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Engine takes a long time to settle

  • Thread starter Thread starter ty998
  • Start date Start date
T

ty998

Guest
Bike: '81 650G

Hey All,

Everything on my bike from an engine perspective is running great now. It's fast, compression is good and it starts great, valves adjusted. However, I have one problem which I cannot figure out: This bike consistently takes a long time for the engine to settle, both on startup and when I rev the engine. So for example, if the bike is in neutral and I rev the engine to 5k and then release the throttle, it will drop to 4k in about 5-10 seconds, then to 3k in another 10-15 or so seconds and over a minute or two later it may finally come to rest and idle perfectly at 1k.

The carbs are dipped and cleaned.
It is running a K&N filter from the airbox.

Other Notes:
If I engage the choke while it is running is revs further out of control (expected, but just curious)
If I mess with the idle speed control while it is at a high rev (5k) it has no affect.
The bike does not leak from anywhere.

It seems that even though the throttle is closed the engine is still getting fuel. In another thread I was reading someone had suggested that possibly the choke was somehow staying open. If you look at the choke rail on from the outside it is closing (going in) all the way when the choke is disengaged. Internally I am not sure how this works or what to look for.

Any other ideas or direction on what to look at next would be great. Also while doing test rides, the revs also hang and take awhile to settle.

FYI: I have not owned this bike at any point when it was fully functional. so I am not sure if it worked correctly before.
 
Your idle mixture is too lean, or your carb sync is messed up. That K&N may be causing part of the grief. Did you replace all the O-rings inside the carbs when you cleaned them? Where are the mixture screws set? Is the exhaust stock or modified?

Bottom line, I'd make sure all the various maintenance items are up to date, including refreshing the carb O-rings if you haven't already done so, and performing a vacuum sync. After that, open up the mixture screws to 3 turns open to richen up the mixture some.
 
Last edited:
Carbs have not been synched yet.
Fuel mixture screw is set at 2 turns out.
Exhaust is not modified (original).
Admittedly, I have not replaced the O-rings.

I will start working through this list.

Would an air leak possbily cause this problem as well? I have not found any specific air leak problems, but just curious if that could also be a possibility to additionally look into.

Thanks.
 
You might also check the mechanical advance springs. If they are not working properly, it would cause the rpm to hang like you describe.
 
subid said:
You might also check the mechanical advance springs. If they are not working properly, it would cause the rpm to hang like you describe.
Click to expand...

Just to be clear, by 'advance springs' you are talking about ignition and timing, correct?
 
Carbs have not been synched yet.
Click to expand...

I would have to say this is most likely the problem. One or more of the carbs is set too high and is not coming down to proper idle speed. As it says you are also on the lean side as you confirm with 2 turns. Go to 2.5 turns.

Carb synching is an absolute must for proper running and its well worth investing in a manometer. They are not cheap at around $100 but well worth it if you want your bike to perform as it was designed to. The Morgan Carbtune, for many of us is the cat's azz but vacuum guage types also work well.

If you don't want to buy one perhaps there is someone close to you that has one and would help you do it.

Good luck with it.
Spyug
 
Don't forget those carb boot o-rings. They are a classic cause of hanging idle.
 
Might be worth checking the throttle cable, if its kinked or twisted it might be dragging.

Tom
 
ty998 said:
Carbs have not been synched yet.
Fuel mixture screw is set at 2 turns out.
Exhaust is not modified (original).
Admittedly, I have not replaced the O-rings.
Click to expand...


So the moral of the story is that your bike won't run right without maintenance.

Please check the Newbie Mistakes thread linked in my signature for a list of common issues and maintenance tasks.

This is your wake up call. Do NOT neglect maintenance. In addition to fixing the items as noted, you should plan to adjust your bikes valves and fix the charging system wiring (at minimum). I also strongly suggest going though the brake system.

Good luck
 
Nessism said:
So the moral of the story is that your bike won't run right without maintenance.

Please check the Newbie Mistakes thread linked in my signature for a list of common issues and maintenance tasks.

This is your wake up call. Do NOT neglect maintenance. In addition to fixing the items as noted, you should plan to adjust your bikes valves and fix the charging system wiring (at minimum). I also strongly suggest going though the brake system.

Good luck
Click to expand...

As mentioned in orignal post, I have done much of the maintenance including adjusting the valves. Charging system is next once I get this fixed. Going with rmstator and compufire rectifier.
 
Ty998 said....
"Also while doing test rides, the revs also hang and take awhile to settle"

Strange that it eventually idles "perfectly" at 1k- with an air boot /o-ring leak, I would think it would be more inconsistent. You sure you got the throttle shaft return springs anchored correctly after reassembling carb rack ? these springs pull throttle plates closed firmly (too firmly for my liking). If cable isn't hanging up or dragging, this thing should drop on idle stop screw asap.
 
tom203 said:
Ty998 said....
"Also while doing test rides, the revs also hang and take awhile to settle"

Strange that it eventually idles "perfectly" at 1k- with an air boot /o-ring leak, I would think it would be more inconsistent. You sure you got the throttle shaft return springs anchored correctly after reassembling carb rack ? these springs pull throttle plates closed firmly (too firmly for my liking). If cable isn't hanging up or dragging, this thing should drop on idle stop screw asap.
Click to expand...

It's something worth looking at again. However I am confident that is is closing securely. I'll spend sometime looking into the different suggestions made in this thread and update it on my findings.

Ya, if you give it enough time (again 30-90 seconds) it settles back down to a perfect 1k idle.
 
Dave8338 said:
Intake boot O-rings. :-\\\

All clamps tight.

Lightly oiled K&N.
Click to expand...

K&N filter is good, newly oiled.
Clamps around boots on each end of carbs are tight. Even clamp around snorkel to airbox is tight. :) I added that since trying to eleminate this problem.
 
If I were you I'd pull the carbs back off and replace all the internal o-rings, and the O-rings on the intake boots. Set the mixture screws to 2.5 - 3 turns open. Install everything back together and make sure all the band clamps are properly sealed, as well as the airbox lid.

Get the bike running again and perform a vacuum sync. Do all that and I'll bet you a beer the problem is gone.

Trying to diagnose running problems on a bike that hasn't been properly maintained is a frustrating exercise.
 
Nessism said:
If I were you I'd pull the carbs back off and replace all the internal o-rings, and the O-rings on the intake boots. Set the mixture screws to 2.5 - 3 turns open. Install everything back together and make sure all the band clamps are properly sealed, as well as the airbox lid.

Get the bike running again and perform a vacuum sync. Do all that and I'll bet you a beer the problem is gone.

Trying to diagnose running problems on a bike that hasn't been properly maintained is a frustrating exercise.
Click to expand...

Ya. I personally know a lot about these frustrations. When I started it wouldn't consistently fire on all cyclinders, had a rusted internal tank, cam shaft tensioner didn't work, 6 of 8 values had almost no clearance and it didn't turn over when you hit the start button. Now on to this issue... :)

I have to fix this issue, then the charging components and (with some luck) it should be ready to commute.
 
I only havea twin but if I have my idle mixture screws too far out then I get this behavior after she warms up.. Once I corrected the screws ( This is after all the maintenance suggested in the thread to ensure no vacuum leaks) The bike settles in RPM as she is supposed to. Not sure if you idle mixture screw controls fule like mine does.. If it controls air then it would be the opposite of having the screws too far in I believe..

Another symptom mine had from the screws was the inability to use the choke. Any attempt to open the choke killed the bike. Now I can use the choke as designed..
 
Fixed it. Took carbs off again. Checked all connections. Examined rings. Did not replace rings. Made some minor changes to boots. Increased mixture screw from 2 to 3 turns out and covered the previously open (whoops) hose connection that ran to airbox from engine breather. Runs great now. Thanks all!
 
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