newbie... backfire on decel
 

Howdy vtwin bretheren. I just bought a 98 superhawk a few weeks ago. I love it except for the constant backfire on decel. Here is what i know about the bike. 13000 miles, twin brothers pipes. The guy I bought it from got it from the original owner. He claims he rode it but I believe it has sat for 2 years. i assume this from the license plate which says 2010, and the fact that he thought the bike ran fine. When I first got on her he had the choke on and it would not run without it. It also had no power. the first thing I thought was wow, this is a slow bike! however, it did accelerate smoothly, and there was no backfiring( probably due to the choke). I went ahead and bought it. the next day I started it up, filled it with 93 octane, and took her for a spin. I was consistantly opening the throttle all the way and after a about 15 minutes the bike came to life. Lots of power, smooth acceleration all the way to the red line. The only negative was the backfire on decel which is constant and loud. I did some research and decided on the pair ectomy. It was already half done. the reed keepers had been flipped but the pair was not removed. I removed it and capped the vacuum ports and linked the hoses where needed. also upon opening the airbox i found a chunk of what looked to be fiberglass house insulation on top of the air filter. it looks like it was put there on purpose! I removed it. cleaned the filter, put it back together ,and no change in performance or backfiring. I went ahead and checked for vacuum leaks and found none. Changed the plugs, but the old ones were actually in good condition. One odd thing I have noticed is that when I start the bike the tailpipe on the left side has hot exhaust and the other has cold exhaust. I find it odd because both pipes intersect and then split again underneath the bike. There appears to be more carbon build up on the left tailpipe than the right. When I throttle the bike above 3000 hot exhaust comes out of both pipes. Bike idles about 1200 rpm smoothly. I am thinking fuel to air mixture? Or possibly carb sync? Do you think I am on the right track or is there something i have missed? Thanks in advance!

welcome to the forum,congrats on the new hawk.
first,if you beleive the bike has sat,do a complete fluid change,oil,brake fluid,coolant.
check wheel bearings for play and grease all appropriate areas that require it.

second,check your choke cable for breaks or slacks.at the nut,where it goes into the carb,is known to break,its plastic.
theres a needle in there with a spring,if one or both is broken,its not gonna sit in its proper place when open or closed. (this happened on my bike,and made big difference in performance when i fixed it)

unless your motor is heavily built up,there is no need for 91 octane,87 is plenty for the bike.that what it calls for.it will run good on it.just go to a good reputable gas station and you will be good.i experimented on my bike with this,and it ran far better with 87 than 91,the most i have gone since than is 89 if there is no other option.

on your next full tank,put 3 1/2 oz of seafoam,it will help clean things up,but nothing is better than taking the carbs apart and cleaning thru everything,plus this will determine if you have a jet kit or not.
you will see too if the tps has been done.click the link,this is probably your best bet https://www.superhawkforum.com/forum...-set-up-24769/

what kind of filter was in the box,from what a ton of hawk owners has said is,the stock filter is best,very few people have made after market work well.

when you first start up the hawk,it seems normal for one side to get hot first than the other.nothing wrong there,just the way it is set up.
but of course,at full temp,if its still running cold or only warm on one side,theres a problem.
the carbon build up could be from not being synced to the choke cable being stuck on one side.

but overall,you are on right track,just try to do things in a certain order so you can figure out good and bad results.

Choke seems to operate properly, but will give it the once over. I have also changed out all of the fluids besides the brake fluid. its next. its dark, as was the clutch cable fluid. the filter appeared to be stock, I am switching that next. As far as the jetting , that is working its way up the list for probable culprits. I am mechanically capable, but no expert, and opening up the carbs is going to happen after I exhaust all other possibilities.... which it looks like I just about have. Thanks Saige

Be sure and run that Seafoam through there.

i have run 2 bottles of techron through it. Should I still do the seafoam?

i would,but dont put full bottle,it will kill everything in there,not in a good way.when you go to fill up tank,only put at the very most is 4oz.
there is a bottle from wally world you can get which is just as good and cheaper,i dont remember what its called.but does the same job as seafoam.

1) you pop on decel because you are running lean. You need to turn the pilot screws out 1/2 turn and adjust from there. It would be a good idea to sync the carbs as well.

2) the reason for one pipe being hot and one being not as hot is the length of tubing from each port and the easiest route for the air to travel. The hot air is pushed out of the easiest passage, while some has to exit through the other pipe travelling slower and allowing more time to cool. You will notice when its cold it will seem to have more back pressure on one pipe.

Aja ... I like your explanation for the exhaust. Makes sense. . Path of least resistance.
Vtrsurfer... most compelling argument as to why I should pull the carbs. So much for the easy way out. Thanks for the advice

Just noticed today that I have a small amount of gas dripping from the over flow port at the bottom on the bowl on the rear Carb. I guess that means sticking float or clogged jet. Could be backfiring because of a rich mixture ... I'm going to attempt a manual cleaning this weekend.

That should help, just take it slow and follow the previously linked thread: https://www.superhawkforum.com/forum...-set-up-24769/

Set your TPS to 500 OHM while your messing with your carbs, might help your timing on decelleration incase it's partially a timing backfire. But thats a whole different thread.

Question about seafoam and others like it.. I bought a bottle of gumout
This is the link. I think basicly the same..
GUMOUT® - Regane® High Mileage Fuel System Cleaner
Just curious. I bought this but before I used it I had other issues and tour down and cleaned my carbs.. bike is almost on the road.. should I put this stuff in still? says it cleans heads ect.. things are pretty black in there I just replaced the head (failed CCT)..
Thoughts?
Thanks

I am pretty sure that is formulated to clean injectors, but it should be fine for carbs

Hey aja, I was more concerned with the "cleaning of the motor" if you see the picture of the valves on teh link.. it has cleaned all the carbon.. Dad's concern (old school mechanic) is that if the valves have any pits in them that carbon has filled this will clean that and I will loose some compression and have oil leaking into the head "burning"
thoughts? ever heard of that? ever heard of any issues from this type of stuff?
over paranoid ;)

Thanks for the quick reply

aja is right. the decel popping is due to a lean mixture with the 2 Bros exhaust cans. Unburned fuel, due to misfiring goes in to the exhaust pipe, then lights off on the next exhaust pulse.

mixture screw adjustment will help. 1 size up on the pilot jet will also work. If it hesitates around 3500 rpm, you'll need to shim the needles in the carbs. Float level is also important. If the float needle is not seating properly, it's a good time to disassemble, clean and inspect.

the exhaust valves are probably pitted. It's unavoidable. I don't think you need to worry about it. It's better to get the carbon off the seats, so you have good heat transfer from the valve to the head.

Well the product never works as well as the manufacturer claims, so don't expect your valves to be that clean. If they are pitted, the carbon around the seat will be cleaned before the pits, as the product will have to works its way into each pit after cleaning the top layer of carbon, which I don't see it doing by just running it through the fuel. It would take some pretty good scrubbing to get it all, so I wouldn't worry about it.

Even if it did clean out any pits, loss of compression would only result from a damaged seat and not just a void on the valve. As long as they seat correctly it shouldn't matter.

If your goal is to clean the carbon build up then it is smarter and more effective to tear the engine down and do it manually. Those additives never work as well as you are led to believe, and excessive use may cause damage to fuel lines or other parts.

To be short, it is safe to use but don't expect a shiny new engine.