1974jh5
Curmudgeon.
Okay, my 1980 has been running great until recently. It's basically stock with a stock bore big fin cylinder, a Mike's 2 into 1, BS34's and pods, stock TCI ignition with Iridium plugs. I'm pretty familiar with motorcycle carbs, messed with a bunch of them over the years. These BS34's are almost exactly like Stromberg CD's as used on British cars and I'm pretty familiar with those, but this problem is whipping my ass.
While riding recently, I noticed at WOT the engine would start breaking up. It was definitely throttle opening related, the engine would pull smoothly all the way to redline unless the throttle was wide open. But off the bottom everything was fine. Then on a short hop I noticed it ran like crap just off the bottom for a few seconds, then cleared up and ran great. The next time I fired it up, it ran perfect at idle but would die as soon as the throttle was cracked. This was (is) so bad that it's unrideable.
Pulling the choke out to the first notch gets rid of the flat spot and makes it rideable so that tells me that for some reason the pilot and progression phase is lean. So I figured the progression holes in the carbs were probably clogged with something or other. I've been through the carbs twice and verified that the progression holes, the idle hole and everything else are clear. Still the same problem. (BTW, it's possible to kill the engine by screwing the idle scews all the way in but cranking them way out doesn't seem to have much effect on how it runs.)
Here's the strange part: if the engine idles for 30 seconds or so and you open the throttle the first time it revs right up, then after that each time you try to open the throttle the flat spot comes back worse and worse until it just dies. If the engine idles for 30 seconds or so, again the first time the throttle is opened it's okay then each successive throttle opening gets worse, like the progression and pilot phase are running out of fuel.
Valve adjustments are correct, the plugs are clean, it has the correct type pilot jets, I've been through the carbs twice to clean everything out, fuel flows freely from the petcock, I've raised the wet fuel level as a test, all to no avail. The carb boots are not leaking vacuum but the throttle shaft seals are. Could this be the problem or am I missing something else equally simple?
While riding recently, I noticed at WOT the engine would start breaking up. It was definitely throttle opening related, the engine would pull smoothly all the way to redline unless the throttle was wide open. But off the bottom everything was fine. Then on a short hop I noticed it ran like crap just off the bottom for a few seconds, then cleared up and ran great. The next time I fired it up, it ran perfect at idle but would die as soon as the throttle was cracked. This was (is) so bad that it's unrideable.
Pulling the choke out to the first notch gets rid of the flat spot and makes it rideable so that tells me that for some reason the pilot and progression phase is lean. So I figured the progression holes in the carbs were probably clogged with something or other. I've been through the carbs twice and verified that the progression holes, the idle hole and everything else are clear. Still the same problem. (BTW, it's possible to kill the engine by screwing the idle scews all the way in but cranking them way out doesn't seem to have much effect on how it runs.)
Here's the strange part: if the engine idles for 30 seconds or so and you open the throttle the first time it revs right up, then after that each time you try to open the throttle the flat spot comes back worse and worse until it just dies. If the engine idles for 30 seconds or so, again the first time the throttle is opened it's okay then each successive throttle opening gets worse, like the progression and pilot phase are running out of fuel.
Valve adjustments are correct, the plugs are clean, it has the correct type pilot jets, I've been through the carbs twice to clean everything out, fuel flows freely from the petcock, I've raised the wet fuel level as a test, all to no avail. The carb boots are not leaking vacuum but the throttle shaft seals are. Could this be the problem or am I missing something else equally simple?
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