jag767
Over 1,000 Posts
Hey all,
Hoping to get some valuable input here, as I am at a loss. 1971 cb175, good compression, probe digital ignition, mikuni vm20 carbs, idles and runs great when cold. Perfectly steady 1200 rpms. Continues to run well when warm, but the idle hunts a 700 rpm range (1500-2200), and the bike will stall if I do not add throttle. Very hard to reproduce the issue when just sitting, happens often while riding.
Because I know someone will ask, exhaust is aftermarket, length is just short of rear axle, and intake is a pod, but, not what you'd expect. I used a piece of turbo hose with stainless couplers to create a substantial volume of air between the filter and carb. The volume if anything is more than the old air box. Also the size of the filter is much larger that a normal pod, similar area for air to pass through. I read a lot of these common issues in other people's builds, made sure to avoid them, and I know math is your friend
.
First thing I did was play with the carbs. Adjusted the air screw and found it was too rich. After adjustment the throttle response is substantially better, but the same issue is there. Apparently I fixed an issue I didn't know I had though ???. Tried raising the idle for shits and giggles, no joy.
This is my first carburated engine, always had fuel injection, so I am at a loss. A buddy of mine suggested a valve clearance issue, which could be because I never checked them. I've never adjusted valves before so if someone would be able to point me in the right direction as to a tutorial to make sure I'm doing it right that'd be great.
also any, and I am mean any ideas would be appreciated.
Hoping to get some valuable input here, as I am at a loss. 1971 cb175, good compression, probe digital ignition, mikuni vm20 carbs, idles and runs great when cold. Perfectly steady 1200 rpms. Continues to run well when warm, but the idle hunts a 700 rpm range (1500-2200), and the bike will stall if I do not add throttle. Very hard to reproduce the issue when just sitting, happens often while riding.
Because I know someone will ask, exhaust is aftermarket, length is just short of rear axle, and intake is a pod, but, not what you'd expect. I used a piece of turbo hose with stainless couplers to create a substantial volume of air between the filter and carb. The volume if anything is more than the old air box. Also the size of the filter is much larger that a normal pod, similar area for air to pass through. I read a lot of these common issues in other people's builds, made sure to avoid them, and I know math is your friend
.First thing I did was play with the carbs. Adjusted the air screw and found it was too rich. After adjustment the throttle response is substantially better, but the same issue is there. Apparently I fixed an issue I didn't know I had though ???. Tried raising the idle for shits and giggles, no joy.
This is my first carburated engine, always had fuel injection, so I am at a loss. A buddy of mine suggested a valve clearance issue, which could be because I never checked them. I've never adjusted valves before so if someone would be able to point me in the right direction as to a tutorial to make sure I'm doing it right that'd be great.
also any, and I am mean any ideas would be appreciated.
