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Engine hesitates at mid RPMs, can I still ride it?

  • Thread starter Thread starter volks28
  • Start date Start date
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volks28

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1983 850 GS no mods except K&N filter

I'm at a loss trying to fight an engine hestiation at mid RPMs. I just did a carb sync and I got it really close (all 4 in the same cm) at 3500rpm. Compression is 150 each cyl. new petcock (doesn't leak). K&N filters are clean and lightly oiled. Spark plugs are new, gapped, getting nice blue spark on all cyl. Just replaced the intake O rings and now the engine doesn't sputter if I spray carb cleaner/wd40 .

Other than that, the bike starts up real nice (within first second of cranking). It doesn't smoke much at startup, maybe a tiny bit, noting major.

After a short 5 mile run, pulled the spark plugs and cyl 1 through 3 are nice and brown/tan. Cyl #4 spark plus was a tad black. I did notice cyl #4 doesn't warm up as quick as #1-3

Question is, can I run the bike and try to live with it? Any risks of damaging the engine/valves?
 
Should be OK, check your valve clearance when you can,if they are out you will have to rebalance the carb's after adjustment.
On number 4 cylinder swap the plug lead's on that coil around to the other spark plug, see if it's a plug lead/spark plug cap prob.
But odd's on carby prob.
You did not say , have you changed the jetting/ needle setting's.
A bit of smoke on startup is no big deal.
 
Thanks for your suggestions!

Haven't "cracked open" the carbs yet to jet. As it is getting close to "high season" here in Canada, I rather try and enjoy a few rides this summer instead of tinkering / destroying a carb. I'm a very impatiant mechanic ha ha! :twisted:

So back to my original question, can I ride it anyways or am I taking a big risk?

gspaul said:
But odd's on carby prob.
You did not say , have you changed the jetting/ needle setting's.
A bit of smoke on startup is no big deal.
Click to expand...
 
That point when you have the hesitation, find a good road and run it at this point for about a mile if you can, hit the kill switch and the clutch at the same time,coast to a stop.
Pull out a spark plug , not No4,if the colour is not white you will be OK.
If it is , you run the risk of valve/piston damage.
 
Re: Engine hesitates at mid RPMs, can I still ride it?

If 1 through 3 are tan/brown and 4 is darker, I dont see any risk of damaging anything. You cant burn a valve or cook a piston with a rich or unburned mixture. If 3 is horribly sooty, you could foul that plug but thats about the worst I see that could happen.

Earl


volks28 said:
1983 850 GS no mods except K&N filter

After a short 5 mile run, pulled the spark plugs and cyl 1 through 3 are nice and brown/tan. Cyl #4 spark plus was a tad black. I did notice cyl #4 doesn't warm up as quick as #1-3

Question is, can I run the bike and try to live with it? Any risks of damaging the engine/valves?
Click to expand...
 
Re: Engine hesitates at mid RPMs, can I still ride it?

I think that it's probably what's happening. #4 is getting "fouled" so it's not always firing. Does that cause a problem in the long run (for valves) because the engine is sorta "unbalanced" for short bursts of time?

Thanks

earlfor said:
If 1 through 3 are tan/brown and 4 is darker, I dont see any risk of damaging anything. You cant burn a valve or cook a piston with a rich or unburned mixture. If 3 is horribly sooty, you could foul that plug but thats about the worst I see that could happen.

Earl
Click to expand...
 
Re: Engine hesitates at mid RPMs, can I still ride it?

With one cylinder burning differently from the other 3, it will increase your vibration levels somewhat. Depends on how far off it is. :-) Mechanically, it will not destroy anything. Its possible to accumulate enough carbon to cause a valve to be unable to seat and close properly. In that event, you would need to remove the head and decarbon it. (not a difficult task)
Before I replaced the engine in my 750, the old engine was just about done for and it would run black plugs no matter what I did. In the last 15K miles of sooty running before swapping out the engine, it never carboned enough to stop a valve from seating although it was fouling a set of plugs in a thousand miles. If your #4 is sooty and you have already done a carb synch, I would check the resistance on the #4 plug/resistor cap. It may be nothing more than need a new plug cap.

Earl




volks28 said:
I think that it's probably what's happening. #4 is getting "fouled" so it's not always firing. Does that cause a problem in the long run (for valves) because the engine is sorta "unbalanced" for short bursts of time?

Thanks
Click to expand...
 
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