Author Topic: Jittery at low revs (Read 11529 times)

darrsi · « **on:** 12 July 2012, 07:03:09 pm »

I've noticed recently that my bike has been what i can only describe as 'jittery' between 2000-2500rpm.

Once i go over 2500rpm it's fine, picks up well, with no other issues or flat spots.

The more i think about it, it's probably been doing it for a while but as it's been gradual i've not taken too much notice of it, but now it's quite obvious.

It feels almost like i'm in the wrong gear, but i've tried different things and it's still there between those rev. ranges.

Any ideas? I'm sure it's not a difficult one if it rings a bell to anyone, but it's not something i've personally encountered before?

chunk166 · « **Reply #1 on:** 12 July 2012, 07:26:54 pm »

I had a similar problem with mine at low revs,turned out to be the plug caps,you might just need to trim a little of the HT leads??

http://foc-u.co.uk/index.php/topic,3648.0.html

hope this can help you?

Ray

AdieR · « **Reply #2 on:** 12 July 2012, 07:32:13 pm »

Is it constant, or does it only happen at particular times (eg cold / hot / wet weather)?
When was it last serviced?

First thing I'd look at is spark plugs / HT leads and replace them if necessary (the plugs will have tell-tale signs by colour / appearance).

Dead Eye · « **Reply #3 on:** 12 July 2012, 07:47:05 pm »

Just my two cents but it could it be that the carbs need balancing? Mine is a little rough below 2.5k revs and im sure its the carbs, just haven't bothered to do anything about it yet as id like to do it myself but its expensive to get the correct tool

darrsi · « **Reply #4 on:** 12 July 2012, 08:16:22 pm »

Weather at the moment is all over the place but i don't think it's made any difference, i was in rain AGAIN on the way home from work tonight but it's been doing it in sunshine as well.

I do my own servicing generally.

It's not missing a beat or anything, it's just kind of of jerky. It seems to idle quite happily as well.

I've already thought about carb balancing and was wondering if that would be suggested.

Chunk166, did you trim the other end of the HT leads at all, or renew them at all, or just change the plug caps?

chunk166 · « **Reply #5 on:** 12 July 2012, 08:21:21 pm »

I just trimmed the plug cap ends about 5mm & put on the new caps,been running really good even in the bloody rain,but i would say it started after a down pour but still done it in the dry!!!

Ray

darrsi · « **Reply #6 on:** 12 July 2012, 08:40:24 pm »

I presume they were just the old push/screw in type?

I'm just looking at the online manual but can't see any reference to the HT leads, ideally i'd prefer to change them as well just in case there's a weak spot in them? I was just curious if they were push/screw fitted the other end as well? I know some can be crimped........and i've no doubt they'll be in a bugger of a tight space as well.

It's hacking it down with rain where i am, otherwise i'd go and have a look.

I need to find where to get those caps from on the quick as well, from a shop, as i'd like to change them this weekend if possible?

red98 · « **Reply #7 on:** 12 July 2012, 08:50:27 pm »

ht leads are sealed to the coils,if you need to replace them its new coils time (two on the fazer) the ends do go hard after a while so trimming the ends is a great tip,look at the plugs and check colour and condition and replace if need be,balancing carbs will give you an instant inprovement if they hav`nt been done for a while...if that lot dos`nt work try cleaning the carbs

.....let us know how you get on

chunk166 · « **Reply #8 on:** 12 July 2012, 09:01:40 pm »

as red98 has said,they are sealed at the coil so not an option to trim that end! your probably looking at £20 for the 4 plug caps

Andy FZS · « **Reply #9 on:** 12 July 2012, 09:25:18 pm »

Mine was rough under 3k revs and felt as if I was in too high a gear, so I balanced the carbs and now it will plod along at 30mph in 6th gear without any bother.
Andy

darrsi · « **Reply #10 on:** 12 July 2012, 09:34:54 pm »

Just checked, i had a full carb overhaul at the beginning of last year at PDQ tune up mechanics, when i also had my new end can put on, and as i only really use the bike for work these days that would only mean around 6000 miles at a guess?

I've fortunately got a Hein Gericke a mile up the road from me, and i've just seen that they sell the NGK caps for £4.35 each according to their website, so i can change them at the weekend now

Hopefully i'll be lucky and it'll do the job, if not i'll address the carbs again i s'pose!

New caps won't hurt anyway, seeing as riding conditions seem to be permanently shite in this country!

chunk166 · « **Reply #11 on:** 12 July 2012, 09:44:06 pm »

Fingers crossed you'll get it sorted soon

darrsi · « **Reply #12 on:** 12 July 2012, 09:55:53 pm »

Yeah, cheers for the help lads, much appreciated, i'll let you know how i get on

darrsi · « **Reply #13 on:** 13 July 2012, 11:37:38 am »

Had to get plug caps from a bike shop near my work, only £3 each, bargain

darrsi · « **Reply #14 on:** 16 July 2012, 10:13:29 am »

UPDATE: Well i must admit i have been pleasantly surprised, i had the HT leads trimmed and plug caps changed to the NGK ones and lo and behold the problem seems to have been fixed!!
I tried different gears in the offending 2000-2500rpm range and all the 'jittering' seems to have gone, and the engine actually sounds and feels a bit smoother as well.
Happy days, and thanks again for the tip, and input.

Andy FZS · « **Reply #15 on:** 16 July 2012, 08:31:15 pm »

Which plug caps did you get straight or angled? Do you know the part No? I ask as I think I may need some.

Cheers
Andy

darrsi · « **Reply #16 on:** 17 July 2012, 12:48:03 am »

NGK SD05F, the straight ones, they worked out cheaper in the shop than Flebay eventually.

Use the old protective rubbers at the bottom of the plugs that should be on the old ones.

It's a cheap way to start if you have a similar issue, although i'm sure cropping the end of the HT leads plays just as much a part!.

darrsi · « **Reply #17 on:** 02 August 2012, 12:45:36 pm »

Worth having a look at this post i found regarding this problem as it hasn't actually gone away like i had first thought!!
At least i've got some shiny new plug caps now anyway

http://www.fzrarchives.com/ipb/index.php?s=2dcae0a7b7721ee4488932b5125ec678&showtopic=56747&st=0&p=473232&#entry473232

renegaderacer · « **Reply #18 on:** 02 August 2012, 01:10:46 pm »

I'm not sure if this has any relevance as it was on a car but my old Impreza had exactly the same problem and I changed the coils (not cheap for 4 Impreza coils!) and, voila, problem cured!

I also had the same probelm on my race bike but that turned out to be a split HT lead and monsoon conditions at Snetterton!

Giles

darrsi · « **Reply #19 on:** 02 August 2012, 03:27:04 pm »

I'm open to any suggestions at the moment!!
For the record, the plugs are absolutely fine, i put Iridium one's in about 8 months ago and the colour of them was spot on, in fact they didn't really even need a clean but i brushed them all up and gapped them anyway.

bikerboys · « **Reply #20 on:** 02 August 2012, 11:24:23 pm »

have you draned the carbs worth a go might be some crap in the bottom of them

ElkWorks · « **Reply #21 on:** 03 August 2012, 08:44:25 am »

my thundercat did this for 35000 miles, didnt change the plugs, or anyhting, just kept on top of oil servicing and put up with it.

fazer does exactly the same, but all i do now, as i did with the cat, was change down a gear.

darrsi · « **Reply #22 on:** 26 August 2012, 03:26:57 pm »

GOOD NEWS

I had a hunch after a while that even though i'd changed the air filter about 2 months ago, the bike felt like it had breathing issues.
So yesterday i changed the filter for a K&N, also noticing what a snug and perfect fit it was, compared to the one that was in there.
I just took the bike out for a blast and i can't believe the difference!
All the jittering and jerkiness has disappeared between the 2-3000rpm and when i opened it right up the response was awesome.
It was like i'd just fed the bike a whole packet of Fisherman's Friends.

The bike was always responsive anyway but now it feels brilliant, and overtaking was just a complete joy with full confidence.
Such a simple and cost effective mod. but with fantastic results, that's just made my day

red98 · « **Reply #23 on:** 26 August 2012, 09:10:57 pm »

nice one darrsi,i take it your pleased with the filter then

......just out of interest,what make was the old filter

darrsi · « **Reply #24 on:** 27 August 2012, 12:56:07 am »

From memory it was Hi-Flo something, but very ill fitting compared to the K&N, not something that bothered me really, as it's not like it was going anywhere.

A fantastic difference though, i highly recommend it by all means, and you don't even have to clean it for 50,000 miles!!!