffles and a Vortex air intake with a K&N filter. The fuel map number is 109-033 from the dynojet website.
 

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Thanks, I'm trying to find the best map for my bubs and hurricane until I can get it dyno'd
 

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I'm really kind of shocked that took care of it. Reason being, I've done all that and it didn't do a thing for mine. Ground fix, battery terminals, pair removal, valves, trimmed coil wires, two different sets of spark plugs... none of it has made a difference. Guess I might try redoing the ground fix, but I doubt that's going to help anything.
 

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I have read through the service manual, and it states that the throttle bodies being out of sync will cause poor operation and backfiring at idle and slow speeds. So, it seems as if that may actually be the problem. Going to have to get my hands on a vacuum pressure guage and check it out. I'll let you know what i find out.

On a side note... Hey Highroller, What pipes are those on your bike? Mine has the same ones. They were on the bike when I bought it, and I can't find pics of any pipes the look like ours on any manufacturer's websites. Closest thing I've seen to ours is Samson warlords. You have baffles in yours? Mine don't, and I love the way it sounds. Thinking about putting in some thunder baffles to increase the backpressure a little and help the engine out, but I dunno. Those things are pricey for a little 2" piece of bent tubing.
They're Samson Warlord Slashers. I like the way they sound but have my gripes. For instance, the upper tube is browning (or turning a golden color) just behind where the slip-on mates to the header. Can't complain too much tho - traded my stockers for them straight up.
As for the baffles, I don't know that I would spend any money on them. Not that I am chief mech on a NASCAR crew but from everything I've learned the only reason you need *any* backpressure on your exhaust is just to keep cold air from getting to the valves and cracking a super-heated exhaust valve. There's hundreds of discussions on this all over the place and there are people that steadfastly hold to one camp or another but IMHO backpressure=torque is a myth and only good, objective scientific data proving otherwise would make me change my mind.
If your plugs are burned then you are running lean and you need to adjust your ECM accordingly - not add backpressure.
One other thing I forgot to mention is maybe try Seafoaming your engine. Just do a general search for it here on the forums and see what you think. It's worked well for me. Like I said, I've done just about every mod here on the forums (same as @FISTer) and I still get hesitation at steady low RPMs (esp in 2nd - like around 25mph). I am resolved to the fact that I am going to need to get an ECM to thin out the mix but I'm not too worried about it. Too lean = burned valves; too rich = I burn a little extra gas. I am interested to see if the throttle bodies are outta whack though so keep me posted if you check them and find anything out weird. FYI: Harbor Freight has vacuum pressure gauges/brake bleeders on sale right now - just bought one to drain my clutch fluid for under $25.
 
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