Stuttering at higher revs.

philw

philw

Junior member
Location
lincs
Before i put my Jota to bed for the winter i went for a ride today, and noticed a pronounced stutter in the revs above 4500RPM- ish, this has happened before, the bike revs cleanly in all gears until i start to open it up at these revs, seems like not enough fuel getting through, usually it clears itself and revs like a good'n past 6K but other times it seems to keep stuttering, i should mention that the carbs were completely rebuilt by Keith at Scozia this time last year and there hasnt been a problem until recently.
One thing that has happened though is that i lost balance of the bike a couple of months ago in my shed and had to lay it gently down on the wooden floor, no damage done thankfully...coincidentally the stuttering might have begun after this, but i cant seem to remember whether it was doing it beforehand...any advice as to what to look at first would be greatly welcomed.

Thanks Phil..
 
The Sock said:
Check floatbowls for water.
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Thanks, i have never ridden it in the rain, so there shouldn't be any water in there, but i was going to remove the float bowls to see if any crud was dislodged when the bike went over, although there shouldn't be ,as stated above they were stripped, cleaned and rebuilt not long back.
 
Depending on what fuel you're using, and how long it's been left, ethanol will see water collecting in the tank and carbs. That's before worrying about what was in the bottom of the tank, now dislodged and pulled into the carbs.
 
Rob said:
Depending on what fuel you're using, and how long it's been left, ethanol will see water collecting in the tank and carbs. That's before worrying about what was in the bottom of the tank, now dislodged and pulled into the carbs.
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Thanks Rob, i guess a good starting point will be to clean the bowls and see if there's anything in there that shouldn't be, bike hasnt really been stood longer than a couple of weeks, its been used pretty regularly and i try to put 98ron in it when i can ,although i have filled up with the cheaper stuff once or twice.
 
Filters on the fuel taps too. Is the tank venting ok?
Also, a long shot, is it possible that lying the bike down has affected the ignition timing or damaged the pickup wiring etc?
 
Andy said:
Filters on the fuel taps too. Is the tank venting ok?
Also, a long shot, is it possible that lying the bike down has affected the ignition timing or damaged the pickup wiring etc?
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Thanks, i will be draining the tank and checking all the filters and carb float bowls etc at the weekend, the bike was very gently laid down on the primary chain (left) side when i lost my balance.
 
If you don't use it often and don't drain the float bowls, carbs are gumming up.
Or you have a loose wire somewhere.

Paul
 
philw said:
Thanks, i have never ridden it in the rain, so there shouldn't be any water in there, but i was going to remove the float bowls to see if any crud was dislodged when the bike went over, although there shouldn't be ,as stated above they were stripped, cleaned and rebuilt not long back.
Click to expand...
You dont have to ride in the rain to get water in your carbs. Most of the time it comes through the pump at the service station! :oops:
 
If fuel / water is not the cause, check battery and voltage reaching the battery while out on the road.
Had the same issue recently, connection spades at the rectifier diode had slight corrosion.
Cleaned up an the bike revs freely up to 8000 rpm.
 
If it's not water, check the following:
-cabeling of the key-switch
-Cabeling on the pickups!!! make sure the insolation is not fallen off of them partly, which might cause shortages...
-check for any lose cable, especially the ignition circuit
-if you have a DMC 2, check the connectors. I had a bike here that had a broken connector. cable still touching the connector but under certain revs, it vibrated so the cable lost contact
-fuses: they must sit tight with clean connectors. Brother had a 1000SFC with a fuse "dancing" in the contacts at certain revs...

Looking for water would also be my first attempt, but might be one of the others, too.
 
Also spark plug caps....the engine vibration ...at least on 120 degree engines, not sure how much of an issues is on 180s...can cause wear on the connections making them a loose fit and intermittent missing at certain RPMs only. If they wiggle around and pull off easy...taking into consideration the friction of the rubber caps....replace them.
 
As an aside, Plenty of additives on the market for over wintering ant ethanol fuel in the tank,mainly USA products which cater for their higher ethanol content..
 
Oh - one thing forgotten... I replaced my ignition coils due to a similar bad running, but even on lower revs. Now running fine again. These things are 35 years old, might simply have developed an issue...
 
Thanks for all the replies, after looking at all the fuel filters and flow it looks like it might be electrical, first port of call is changing the plugs and checking all HT connections, although the system is a new Ignitech fitted last year.
 
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