Bike running rich & jerky at low rpm

Need advice on which oil to use or which tyre best suits you? Share your topic and get help here.
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Bike running rich & jerky at low rpm

Post by dkj1000 »

Hi, I'm hoping someone can help with my VTR it is running rich and is very jerky in the 3 to 4000rpm range which is about 100 - 110kph, once I open the throtlle it seems to be fine.
When I first test rode the bike before buying I didn't notice this probably because I only took it for a short ride and I was giving it a bit of a handful.
I went back a week later to pay for the bike and on my first ride after picking it up a wa-ker in an SUV deliberately brake checked me at 100kph on a damp road and I crashed sliding down the road. I was probably riding a bit close but it was the last thing I expected to happen and have never had that sort of thing happen to me in 30+ years of riding. Stupid thing was I had ridden all the twisties and was on my way back home.
I was lucky enough not to brake any bones and was able to ride it home with my pride dented, I couldn't fu-king believe it. Riding it back home was the first time I noticed the jerking maybe because I was taking it easy?

I was insured and managed to get the bike repaired and got it back just before christmas.
I pulled the carbs apart the pilot jet, main jet and needle were caked in old crusty fuel the previous owner must have not ridden it for some time.
I got new pilot jets (45's) and main jets (175 front, 178 rear), cleaned up the needles and got the main jet holders ultrasonically cleaned, the rest of the carbs looked OK floats, chokes & diaphragms etc.
I set the fuel screws at front 3 turns out and the rear 2.3/4, put the bike back together balanced the carbs and it is till running rich on both cylinders (pulled the plugs ) and the jerky running seems to be more pronounced :-(
I've pulled the carbs off 2x more times to recheck everything and it is still the same.
From what I've read the pilot jets control from 0-25% throttle opening and maybe the fuel screw settings need to be fine tuned, I don't have access to a 90 degree screwdriver to make the adjustments with the carbs in place, the bike seems to idle fairly good perhaps a little bit of rpm variation.
I have done a compression test and the front cylinder is 140psi and the rear 150psi (late model VTRs are supposed to be 176psi). looking down the inlets ports the back of the valves are also caked in old crusty fuel.
The other thing is I can't be sure that the bike was 100% before I crashed it??

Any ideas or assistance would be greatly appreciated, luckily I have my trusty 99VFR800 to ride at the moment but I miss the throbbing V-twin...........
User avatar
MacV2
Posts: 17418
Joined: Sun Jan 21, 2007 12:07 pm
Location: Grain

Re: Bike running rich & jerky at low rpm

Post by MacV2 »

Making up since 2007, sometimes it's true...Honest...
User avatar
popkat
Posts: 2804
Joined: Sat Apr 28, 2012 9:32 am
Location: Devon

Re: Bike running rich & jerky at low rpm

Post by popkat »

Check that you have the chokes seated correctly, the front cable holder is easily broken too.

Don't worry too much about compression figures being a b it low, that could just be down to the tester your using, better to look at the difference between cylinders, 140-150 isn't too bad, but closer together would be better. Have you checked the valve clearances, this would give a slight drop or difference.

Once you've checked that stuff out try putting some fuel additive/cleaner in the tank, I use Forte Moto 1&2, you put both bottles in with half a tank then fill it up. it will improve things once it starts getting through the system, will clean up internal passageways in the carbs and helps clean carbon deposit's from valves. you should notice a difference after a few hundred K's.


.
http://www.bidefordmotorcycles.co.uk
2014 CRMC Post classic Superbike champion.
2014 CRMC Post classic senior production champion. On a Suzuki Katana 1100
My bikes, Firestorm, Suzuki GSX-s1000 Katana, VFR800Fi. Projects, 1986 popup Katana, 3 XJ600’s
User avatar
fabiostar
Posts: 7542
Joined: Sat Jun 01, 2013 3:53 pm
Location: sunny belfast

Re: Bike running rich & jerky at low rpm

Post by fabiostar »

as popcat said the choke can give all sorts of problems, i know this because i chased the problems you are having and it turned out the front choke wasnt returning to the seated postion when i knocked it of...

also your pilots seem a little far out, try a half a turn in each.
the older i get,the faster i was :lol:
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Re: Bike running rich & jerky at low rpm

Post by dkj1000 »

Thanks guys for your feedback much appreciated.
I'm fairly confident that the chokes are all good and seating properly, but will recheck if I end up having to take the carbs out again.
Will definitely get some fuel system cleaner this weekend and hopefully after a couple hundred kms I will notice a difference
I will need to borrow or make a 90 degree screwdriver to adjust the pilot screws in place.
Regarding the valve clearances I wouldn't of thought that they would need checking with the low kms and the previous owner was a senior citizen? but I will keep that in mind.
I was also speaking to a workmate and he said I should try removing both washers from under the needles, but from reading 8541hawk's post he said to only remove the front one....

Wiil report back with how the cleaner goes.
User avatar
8541Hawk
Posts: 2066
Joined: Sat Jul 21, 2012 5:21 am
Location: Bella Vista, AR

Re: Bike running rich & jerky at low rpm

Post by 8541Hawk »

Just to cover all the bases, have you check the drive chain?
If it is too tight or if it has frozen links it could also cause some of the issues you have described.
Loud pipes don't save lives, knowing how to ride your bike will save your life.
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Re: Bike running rich & jerky at low rpm

Post by dkj1000 »

Have checked the chain tension and for frozen links, it all looks good.
I brought some Penrite fuel system cleaner today so will add the recommended dosage and use the VTR next week and hopefully I'll see an improvement
tony.mon
Posts: 15943
Joined: Wed Jul 25, 2007 10:46 pm
Location: Norf Kent

Re: Bike running rich & jerky at low rpm

Post by tony.mon »

That's a good point re the chain tension.
It's hard to check it on these bikes unless you have someone of a similar weight sitting on it while you check the tension.
It's not falling off, it's an upgrade opportunity.
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Re: Bike running rich & jerky at low rpm

Post by dkj1000 »

Unfortunately I haven't any luck with my bike yet and I'm really not sure what to look at next.
I have checked or rechecked the following
- valve clearances and they were fine
- rechecked the carb balancing and made a slight adjustment
- I have only done approximately 100kms with the fuel system cleaner not 200kms as suggested, mainly
because the low speed surging is pissing me off!
I took it for a short test ride yesterday trying to make sure that the symptoms I had identified were correct.
It is definitely crap below 4000rpm and gets better above that but I'm fairly sure that there is some slight surging in the higher rpm but it's definitely less noticable (maybe it's my imagination ?) When you open the throttle it pulls nicely.
It starts easy enough, the idle isn't as smooth as it should be and gets better once it warms up (maybe the pilot screw adjustment would help that)
I haven't checked the throttle position sensor and haven't replaced the spark plugsyet, someone suggested removing the washer from underneath each of the needles but my thoughts are that that shouldn't be necessary...
It is definitely running rich from the condition of both spark plugs and I'm fairly sure my problems all started after I crashed it? could it be electrical??
Any more suggestions would be greatly appreciated
tony.mon
Posts: 15943
Joined: Wed Jul 25, 2007 10:46 pm
Location: Norf Kent

Re: Bike running rich & jerky at low rpm

Post by tony.mon »

Choke stuck on?
It's not falling off, it's an upgrade opportunity.
User avatar
fabiostar
Posts: 7542
Joined: Sat Jun 01, 2013 3:53 pm
Location: sunny belfast

Re: Bike running rich & jerky at low rpm

Post by fabiostar »

turn your pilots in a bit. you said one of them was 3 turns out? thats pretty rich.
the older i get,the faster i was :lol:
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Re: Bike running rich & jerky at low rpm

Post by dkj1000 »

I'm fairly sure the chokes are all good, they feel like they are returning and moving freely. But I have noticed that when I pull the choke out after it's warmed up it does't seem to affect the running in any way.

I've managed to borrow a 90 degree pilot jet adjusting screw driver but it's fairly difficult to adjust and count the turns, I might be better off taking the carbs off to do it.
I did read on a post that with 45 pilot jets the fuel screw should be Front 3.0 turns out and 2.75 for the rear. (This was fairly close to the original settings before I took the carbs apart). With 48 pilot jets it should be 2.5 & 2.25 respectively
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Re: Bike running rich & jerky at low rpm

Post by dkj1000 »

Have just pulled the carbs apart for another look and checked the needle jets (guides) as suggested my a workmate, they are definitely worn oval in particular the rear one.
As previously mentioned the bike has only done 14K, but there was a lot of old hard petrol varnish build up on the needles which I managed to clean off.
It appears that the needle jet is not a replaceable OEM part but I have read on the forum that it has been done.
"The needle guide is pulled out with a slide hammer and pressed in with a guide rod machined fit to the ID"

I googled VTR needle jets and could only find "Factory Pro" in the states and they want the whole carburetor sent to them
Can someone please advise if there is a company in the UK that makes them and what is involved in removing the old jets (guides)
Attachments
worn needle jet.jpg
User avatar
Stephan
Posts: 983
Joined: Sun Apr 15, 2012 6:58 pm
Location: Prague, Czech

Re: Bike running rich & jerky at low rpm

Post by Stephan »

dkj1000 wrote: Mon Mar 05, 2018 7:10 am I'm fairly sure the chokes are all good, they feel like they are returning and moving freely. But I have noticed that when I pull the choke out after it's warmed up it does't seem to affect the running in any way.

I've managed to borrow a 90 degree pilot jet adjusting screw driver but it's fairly difficult to adjust and count the turns, I might be better off taking the carbs off to do it.
I did read on a post that with 45 pilot jets the fuel screw should be Front 3.0 turns out and 2.75 for the rear. (This was fairly close to the original settings before I took the carbs apart). With 48 pilot jets it should be 2.5 & 2.25 respectively
I played with pilot jet sizes and settings quite a lot, including aft reading on each cylinder, and realized that if you set 1.75+2 or 2+2.25, it will always work good. Turns above 2.5 are too much.
dkj1000
Posts: 9
Joined: Tue Feb 06, 2018 7:22 am

Re: Bike running rich & jerky at low rpm

Post by dkj1000 »

Hi Stephan,
thanks for your advice, but as far as I know those settings are for "48" pilot jets which are larger than my "45's therefore when you have "45's" they have to be screwed out further.

I really need someone to advise if they know how to remove worn needle jets (guides) or where to buy them from please
Post Reply