The air cut off valve comes into play when you have a high intake vacuum like when cruising or backing off the throttle in a higher RPM range . It cuts the air to the pilot curcuit and rich ens the mix to stop a lean mix and popping and banging on over run or when using very little throttle.
So if the valve diaphram is faulty or damage to the cover, it doesn't matter what you do with the mixture screw on the idle circuit, it won't solve the problem.
Flat spots on very low throttle.
Moderators: trixynut, Mincehead, dicky, phuk72, Jak, Kevtrx849
-
cobbadiggabuddyblooo
- Site Sponsor
- Posts: 6809
- Joined: Thu Aug 28, 2008 9:19 am
- Location: Brisbane,Australia
Re: Flat spots on very low throttle.
laughter is the best medicine
-
goose202
- TRX-Enthusiast
- Posts: 30
- Joined: Mon Jul 20, 2015 5:05 am
- Location: Adelaide, Australia
Re: Flat spots on very low throttle.
Continuing my story...
One of the air cut valve covers didn't look brilliant on closer inspection, although I can't see how it could have been leaking.
Just the same, for now, I've built up the outside of the cover with epoxy and sanded the mating side flat.
All diaphragms have been checked leak free.
I've put the original dyno-tuned needles, jets and tubes back in, as well as the old float valves.
I've also put on the loud aftermarket exhaust cans on in place of the stockies. Reason being that I'm not completely sure if I've got a tuning problem across both cylinders, or I'm just losing one. I think I'll be able to hear that with the loud exhaust.
A quick lap didn't show up any of the issues I've been having, but I've been through this before. I'll report back after I've had an opportunity for a longer ride.
One of the air cut valve covers didn't look brilliant on closer inspection, although I can't see how it could have been leaking.
Just the same, for now, I've built up the outside of the cover with epoxy and sanded the mating side flat.
All diaphragms have been checked leak free.
I've put the original dyno-tuned needles, jets and tubes back in, as well as the old float valves.
I've also put on the loud aftermarket exhaust cans on in place of the stockies. Reason being that I'm not completely sure if I've got a tuning problem across both cylinders, or I'm just losing one. I think I'll be able to hear that with the loud exhaust.
A quick lap didn't show up any of the issues I've been having, but I've been through this before. I'll report back after I've had an opportunity for a longer ride.
-
cobbadiggabuddyblooo
- Site Sponsor
- Posts: 6809
- Joined: Thu Aug 28, 2008 9:19 am
- Location: Brisbane,Australia
Re: Flat spots on very low throttle.
A number of guys have also used an epoxy over the air cut out valve cover with success . Easiest way to isolate the problem as a temporary fix.
Some have found them crazed and or brittle and small cracks and others like yours where visually it didn't look too bad, just aged and faded to an off white/yellow.
It's one of those annoying bugs that raises it's ugly head on many carbies at this age but may not look damaged and you can be pulling your hair out going through all the other options with no luck.
Some have found them crazed and or brittle and small cracks and others like yours where visually it didn't look too bad, just aged and faded to an off white/yellow.
It's one of those annoying bugs that raises it's ugly head on many carbies at this age but may not look damaged and you can be pulling your hair out going through all the other options with no luck.
laughter is the best medicine
-
goose202
- TRX-Enthusiast
- Posts: 30
- Joined: Mon Jul 20, 2015 5:05 am
- Location: Adelaide, Australia
Re: Flat spots on very low throttle.
To follow up on this, it seems fixed.
So because I changed three things at once (back to the original jets/needles/emulsion tubes/float valves, epoxied the cut-off covers, and the loud exhausts), I can't be completely sure exactly what fixed it.
My best guess is that changing out the seals at the start of all this disturbed marginal cut-off covers.
From here I think I'll get new cut-off covers, new intake seals, and set the carby settings back to what they were (in half a turn on the air screw and drop the needle a clip).
So because I changed three things at once (back to the original jets/needles/emulsion tubes/float valves, epoxied the cut-off covers, and the loud exhausts), I can't be completely sure exactly what fixed it.
My best guess is that changing out the seals at the start of all this disturbed marginal cut-off covers.
From here I think I'll get new cut-off covers, new intake seals, and set the carby settings back to what they were (in half a turn on the air screw and drop the needle a clip).