need advice on engine hesitation/knocking sound
03-12-2010, 08:29 AM
#1
Bobby
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Location: Seattle
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need advice on engine hesitation/knocking sound
Hi there-
I have a problem with my bike that I want to fix but have no clue where to start. I have viewed this forum many times and have been impressed with all the info and now fortunately/unfortunately, I need some help myself if anyone is willing.
I have a 99 Superhawk I have had for 3 years and I have about 21K miles on it. My issue: When my bike is warmed up and I am on the road, my engine will randomly hesitate for a quick second and lose power briefly before kicking back in back to normal like nothing happened. It happens only in lower RPMs, usually during noraml acceleration between 2-5K RPMS (never at higher RPMS). I can both physically feel the hesitation and also hear a click/clack, knocking sound that lasts for about 1 second.
It sounds pretty nasty but does not seem to affect the power overall once I am past this hesitation when accelerating.
I believe it is a carb issue, maybe not, but wanted advice on that. Only mod I know about on the bike is a couple of slilp on Two Brother's exhaust pipes and the carbs may have been modified slightly but not positive. Where should I start to repair this problem? If I check the carbs, clean them, etc. is there a certain setting I need to be aware of? I have a mechanic buddy who is going to help me and actually knows what he is doing.
Thanks in advance for any suggestions!
Bobby
I have a problem with my bike that I want to fix but have no clue where to start. I have viewed this forum many times and have been impressed with all the info and now fortunately/unfortunately, I need some help myself if anyone is willing.
I have a 99 Superhawk I have had for 3 years and I have about 21K miles on it. My issue: When my bike is warmed up and I am on the road, my engine will randomly hesitate for a quick second and lose power briefly before kicking back in back to normal like nothing happened. It happens only in lower RPMs, usually during noraml acceleration between 2-5K RPMS (never at higher RPMS). I can both physically feel the hesitation and also hear a click/clack, knocking sound that lasts for about 1 second.
It sounds pretty nasty but does not seem to affect the power overall once I am past this hesitation when accelerating.
I believe it is a carb issue, maybe not, but wanted advice on that. Only mod I know about on the bike is a couple of slilp on Two Brother's exhaust pipes and the carbs may have been modified slightly but not positive. Where should I start to repair this problem? If I check the carbs, clean them, etc. is there a certain setting I need to be aware of? I have a mechanic buddy who is going to help me and actually knows what he is doing.
Thanks in advance for any suggestions!
Bobby
03-12-2010, 08:40 AM
#2
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the only thing I can think of that would cause the hesitation at the low rpm range is a jetting issue. so if the carbs have been rejetted from stock but not jetted correctly, that might be causing the hesitation you feel. as for the noise. hmmm. its only at low rpms too or is the bike too loud to hear it at high rpms? that sounds like a different problem than carbs.
03-12-2010, 08:48 AM
#3
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Superstock
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sounds like a "carb fart", it should sound like a metal clank/clackish.
look at shimming the needles .0400 or so and you should be alright. search for carb shim and you should be able to find some good write up's on this. also you may be a hair lean on the pilot... check your fuel screw settings and see what your setting is.
look at shimming the needles .0400 or so and you should be alright. search for carb shim and you should be able to find some good write up's on this. also you may be a hair lean on the pilot... check your fuel screw settings and see what your setting is.
03-12-2010, 08:52 AM
#5
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Which air filter is installed? I had same symptoms while trying to tune bike with an after market filter. Went back to Honda filter and it was fine. You might want to sync the carbs and find out how they actually are jetted as well.
03-12-2010, 10:11 AM
#6
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Here is a thead that my contain your problem: https://www.superhawkforum.com/forum...ad.php?t=11977
I had a simmiar problem and I ended up sending my bike to the show to have it rejetted and the carbs sync. This has solved the problem so far. (I should have just kept the stock air filter)
I had a simmiar problem and I ended up sending my bike to the show to have it rejetted and the carbs sync. This has solved the problem so far. (I should have just kept the stock air filter)
03-12-2010, 12:36 PM
#7
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I've recently noticed a problem basically identical to what you're saying, but I wouldn't describe a 'clunk.' Based on my 1980 Chevy 350, I'd be more inclined to say it's a carb backfire. I've heard it called 'coughing' before. It'll scare you really good when you go around a corner in town at low revs and it does it. I nearly fell in the middle of the street! I'm going through the carbs now just for a routine rebuild (hasn't happened in forever). I'll let you know what happens if this thread is still running.
03-14-2010, 10:21 AM
#8
Bobby
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Thanks a ton for all of the suggestions, really appreciate it. To fill in a little more detail, this problem has been happening for about a year. I live in Seattle and not too huge on riding in rain, so the bike does sit a lot. It does sound like a clacking noise and I do not believe it happens at higher RPMs because I would at least feel the hestiation even if I could not hear it. The hiccup is pronounced enough, even if it made no noise, to tell that it is happening. Anyways, I think it is the carbs and I think messing with the needles and adjusting properly plus seeing if the jetting is jacked up is going to be the key. Any suggestions further on how to adjust the carbs to the correct settings would be huge. I will check the fuel screw and the link below as well....Thanks again...this would have already cost me around $500 at the shop I used to take it too!
03-14-2010, 05:44 PM
#9
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SuperSport
Join Date: Feb 2010
Location: NY State
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If it used to run ok, and you have not changed anything like pipes or air-filter, and now it doesn't run well, you may need to just clean the carbs. They do get gunked up if old gas sits in them for an extended period of time.
JB
JB
05-11-2010, 10:57 AM
#12
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mine does something similar but I can only feel it when I have ridden at higher rpms and stop at a traffic light and the engine idling or when starting the engine. This morning it knocked once, a fraction of the second after I pressed the starter button. Then it knocked once or twice only (at traffic lights) for the whole day. Could it be a starter/bendix issue? My car knocks the same way when I turn the ignition key.....
05-11-2010, 02:15 PM
#13
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"carb fart". Jetting issues. I had them with the stock pipes debaffled and now i have to shim the stock needles really bad because of devil high mounts just being installed. They sound awesome but now i have a flat spot in the power range from jetting problems. Eh. I like working on it. Try that avenue before sinking any money into it.
05-11-2010, 03:04 PM
#14
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if you must get into the carbs, you may as well do it right, especially since it costs nothing but time and little patience. Use a little ratchet strap to hold up the front of the tank so you don't have to remove it. Just like opening your car hood and there are pics of how it's done on this forum. check your air filter and replace if dirty. Set your TPS to 500 ohms. Pull the tops off the carbs and see if the needles have grooves. If they do, most likely someone jetted it. Tell us which groove it's in. If it's smooth, you'll need to put a washer .40 thickness under it before replacing. Turn out your air mixture screw with a tweezer or similar tool, slot it with a dremel so that it can be adjusted with a screwdriver and set at 2.25 turns out. Remove PAIR system. These adjustments will give you a baseline so you can assess from there. Finally, make a carb tool for from fish tank tubing and sync carbs. These adjustments are those most commonly done to SHs with aftermarket pipes or gutted mufflers and usually alleviate hesitation, missing, backfiring, other.
Welcome aboard Apjohns, Type T, and Bobby
Welcome aboard Apjohns, Type T, and Bobby
05-11-2010, 04:10 PM
#15
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I had a similar issue that isn't addressed all that much...probably since it doesn't happen all that often.
Check the fuel petcock diaphragm...located inside the petcock.
Its pretty easy to access. You just have to take the tank off and remove and open the petcock and you will find the diaphragm inside.
Mine had a 1/2 tear in it, and that's what caused mine to hickup/backfire/misfire...or at least thats how it felt.
Check the fuel petcock diaphragm...located inside the petcock.
Its pretty easy to access. You just have to take the tank off and remove and open the petcock and you will find the diaphragm inside.
Mine had a 1/2 tear in it, and that's what caused mine to hickup/backfire/misfire...or at least thats how it felt.
06-14-2010, 04:37 PM
#16
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After searching/and blaming the rectifier, i now think this is my problem also. I have a miss - clunk between 1500 - 2500 rpm on constant speed. my issue is that a regularly ride at 2000rpm for 20 mins at a time, due to speed limits. I have just had the carbys balanced and A/F ratio checked, and it is worse than ever. I'll get back to you later.
08-06-2010, 10:33 AM
#17
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My Hawk is also acting very similarly and I don't have any idea how to solve the problem. It is happening only between 3000 and 4000 rpm in all gears. Actually it is not noticeable in the first gear probably because it takes only a fraction of a second between 3 and 4k rpm. It is more noticeable when I try to accelerate hard. For example if I am in the third gear at 3000rpm and open a full throttle it is very noticeable that something is wrong. It sounds like krrr...krr..krr..kr, accompanied with a loss of power. After 4000 bike is performing perfectly and runs like a bullit. Two mechanics tried to solve the problem and they did nothing. They cleaned carburetors, synchronized them, played with needles and jets.... It is realy frustrating and I don't know wath to do. Please help!!!!! 
08-06-2010, 10:50 AM
#18
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My Hawk is also acting very similarly and I don't have any idea how to solve the problem. It is happening only between 3000 and 4000 rpm in all gears. Actually it is not noticeable in the first gear probably because it takes only a fraction of a second between 3 and 4k rpm. It is more noticeable when I try to accelerate hard. For example if I am in the third gear at 3000rpm and open a full throttle it is very noticeable that something is wrong. It sounds like krrr...krr..krr..kr, accompanied with a loss of power. After 4000 bike is performing perfectly and runs like a bullit. Two mechanics tried to solve the problem and they did nothing. They cleaned carburetors, synchronized them, played with needles and jets.... It is realy frustrating and I don't know wath to do. Please help!!!!!
Is there any thread that explains how to do it?
08-06-2010, 04:59 PM
#20
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yeah, plenty of info, some with pics. pretty easy once you understand how to do it. I made the mistake of turning mine the wrong direction, but turned it so far it worked flawlessly for years before I discovered through helping another forum member do his.haha. Make yourself a $5.00 sync tool, buy the extra carb fitting for the quick sync and you'll be off to a good start.
Oh yeah and welcome to the forum.
Oh yeah and welcome to the forum.
08-06-2010, 06:08 PM
#21
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I've had this (similar) problem with my '03, since I got it at 5000 miles. It now has 8000 miles, but it has always suffered from a "clack/slap" under the gas tank (carbs) which seem to occur at 3500 rpm. -with Jardine Hi-pipes.
I've seen many variations on this issue, and what it all seems to boil down to is that when you have some of the largest carbs ever put on a bike, they will require fine tuning.
I've seen many variations on this issue, and what it all seems to boil down to is that when you have some of the largest carbs ever put on a bike, they will require fine tuning.
08-06-2010, 08:37 PM
#22
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There's several things involving the carbs that should be done when you alter the pipes if you want a smooth running hawk. If you're interested there is much info at your fingertips and many of us willing to help you along the way.
08-07-2010, 05:49 AM
#23
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So I used to have this problem as of a few months ago on a COLD bike. Idle was a little weak as well.
I ended up doing a few things all at once because they were all in the same area and I thought the bike needed a tune up anywase.
New spark plugs
carb sync (it was already close enough that I didn't adjust anything but now I have the vacuum lines run out so I can adjust without taking bike apart)
new air filter
new R/R and associated connector (reason the bike was down for maintenance)
manual cam chain tensioners
new battery (R/R destruction)
My air filter was TERRIBLY dirty for what I was expecting and I was getting what I believe was cam chain slap around 3k rpm.
If your bike hasn't had a tune up yet with some of the parts above it may be worth it to just get them replaced and see what happens. After I did all this my bike runs MUCH better below 3k RPM. It doesn't act like it's running too low an RPM unless I'm around 1500-1750 RPM or lower, but I hardly run it down there anywase because the power pulses are so separated that it shakes the bike about.
As many others have mentinoed, could be a carb issue. I always hated draining coolant to get to the carbs so these may be first steps. Don't want to tune the carbs for old spark plugs and a dirty air filter anywase right?
I ended up doing a few things all at once because they were all in the same area and I thought the bike needed a tune up anywase.
New spark plugs
carb sync (it was already close enough that I didn't adjust anything but now I have the vacuum lines run out so I can adjust without taking bike apart)
new air filter
new R/R and associated connector (reason the bike was down for maintenance)
manual cam chain tensioners
new battery (R/R destruction)
My air filter was TERRIBLY dirty for what I was expecting and I was getting what I believe was cam chain slap around 3k rpm.
If your bike hasn't had a tune up yet with some of the parts above it may be worth it to just get them replaced and see what happens. After I did all this my bike runs MUCH better below 3k RPM. It doesn't act like it's running too low an RPM unless I'm around 1500-1750 RPM or lower, but I hardly run it down there anywase because the power pulses are so separated that it shakes the bike about.
As many others have mentinoed, could be a carb issue. I always hated draining coolant to get to the carbs so these may be first steps. Don't want to tune the carbs for old spark plugs and a dirty air filter anywase right?
01-19-2011, 01:44 PM
#26
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jets shimmed .045"............in your signature? what's that mean?
Last edited by nath981; 01-19-2011 at 02:00 PM.
01-19-2011, 03:10 PM
#28
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01-19-2011, 04:40 PM
#29
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set the tps @500+-, shim needles to .040in, dremel and remove air mix screw and set to 2.25 turns out, sync carbs, pull vac lines out from between carbs and let them hang, desmog, bafflectomy(partial)or aftermarket pipes, k&n or not, and there will be no more burping, farting, coughing or other similar symptoms. Mine was doing this ****, so I can speak from experience.
If your bike has 20K or more set the valves and do the CCT mod while your in there.
If your bike has 20K or more set the valves and do the CCT mod while your in there.
01-19-2011, 07:16 PM
#30
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i am going to desmog it when my airfilter comes in, i think the bike has a jet kit in it but non the less, i find were i live and ride because of altitude, it is right at the 5kft range. i might leave the jetting alone. in my other bikes with CV carbs i richened them up and they run great till pulling a hill on the parkway at 5kft= so i have put my others back to stock and my gas millage is good and i don't have trouble loading up on hills. the exhaust pipes have nice dry soot in them. so i may be rich enough??
