[texasgrape]

The bike idles great, it runs great. It is fantastic. However, upon deceleration, or downshifting, it backfires with a popping sound. Been reading on these forums that perhaps the fuel screw just needs to be turned out a bit. Before I do it, I thought I'd check in to see if anyone has any words of wisdom, and to see if you agree. (Bike is all stock except for Cobra drag pipes w/baffle intact.) Thanks!

1996 800 Classic

UPDATE: See last post #32 for this problem is now solved!

 

[Shores]

Has it run good in the past? Did you recently install new pipes or intake? If so, maybe it is running lean. Is there an air injection system on the Vulcan that puts fresh air into the exhaust port upon deceleration to burn unburned gas fumes (an EPA thing)? If so, remove the pump and cap the ports.

 

[rick]

Look on the valve covers in the middle, back of front and front of back. Is there a hose going between the 2, should have a "T" in it. If its still there, remove the hose at each valve cover and cap the short nipples sticking out of the cover this hose was connected to. This is part of the pollution control system and inject air into the exhaust to burn unburnt fuel, thats the popping and back firing you are hearing. This is all considering its stock, maybe aftermarket pipes.

 

[texasgrape]

Yes, there is the hose you described. I remember taking it off when I adjusted valve clearances last week. I think it tees into the vacuum pump where the fuel inlet goes, maybe?? (I couldn't see exactly where it went to just now.) I take it then that the popping is normal, and not a too lean condition whereas I need to tweak the fuel screw?

FYI to both Rick and Shores: No modifications other than the Cobra exhaust. Everything else on bike is 100% original. I just bought the bike, so it ran this way since I got it a few weeks ago. Like I said, the bike is strong, runs great, idles like a dream, easy to start, blah, blah, it just pops on deceleration. I will try plugging per your suggestions. But wanted to be sure whether or not to mess with the fuel screw.

 

[sfair]

Also make sure idle speed is set to Kawasaki specifications.
Low idle promotes popping.

 

[Abominog]

I recommend checking the easy stuff first; in my case, it was a loose connection from exhaust pipe flange to the cylinder head. The stealership tried to convince me that there was a serious problem with "Exhaust Leak "... I wasn't prepared to just take him at his word and notice the flange was missing an acorn nut. I then notice the flange was loose so I bought a new pair of acorn nuts, re-seated the flange and I was good to go.. no more popping/back-firing upon deceleration.

 

[texasgrape]

Also make sure idle speed is set to Kawasaki specifications.
Low idle promotes popping.

Crap, I just lowered my idle (a lot) yesterday. Then after I rode it is when I first noticed the popping. Why did I lower the idle, I don't know. Trying to think of a reason, but coming up empty! Maybe to show a Harley rider mine says 'potato-potato' too.

So here is what I am going to do: 1. Lower the idle. 2. Double check for an exhaust leak. Take for good spin. If it still pops, then I'll plug the vent tubes. If that doesn't work, I'll tweak the fuel screw. OK, I'll report back.

Any quick/simple ways to plug the valve cover nipples/tubes? I was just going to pinch them with a tie-wrap to see if it was the problem, then come back with a permanent fix later. Thanks to all, much appreciated!

 

[texasgrape]

When plugging the nipples on the valve covers, what do I do with the bull portion of the tee? Leave it open?

I put the idle back to about 1300. Checked for exhaust leaks, none. Took bike for a spin after it was warmed up good. It still backfired/popped, but not as badly. So should I tweak the fuel screw next or cap off the vent tubes first?

 

[spuldup]

The Wolf's Bike Shop; just how far do you trust me? <<----- Though dated, this page is a good resource for removing the EPA equipment on an 800.

I ran a dedicated 1/4" line from the carb to fuel petcock (no capped tee), and capped the head covers with 3/8" caps. No marbles.

russian wolf (main site from link above) also has good info on grampsizing/scooterizing which will wake up your 800 quite a bit. Im running the dynojet needle, 3rd position from the top, 165 main jet, a 50 pilot, tweaked idle screw. Even with 18/40 sprockets it's a serious grin when you twist 'er in the first 4 gears.

BTW, Normal idle is about 1000rpm, fully warmed up. Or whatever doesnt cause the lights to dim/fluctuate. On cold mornings i pull the enrichment knob to run about 1300rpm till she warms up. Although, thats at 30 degrees - something you texas guys dont much have to worry about.

 

[texasgrape]

Thanks for the info/advice! The article is just what the doctor ordered. Will modify this weekend and will report back. Too cold to work on it today, supposed to stay in the 50s all day!

 

[rick]

On your idle, if it has much of a lope to it, its too low, should idle smoothly. I know from experience, too low a idle is bad on the cams, starves top end of oil at low speed.

 

[texasgrape]

Good advice, thanks. Turned idle up, less backfiring. Haven't plugged tubes yet.

 

[grim]

I went from a 48 to a 50 on the pilot jet on my 800. She warms up a lot better than before.

 

[Keef]

A certain amount of popping on the overrun is normal.
Low oil pressure from a really slow idle is bad news.

The current trend is to eliminate popping on tuned engines, which means cutting fuel entirely on a closed throttle (efi engines), this is also bad as a small amount of unburnt fuel, which causes the popping, also helps to cool the engine.

A lot of people say that popping is caused by an over lean engine, but mine runs slightly rich due to the O2 eliminator I run, and it still pops with standard pipes.

You pays your money and takes your choice I think.

 

[ecm_this]

Too cold in the 50's? Man,that's t-shirt weather for me up here in the Great White North of Canada!High 50's out there right now and I'm loving it. Now if I can find my keys to the igloo......lol

 

[Timbhmaxx22]

question on changing pipes

If i change my pipes do i need new exhaust flange gaskets ? i liked to never found the ones i used the first time i put the pipes on ?

thanks.

 

[rick]

If you loosen the mounting nuts for the pipes, you should replace the gaskets. That said, I have reused them on my 05 800 at times.

 

[skiluvr03]

Glad I found this article. I found all that extra EPA BS on my Bike and from my little experience, such things always hurt performance, like on my truck that I did that Air Intake Mod and added bigger pipes. Does taking that reed off that I found on my bike help performance as well? We don't even have inspections where I live, so I'm all for taking that extra crap off if it's worth it. On the Air intake Mod, not only did I notice more power, but better gas mileage. One question on the Reed Removal; I'm not much of a mechanic; when you take the reed off and do the straight line method, do you have two straight lines, or one? Does the one line go from the valve to the Petcock, or was there another opening that had to be used? I read it twice and I maybe got mixed up with California model or something. I know it will all make sense when I get the tank out of the way and will be able to see everything. Where do you get the Caps and what size Radiator hose is that? I don't plan on doing the ball-bearing thing, do you suggest that I do? I'm sure when I get started, all of my questions will answer themselves, I just get paranoid before I start on a project like this; nothing ever goes as smoothly as planned, lol.

Disregard my question about the number of hoses, I see now reading back in the thread that you have one hose then use a valve cap

 

[spuldup]

SK,
The reed valve connections on the jugs can be capped without using a plugged hose for cleanest look. Use caps and hose clamps.

You only need one either 1/4" or 3/16" line from the carb to the petcock. The stock hose it preformed to turn a sharp 90 upward so I used that preformed piece and replaced the tee with an inline barb.

At the auto parts store, just buy a plug cap assortment and a hose clamp assortment, and a few lengths of 1/4 and 3/16 vacuum hose. You might have $20 in the whole thing. Always good to have around the garage, along with spare fuel line!

 

[skiluvr03]

Thank you very much! I guess I had the notifications turned-off on this thread. I will take your advice Sir! I got lucky since I last posted! Got off the interstate, with no helmet, and felt a little thump, thump, so I thought it was those lines in the road, and got on a smoother road. It still kept thumping, so I went to the house, which wasn't far, and there was a huge goose-egg right on the center tread of the front tire! I was lucky as hell! Not to be hi-jacking this thread or nothing, just throwing that in to remind people to be safe, although there was nothing I could have done, except maybe wear a brain bucket, which I shall more often.