Cbr900 Bike Carbs

[tractor]

from the colour of that pipe you are getting oil or fuel going where it shouldn't not enough vacuum on that cylinder

[Longboarder]

Am I being a bit daft here. The movie shows you running the engine. Three of the gauges connected to inlet runners show a positive pressure of about 3 psi and absolutely stable. One shows a vacuum of around -12psi and oscillating. How do you get positive pressure in an inlet runner if you don't have a blower?

I suggest you use that one gauge and its tube and try it on each vacuum take-off pipe in turn. Put the other three gauges aside for a while. Make sure all four vacuum take-off pipes welded into the runners are patent.

 

Nigel

Edited April 22, 2015 by Longboarder

[tractor]

the gauges oscillate a lot you use the valves on the pipes to reduce it and wot psi is reading is irrelevant you just want all the needles to point in same direction that's how I used them

[Guest 2b cruising]

Hi Dino.

Where does the vac pipe go to.

It is quite possibly that component causing your fault.

It must be discoloured thru lack of vacuum.

[cb750]

As Longboarder said, 3 of the gauges are showing positive pressure? Did you zero the gauges to the correct mark before you started? Have you tried swapping the gauges over to check that the one gauge isn't faulty?

[Dean Roberts]

Sorry for the delay, been working all day & night & day again.....

 

Last night I found that one of the connections to the vacuum pipe was leaking a small amount of air.

I have removed all connectors and applied new PTF tape and re-connected them and tested for more leaks (none so far).

I was hoping this would explain the dirty pipe, but the leak was from another one

 

 

 

Back to the carbs and inlets, which when attempting to balance do not require the above vacuum pipe mentioned.

 

I have connected the same erratic sensor from inlet 1 to each of the other inlets (as Nigel suggested)

one at a time (using the damper valve to steady the needle as shown in the video).

All the other inlets are still registering 3...ish on the Richter scale and seem to be functioning as intended.

When I reconnect it back onto inlet 1 it should be reading the same, but like you can see not enough vacuum.

 

I'm now a little concerned if it's the engine, inlet manifold or the first carb at fault

 

Would a compression test on the engine confirm/deny if there are any internal issues?

Should I strip down the first carb and see if there are any blockages?

Should I be driving on it while its like this or will I cause more damage?

Could this be the reason why the car feels a flat as a wet fart in a space suit?

 

These questions and many others will be answered on the next episode of SOAP (queue the theme tune).

 

 

 

The inlet manifold seems solid (no cracks break or leaks).

I have another set of CBR900 carbs without any jets, gasket, seals etc....

Maybe I should disconnect the bike carbs and transfer everything over onto the other set and test to see if they are any better.

Edited April 23, 2015 by Dino

[Longboarder]

I have to admit I'm not understanding the process. Do the carbs have individual adjustment for each butterfly so they can be synchronised? This is usual and the first operation in balancing. Index carb is usually on one end and usually the one with the throttle cable activating it directly and also the only one with a idle stop to set idle butterfly position. All idle air bleed screws should be closed. Then run the engine adjusting the idle stop to get a tickover. Then start adjusting individual butterflies, progressively away from the index carb till they all balance. You may need to reset the idle stop to keep the revs at 1000.

If the index carb is number 2 on your set-up and 3 & 4 are close to its figure then you should just need to adjust the butterfly link between 1 & 2 to bring 1 into line. The idle air bleed screws are just for fine tweeking? Or on your set-up are the butterflies all solidly connected and all the balance is done on the idle air bleed screws? This seems most unlikely!

 

Nigel

[Dean Roberts]

You may already know this but my notes say to initially balance carbs (I think mine are the same as yours) screw the mixture screws out by the same number of turns (I think about 2 1/2 turns?) then balance #1 and #2 carbs with their screw. Then balance carbs #3 and #4 with their screw. Finally balance pair 1&2 to pair 3&4 using the centre screw.

 

Rob

 

Nigel, as above

 

The 4 carbs have adjustment screws on the linkage between.

You adjust the screws up or down to control the needle and balance them to match each other so they fire evenly and controlled.

 

The problem I have is that the carbs are all adjusting as intending and balancing except the first one.

I assumed it was a fault with the bike carb, but the dirty pipe, gutless engine seems to point to something little more damning.

[tractor]

have you done a compression test yet if not do that before you strip carbs down

[Dean Roberts]

have you done a compression test yet if not do that before you strip carbs down

 

Cheers dude, I'm picking up a compression tester on the way home tonight and will give feedback later.

[Guest 2b cruising]

Might also be an idea to just check the tappet gap on that inlet valve. If it's to tight, that could cause your problem.

[Dean Roberts]

Finally got my hands on a compression tester and got the following results

 

No 1 - 148

No 2 - 128

No 3 - 138

No 4 - 140

 

So looks like the engine is ok, time to start stripping the carbs and checking for blockages on the no1 carb

 

[HAWKNORTH]

Blockages, holes in diaphrams (I think that's how its spelt) bent needles etc. Good luck.

[tractor]

if its not the diaphragm I had the same problem on my pinto bike carbs I didn't do a compression check I just changed head gasket and that cured it

[Dean Roberts]

I think I have found the issue...

 

Possibly the manifold, will confirm this a bit later and try to get some pictures.

 

I stripped the carb and the diaphragm, needles and pipes are ok.

 

Refitted the carb and fired her up and attached the balancer. I then noticed a tiny piece of metal lodged in the inlet pipe. So after borrowing the wife's tweezers manage to pull it out and got a picture.

 

I think this didn't help matters, but also guided me to check the other inlets and to my horror....

 

..... To be continued shortly after dinner!

Edited April 25, 2015 by Dino