[1994cbr900rr]

I have a 1994 CBR900RR which after rebuilding ran great and rode nice. One day while starting it up after a 2 day rest, it started roughly and and while applying a little choke it stalled, never to start again! Spin, Spin, Spin no bang! Checked Spark, it's good. Checked fuel, it's getting it.

After many attempts to start it, it finally started backfiring as the only sign of life. After another 6 days of checking, testing, verifying electrical, etc. it started making the weirdest gurgling sounds in the exhaust (like it was under water and sloooowww...), neat, but not the sounds I or anyone would really want to hear from a Blade... it started backfiring along with the gurgling and at one point it started and ran! Rev'd somewhat decently, but still with loud backfiring intermitently. Turn it off, won't start.

Checking the plugs throughout the trials and tribulations, it seemed they were consistently wet with gas each time. This leads me to believe 2 things, the bike is flooding for one of 50 different reasons, or the cam timing has skipped a tooth and valve timing is off. Checking the carbs and float needle operation turned up no visible signs of malfunction.

Is it possible that the pressure switch has gone on the fuel pump? Does it have one on this model? Can the fuel pump provide too much pressure and force fuel past the needle valves? This is extremely frustrating given that the bike was running fine 2 days earlier! Several bike mechanically/electrically inclined friends with loads of experience are scratching their heads as their particular area of expertise seems to check out.

Your help and wisdom is greatly appreciated by a new member without his ride... Thank you.

 

[gsxrfxr]

have you checked the timming? just in case as you mentioned it might have skipped a teeth or 2.

 

[cbr lonner]

what was done on the rebuild stakes?


are all the inlet manifold rubbers tight and in good condition?

is the fuel ok as it may be contaminated with water etc (worth checking with fresh fuel)drain carbs and try a gallon of fresh petrol.

do all the carb pistons rise and fall with a little resitence (if they move with no resistance then it could be the carb diaphragms are shot or incorrectly fitted)
check the igniter box connections are clean and also make sure the reg rec wires at the connector block are clean and good.

as the bike ran well at first its not likely to be a cam timing issue.
its most likely a fuel or electric issue

hth

 

[gsxrfxr]

as the bike ran well at first its not likely to be a cam timing issue.
its most likely a fuel or electric issue
:thumb:

 

[bladeracer]

I have a 1994 CBR900RR which after rebuilding ran great and rode nice. One day while starting it up after a 2 day rest, it started roughly and and while applying a little choke it stalled, never to start again! Spin, Spin, Spin no bang! Checked Spark, it's good. Checked fuel, it's getting it.

After many attempts to start it, it finally started backfiring as the only sign of life. After another 6 days of checking, testing, verifying electrical, etc. it started making the weirdest gurgling sounds in the exhaust (like it was under water and sloooowww...), neat, but not the sounds I or anyone would really want to hear from a Blade... it started backfiring along with the gurgling and at one point it started and ran! Rev'd somewhat decently, but still with loud backfiring intermitently. Turn it off, won't start.

Checking the plugs throughout the trials and tribulations, it seemed they were consistently wet with gas each time. This leads me to believe 2 things, the bike is flooding for one of 50 different reasons, or the cam timing has skipped a tooth and valve timing is off. Checking the carbs and float needle operation turned up no visible signs of malfunction.

Is it possible that the pressure switch has gone on the fuel pump? Does it have one on this model? Can the fuel pump provide too much pressure and force fuel past the needle valves? This is extremely frustrating given that the bike was running fine 2 days earlier! Several bike mechanically/electrically inclined friends with loads of experience are scratching their heads as their particular area of expertise seems to check out.

Your help and wisdom is greatly appreciated by a new member without his ride... Thank you.

What was the reason for the rebuild?
Was anything improved or was it built totally stock?
Have you done compression and leakdown tests?
Is the vacuum line to the fuel tap dry?

 

[cbr900racer77]

These things are notorious for fouling plugs. I'd start simple and put a new set in. If I ever foul a set, I just replace them. Never had any luck cleaning them. And yes, 94s have a fuel pump with mechanical petcock (no vacuum line).

 

[1994cbr900rr]

I have checked all components of the fuel systems as far as I can without being a professional... intake boots, diaphragms, passages, etc. As far as the rebuild, it was structural rather than engine rebuild, forgot to clarify. it has been put back together in stock form. Have had no luck with tracking it down to an electrical problem, as a senior automotive electrical engineer I know has even looked into it and performed all sorts of tests and bypasses, checked with a crazy scope, etc... all is well with the electrical.

Fresh fuel used every time we changed something and tried again, and like I said it did run for a minute or so, just popping alot and really loud!

I'm not sure how to check if the timing may have skipped, other than to follow my haynes and align the timing marks under the case cover. I do have a timing light come to think of it...

All your help is greatly appreciated, I'm lost as to what I should do next other than check the timing. But why would that go out if it was running just fine before? Not crashed, just one tip over long before bike was ever disassembled in the first place.

All suggestions welcome, and thanks again..

-CBRless guy

 

[bladeracer]

Fresh fuel used every time we changed something and tried again, and like I said it did run for a minute or so, just popping alot and really loud!

I'm not sure how to check if the timing may have skipped, other than to follow my haynes and align the timing marks under the case cover. I do have a timing light come to think of it...

Popping or backfiring? Popping indicates a leak in the exhaust system. Backfiring is an ignition or cam timing problem.
A timing light doesn't do valve timing - it's for ignition timing.
If the camchain tensioner wasn't removed at all then it's unlikely the timing has altered - unless it's very high mileage and about due to skip anyway?
Does the crankcase smell of fuel?
Are the plugs new?
How long was the bike sitting before you've tried starting it now?
If it's been a while my guess is it needs a thorough carburetor strip and clean and probably new needles and seats.

 

[eepromking]

sounds like over fueling ..turn it over ,after it wont start ,remove the down pipes and exhaust and fuel should be inside. If running from the carbs will be in the crank also ...

 

[1994cbr900rr]

@Bladeracer: backfiring... I used the wrong word. popping is something my ol' school GS750 does on decel. with the after market megaphone pipes (sounds Niiiiceee lol)
30K on engine, never disassembled other than removal from frame, never really abused. Tensioner never touched. Haven't smelled crankcase for fuel, and the plugs are new. It sat for 1 month between initial problem and initial repair attempts as I was moving from Ontario to BC. Bike has sat no more than 3 days in a row between wrench sessions.

@ Eepromking: Will check the exhaust system for fuel, although I'm certain it's there... it backfires readily and smells a bit like gas at the can when cranking for a bit.

I'm going crazy here.. I've had 5 bikes, most of which have had various perplexing problems, but have managed to figure out the cause and solutions with only a fairly small amount of difficulty. This one takes the cake and is honestly starting to shake my faith in Honda a little, with many others I know having horrid times with their various models... but boy they sure are top dogs when running right! Which is why I want this fixed so badly that I'm now starting to be tempted to turn it over to the clutches of commercial thievery. At least if it doesn't run, I don't pay (much).

Thanks again and all suggestions are welcome. I really don't like the shops around here (small area, big costs), so would like to avoid them if I can, other than for parts.

 

[cbr lonner]

just a couple of things that havent been mentioned yet.

does the bike have an alarm immobiliser?
if so is the thing faulty as this is a very common prob on old alarms.

are the sparks at the plugs bright and strong and not just feeble one's'

as you say its been looked at by others so its probably a electric component thats causing all your woes as its getting plenty of fuel.

if the float bowls were over filling id expect it to pour on the floor via the overflows on the carbs which it isnt.


this is a good site for some pointers to a possible cause and might help you pin point the issue

Motorcycle Repair Course

hth

 

[eepromking]

iam sure its over fueling ...:eyebrows: . execess fuel doesnt always pour out of the carbs onto the engine ...but can go into the engine and not be visible outside , hense the cranck case will fill with fuel and the exhaust will show signs of un burnt fuel in one or more of the down pipes ...if try turning the bike over for to long with out ignition and the fuel will pool at the lowest point of the exhaust. if you find this then thats your problem and carbs need to be cleaned or serviced.

 

[bladeracer]

if the float bowls were over filling id expect it to pour on the floor via the overflows on the carbs which it isnt.

Overflows on the carbs?
The only overflow I know of is the main jet where the fuel then runs down into the cylinder.

 

[cbr lonner]

Overflows on the carbs?
The only overflow I know of is the main jet where the fuel then runs down into the cylinder.

im thinking of the float needle valve sticking so if the carbs just dump all the fuel into the cylinders that woud figgure.

they used to have an over flow on all carbs once so you could tell it was leaking

 

[bladeracer]

im thinking of the float needle valve sticking so if the carbs just dump all the fuel into the cylinders that woud figgure.

they used to have an over flow on all carbs once so you could tell it was leaking

I can't see how a carb would function though if the float bowl were vented other than through the jets. The principle of the carb relies on it being sealed from atmosphere except through the jets.
Where did the overflows come out of?

 

[denzee]

I can't see how a carb would function though if the float bowl were vented other than through the jets. The principle of the carb relies on it being sealed from atmosphere except through the jets.
Where did the overflows come out of?

Float bowls are vented blade. They need atmospheric pressure to operate. Sometimes bowl vents also double as overflow protection as well. It'll dump the fuel on the ground or into the engine instead on all over the engine and create a fire.

 

[bladeracer]

Float bowls are vented blade. They need atmospheric pressure to operate. Sometimes bowl vents also double as overflow protection as well. It'll dump the fuel on the ground or into the engine instead on all over the engine and create a fire.

I know it is kept at atmosphereic pressure via "venting" through the jets but those vent into the carburetor still.
I've never seen "overflows" that allow fuel out of the carb though.
There are drains on float bowls that are opened manually to drain the carbs though.

 

[denzee]

You know all this stuff blade, you're just not thinking of it right. Bike carbs typically had the hoses come out the bottom of the bike, They are teed in at the top of the float bowls to vent and supply a path to dump fuel if the float sticks and overflows. Here's a couple of pics I founf of both types of venting.

 

[bladeracer]

You know all this stuff blade, you're just not thinking of it right. Bike carbs typically had the hoses come out the bottom of the bike, They are teed in at the top of the float bowls to vent and supply a path to dump fuel if the float sticks and overflows. Here's a couple of pics I founf of both types of venting.

You may be right Den
The first pic shows the air vents (not overflows) and I'm fairly sure I've never seen fuel come of them.
The second shows the vent back into the throat.
In both cases, if the float valve stays open fuel will flow into the engine, not to the outside of the carbs.
The only time I can ever recall seeing fuel running from an overflow is from the fuel tank overflow.

 

[cbr lonner]

Float bowls are vented blade. They need atmospheric pressure to operate. Sometimes bowl vents also double as overflow protection as well. It'll dump the fuel on the ground or into the engine instead on all over the engine and create a fire.

that was my thought's denzee.

when i fitted dynojets to my carbs the other day fuel pissed out when i tipped them up as i didnt bother to drain them fully .
i dont smoke any more and i do miss the danger:smilebig:

carbs used to just have a pipe that ran down to the bottom of the engine and you got a pool of fuel on the floor if you dropped the bike or the floats got stuck.

suppose with the strict emission laws its changed a bit now