Did some trial and error today....

[krooozn]

I have posted in the past about this backfiring, popping, snapping that I am getting on decel with my 2003 Honda Shadow 750cc...and I got several suggestions. I checked the exhaust manifold bolts and they were a little loose, so I tightened them, I checked the carb boots for tightness and they were all tight, so I then got a friend who is a bike mechanic on the side to come over and set the air/fuel mixture in case it was running lean......and when we adjusted this, the bike ran worse. So we set them back to 2 1/4 turns which is where the bike seemed to want to be and began a little investigative work and what we discovered is this.....with the airbox removed from the bike and placing your hand over the air intake the bike smoothed right out, took the gas without any hesitation and no backfiring, put the airbox back on and tried covering the air intake port that is inside the airbox and the bike still ran like crap, didn't want to take the gas on throttle, backfired and popped as it was doing, took the box back off, covered the intake and it smoothed right out again. So we took a wire tie and replaced the clamp with it so that we could get the rubber boot tighter and put it all back together and the bike is running some better, but still getting some backfiring on decel.....so can anyone offer me any suggestions, thoughts, ideas, etc as to what the problem might be or how I can go about fixing it......it just doesn't make any sense to me that with the air intake completely covered the bike ran like a top....but with the airbox back in place, again I get the throttle hesitation and backfiring....I am at a loss here.

Thanx...and sorry for writing a book here....just wanted to try to explain what we did and our findings....

Anita epper:

 

[Ol' Grey]

Good on ya for doing some experimenting and making some progress :wtg:

On the exhaust manifold bolts, please keep in mind that they want to be "snug", but not overly tight. If overtightened, heat expansion can make 'em snap off. Just a good, simple snug should do it.

With the bike running much smoother by covering the intake with your hand, it would seem like the carb jet(s) need to be bumped up as the intake is providing too much air for a proper air/fuel mixture. Normally one starts with pilot jet, then needle jet setting position for mid-range, then main jet. If your idle is good, you may luck out and only have to check the needle jet position and/or bump up the main jet by one size fatter (larger).

 

[CadtoChrome]

Something that would help would be to tell us when this started happening.
Is it something new or what was done just prior to this starting to happen.

Regards,
Chuck

 

[Gorilla]

Also had the trike sat for awhile then this started to happen.

 

[3W-lonerider]

2 things are possible..either it has sat for awhile and has plugged up jets in the carbs or the exhaust has been changed and somebody did'nt increase the jet size to compensate for the change.. if you can hold your hand over the carb throat and get it to run perfect, and your pilots have to be 2 and 1/2 turns out.then your not getting enough gas your going to have to do one of 2 things..either clean the carbs if nothing was changed to cause this i would order all new oem jets if that were the case..2 if the exhaust was changed to say cobra exhaust then your going to have to contact the exhaust manufacturer to get their recomendation on jet sizes and go from there..

 

[krooozn]

The bike came to me running this way, I was told that it was ridden once a month to keep the carbs from gumming up and also had stabil added back in the fall for winter storage. The pipes are definitely an aftermarket pipe I do believe as they are straight and very loud....they do have baffles in the end of them, but as far as who made them...I have no clue....don't even know how to tell. So I guess I'll just have to get the bike into a shop and have them go through the carbs and see if they can figure out what the problem is. Which I know will cost me a small fortune.....will it hurt anything to ride the bike as it is? I know it is annoying with the noise, but other than that...can it damage the motor? I really don't have the money right now to invest into taking it into the shop.

Thanx...Anita:Trike1:

 

[Ol' Grey]

Quick check for engine health = Look at the spark plugs.

If you see whitish deposits on the electrodes and/or by the ceramic spark plug bases, the trike is running way too lean and, yes, it could definitely toast the top end. White spark plug reads require attention to fix the problem ASAP.......a light tan spark plug read would be ideal and less cause for concern except that you still want to smooth out the running thru the entire range from idle to WOT.

As others have noted, it sure sounds like a good carb cleaning and probably a carb re-jet is needed. You already know that a shop won't be cheap as with dual carbs, it's a labor intensive job.

If you've got a service manual for your Shadow and someone to help you, it's possible to do the work yourself. Not going to try to make it sound "easy", but with patience, taking lots of pics to show where everything was, jotting down notes, etc., it's definitely possible to do it yourself.

I looked at the schematics at Motorcycle Parts, Motorcycle Accessories and depending on whether or not you've got the Ace or the Spirit, they're showing that the Ace has a #105 Main Jet on the front carb, #110 Main Jet on the rear carb. The Spirit shows #105 front, #108 rear. The pilot/slow jets on both models are probably the same size for both carbs.

You could buy carb rebuild kits and some larger jets as you'd probably have to do trial 'n error on re-jetting, bumping 'em up one # size at a time until you've gotten it in the ballpark where you can make the final adjustments as per the manual.

 

[krooozn]

I just pulled the plugs on the bike and examined them as per your instruction...here is what I found.....the one that came out of the back cylinder had a little bit of tan/yellow looking deposit on it, the guy at the parts store said that was from the ethanol in the gas, the one that came out of the front cylinder had no deposit and looked to be burning in a normal range I would think.....neither plug had any what I would consider to be a white deposit. I have seen plugs before that were burnt white and these plugs had nothing like that on them...if anything at all....it may seem that the bike was running a little too rich by looking at the plugs, they were both black in coloration. Anyway...I just wanted to share my findings and hopefully in the next month or so I will be able to get the bike into a mechanic and maybe they can figure out why all the decel backfiring and popping. Could just be something that is coming from the pipes...I just don't know.

Thanx and Happy Easter!epper:

Anita

 

[Gorilla]

Anita I have one suggestion that you might try. This has only worked a couple of times for me. If you have plugged up jets. Try: remember when you were keeping the bike running with your hand over part of the carburetor, we are going to go one step further. Get your air cleaner off to that point. Get the bike running in neutral, when you got it up to a couple of thousand RPM's then completely block the air off chocking it out. Let go of the chock just before it quits and get the RPM's back up. Do this several times. If the blockage is not to bad then the resulting vacuum from covering the intake MAY pull it loose. If no luck the first time then try putting something like "Sea Form" or other carb cleaner) in the gas, run bike to get it down into the fuel system. Then let it sit over night and try the procedure again. Like I said this has worked a couple of times for me, but has not more than has.

 

[vwjoe]

That sounds more of a vacuum leak in the carburetor or fuel system you are running to rich. I would check vacuum lines. Easy way to check is run bike and use a propane bottle and trace the lines if the idle changes there is a leak in that area of the line....Hope this will help..

 

[Ol' Grey]

Looking back.....here's a couple more threads from Anita......It started out with her having to run with the choke on. The blackish plug reads may be from running with the choke on, Anita, but I think you're still running in the safe zone (relatively). A "little" popping on decel is acceptable. But repeated popping and backfiring needs attention.

http://www.triketalk.com/forum/honda-trikes/5864-rough-idle.html

http://www.triketalk.com/forum/honda-trikes/6136-torque-cones.html

And from your 1st post in this thread, quote: "....with the airbox removed from the bike and placing your hand over the air intake the bike smoothed right out, took the gas without any hesitation and no backfiring, put the airbox back on and tried covering the air intake port that is inside the airbox and the bike still ran like crap, didn't want to take the gas on throttle, backfired and popped as it was doing, took the box back off, covered the intake and it smoothed right out again."

It's been mentioned before that there's either too much air coming in due to an air leak or that the carbs need to be re-jetted up due to the aftermarket pipes on the trike.

From your quote above, you might have narrowed down the possibility of an air/vacuum leak from the airbox area. Carefully inspect the airbox and larger duct hoses for any cracks or breaks. Covering more bases here....there IS an air filter element inside the air cleaner housing, yes ? There's no drilled holes in the air cleaner housing or the airbox from a previous owner, right ? If everything checks out in the airbox area, then my guess would be that the carbs need a re-jet. Theory being that if all checks out O.K. in the airbox area, giving you normal air intake coming in, then the carb jets are simply too small to compensate for even normal air flow due to the aftermarket exhaust on there.........

 

[krooozn]

Yes there is a K & N air filter in the airbox, but I must say it fits really loose in there...it doesn't seem to fit the area that it is supposed to...it is very sloppy...it just kind of hangs there.....should this filter fit nice and tight on the airbox? I am going to remove the airbox once again and give it a good once or twice over...I didn't notice any drilled holes or anything like that...I did notice that it appears to have a factory hole in it that is capped off with some kind of clear plastic cup held on with a clamp. But other than that...didn't notice anything else....but I didn't inspect the rubber boot real well that connects the airbox to the intake....I did remove the clamp that holds the boot to the intake and replaced it with a wire tie....because it felt like the clamp wasn't getting tight enough on the boot...I could tighten it down as far as it would go and still able to slip the boot off the intake without loosing the clamp....so I replaced it with the wire tie..something I knew I could get tight....My step-father and brother told me yesterday as I rode it over to my mom's house....they both said that if I were to put the factory exhaust or even some type of slip-on muffler on the bike that it would stop doing the backfiring, etc.....they both seem to think that the backpressure isn't adequate....what do you guys think? The bike is really loud and the pipes do have a small baffle in the very end of them...but that's it....

I'm okay with putting the factory exhaust back on if it will cure this problem...my ears rang so bad when I got home yesterday from the popping and snapping and just the general loudness of the pipes....:Shrug:

Thanx again for all the help and suggestions.....:Trike1:

Anita

 

[jim peacock]

Another thing that can cause that is timing.
I am not familiar with the 750,but if it uses a chain to turn the cams and the bike has over 60 thousand miles on it the chain could be getting lose and throwing the timing off.
:banghead::banghead::banghead::banghead::banghead:

 

[Snyiper]

May try and run some seafoam through the carbs if you dont really want to take them off. My first instinct tells me the previous owner put the pipes on didnt rejet and could not figure the popping out. I think a good cleaning and possible rejet as said before will make that bike scream. Just my .02

 

[Ol' Grey]

I've never worked on a Shadow, but it doesn't seem like the air filter should have a lot of sloppy movement. Normally, there'd be a formed "guide" or tension band, something to keep the air filter in place to allow it to direct air flow and still do it's job of filtering. Too much slop "might" be a source of some excess air coming into the routing of air flow. Same/same with the clamp that doesn't tighten sufficiently. And if you find any cracks in the rubber boots, that would be another source of air leaks. Replacements are cheap enough at places like Motorcycle Parts, Motorcycle Accessories

Opinions can vary on whether or not the pipes are the issue. I ran short, open headers (approx. 27" long) with stock airbox on a Jap bike and lost the mid-range of the power band due to lack of back pressure, BUT there was ZERO backfiring. Instead of re-jetting, I added slip-ons to regain the needed back pressure. In your case, with full length headers and baffles, I'm less likely to suspect the pipes as being the problem (other than a possible need to re-jet).........Also had a trashed carb to manifold seal on the Harley and it backfired like a machine gun! Please note, in this case, the cause of the backfiring was from the intake side.

My .02 would be to approach your situation from the intake side to eliminate any possibility of air leakage. If that doesn't do it, then I'd be looking into re-jetting the carbs.

(On a side note, you can inspect the exhaust pipes to insure that there's no hairline cracks in the pipes anywhere's, but this would usually only cause popping. Thing is, when you held your hand over the intake, the bike smoothed out, which is why I'm leaning towards intake side or re-jet. As regards the possible need to re-jet, when you cut off air flow, the current jets were able to manage it. With full air flow, the jets might not be able to manage the excess. Jim is also correct about bad timing being able to cause backfiring, but again, when you cut off air flow, everything seemed to even out).

 

[krooozn]

The air filter was so loose that it just hung on the guide or whatever you call it and if you bumped it or shook the bike it dropped off onto the driveway. I felt this was a little odd, but who am I to say.....just seems that without some way to hold it tight onto the airbox base, once you placed the airbox cover on, the thing would just drop off the guide and up against the backside of the airbox cover. I know when I removed the cover the first time, the filter hit the floor...I feel pretty certain that the air/fuel mixture has at least been tampered with on the bike because the brass plugs were gone. Whether or not it was ever re-jetted I have no way of knowing. The PO never mentioned it to me and since he bought it used as well, I doubt he would even know the answer. So I am going to delve further into the airbox/intake side of the bike and look for any signs of air leakage around the airbox....and if that turns up with nothing, then I'll either have to decide if I want to incur the expense of taking the bike to the shop and have them possibly rebuild/re-jet the carb or whether to go ahead and put stock exhaust back on the bike....I just know that I need to stop all that racket...it will drive you nuts when riding and the slightest bit of decel and the thing sounds like a gun going off! I passed several deer out in the middle of a field yesterday and was afraid to slow down because it the damn thing popped they might think it was a gun and run out in front of me! So I just need to focus on this issue and get it fixed. I do realize that with the straight aftermarket pipes you are going to get a certain amount of backfiring/popping....but what mine is doing is insane....way too much of it! In regards to the timing part of it....the bike only has 5800 miles on it, I wouldn't think it would need to be re-timed or that the chain would need to be replaced....

Thanx again for all the efforts to help me with this...sure wish you guys lived closer!:wtg:

Anita :blahblah:

 

[Ol' Grey]

Real quick on the air filter here as I've gotta get in motion........

As long as there's some sort of guide for the inner side of the air filter and if the air filter housing cover butts up against the outer side of the air filter to hold it in place when assembled, this could be the normal design and a non-issue.......only other thing I can think of would be whether or not the air filter itself is the right one for your housing. If you can find a Part # on the K&N, maybe we can check that out.........burning daylight here, gotta run........:Biker:

 

[Ol' Grey]

As Snyiper and probably others (without going back and re-reading the thread) have suggested, whoever put the aftermarket pipes on probably didn't re-jet. But they probably did remove the limiter caps for the mixture screws to try to enrichen the mixture but couldn't quite get enough fuel in the mix with only turning the mixture screws.

If you put a ruler across the center end of the exhaust pipe, what measurement are you getting ? 1 1/2" ? 1 5/8" ? 1 3/4" ? 2" ?

I'd still try to nail down the possibility of an air leak first. Once you feel confident that that's been managed and if it's still backfiring/popping, you can decide what you want to do.

"the slightest bit of decel and the thing sounds like a gun going off!"....this is still speaking of air leak or a need to re-jet. On decel/off throttle, the fuel stops pumping and any excess air in the mix will show itself by the symptoms you're getting.

Again, when you get to the point of feeling that any air leaks (if any) have been contained and if you're still getting the backfiring/popping, your options are:

1) Spring for a carb cleaning, re-jet and dial-in, which with the aftermarket pipes will give you more power. It's a matter of whether or not you want to spend the money on it.
2) Put the original pipes back on and HOPE that the carbs are clean enough to not require having to be pulled anyways.

When you're going thru the gears from 1st thru 5th ? gear, does the power band feel smooth throughout ? No flat spots ? If so, the carbs might be O.K. except that they're dialed-in for the stock exhaust, in which case option #2 might be the cheapest and easiest way to go, but it's your call entirely.

 

[krooozn]

When running through the gears, there is absolutely no flat spot, the bike accelerates just fine. No hesitation, no bogging down.....it responds nicely to the throttle. I have pretty much decided that if it doesn't boil down to an air leak, then I am going to go back with the OEM exhaust system. I was looking last night on ebay and I saw a couple different OEM setups....one was the two pipes going into a single muffler and then the other was two separate pipes, one for each cylinder. I took a look at the owner's manual and it shows that on my bike, it came stock with the two pipes going into one muffler....but wondering if either one would work. Anyone know? I am going to try to take a look at the airbox setup a little later this week.....will let you know what I find.

Thanx again.....:yes:

Anita :Trike1:

 

[Gorilla]

If the exhaust is that loud that your ears hurt then I would strongly suggest getting rid of it. You will hurt your ears for sure.

 

[Ol' Grey]

Either exhaust set-up should work and it's a personal choice, but 2 into 1's have been known to offer better performance.

If you decide to go back to OEM, you might only have to re-set the mixture screws to ballpark settings and adjust the idle. Good luck and please keep us posted.........Ride Safe.......

 

[3W-lonerider]

ya know..that tidbit of info about the bike accelerating threw the gears fine and not bogging down or missing a beat would've been nice to know from the start. so heres my conclution. your jets are fine right where they are..you either have exhuast gaskets that arn't sealing properly or a vacumm leak. if there are vacumm hoses of any kind on that bike i'd take serious look at them..they can look fine but can be split from age and heat. i'd suspect the vacuum leak over anything else.

 

[Ol' Grey]

Between all of us trying to figure this out, we've been concentrating on air leak, vacuum leak, rejet......sure seems like either too much air or not enough fuel.....It sounds like the power band is smooth going UP thru the gears, but a nightmare on decel. What confused me is that if the symptoms were that dramatic on decel, I'd think there'd also be some backfiring/popping between shifts going up thru the gears. Decided to check out some manuals and found something interesting to add to the list of possibles:

Air Cut-Off Valve.............

Directly from a motorcycle carb manual:

"The current move towards weaker mixtures in the interests of reduced hydrocarbon emission has caused one or two minor side effects to become apparent. One of these is a tendency for backfiring to occur when the machine is on the over-run (decelerating with the throttle(s) closed). This is caused by unburnt fuel being ignited by the hot exhaust pipe, and is similar to the condition caused by air leakage at the exhaust pipe joint.

On many new Honda models, the Keihin carburettors have been equipped with an air cut-off valve which partially shuts off the air supply during deceleration. The valve is of the diaphragm type, very similar in construction to an accelerator pump, and is normally mounted on the side of the instrument (carb).

Little maintenance should be required, but if backfiring symptoms suddenly appear, check that the diaphragm has not split, and thus allowed air to be drawn into the exhaust system. In the unlikely event the valve jams open or closed, it's effect will be to allow backfiring on overrun (decel), or to cause poor acceleration in the case of the latter. If either condition is suspected remove and clean the valve plunger/diaphragm and note whether any improvement is obtained."

I looked at the carb schematic over at http://www.bikebandit.com and your carbs indeed have these air cut-off valves. Seeing as you haven't found any obvious other cause for the backfiring/popping, I'm now leaning towards this one...........

 

[Ol' Grey]

Quick p.s. here........when you held your hand over the intake, it could be that your hand was acting as the "air cut-off valve" and doing what the air cut-off valve might not be doing....

 

[Ol' Grey]

Couple related threads found thru the search engine. Not saying with certainty that this is the problem/solution, but if I were a betting man, my money would be on this one :yes:

carb air cut-off valve (TRX 350) - Honda TRX ATV Forum

Splitting carbs and air cut off valves? - Yahoo! Answers

 

[krooozn]

Wow Ol' Grey.....you are the bomb! Never heard of these air cut-off valves before, but I will definitely take a look at them. Can't be but so hard to do I wouldn't think...I have changed many accelerator pumps on carbs before, I would think it is basically the same principle. I also bought a set of OEM exhaust today off ebay, I went with the 2 into 1 setup as this is what came on the bike. I got them off ebay because new it was over $700.00 plus shipping. So just in case this air cut-off thing isn't the problem, I'll put the OEM's back on it. Also noticed that the ends of the pipes that are currently on the bike are really black on the inside...I mean looks like soot.....so my guess is that somewhere along the way the bike has ran rich for an extended period of time.....I don't know what the issue will finally end up being, but what I do know is I have to figure it out cause that is just way too much noise with all the popping and backfiring.....I wouldn't mind keeping the drag pipes on it if I could get them to perform correctly, but I am also open and okay with putting the OEM back on.....anyway....I'll try to take a look at these air cut-off valves sometime over the next couple days and post back here what I find. I guess if the diaphram is damaged or compromised in any way I will be able to tell.....do you know of any way to check these things?

Thanx again for all your help and effort with trying to figure this out for me...you have been a real friend and I appreciate your willingness to not give up on me or my bike......you absolutely rock! :woohoo::woohoo::woohoo:

Anita epper:

 

[Ol' Grey]

Just knowing that you appreciate the help that all of us have tried to offer is thanx enough, Anita........I just hope that this is the fix you need. Sorry, but I'm not familiar with the air cut-off valve, either. It does look like a relatively easy fix that you should be able to do yourself, but looking at the parts list for the carb, it looks like one has to buy certain sets of parts rather than only the individual part(s) that might be needed and, unfortunately, the sets aren't cheap. Couldn't copy 'n paste the carb schematic, but hoping that this link will take you to the page and then you can click on the "carb" section schematic. If it works, you'll see the air cut-off valve parts numbered as sets 11 and 12. (If or before ordering anything, please go to the actual Shadow model section at Bike Bandit for your bike as I just went with the first Ace model for this link)

2003 Honda VT750CDA SHADOW ACE DELUXE-BLACK Parts, 2003 Honda VT750CDA SHADOW ACE DELUXE-BLACK OEM Parts - BikeBandit.com

Do you have a service manual for your Shadow ? It'd certainly help you a lot for this and many other repairs.

Good eye on the carbon build-up in the exhaust and you're no doubt right about the rich running. You were running with the choke on for awhile and the previous owner might have had to do the same thing as well, which could account for the soot.

Right on about scoring the OEM exhaust and I respect your preference to keep running the aftermarket ones once you get this backfiring/popping issue sorted out. If it is the air cut-off valve, it wouldn't matter what pipes were on there as it'd still be problematic until fixed.

Keep after it........you'll get there! :wtg:

 

[3W-lonerider]

there is a test that can be done on those cutoff valves before ordering them. as mentioned they arn't cheap..those valves should allow air to go threw them..if you blow threw them you should be able to..supply a vacuum to them..they should close anywhere from 7 to 12 on a vacuum guage. at which point no air should pass threw them.