1988 CBR 1000f backfiring SOS
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1988 CBR 1000f backfiring SOS
I just got my first bike not long ago, '88 1000F. The bike had been sitting many years prior to my ownership, so, I took it straight to a mechanic to go through it and get it running. Mech cleaned the tank, rebuilt the carbs, installed new spark plugs, changed oil and filter, new throttle assembly, etc. He said he did not sync the carbs after the rebuild. The bike appears all original with the exception of a Kerker 4 to 1 exhaust. Just got the bike home today. When I went to pick the bike up I had the mech start it. Initially the bike wouldn't start even with choke on. He gave it a squirt of starting fluid to the air cleaner and it fired up, backfiring out exhaust at idle and part throttle in neutral. idle was steady, not up and down.Spark plugs are reading black. After running for about 1 minute we shut it off, the bike fired right back up on its own and the backfiring at idle was gone but it would still backfire out exhaust with throttle in neutral. Would the carbs being out of sync cause this issue or any ideas? I also noticed where the muffler meets the header there is no clamp there. Thank you.
Last edited by NEKansas; Dec 30, 2022 at 08:18 PM.
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I’m going to go out on a limb and say the mechanic isn’t well versed in carbs.
if the carbs are thoroughly cleaned and the most basic settings are correct, the bike should start. It won’t run great but it should start.
if the carbs are thoroughly cleaned and the most basic settings are correct, the bike should start. It won’t run great but it should start.
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...
I went to pick the bike up I had the mech start it. Initially the bike wouldn't start even with choke on. He gave it a squirt of starting fluid to the air cleaner and it fired up, backfiring out exhaust at idle and part throttle in neutral. idle was steady, not up and down.Spark plugs are reading black. After running for about 1 minute we shut it off, the bike fired right back up on its own and the backfiring at idle was gone but it would still backfire out exhaust with throttle in neutral. Would the carbs being out of sync cause this issue or any ideas? I also noticed where the muffler meets the header there is no clamp there. Thank you.
I went to pick the bike up I had the mech start it. Initially the bike wouldn't start even with choke on. He gave it a squirt of starting fluid to the air cleaner and it fired up, backfiring out exhaust at idle and part throttle in neutral. idle was steady, not up and down.Spark plugs are reading black. After running for about 1 minute we shut it off, the bike fired right back up on its own and the backfiring at idle was gone but it would still backfire out exhaust with throttle in neutral. Would the carbs being out of sync cause this issue or any ideas? I also noticed where the muffler meets the header there is no clamp there. Thank you.
https://customcarbservices.com
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Hello. Quick update haven’t messed with the bike much since it came back from mech. I should’ve added to the original post: ether is needed for initial start. Once started it runs on its own off of fuel in tank. when I picked the bike up initially and he got it started with ether he then went to (if I remember correctly) left (when sitting on bike) side of engine and started turning a screw that is on the outside of the carb..I remember the idle changing when he did it. I did some more research and I believe that would be the idle speed screw. From another thread: “The idle **** adjusts the throttle butterfly opening of all four carburetors at the same time.
The idle **** must be set to close the throttle butterflies all the way so engine vacuum will be maximized for starting.
The idle mixture screws should be set to 2.0 to 2.5 turns out.
If you set them too far out the engine will run rough.
The typical home tuner then turns the idle speed **** clockwise and this makes the engine idle faster, but then the engine gets fuel from the three idle bypass ports and the mixture is far too rich, and the engine won't idle down immediately after the throttle is blipped.
Turning the idle mixture **** too far clockwise interferes with the operation of the cold starting enrichener system.”
Is it possible this screw could be too far clockwise and be the cause of my no start even with choke on? First start almost never happenes until hit with ether. Once warm starts on its own if I remember correctly (been a while).
edit: I understand the carbs will still need synced. Just curious when provided with this new info do you guys think that wrong adjustment could be my choke on no start issue instead of the initial thought of choke circuit clogged? Thanks
The idle **** must be set to close the throttle butterflies all the way so engine vacuum will be maximized for starting.
The idle mixture screws should be set to 2.0 to 2.5 turns out.
If you set them too far out the engine will run rough.
The typical home tuner then turns the idle speed **** clockwise and this makes the engine idle faster, but then the engine gets fuel from the three idle bypass ports and the mixture is far too rich, and the engine won't idle down immediately after the throttle is blipped.
Turning the idle mixture **** too far clockwise interferes with the operation of the cold starting enrichener system.”
Is it possible this screw could be too far clockwise and be the cause of my no start even with choke on? First start almost never happenes until hit with ether. Once warm starts on its own if I remember correctly (been a while).
edit: I understand the carbs will still need synced. Just curious when provided with this new info do you guys think that wrong adjustment could be my choke on no start issue instead of the initial thought of choke circuit clogged? Thanks
Last edited by NEKansas; Jun 30, 2023 at 10:40 AM.
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Yes - if the idle screw is set too far open, the bike will absolutely not start, but the same is true if it's too far closed. There's a small window of correct setting to ensure a reliable cold start.
It's easy to find that setting if you can get the bike started - just start it up, let it warm up so it runs with the choke closed, and set the idle to about 1000 rpm. Done.
It's easy to find that setting if you can get the bike started - just start it up, let it warm up so it runs with the choke closed, and set the idle to about 1000 rpm. Done.
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On my f3, the idle adjustment screw can be turn a little over eleven full turns counterclockwise before it comes out. This is with a starting from a fully seated (clockwise) position.
Be very, very careful not to screw it counterclockwise too many times. There is no stop on the screw and it you turn it too many times, it will come free and you will be looking for the washer and tension spring, which are incredibly hard to find.
my suggestion would be to fully seat it, then back it out 5 or 6 complete turns and try and start it from there. Back it out a half turn two or three more time until it starts. Let it warm up and adjust it to the appropriate rpm. Record how many turns it took. That will be the baseline for when you sync the carbs
Be very, very careful not to screw it counterclockwise too many times. There is no stop on the screw and it you turn it too many times, it will come free and you will be looking for the washer and tension spring, which are incredibly hard to find.
my suggestion would be to fully seat it, then back it out 5 or 6 complete turns and try and start it from there. Back it out a half turn two or three more time until it starts. Let it warm up and adjust it to the appropriate rpm. Record how many turns it took. That will be the baseline for when you sync the carbs
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Rather than continually messing with ether and idle-speed settings, why not just get carbs restored properly to factory OEM condition? It ran perfectly fine when leaving showroom floor. It will again when carbs are restored back to factory-fresh clean condition.
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**very long post** I tried to lay everything out that I can recall about my experience with this bike starting from the very beginning (down below) to give everyone the full picture.
let me start by saying I appreciate the input everyone. As always very helpful.
As far as the why not get the carbs refreshed comment..I have already paid a decent amount to have that done once, by a guy that supposedly had prior experience of working on bikes at a Honda dealer for close to 10 yrs.
Once I received the rebuild kit I dropped it off to him. Almost exactly 8 hrs later I get a video from him of the bike running in neutral; a few seconds at idle and a few revs (when video started the bike was already running, keep in mind this is prior to me seeing the bike run in person (where he had to use ether on initial start.) He claimed it was running like a top when he sent the video. I didn’t think it sounded quite right running at certain points in the video but I chalked it up to bad sound quality because it was filmed in a small garage. So up to that point I thought everything was operating as it should. He says he has to button the bike back up. I don’t think anything of it, and acknowledge him.
Quite a few days go by, I don’t hear anything from him, then he says to get in contact so I do. He starts rambling about may be a good idea to part the bike out. I ask why’s that? He says rusty chain, sprocket, etc. While they do have surface rust it’s not worth junking the bike for..I’d gladly replace them. I tell him please continue working on it like we initially discussed. He agrees.
again a day or 2 goes by and I don’t hear from him. I ask if I can pick up my bike. He then says he is having an issue of the carbs pouring fuel from the float bowls but otherwise runs great. He says the cause of this is something to do with something in the fuel pump (I don’t recall what exactly) failing and that it is a common issue for these bikes.
so now I do some research and find that some people bypass the fuel pump on these specific bikes and gravity feed the carbs with no rideability issues (as long as gas tank is plenty full and you turn fuel off when done riding to keep from washing out cylinders w gas) so to keep from putting more $$ into bike than it is worth (think- purchase price of bike, parts for carbs, labor, etc and now a fuel pump R&R on top) I tell him to bypass pump and gravity feed carbs please.
He does bypass & says that fixed the pouring of gas from the bowls & bike is ready for pick up. He never mentions ANY issue whatsoever with the way the bike runs at any time..I go and listen to it run in person and to pick the bike up..thats when now “suddenly” it will not start on its own with choke..he gives it some throttle, choke still on, no start, tries it with no choke, no throttle. Tries to start it with no choke, some throttle.. no matter what it just cranks. He hits it with a spray of ether, and bike starts. Pretty soon (within 10 sec or so of running) it starts backfiring out exhaust. He now starts messing with the screw I described in my last post. Popping at exhaust gets better once it runs for maybe 10-15 more secs. I shut bike off for roughly 30 sec - 1 min while we discuss some things. I start bike (no ether) it fires up and runs. Backfiring is back just as before. I shut bike off, load it up & leave.
Now I’m home, it’s next day and I unloaded bike. Frustrated after all I had done and still have a same as non functioning bike- I store it and don’t touch it up until a month or so ago. (During that time bike sat probably 60 days with ethanol free gas) I go to start it for first time since bringing it home and again it needs a gulp of ether to fire. Once bike is running but still cold to touch I move the choke lever around, it does change RPM but not much, even after warmed up.
if I recall correctly the bike will idle on its own briefly, once warm, with choke off and no throttle then it will die. It will start back up again.
Ever since the day I picked up the bike from mech it has had these issues I described.
keep in mind I bought this bike from an individual in 2022 and the tag has a date of 20 some yrs ago…never heard it run until the carbs rebuild.
I’m mechanically inclined but wrenching on motorcycles is unfamiliar territory for me…IF it comes to my carbs needing torn apart again, I may attempt to do the cleaning / rebuild of the carbs myself with the fact serv manual. I have rebuilt automotive carbs before & a few different ATV carbs, but again never four carbs on one bike.
The guy who rebuilt the carbs for me said he used an ultra sonic cleaner when he did the job so I’m hoping the different circuits of the carbs are clean from the rebuild and my issues with how it runs is an error of an adjustment or two out of whack causing the choke to not work properly and or my other issue of backfiring out of exhaust. (Though doubtful) after the run around I experienced from Mech. I understand that backfiring out exhaust could be from a rich condition. I have not read spark plugs yet. Mech installed new plugs while waiting for carbs kit.
Another issue is bad throttle response, it breaks up when rpms are rising and then it delays / hangs up when you let off the throttle & rpms are dropping. All my operations of the bike & use of choke, throttle, etc have been in neutral. I have not tried to put the bike in gear and ride to see how it acts because of the issues mentioned in my posts.
From what I understand the throttle response issues could be from plugged jets, etc OR the carbs out of sync. Am I wrong to assume any bike Mech worth their salt would of correctly synced the carbs via bench sync & vac sync after a rebuild of the carbs. Mech claimed when he worked at the dealer they rarely vac synced carbs after a rebuild, just a bench sync. Under any scenario is that procedure normal? Especially if a bike has sat for the last 15+ yrs like mine?
Engine itself sounds good as in no knocks, ticking, rattling, smoke, etc. Anyone have advice on anything to double check before pulling carbs again?
any input is welcome, thanks.
let me start by saying I appreciate the input everyone. As always very helpful.
As far as the why not get the carbs refreshed comment..I have already paid a decent amount to have that done once, by a guy that supposedly had prior experience of working on bikes at a Honda dealer for close to 10 yrs.
Once I received the rebuild kit I dropped it off to him. Almost exactly 8 hrs later I get a video from him of the bike running in neutral; a few seconds at idle and a few revs (when video started the bike was already running, keep in mind this is prior to me seeing the bike run in person (where he had to use ether on initial start.) He claimed it was running like a top when he sent the video. I didn’t think it sounded quite right running at certain points in the video but I chalked it up to bad sound quality because it was filmed in a small garage. So up to that point I thought everything was operating as it should. He says he has to button the bike back up. I don’t think anything of it, and acknowledge him.
Quite a few days go by, I don’t hear anything from him, then he says to get in contact so I do. He starts rambling about may be a good idea to part the bike out. I ask why’s that? He says rusty chain, sprocket, etc. While they do have surface rust it’s not worth junking the bike for..I’d gladly replace them. I tell him please continue working on it like we initially discussed. He agrees.
again a day or 2 goes by and I don’t hear from him. I ask if I can pick up my bike. He then says he is having an issue of the carbs pouring fuel from the float bowls but otherwise runs great. He says the cause of this is something to do with something in the fuel pump (I don’t recall what exactly) failing and that it is a common issue for these bikes.
so now I do some research and find that some people bypass the fuel pump on these specific bikes and gravity feed the carbs with no rideability issues (as long as gas tank is plenty full and you turn fuel off when done riding to keep from washing out cylinders w gas) so to keep from putting more $$ into bike than it is worth (think- purchase price of bike, parts for carbs, labor, etc and now a fuel pump R&R on top) I tell him to bypass pump and gravity feed carbs please.
He does bypass & says that fixed the pouring of gas from the bowls & bike is ready for pick up. He never mentions ANY issue whatsoever with the way the bike runs at any time..I go and listen to it run in person and to pick the bike up..thats when now “suddenly” it will not start on its own with choke..he gives it some throttle, choke still on, no start, tries it with no choke, no throttle. Tries to start it with no choke, some throttle.. no matter what it just cranks. He hits it with a spray of ether, and bike starts. Pretty soon (within 10 sec or so of running) it starts backfiring out exhaust. He now starts messing with the screw I described in my last post. Popping at exhaust gets better once it runs for maybe 10-15 more secs. I shut bike off for roughly 30 sec - 1 min while we discuss some things. I start bike (no ether) it fires up and runs. Backfiring is back just as before. I shut bike off, load it up & leave.
Now I’m home, it’s next day and I unloaded bike. Frustrated after all I had done and still have a same as non functioning bike- I store it and don’t touch it up until a month or so ago. (During that time bike sat probably 60 days with ethanol free gas) I go to start it for first time since bringing it home and again it needs a gulp of ether to fire. Once bike is running but still cold to touch I move the choke lever around, it does change RPM but not much, even after warmed up.
if I recall correctly the bike will idle on its own briefly, once warm, with choke off and no throttle then it will die. It will start back up again.
Ever since the day I picked up the bike from mech it has had these issues I described.
keep in mind I bought this bike from an individual in 2022 and the tag has a date of 20 some yrs ago…never heard it run until the carbs rebuild.
I’m mechanically inclined but wrenching on motorcycles is unfamiliar territory for me…IF it comes to my carbs needing torn apart again, I may attempt to do the cleaning / rebuild of the carbs myself with the fact serv manual. I have rebuilt automotive carbs before & a few different ATV carbs, but again never four carbs on one bike.
The guy who rebuilt the carbs for me said he used an ultra sonic cleaner when he did the job so I’m hoping the different circuits of the carbs are clean from the rebuild and my issues with how it runs is an error of an adjustment or two out of whack causing the choke to not work properly and or my other issue of backfiring out of exhaust. (Though doubtful) after the run around I experienced from Mech. I understand that backfiring out exhaust could be from a rich condition. I have not read spark plugs yet. Mech installed new plugs while waiting for carbs kit.
Another issue is bad throttle response, it breaks up when rpms are rising and then it delays / hangs up when you let off the throttle & rpms are dropping. All my operations of the bike & use of choke, throttle, etc have been in neutral. I have not tried to put the bike in gear and ride to see how it acts because of the issues mentioned in my posts.
From what I understand the throttle response issues could be from plugged jets, etc OR the carbs out of sync. Am I wrong to assume any bike Mech worth their salt would of correctly synced the carbs via bench sync & vac sync after a rebuild of the carbs. Mech claimed when he worked at the dealer they rarely vac synced carbs after a rebuild, just a bench sync. Under any scenario is that procedure normal? Especially if a bike has sat for the last 15+ yrs like mine?
Engine itself sounds good as in no knocks, ticking, rattling, smoke, etc. Anyone have advice on anything to double check before pulling carbs again?
any input is welcome, thanks.
Last edited by NEKansas; Jul 1, 2023 at 03:03 AM.
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Joined: May 2011
Posts: 1,988
Likes: 439
From: Mesa, AZ
You messed up once by sending it to idiot mechanic who did all sorts of things wrong.
You are messing up again trying to fix it yourself and will actually make it worse.
It takes decades of experience and tonne of specialised equipment to properly restore carbs. It will take you A LONG time to learn this trade,decades or more, and destroy many carbs in process of learning how to restore carbs back to factory-fresh condition. Will you attempt brain-surgery on yourself 1st time around, trying to learn as you go?
Send it to someone with actual experience, skills and equipment to do job right 1st time around.
https://www.ninjette.org/forums/showthread.php?t=369351 - ColoradoCal
https://www.ninjette.org/forums/showthread.php?t=367339 - Detrailers <-- this guy is actually mechanic with moto-shop
https://www.ninjette.org/forums/showthread.php?t=365823 - ChicagoBob
https://www.ninjette.org/forums/showthread.php?t=354327 - clakmurrick
https://www.ninjette.org/forums/showthread.php?t=352293 - notunderweight
https://www.ninjette.org/forums/showthread.php?t=366273 - KurtF
https://www.ninjette.org/forums/show...13#post1225613 - MakoMoto
https://www.ninjette.org/forums/show...8&postcount=48 - aaronbtxnc
https://www.ninjette.org/forums/show...9&postcount=56 - 22R88
https://www.ninjette.org/forums/show...&postcount=100 - DevinWolfe
https://www.ninjette.org/forums/show...&postcount=102 - atomicrider266
https://www.ninjette.org/forums/show...&postcount=107 - FSTASFCK
https://www.ninjette.org/forums/show...&postcount=132 - roundhouse
https://www.ninjette.org/forums/show...&postcount=134 - Ghostt
https://www.ninjette.org/forums/show...&postcount=150 - inconer
You are messing up again trying to fix it yourself and will actually make it worse.
It takes decades of experience and tonne of specialised equipment to properly restore carbs. It will take you A LONG time to learn this trade,decades or more, and destroy many carbs in process of learning how to restore carbs back to factory-fresh condition. Will you attempt brain-surgery on yourself 1st time around, trying to learn as you go?
Send it to someone with actual experience, skills and equipment to do job right 1st time around.
https://www.ninjette.org/forums/showthread.php?t=369351 - ColoradoCal
https://www.ninjette.org/forums/showthread.php?t=367339 - Detrailers <-- this guy is actually mechanic with moto-shop
https://www.ninjette.org/forums/showthread.php?t=365823 - ChicagoBob
https://www.ninjette.org/forums/showthread.php?t=354327 - clakmurrick
https://www.ninjette.org/forums/showthread.php?t=352293 - notunderweight
https://www.ninjette.org/forums/showthread.php?t=366273 - KurtF
https://www.ninjette.org/forums/show...13#post1225613 - MakoMoto
https://www.ninjette.org/forums/show...8&postcount=48 - aaronbtxnc
https://www.ninjette.org/forums/show...9&postcount=56 - 22R88
https://www.ninjette.org/forums/show...&postcount=100 - DevinWolfe
https://www.ninjette.org/forums/show...&postcount=102 - atomicrider266
https://www.ninjette.org/forums/show...&postcount=107 - FSTASFCK
https://www.ninjette.org/forums/show...&postcount=132 - roundhouse
https://www.ninjette.org/forums/show...&postcount=134 - Ghostt
https://www.ninjette.org/forums/show...&postcount=150 - inconer
Last edited by dannoxyz; Jul 1, 2023 at 12:54 PM.
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From: Alabama
@dannoxyz and I are in similar, but different camps.
I think you should chock the mechanic incident as a lesson learned. From what you write, it's painfully apparent he either didn't have the adequate knowledge or desire to do the work properly. My guess is both. Mike Tyson had a great quote. "Everyone has a plan until they get punched in the mouth." My guess is that the mechanic got punched in the mouth by the job not being as simple as he thought and gave up.
Where Dan and I have different thoughts is that I think you can do the work yourself, given some caveats. One, you have to be somewhat mechanically inclined. Two, you have to be able to follow the advice of others and not get offended. Three, you need to be willing to lay down $$ on tools, equipment, and supplies you probably won't have much use for otherwise. Lastly, you have to like details and tedium. There is absolutely no "good enough" when it comes to these carbs. You will swear you have them spotless, then another round of cleaning will yield more crud. You can't get tired of it or frustrated. If any of that isn't your cup of tea, then I fully agree with Dan, send them off to someone who understands them and can do a proper job. There is also the fact that as time marches on, it's getting harder to find local mechanics who know how to work on multi-carb engines. It is definitely becoming more of a specialized niche.
Regardless if you tackle them yourself or send them off, when it comes to syncing, they must be on the bike. If anyone tells you otherwise, run.
I think you should chock the mechanic incident as a lesson learned. From what you write, it's painfully apparent he either didn't have the adequate knowledge or desire to do the work properly. My guess is both. Mike Tyson had a great quote. "Everyone has a plan until they get punched in the mouth." My guess is that the mechanic got punched in the mouth by the job not being as simple as he thought and gave up.
Where Dan and I have different thoughts is that I think you can do the work yourself, given some caveats. One, you have to be somewhat mechanically inclined. Two, you have to be able to follow the advice of others and not get offended. Three, you need to be willing to lay down $$ on tools, equipment, and supplies you probably won't have much use for otherwise. Lastly, you have to like details and tedium. There is absolutely no "good enough" when it comes to these carbs. You will swear you have them spotless, then another round of cleaning will yield more crud. You can't get tired of it or frustrated. If any of that isn't your cup of tea, then I fully agree with Dan, send them off to someone who understands them and can do a proper job. There is also the fact that as time marches on, it's getting harder to find local mechanics who know how to work on multi-carb engines. It is definitely becoming more of a specialized niche.
Regardless if you tackle them yourself or send them off, when it comes to syncing, they must be on the bike. If anyone tells you otherwise, run.
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