Very good carbie man in Osborne Park...…..
Another R17 owner planning to upgrade
- Thread starter Shoji
- Start date
As I may have told you I built a home made flow meter. I also found that each cylinder flowed at slightly different rates even though the compression was almost identical. Unfortunately I cannot remember which cylinders did what now. But after a rebuild of the engine and carbs there was a change again. I was never sure why but as the motor seemed, to my poor tuning ear, to run ok I just did the best I could and left it at that. Remember R12G actually had a two different DCOE's. Forget which end had what but one had an additional adjustment. ( Perhaps for air at the progression holes. ) An old tuner of the factory 16 rally cars once mentioned that number 4 on a 16, (Near the fire wall on a 16) , had different jetting. Was that because it is buried up under the dash and it got hotter? I guess you could get all pedantic and try and work out why. Or just getting it running as nicely as you can and so long as it runs nicely on the road, all could be ok.
Slightly twisted throttle shafts? It doesn’t take much to make a significant difference in flow. This twist can happen when the carbs are off the car and someone opens the butterflies fully, and then allows them to slam closed. The throttle arm hits the idle adjustment stop with force and twists the shaft
If that is the case Alan then no, 1 would be lower than No, 2 which is not the case. The idle screw is in the middle of both carbs. Hmm interesting
You're living up to the challenge of learning something every day!
Perhaps over enthusiastic tightening of the shaft nuts? Too much effort to find a DCOE in storage to see if this works for your problem.
The position of the butterflies can be checked through the little brass bungs that cover the progression holes, comparing the butterfly plates to see the amount of hole exposed to the main airflow.
Hi Alan. Thanks for your input. These are about two years old from new. 40 151 with air bleeds. Jetting as close to perfect.
Recently I drilled with a template another set of progression holes. see post #671
They are set to come in just as you slightly accelerate.
Meaning that at just crack at idle I can see the throttle plates covering these holes.
I also have checked & adjusted the plates to make sure they are aligned and shut in the bores. Off the car of course and no idle screw touching the shafts.
I see your conundrum. You have the butterflies fully seating in both carbs with no idle screw in place, and yet at idle you have significantly more airflow on two cylinders using separate carbs.
I do think the additional progression holes can only help in the driveability stakes, although you have been far more scientific in you approach to this than I have been in the past. Nicely done.
I still like DCOEs, but nowadays I find the accuracy and adjustability of tuning fuel injection hard to beat.
I do think the additional progression holes can only help in the driveability stakes, although you have been far more scientific in you approach to this than I have been in the past. Nicely done.
I still like DCOEs, but nowadays I find the accuracy and adjustability of tuning fuel injection hard to beat.
I would take the carbs off and put a dial test indicator on the butterflies to make sure I am not chasing my tail around forever. If there's any difference in butterfly position it will show up immediately.
But before that, if the carbies are not new or have some subtle manufacturing defect there may be some air leak past one of componentry that needs to be located. I would let the car idle until it warms up and try spraying a little start you bastard or similar (brake cleaner, etc) focused very accurately (little pipe/tube in the nozzle) at suspected points (throttle spindle, mating faces' gaskets, etc). If there's any response in idle speed, you've got your culprit. Just take care not to start a fire.
But before that, if the carbies are not new or have some subtle manufacturing defect there may be some air leak past one of componentry that needs to be located. I would let the car idle until it warms up and try spraying a little start you bastard or similar (brake cleaner, etc) focused very accurately (little pipe/tube in the nozzle) at suspected points (throttle spindle, mating faces' gaskets, etc). If there's any response in idle speed, you've got your culprit. Just take care not to start a fire.
Another test
Thanks Alan. After talking with Ray, I may have setup the throttle plates incorrectly. So I will do it again this way.
Thanks Alan. After talking with Ray, I may have setup the throttle plates incorrectly. So I will do it again this way.
- Remove the carbs
- wind out the idle screw on the lead
- undo the screws to loose so the butterflies are loose.
- in its closed position tap the shafts lighly between the screws
- This should vibrate enough to seat both butterflies
- check with a good source of light from the intake
- check for light and good seating
- if all good nip up the screws carefully keep it in a closed position
- check for light and good seating
- tighten screws
- install carbs
- 1.5 turns on all idle mix
- 1/2 turn for idle screw
- start and warm
- balance both carbs (which cylinders is best????)
- adjust idle mix and rpm until good
- check airfow on all again
- BETTER???
- try air bleeds to balance all low cylinders
- adjust idle mix and rpm until good
- check airfow on all again
- BETTER??
- HOPE SO
Eek. I thought I was systematic, but you get the prize!
LoL JohnW. I think you'll find I've done the bullet point stuff often through out this thread.
I do this for wood machine procedures too.
It's the way to go, I agree. If you fix the Webers like you fix wooden joints they'll be perfect.
This is the sort of trouble you get into when you mess with things by making careful measurements!! :roflmao:
Seriously, I wonder whether John's slight hesitancy will disappear? His car's that is....
And the barrels of both carbs have the same air flow & same the fuel consumption JohnW. I like problem solving like MacGyver. Always a big laugh :roflmao: