Anyone explain this problem??

[Gizzard1533]

Right guys and gals as you all know i've been sorting out the fzr and have run into a few teething problems with the bike. I'll explain the things i've changed and then my problem im having, which has got me really confused!!!

Right I rebuilt my engine with my old cylinder head, my old one was naffed at the exhaust ports, so like i said i've replaced this with my old one, the engine runs fine, has good compression.
I haven't touched the carbs nor the airbox as these where both fine when I took the bike off the road.
I've replaced the old mild steel with a new set of stainless downpipes, specially made for the fzr and using the same silencer the bike had before i took it off the road.
I've replaced the fuel filter.
The spark plugs are the same plugs, cleaned and produce a healthy blue spark.
Regulator is a new r6 one, that works as it should.
Theres no cracks in the inlet manifold,
And the airbox attaches to the carbs correctly, not a perfect fit but its an air tight fit.

Now my problem....

So far with the bike on the road, i've pushed it as far as i've rode it. The bike ran fine when i set of it idled lovely, pulled through the gears lovely. Then all of a sudden the bike started to die and cut out. The bike then wouldn't start up again, unless i had the throttle wide open, but even when the bike fired up, it wouldn't run above 500RPM, and as soon as i closed the throttle the slightest touch it cut out. Now I thought this would of been a fuel problem, so I decided to strip the carbs and clean then, admittedly there was some crap in the float bowls and some dirt in the jets, so i cleaned them out and dried the thoroughly, so the carbs are all nice and clean now.

Today i put the carbs back on and got the bike fired back up and running as she did, revved through the range quite happily and idled like a good'un. So i put the air box back on and went for a quick ride, I done a quick lap of my area (about a mile) and then the problem striked again, she just died and wouldn't start up again.

I got the bike running the same way as before, full throttle and it was barely clearing 500RPM. Wild thinking kicked in, and I decided with the engine running, i'm gonna pull off the air box, upon doing the something strange happened, the revs began to build and once the final volocity tube was off (airbox not attached) the revs shot up and the bike ran fine.

I now began to think about the air filter, took it off, the filter is starting to turn grey and is slightly buckled, but i haven't removed/touched the air filter since the bike came off the road as a runner. So i pulled the volocity tubes out from the airbox and attached those to the carbs. The bike started and ran fine. I then decided to slightly cover each tube one after the other. Upon doing this the bike started to bog again, I whipped off the tubes and the bike started to run fine again.

I am now really stumped, I can understand that a blockage would cause it to run rich and starve it off fuel causing it to cut out, but theres no blockages anyway, fuel side or air side. I dont know where to turn, the old man suggested dynoing it to see if that shows up anything else, but with the air box on the bike will more than likely cut out, air box off i wont get the true reading, so i really dont know where to turn, I was thinking that pod filters would of sorted my issue but since the bike bogged with just the tubes on, I got see how the pod filters will solve anything.

I hoping one of you guys will know more about this as i've never come across anything like this before.

Cheers in advance

Mikey

[SouthendChris]

Did you have the carb tops off? Easy to nip a diaphragm when refitting them.

You say you fitted an old cylinder head to this engine, did you check valve clearances to make sure the inlets weren't nipped up too tight?

Fuel filter on right way round Double checked float height levels

Choke mechanism stuck on????

Chris

[Gizzard1533]

Did you have the carb tops off? Easy to nip a diaphragm when refitting them.

You say you fitted an old cylinder head to this engine, did you check valve clearances to make sure the inlets weren't nipped up too tight?

Fuel filter on right way round Double checked float height levels

Choke mechanism stuck on????

Chris

I had one carb top off and made sure i didn't nip the diaphragm, bloody swine getting it back in!!!

The valve clearances were all set within tolerence of manual.

Fuel filter is in right way round, arrow pointing away from pump towards carbs.

float heights haven't been touched as they were fine when i took the carbs off the bike,

the choke mechanism works and frees off fine.

Surely these would cause trouble with airbox on or off???

[ramster]

These are guesses ok. It appears you maybe have some carburetion issue's

The fuel cap has a vent, it could be blocked (unlikely) remove the fuel cap, see what happens.

When you cleaned the carbs you did also clean the "Main Air Jet" and the "Pilot Air Jet"?

I now began to think about the air filter, took it off, the filter is starting to turn grey and is slightly buckled, but i haven't removed/touched the air filter since the bike came off the road as a runner.

Personally I would remove the air filter, refit the air box, go for a short test ride and see what happens.

Good luck

[Gizzard1533]

the tank vent isn't blocked as i tried it with both cap in and cap out.

I cleaned all the jets when the carbs where apart.

If the poxy english weather will hold off im gonna refit the air box (without filter) and go for a ride, if problem persists, I may look into pod filters but im not 100% if thet'll help.

[sweekster]

There isn't mention of you synchronizing the carbs after cleaning them. I'm talking about a full dynamic synch session not just bench synching when you had the carbs aparts. I can't say for sure it will solve your problem but it can help tremendously.

[Gizzard1533]

There isn't mention of you synchronizing the carbs after cleaning them. I'm talking about a full dynamic synch session not just bench synching when you had the carbs aparts. I can't say for sure it will solve your problem but it can help tremendously.

Buut the bike idles fine, not lumpy, non of the usual sign of unbalanced carbs, and i forgot to mention that the carbs where originally balanced to this head. doesn't carb balance only affect it at low revs?

[ramster]

the tank vent isn't blocked as i tried it with both cap in and cap out.

I cleaned all the jets when the carbs where apart.

If the poxy english weather will hold off im gonna refit the air box (without filter) and go for a ride, if problem persists, I may look into pod filters but im not 100% if thet'll help.

Pods, I'd say for street riding stay well clear of them. Out of interest (it appears you know what your talking about btw) do you realise each carb has 5 Jets that should be cleaned? many overlook 3 of the jets.

We have obviously inside the float bowl's the Main and Starter Jets, then there's the Pilot Jet which is a pain to remove. Many ignore the other two which are the "Main Air Jet" and the "Pilot Air Jet" both of which are located in the mouth of the carb. I'm not saying they are your problem, I'm also assuming you know the Main and Starter Jets have the same thread and can be installed in the wrong location.

Good luck.

[Gizzard1533]

Pods, I'd say for street riding stay well clear of them. Out of interest (it appears you know what your talking about btw) do you realise each carb has 5 Jets that should be cleaned? many overlook 3 of the jets.

We have obviously inside the float bowl's the Main and Starter Jets, then there's the Pilot Jet which is a pain to remove. Many ignore the other two which are the "Main Air Jet" and the "Pilot Air Jet" both of which are located in the mouth of the carb. I'm not saying they are your problem, I'm also assuming you know the Main and Starter Jets have the same thread and can be installed in the wrong location.

Good luck.

Yeah i know about the 3 other jets, they were all clear, i dont think its a fueling issue as the bike will run with without fault with the air box removed. the starter and main jets weren't put in the wrong way round, due to only removing one at a time and making notes of which jet goes where, (i.e. big holed jet at top).

Someone suggested the ignition coils and a dodgy connection, this sounded plausable to me as i have to use a fair bit of strength to get the thing on, which leads me to believe that wrestling the airbox on knocks a connection, and as i pull it off i relieve the pressure on the coils allowing them to run properly?? Does that sound logical to you??

Out of interest, why would you suggest staying away from pod filters???

[DonTZ125]

They can be difficult to tune, and nigh-impossible to remove a large mid-range hole. Yamaha-George has presented a solution (maintain the intake throat length with a piece of PVC, vs mounting the pod directly on the carb) which has made some improvement for several people, but it is still a significant effort as you are basically re-jetting from scratch. The gains you make tend to be top-end oriented, and thus of limited value on the street.

On the track? Do it, absoutely.

[Gizzard1533]

Ah okay then, i shall stay away from pods then. Im not thinking my mixture could be very rich, the plugs are slightly black. im think the rich mixture only causing real affect when engine is warm, the bike felt down on power as well???

[DonTZ125]

When the bike is warm, the air going through the intakes is less dense = a main jet that is slightly oversized when cold is just too big.

Drop your mains a size or two.

[Gizzard1533]

shall have to do some investigating, do you know what the stock sizes are?

[DonTZ125]

Stock mains on a US-market FZR600 are #107.5; pilots are #32.5, and fuel level is 3.8-4.8mm above the index line on the carb bowl.

[Gizzard1533]

ah shall have to research for the UK market, was hoping they'd be the same. Carb stripping tomorrow and research for tomorrow then