Cyl 4 running lean?
05-24-2010, 04:52 PM
#21
You need to get a carb balancer and make sure each cylinder is flowing the same air at idle.
My psychic diagnosis is that your #4 throttle plate is open slightly more than the others. #4 is running lean and not firing consistently causing spitting back up the trumpet, and unburnt air/fuel to burn in the header.
If you have idle bleed screws, set them all the same, eg 3 turns from fully closed. Back off the interconnect screws between the cylinders so each cylinder is sitting on its idle stops. idle the motor and syncronise the air flow, then carefully, working from the master linkage, take all the slack our of the interconnect adjustments so all 4 plates crack open at the same time.
You can now use your air bleeds to fine tune the sync. If you adjust the idle, open or close the air bleeds 1/4 turn across the board.
Dont forget to keep track of your TPS during the adjustment. I normally make idle = 0 tps. Some other tuners back off the throttles till the plates are closed and set that as zero, then adjust to the idle position which becomes 1-2%. I prefer to set idle position =0 as its easier to reset the TPS 0 position later.
Good luck with it.
Chris.
My psychic diagnosis is that your #4 throttle plate is open slightly more than the others. #4 is running lean and not firing consistently causing spitting back up the trumpet, and unburnt air/fuel to burn in the header.
If you have idle bleed screws, set them all the same, eg 3 turns from fully closed. Back off the interconnect screws between the cylinders so each cylinder is sitting on its idle stops. idle the motor and syncronise the air flow, then carefully, working from the master linkage, take all the slack our of the interconnect adjustments so all 4 plates crack open at the same time.
You can now use your air bleeds to fine tune the sync. If you adjust the idle, open or close the air bleeds 1/4 turn across the board.
Dont forget to keep track of your TPS during the adjustment. I normally make idle = 0 tps. Some other tuners back off the throttles till the plates are closed and set that as zero, then adjust to the idle position which becomes 1-2%. I prefer to set idle position =0 as its easier to reset the TPS 0 position later.
Good luck with it.
Chris.
05-24-2010, 04:54 PM
#22
BTW, I use a SU carb balancing tool. you hold it over the trumpet and put your finger over a port. It has a plastic ball that gets sucked up a tube.
vacuum ones work well. Just be careful if its an old fashioned mercury one. A mate of mine was using one on a motorbike and gave it a rev. No more mercury after that ( was sucked into the motor)
vacuum ones work well. Just be careful if its an old fashioned mercury one. A mate of mine was using one on a motorbike and gave it a rev. No more mercury after that ( was sucked into the motor)
05-24-2010, 07:04 PM
#23
Thread Starter
Originally Posted by chris_barry,May 24 2010, 07:52 PM
You need to get a carb balancer and make sure each cylinder is flowing the same air at idle.
My psychic diagnosis is that your #4 throttle plate is open slightly more than the others. #4 is running lean and not firing consistently causing spitting back up the trumpet, and unburnt air/fuel to burn in the header.
If you have idle bleed screws, set them all the same, eg 3 turns from fully closed. Back off the interconnect screws between the cylinders so each cylinder is sitting on its idle stops. idle the motor and syncronise the air flow, then carefully, working from the master linkage, take all the slack our of the interconnect adjustments so all 4 plates crack open at the same time.
You can now use your air bleeds to fine tune the sync. If you adjust the idle, open or close the air bleeds 1/4 turn across the board.
Dont forget to keep track of your TPS during the adjustment. I normally make idle = 0 tps. Some other tuners back off the throttles till the plates are closed and set that as zero, then adjust to the idle position which becomes 1-2%. I prefer to set idle position =0 as its easier to reset the TPS 0 position later.
Good luck with it.
Chris.
My psychic diagnosis is that your #4 throttle plate is open slightly more than the others. #4 is running lean and not firing consistently causing spitting back up the trumpet, and unburnt air/fuel to burn in the header.
If you have idle bleed screws, set them all the same, eg 3 turns from fully closed. Back off the interconnect screws between the cylinders so each cylinder is sitting on its idle stops. idle the motor and syncronise the air flow, then carefully, working from the master linkage, take all the slack our of the interconnect adjustments so all 4 plates crack open at the same time.
You can now use your air bleeds to fine tune the sync. If you adjust the idle, open or close the air bleeds 1/4 turn across the board.
Dont forget to keep track of your TPS during the adjustment. I normally make idle = 0 tps. Some other tuners back off the throttles till the plates are closed and set that as zero, then adjust to the idle position which becomes 1-2%. I prefer to set idle position =0 as its easier to reset the TPS 0 position later.
Good luck with it.
Chris.
05-24-2010, 08:02 PM
#24
A dirty way to sync the throttles is to use a piece of tube to listen down the trumpets.
There should be a similar pulsing noise from each throttle, and if you just crack the throttle a whisker they should make a similar clack/clack.
The one that opens too early will go quiet when you crack the throttle.
There should be a similar pulsing noise from each throttle, and if you just crack the throttle a whisker they should make a similar clack/clack.
The one that opens too early will go quiet when you crack the throttle.
05-25-2010, 12:07 PM
#25
Thread Starter
Originally Posted by chris_barry,May 24 2010, 07:52 PM
You need to get a carb balancer and make sure each cylinder is flowing the same air at idle.
My psychic diagnosis is that your #4 throttle plate is open slightly more than the others. #4 is running lean and not firing consistently causing spitting back up the trumpet, and unburnt air/fuel to burn in the header.
If you have idle bleed screws, set them all the same, eg 3 turns from fully closed. Back off the interconnect screws between the cylinders so each cylinder is sitting on its idle stops. idle the motor and syncronise the air flow, then carefully, working from the master linkage, take all the slack our of the interconnect adjustments so all 4 plates crack open at the same time.
You can now use your air bleeds to fine tune the sync. If you adjust the idle, open or close the air bleeds 1/4 turn across the board.
Dont forget to keep track of your TPS during the adjustment. I normally make idle = 0 tps. Some other tuners back off the throttles till the plates are closed and set that as zero, then adjust to the idle position which becomes 1-2%. I prefer to set idle position =0 as its easier to reset the TPS 0 position later.
Good luck with it.
Chris.
My psychic diagnosis is that your #4 throttle plate is open slightly more than the others. #4 is running lean and not firing consistently causing spitting back up the trumpet, and unburnt air/fuel to burn in the header.
If you have idle bleed screws, set them all the same, eg 3 turns from fully closed. Back off the interconnect screws between the cylinders so each cylinder is sitting on its idle stops. idle the motor and syncronise the air flow, then carefully, working from the master linkage, take all the slack our of the interconnect adjustments so all 4 plates crack open at the same time.
You can now use your air bleeds to fine tune the sync. If you adjust the idle, open or close the air bleeds 1/4 turn across the board.
Dont forget to keep track of your TPS during the adjustment. I normally make idle = 0 tps. Some other tuners back off the throttles till the plates are closed and set that as zero, then adjust to the idle position which becomes 1-2%. I prefer to set idle position =0 as its easier to reset the TPS 0 position later.
Good luck with it.
Chris.
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