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Discussion Starter · #1 ·
Hi everyone!

I have bought a used and neglected ZR7-S a few years back as my first bike. I put some money into fixing it, and I believed my mechanic knew what he was doing at the time. But as time went on, i have noticed a few problems with my bike and started researching etc. Right now i've a brand new Vulcan S as my primary bike, but I still want to bring back to life my old ZR7-S. So i went to my storage, and my bike was runnning like a pile of ... .
Here are the list of problems:
  • The smell coming from exhaust is very strong and bad (smells like a burnt petrol)
  • Once i heat up the engine, revving makes bike to die slowly
  • Also, revving feels like one or two cilinders are not working (here's an example, video NOT MINE: Youtube Link)
  • Engine knocking
  • One spark plug was black, which i cleaned (spark plugs were changed to brand new before this happened)
I know a lot of ppl told me it must be a carb issue and stuff. So i took the carbs and started cleaning them myself. I don't believe my mechanic cleaned the carbs properly to be honest. I will clean every inch of the carbs and put them back to see if my problems went away. Before you ask - yes the manifolds were changed to brand new OEM ones when mechanic did the cleaning.

To add to all this, i am using a stock air box, which i will also clean and try to seal (the airbox smell like petrol and have some sticky resedue on the bottom). I was thinkning of using the carb pods, but since i have a lot of rainy days in my country, i will stick to the airbox.

Also, the video i mentioned, is not mine, but my bike has exactly the same problem as the one in the video! It sounds the same, which i think something's really bad with the engine (Youtube Link).

I hope you guys could help me out here and possibly point to the right direction, so i can join my old bike this season. Thanks!

Here's the picture of the bike which i first fell in love with:
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Welcome aboard. 🍻
If the bike revs freely above idle I suspect a good and proper carb cleaning will fix it rather than looking at the ignition. The idle circuits are the first to clog.
(BUT, it wouldn't hurt to check both ends of your spark plug wires. Check for corrosion and that they are firmly screwed onto their contacts. I had one wire not even touching the screw inside the boot yet somehow it was still firing though it wouldn't have for long.)

Another thing to check are the valves. Getting out of spec causes starting and running problems.
My money is on the carbs though. It wouldn't be the first time a mechanic didn't do a good enough job.
 

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Discussion Starter · #4 ·
Welcome aboard. 🍻
If the bike revs freely above idle I suspect a good and proper carb cleaning will fix it rather than looking at the ignition. The idle circuits are the first to clog.
(BUT, it wouldn't hurt to check both ends of your spark plug wires. Check for corrosion and that they are firmly screwed onto their contacts. I had one wire not even touching the screw inside the boot yet somehow it was still firing though it wouldn't have for long.)

Another thing to check are the valves. Getting out of spec causes starting and running problems.
My money is on the carbs though. It wouldn't be the first time a mechanic didn't do a good enough job.
Thanks man, i will definitely check the carbs. So far i see there are quite a few black pieces inside the carbs, prob rubber pieces from the old manifolds, which makes me believe the mechanic did the bad job indeed. After i clean carbs i am checking spark wires and boots. Ps i bought new spark plugs with new NGK boots and new ignition coils back then and the bike was running very good, it's just now it runs like a garbage... If interested, i will keep updates here, so maybe other ppl will find this useful.
 

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Discussion Starter · #6 · (Edited)
Here's an UPDATE #1

So i was taking apart the carbs and i've noticed a few things i wanna talk about. The obvious one is that my mechanic did a very bad job! I am dissapointed.

The inside of fuel tank looks clean to me, but other stuff around it - terrible! He left an old gasket there (all 4 of them actually), which has cracks and rust around it. It was very hard to remove it, cuz it was glued (factory i think). Here are some pics:
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Bought new gaskets. 4 bolts in total were busted so i have ordered a pack of new 4mm bolts - will replace them all! Also found a fuel filter inside the fuel line where it connects to the carb. Never thought i would find something there.. Its going to the trash bin, cuz i ordered a new fuel line and a bigger (supposedly better) fuel filter, which lets a decent amount of fuel in!
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Next thing was removing carburetors diaphragm. All 4 of them looks healthy, with a tiny bit of rust around it, which can be cleaned, so i wont need to replace em. One thing though, one of the diaphragm housing was completely black.. I wonder what does that mean? Is it bad? (The one circled in red)
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To conclude - i have started the complete washing process.. The jets and other tiny components are in a very healthy state. Cleaned them first anyway. Next update will be probably putting all crap together..

If any of you find something to add, please do, cuz it is my very first time taking apart carbs and cleaning em. I am learning as i go, ofc doing tons of research beforehand.

Thanks 🤞
 

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The factory doesn't use glue on the bowls. The rubber seals do all the sealing. Judging by your pic, your 'mechanic' didn't have replacement seals so just used some adhesive. I've never seen that type of in-hose fuel filter before - for sure it would be seriously limiting fuel flow.
 
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There is a tiny fuel filter in the line, before the T connecting to all carbs......that is factory, in addition to the ones on top of petcock inside the tank.

The black below the diaphragm is hard to explain. It may have been flooded at some point. That chamber is supposed to only be exposed to air from the air box.........also the enrichening plunger opens this chamber to the cylinder intake, to supply air (from air box) producing fast idle.......which mixes with the enrichening fuel from the starter jet circuit. But all this should be sucked by the engine vacuum and no fuel should go in there at all.


....can you clean the black????
 

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Discussion Starter · #9 ·
The factory doesn't use glue on the bowls. The rubber seals do all the sealing. Judging by your pic, your 'mechanic' didn't have replacement seals so just used some adhesive. I've never seen that type of in-hose fuel filter before - for sure it would be seriously limiting fuel flow.
Yeah i thought the same - it shouldn't be glued.
 

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Discussion Starter · #10 ·
There is a tiny fuel filter in the line, before the T connecting to all carbs......that is factory, in addition to the ones on top of petcock inside the tank.

The black below the diaphragm is hard to explain. It may have been flooded at some point. That chamber is supposed to only be exposed to air from the air box.........also the enrichening plunger opens this chamber to the cylinder intake, to supply air (from air box) producing fast idle.......which mixes with the enrichening fuel from the starter jet circuit. But all this should be sucked by the engine vacuum and no fuel should go in there at all.


....can you clean the black????
Yes you can. I cleaned it. I sprayed carb cleaner and wiped it off easily. Actually my 2nd chamber was lightly coated with that black resedue. I know that the owner before me didnt care about the bike at all, so maybe he flooded the engine.. anyways, i am happy that i took it apart and cleaning myself haha.
 

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Discussion Starter · #11 · (Edited)
The factory doesn't use glue on the bowls. The rubber seals do all the sealing. Judging by your pic, your 'mechanic' didn't have replacement seals so just used some adhesive. I've never seen that type of in-hose fuel filter before - for sure it would be seriously limiting fuel flow.
Thinking about it now - if "mechanic" was glueing it back, he couldve removed the rust, but he didnt bothered. I remember i left my bike for a week at his bike shop and the very last day he called me in the morning saying i can collect the bike at the end of the day, and later he sent me vids and pics with my carbs open. I thought that he was literally waiting the whole week just to fix my bike a few hrs before i came collect it. So it would make sense that he left all the crap around the carbs.. I was new to bikes and didnt had a clue. Never going back to him!
 

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Discussion Starter · #12 ·
There is a tiny fuel filter in the line, before the T connecting to all carbs......that is factory, in addition to the ones on top of petcock inside the tank.

The black below the diaphragm is hard to explain. It may have been flooded at some point. That chamber is supposed to only be exposed to air from the air box.........also the enrichening plunger opens this chamber to the cylinder intake, to supply air (from air box) producing fast idle.......which mixes with the enrichening fuel from the starter jet circuit. But all this should be sucked by the engine vacuum and no fuel should go in there at all.


....can you clean the black????
When you mentioned about the flooding, i remembered one odd thing. Every time i ride in the rain, if feels like only one cylinder is working - loss off power, insane and loud backfires and i can't literally ride a bike - it stalls. I think i will get one of those K&N filters and take the airbox out to see if there are any cracks or something that the water can come in. Maybe this could be a problem why the chamber is black?
 

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Discussion Starter · #13 · (Edited)
UPDATE #2

So this update is very short. Basically cleaned everything as much as i could without taking apart all the parts (splitting carbs). The insides are all clean. Every opening and every tiny hole was cleaned properly! Also, all the hard dirt and rust that was building up inside - scraped and cleaned as much as possible. The diaphragm chamber was cleaned as well as diaphragms. It looks good to me. Here are some pics:
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I know, outside of the carbs should be degreased and cleaned, but i don't have time for this at the moment. For now i need to get this bike working and bring to one mechanic some ppl recommended to ask him to run a check to see if it's worth rebuilding the bike. Specially the engine etc. (the engine has 68k miles on the clock).

So that's it for now, waiting new gaskets, bolts, fuel lines and a fuel filter, so i can close all the caps and get it installed back to my bike. Also, in the mean time i will be checking the airbox and installing an aftermarket K&N filter.
 

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I rebuild my carbs in one of those large rectangular foil pans that you buy at a dollar store. It's great for keeping parts from rolling off into oblivion. Plus you can scrunch up the sides of the foil pan to support the carbs.
Don't forget those tiny o-rings on the pilot screws. Easy to overlook.
Looking good. It's satisfying cleaning the carbs to get your engine running right.
 

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Discussion Starter · #15 ·
I rebuild my carbs in one of those large rectangular foil pans that you buy at a dollar store. It's great for keeping parts from rolling off into oblivion. Plus you can scrunch up the sides of the foil pan to support the carbs.
Don't forget those tiny o-rings on the pilot screws. Easy to overlook.
Looking good. It's satisfying cleaning the carbs to get your engine running right.
Yeah u right, next time i will buy a pan or a tray, now i had to improvise lol. Yes i took out the o rings. They were in a very good shape so i kept them.
 

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Yeah u right, next time i will buy a pan or a tray, now i had to improvise lol. Yes i took out the o rings. They were in a very good shape so i kept them.
Years ago I saved some pans left over from a party so I had them on hand or I may not have thought of it. Now I use them for everything with small parts, especially springs.
My pilot screw o rings were in good shape as well so I reused them (and also mainly because I forgot to order them when I ordered the other gaskets and float bowl o rings, which were probably able to be re-used).
At the same time I adjusted my valves, which were way out of spec, and that helped most with easy start up and running.
It would be a good time to replace the small o ring in your vacuum petcock.
 

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Discussion Starter · #17 ·
Years ago I saved some pans left over from a party so I had them on hand or I may not have thought of it. Now I use them for everything with small parts, especially springs.
My pilot screw o rings were in good shape as well so I reused them (and also mainly because I forgot to order them when I ordered the other gaskets and float bowl o rings, which were probably able to be re-used).
At the same time I adjusted my valves, which were way out of spec, and that helped most with easy start up and running.
It would be a good time to replace the small o ring in your vacuum petcock.
Nice one. Yeah i will change fuel petcock o rings when i will be cleaning the fuel tank.
 

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Discussion Starter · #18 ·
UPDATE #3

On this update i want to share some stuff i found taking apart the air filter housing. First of all, when i took out the airfilter housing i noticed the oil on the bottom of the airbox, i don't think it should look like that at all! Also, the rust.. That got me thinking is it worth restoring this bike (my plan was to make a scrambler / cafe racer)?
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Also i have checked the inside of the airbox. It looks very bad.. The problems:
  1. The hose that is supposedly to be the air intake, it drips with oil. I think it's supposed to do that because it connected to the engine top. One thing though is it supposed to be this short? Also, it looks like it was cut. This brings me to the next point.
  2. The roof of the airbox looks like the oil was literally spraying all over the box. Wouldn't that short hose blow some oil into the carbs?
  3. The last one i know why the bottom is oily, cuz it collects the oil to the collector, but the question would be - should i attach a short tube to at least block the oil spray to the carbs?
And here's a pic with the numbers to my questions:
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There should be no oil spray to the carbs as the crankcase vent tubes to the airbox are, or should be, on the outside of the airfilter, so that any oil spray/mist is caught by the air filter. Judging by the appearance of the bike, I'm guessing that the oil build up is a result of many years of neglect. Also, if there is excessive oil from the crankcase, then you might want to do a compression test as worn rings increase crankcase pressure causing more oil mist/vapour to be expelled.

Finally, the surface rust on the frame seems to be no biggie, but maybe you should strip the bike and get the frame sand/bead blasted and repainted. It really depends on what you want to do with the bike. If you want to make a cafe racer, then I would do that - if you just want a bush basher, I wouldn't bother.

In the meantime, you can just hit the rust with some rust converter to prevent further corrosion.
 
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Discussion Starter · #20 ·
There should be no oil spray to the carbs as the crankcase vent tubes to the airbox are, or should be, on the outside of the airfilter, so that any oil spray/mist is caught by the air filter. Judging by the appearance of the bike, I'm guessing that the oil build up is a result of many years of neglect. Also, if there is excessive oil from the crankcase, then you might want to do a compression test as worn rings increase crankcase pressure causing more oil mist/vapour to be expelled.

Finally, the surface rust on the frame seems to be no biggie, but maybe you should strip the bike and get the frame sand/bead blasted and repainted. It really depends on what you want to do with the bike. If you want to make a cafe racer, then I would do that - if you just want a bush basher, I wouldn't bother.

In the meantime, you can just hit the rust with some rust converter to prevent further corrosion.
Ah man, this is very useful!!! Thanks for an advise! Yes the bike was neglected by the previous owner.. He was riding with the broken front fork seals and rear shock absorber. Heck, even left there for a half a year literally on the sun wind and rain! What do you think if i pull the tube out, tape the airbox hole and leave the tube hanging outside for the time being? would that be a huge impact on a fresh air intake? (i wont be riding daily, i would just ride to the mechanic to see if he can do the compression test etc..)
 
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