Custom Fighters - Custom Streetfighter Motorcycle Forum banner
1 - 11 of 11 Posts

·
Buy all my shit!
Joined
·
6,042 Posts
Discussion Starter · #1 ·
Ive been workin on this guys show bike for a couple days. He said it was just a simple carb problem.. the bike will run, idle, and rev no problem while its in neutral OR if the clutch is pulled in while its in gear. As soon as you take off and get it up to 1/4 throttle it dog's and wants to die right out. So I figured Id just clean the jets out figuring it's just a primary jet problem and he'd be on his way,.. NOT

3 days later Ive found out that..

1. Someone tried to put a stage 1 jet kit in it and did a half a$$ job
2. The fuel pump was clogged
3. It was filled with REAL BAD gas
4. All 4 spark plugs were hand tight
5. Also found some faulty wiring at the start switch cluster (which I fixed pretty quick)

What Ive done..

1. I set to float height back to stock which is 13mm.. it was set at 9mm when I opened the carbs up.
2. Cleaned the carbs TOTALLY
3. Changed the jetting back to stock
4. Checked and tightened the plugs (great spark)
5. Cleaned out the fuel pump and filters

The only engine mod it has is a Muzzy slip on, its still running the air box and a k&n filter.

I was thinkin it could be something more like a Voltage regulator but wasnt quite sure.. I can rev it in neutral and theres no problem, I can run it in any gear and rev it while its on a race stand and it's perfect.

As soon as I put a load on it and drive away it dog's right at 1/4 throttle..
 

·
Senior Member
Joined
·
890 Posts
Has it still got all the Ram Air stuff? Sounds like the carb pressure balance pipe might be blocked / disconnected.
 

·
Fresh outta Fighter camp!
Joined
·
357 Posts
Seems like definite fuel issue. It cant be spark. Spark is not affected by engine load, only rpm. I would be looking to the intermediate circuits on the carbs. If it idles fine, but wont transition smoothly to the high speed circuit on the carbs, intermediate is buggered some how. Sounds like the emulsion tubes (round pipe going from main jet, with metering holes, going to carb venturi-throat) are clogged.

Another thing to check too, if these carbs were messed with by an amateur; its possible you could have an internal air leak in the carbs. Buggered threads where a jet goes, or a seal around a mixture screw.

Compression test yet?
 

·
Buy all my shit!
Joined
·
6,042 Posts
Discussion Starter · #6 ·
cRaZy8 said:
Seems like definite fuel issue. It cant be spark. Spark is not affected by engine load, only rpm. I would be looking to the intermediate circuits on the carbs. If it idles fine, but wont transition smoothly to the high speed circuit on the carbs, intermediate is buggered some how. Sounds like the emulsion tubes (round pipe going from main jet, with metering holes, going to carb venturi-throat) are clogged.
Nope I cleaned and checked everything



cRaZy8 said:
Another thing to check too, if these carbs were messed with by an amateur; its possible you could have an internal air leak in the carbs. Buggered threads where a jet goes, or a seal around a mixture screw.

Theres no air leak in or around the carbs.. I checked that already too. Every thread, rubber seal is in mint shape.. The mixture screws still have the caps over them which are sealed tight and arent leaking.

The bikes only got 2,498 miles on it, its brand fucking new
 

·
Fresh outta Fighter camp!
Joined
·
357 Posts
Do you have an IV setup for gas you can use? Or some way of leaving the tank connected and propped up so you can get to the carb throats while its running?

With some gas (please dont use starting fluid, lol) in a spray bottle, and the bike running, open the throttle to the point when it starts to bog. Spray fuel into each carb, one at a time, and see if the goes past the sticky spot. Try and isolate the problem, whether its all 4, or just one.
 

·
the mad doctor
Joined
·
3,399 Posts
what year is it? i had a zx7 with a 9 motor in it a while back that had the same problem. drove me freakin NUTS trying to get it sorted out. i literally tried everything from the carbs, fule pump, cdi, ignition trigger, the whole freakin wiring harness, etc. (i was working at a salvage yard at the time so i had access to those parts to try)

turns out it was the voltage regulator (which on the old style zx9's is internal in the alternator) spark IS directly effected by engine load b/c at varying loads you'll get varying amounts of intake charge, and on a carb'ed bike it'd be damn near impossible to get it to have the same air/fuel mixture thoughout the load/rev range. the voltage regulator would work enough to keep the battery topped off for the most part, but at a higher load on the motor it wouldn't put out a hot enough spark to let it run smoothly thru the rev range. the battery was partly to blame for that also though. it was by far the strangest problem i've encountered on a bike like that, but a simple swap of the alternator cleared it right up.

basically the alternator wouldn't put out enough power to keep the spark hot enough to fire thru the midrange. it still doesn't make much sense, as you would think that just having a known good and freshly charged battery would be enough for it to run right until the battery started to get weak. that wasn't the case though. i even put the rest of the bike back to the way that it was when it came to me, with the exception of the voltage reg/battery, just to rule out whether or not it was a combination of small problems, and it was fine.

worth a shot anyway.
 

·
Buy all my shit!
Joined
·
6,042 Posts
Discussion Starter · #9 ·
cRaZy8 said:
With some gas (please dont use starting fluid, lol) in a spray bottle, and the bike running, open the throttle to the point when it starts to bog. Spray fuel into each carb, one at a time, and see if the goes past the sticky spot. Try and isolate the problem, whether its all 4, or just one.
Did that.. while it was at idle to see if it dogged out.. It only dog's when I drive it, not when its parked or in neutral
 

·
Buy all my shit!
Joined
·
6,042 Posts
Discussion Starter · #10 ·
skr00zloose said:
what year is it? i had a zx7 with a 9 motor in it a while back that had the same problem. drove me freakin NUTS trying to get it sorted out. i literally tried everything from the carbs, fule pump, cdi, ignition trigger, the whole freakin wiring harness, etc. (i was working at a salvage yard at the time so i had access to those parts to try)

turns out it was the voltage regulator (which on the old style zx9's is internal in the alternator) spark IS directly effected by engine load b/c at varying loads you'll get varying amounts of intake charge, and on a carb'ed bike it'd be damn near impossible to get it to have the same air/fuel mixture thoughout the load/rev range. the voltage regulator would work enough to keep the battery topped off for the most part, but at a higher load on the motor it wouldn't put out a hot enough spark to let it run smoothly thru the rev range. the battery was partly to blame for that also though. it was by far the strangest problem i've encountered on a bike like that, but a simple swap of the alternator cleared it right up.

basically the alternator wouldn't put out enough power to keep the spark hot enough to fire thru the midrange. it still doesn't make much sense, as you would think that just having a known good and freshly charged battery would be enough for it to run right until the battery started to get weak. that wasn't the case though. i even put the rest of the bike back to the way that it was when it came to me, with the exception of the voltage reg/battery, just to rule out whether or not it was a combination of small problems, and it was fine.

worth a shot anyway.
You know I did actually think about that..

Come to find out I dont think he even has the Y pipe ram air duct thats supose to be behind the headlights in the upper. The only thing he has is a ram air duct on each side that comes out of the frame. To be honest I think thats the problem.. letting in too much air.

Im gonna duct tape off each ram are pipe about 3/4 of the way on each side and see if that solves the problem... It makes perfect sence. If that dont work Im gonna test the VR and see if that could be the deal.. But the bike is brand fuckin new, it doesnt even have 3,000 miles on it.

We'll see tommorow
 
1 - 11 of 11 Posts
Top