The problem: When the engine on my '65 CP77 gets up around 4000 rpm, it refuses to return to idle after I roll off the throttle. I had this problem last summer and believed that a slight gap between the left carb body and the slide was allowing air leakage past the slide under high vacuum. I replaced the left carb, and problem solved. But the problem returned last November, and I figured, well, time to replace the right carb, which I just did. But this time, no improvement. I'm tired of rebuilding and replacing carbs! Anyone have a better idea? I still believe it's air leakage past the slide, but I'd like to hear from someone else. I've filed the carb flanges flat, checked the phenolic spacers for cracks, and installed new O-rings, so I don't believe there's air leakage around the spacers.
Thanks,
Jesse
engine races
Re: engine racesContact me direct. ............lm
I have a similar problem. Mine occasionally takes a long time to come down from 4000 rpm.
When idling, it will sometimes just take off on its own to around 4000, then come back down again (without touching the throttle). I haven't driven it any further than around the block a few times, so I have not had this happen while driving. It doesn't happen when the engine is warming up, just after running for more than 5 minutes. The carbs have had a rebuild kit, the idle screws are in as far as they will go, and the air screws are open 1 1/4 turns. Terry McKitrick
CP1000077, CP77E1000074 St. Albert, Alberta Canada
The slide screws are not suposed to be all the way in.
I'm surprised that engine ever comes down to idle. Have you adjusted the points per the directions in the FAQ section? ......lm
Problem solved.
I had secured the throttle cable with a nylon strap that was too tight. When I turned the handlebars too far to the left, it pulled on the throttle cable. I have a few more "issues" that I will address in a later post. Thanks to all who replied. Terry McKitrick
CP1000077, CP77E1000074 St. Albert, Alberta Canada Well, in case anyone else is fighting the same problem, here's an update on mine:
1. I've checked the high-speed timing and verified that the "max advance" is not being exceeded, and that the advance mechanism is not loose or malfunctioning. 2. I've attempted to seal around the throttle cable inlets to the carbs, in case air was leaking in that way. No improvement. Michael Stoic said he had a similar problem that went away when he re-routed his throttle cables, but no amount of fiddling with my throttle cables has helped. 3. I've re-checked the phenolic spacers and O-rings for cracks/leaks, and there are none. 4. I've replaced both carbs with used carbs from eBay which I carefully rebuilt myself. Danged if the engine doesn't still race! 5. The only thing that helps is closing the idle air screws completely. The engine runs almost correctly this way (though it's still a bit slow to return to idle), but the mixture is rich and the plugs foul after 100 miles or so. 6. I checked every possible combination of left/right air screw adjustment and idle setting to try to find whether one carb or the other was the problem, but they both seemed to equal contributors. Both idles air screws have to be closed for the engine to return to idle. Closing the idle air screws effectively reduces the amount of air flowing through the carb at idle (as far as I know), which says to me that the problem is an internal air leak through the carb, possibly around the throttle valve slides. I've ordered a couple of new slides to see if they help. Meanwhile, I'm making do with the idle air screws closed and having to clean the plugs every 100 miles or so. idlefirst off
those are not " air screws" they are idle fuel screws. the adjustment is oposit of an air screw. in is leaner. your problem is usually caused by worn needles and or needle jet. try setting your needle clips to a leaner setting. report on effect. Joe
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