Sameoldclifford
New Member
I went through a progression of unsuccessful repairs to address what I thought was a carb problem. When starting it would frequently flood or bog above idle. The needle valves constantly needed adjusting, so much so I had to keep a screw driver on hand to keep it running. The needles also had to be 2 or more turns out (about twice normal) and the idle was way too high even with the idle screw all the way out.
The repairs I tried included rebuilding the carb, replacing the carb and replacing the impulse hose. Nothing made any difference until I replaced the crank seals. Now, after years of frustration, it starts and runs like new.
Looking back, it all makes sense. Since the fuel mixture passes through the crank case, and because the crankcase is under vacuum, air leaking IN through seals will make the mixture lean and cause bogging. Backing out the H needle valve will compensate but results in extra air AND fuel which I believe caused my high idle. And because seal leakage varies with saw position, temperature and who knows what else, there is no carb adjustment that will keep the saw running consistently. When the leakage drops back down, the mixture becomes rich and floods repeatedly when starting.
Checking the vacuum is the official way to diagnose leaking seals but by the time you get the carb off and seal up all the ports for the test, you could just as easily replace the seals. I bought 10 seals for $7. But it is a bit of a gamble - there could be other sources of leakage into the crankcase, in which case replacing the seals would be a wast of time.
It's not hard to see how this could be misinterpreted as a carb problem. I cant help wondering how many of the chainsaw carb complaints I have read about are actually crank seal problems. Hope this was helpful.
The repairs I tried included rebuilding the carb, replacing the carb and replacing the impulse hose. Nothing made any difference until I replaced the crank seals. Now, after years of frustration, it starts and runs like new.
Looking back, it all makes sense. Since the fuel mixture passes through the crank case, and because the crankcase is under vacuum, air leaking IN through seals will make the mixture lean and cause bogging. Backing out the H needle valve will compensate but results in extra air AND fuel which I believe caused my high idle. And because seal leakage varies with saw position, temperature and who knows what else, there is no carb adjustment that will keep the saw running consistently. When the leakage drops back down, the mixture becomes rich and floods repeatedly when starting.
Checking the vacuum is the official way to diagnose leaking seals but by the time you get the carb off and seal up all the ports for the test, you could just as easily replace the seals. I bought 10 seals for $7. But it is a bit of a gamble - there could be other sources of leakage into the crankcase, in which case replacing the seals would be a wast of time.
It's not hard to see how this could be misinterpreted as a carb problem. I cant help wondering how many of the chainsaw carb complaints I have read about are actually crank seal problems. Hope this was helpful.
