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Discussion Starter · #1 · (Edited)
Hi, guys!


After fixing an issue with my right cyl (inconsistent spark) with a new condenser, I am left with one problem on my bike:

when hot, the bikes stays at a high RPM (like 2400) after I rev it and only comes down if it put it into 1st gear and release the clutch a notch. Then, it stays at 1200 rpm, ok. If I rev it up, the idle rises again.


Can any of you magnificent folks tell what I can do to troubleshoot this issue? I have already thoroughly checked the points and tightened the springs on the mechanical advancer. Also thoroughly cleaned the carbs, then changed its parts with those of an aftermarket kit (seals, jets, floats, etc.) and checked float height (20mm). Did the straw test on the carbs and the vaccuum piston slides OK.

Thank you very much.
 

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Disconnect the throttle cables to check that nothing is misadjusted or binding, if idle is still hanging,Then check that the idle screws are set the same on each carb. Then move on to checking for air leaks by spraying some carb cleaner around the intakes and throttle shafts.
 

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Try pressing the throttles down by hand, to see if something is causing them to hang up. Also, check the timing with a light, to see that it advances and returns properly (when cold). Slightly advanced timing has more effect when the engine is hot, and if the timing sticks a bit before coming down to idle when cold, it can get worse after warm up.
 

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Are the compression numbers,left and right, reasonably close to even? Carbs vacuum synced?
 

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Discussion Starter · #6 ·
Disconnect the throttle cables to check that nothing is misadjusted or binding, if idle is still hanging,Then check that the idle screws are set the same on each carb. Then move on to checking for air leaks by spraying some carb cleaner around the intakes and throttle shafts.
Hello, middletons. I have already checked for clearance at the cable and checked the idle screws - not only they were the same but I also replaced them with new ones. Same problem. Will definitely check for air leaks!! My carb cleaner is probably not flammable. Maybe WD40?

Thanks!
 

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Discussion Starter · #7 ·
Try pressing the throttles down by hand, to see if something is causing them to hang up. Also, check the timing with a light, to see that it advances and returns properly (when cold). Slightly advanced timing has more effect when the engine is hot, and if the timing sticks a bit before coming down to idle when cold, it can get worse after warm up.
Hello, WintrSol! Thank you!

No issue with cable clearance or throttles. They go back all the way down, just fine.

In regards to the advance, I have indeed checked with a timing light that (engine cold) when I rev it, both the LF and F marks do NOT stay at the index mark at the alternator, they either fluctuate to the right or stay to the right of the index mark. I guess they should always stay at the index mark, right? What could cause this??
 

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Discussion Starter · #8 ·
Are the compression numbers,left and right, reasonably close to even? Carbs vacuum synced?
Hi, Mike! Thank you!

I had a compression test with a faulty, leaking meter and got 125PSI exactly on both carbs. As the bike (with the new condenser) has power, I'm simply guessing compression might be just fine. Need to do another test with a not so China kit.

Carbs were syched using the guitar string method of CommonMotor.com.
 

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Discussion Starter · #9 ·
Did you replace the handlebar grips?
Hello, Bill! No, I haven't. But the cable clearance is a-ok and throttles sit all the day down. The throttle grips snaps right back to the closed position and the cable has a little tolerance before the throttles are activated.
 

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Sitting at idle, there is usually some bounce in the timing, but not a lot; as you rev the engine, the timing usually smooths out as it approaches the advance marks, with only a little blur in position. Let it back down to idle, the timing usually comes down as smoothly as it rose, and any bounce should settle down to a degree or two - less than the distance between the T and F mark. If yours bounces around, assuming the stock advancer, it usually means the springs aren't as tight as they should be, or the cam needs cleaning and is sticking. This has been discussed many times; just search for advancer springs.

BTW, got a propane torch? Use it (not lit) to aim the gas around the suspect areas, or use some spray carb cleaner. Even isopropyl alcohol in a squirt gun will work.
 

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Discussion Starter · #11 ·
Sitting at idle, there is usually some bounce in the timing, but not a lot; as you rev the engine, the timing usually smooths out as it approaches the advance marks, with only a little blur in position. Let it back down to idle, the timing usually comes down as smoothly as it rose, and any bounce should settle down to a degree or two - less than the distance between the T and F mark. If yours bounces around, assuming the stock advancer, it usually means the springs aren't as tight as they should be, or the cam needs cleaning and is sticking. This has been discussed many times; just search for advancer springs.

BTW, got a propane torch? Use it (not lit) to aim the gas around the suspect areas, or use some spray carb cleaner. Even isopropyl alcohol in a squirt gun will work.
When idle, there is almost no bounce. When rev, there is almost a 90º between the LF (for example) and the index mark. Regarding F (for the right cyli), it almost zizagsaround.
While the bike is cold, the timing smooths down to the index mark really nicely. When warm, I haven't seen what happens with the strobe but I bet it stays in full advance..

Well, I have indeed already tightened the springs in the advancer. Same issue. Maybe they need to be even tighter (altough the weights snap back quite easily)?? Wish someone sold springs that meet the exact specifications, in Europe..

No torch. Will try it with WD40 or alcohol indeed.

Thank you, mate!!
 

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When idle, there is almost no bounce. When rev, there is almost a 90º between the LF (for example) and the index mark.
There should be two sets of timing marks on the rotor for each side: those labeled F and T (or LF and LT), and another unlabeled set to indicate full advance. The timing should reach the second set at around 3000 rpm.
Regarding F (for the right cyli), it almost zizagsaround.
So, while the left is steady, the other is bouncing around? That is odd, and implies something wrong with the points for that side. Or, I suppose the connections in the wiring may contribute, if loose, or maybe a cut in the wire, where it crosses a sharp corner. Whatever the cause, I suggest you find a way to make both sides more or less the same; randomness in spark could be the source of the problem. It shouldn't be the advancer springs causing this, as they would affect both sides the same.
 

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Discussion Starter · #13 ·
There should be two sets of timing marks on the rotor for each side: those labeled F and T (or LF and LT), and another unlabeled set to indicate full advance. The timing should reach the second set at around 3000 rpm.

So, while the left is steady, the other is bouncing around? That is odd, and implies something wrong with the points for that side. Or, I suppose the connections in the wiring may contribute, if loose, or maybe a cut in the wire, where it crosses a sharp corner. Whatever the cause, I suggest you find a way to make both sides more or less the same; randomness in spark could be the source of the problem. It shouldn't be the advancer springs causing this, as they would affect both sides the same.
Once again, thank you very much for your tips. I will try to make a video of the lightgun on both sides so you see what I mean. Thank you very much, as always, for your precious help.
 

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Haven't read through everyone's responses so forgive me if I am repeating someone. In addition to whatever good advice has been given above, I would recommend you make ALL carburetor adjustments with the engine at operating temp. GOODLUCK
 

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Discussion Starter · #15 ·
Haven't read through everyone's responses so forgive me if I am repeating someone. In addition to whatever good advice has been given above, I would recommend you make ALL carburetor adjustments with the engine at operating temp. GOODLUCK
This is actually something that I have not done. I usually do it in my garage, which is located in an apartment building, so... Not much noise can be made. Will remember that next time! Thanks!
 
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