Kr1 wont rev + backfire

ScottaKR · Post by **ScottaKR** » Fri Sep 16, 2011 11:07 pm

scooby_hugh wrote:my flywheel puller hasnt arrived yet but iv had the bike running, it will run for a while with about half throttle but still wont rev and theres alot of induction noise with the carbs being half open and the revs are only about 1000 or so, it runs on both cylinders occasionally backfiring

where should the vac hose on the fuel tap go to? mines plugged!

One end goes to the left side carb (you should find a brass nipple to plug it to) and the other end goes to a nipple on the fuel tap. If your left carb dosn't have this nipple (also assuming that the left carb isn't fitted to the right hand side) you could just set the tap to the prime position which bypasses the vacum circut in the fuel tap.
Also, do you have a proper fitting support under your air filter? Some people have found them missing before and had similar problems caused by the air filter being sucked into the carbs and choking them.

All that said, the woodruff key is sounding a more likely suspect with these latest symptoms you describe, but it's always worthwhile checking over the simple things first.

scooby_hugh · Post by **scooby_hugh** » Sat Sep 17, 2011 12:07 pm

No it starts without choke! Carbs are squeaky clean inside, no blocked jets, engine mounts are fine not cracked i shimmed them a little too so they are perfect, i could try no exhausts! Wouldent hurt, i start it in the prime position but i will re attach the vac hose. Im almost sure the backfire switches sides when leads are swapped but im not 100%, need to get that flywheel off and have a look!

Howie · Post by **Howie** » Sat Sep 17, 2011 3:03 pm

Im almost sure the backfire switches sides when leads are swapped but im not 100%

You need to find out for sure fella. But in the mean time pop your plugs out & describe the condition & colour, run the bike for a while just at idle then have a look once the plugs have had time to cool.

I just want to rule out the carbs running too rich or too lean. The fact your Kr will start without choke may point to incorrect fueling

And as Scottakr pointed out, just pop your airbox lid off to make sure the filter hasn't fallen in or isn't knackered.

One last thing for the mo, are your needles set to the correct ring position? It should be in the fourth groove if I remember rightly(?)

If I get time when I get in tonight (we're all off out for a Chinese $\:D/$ ) I'll pop all the relevant carb details on this post.

scooble · Post by **scooble** » Sat Sep 17, 2011 6:04 pm

I helped to rebuild a friends NSR125 and found it wouldn't rev if you blipped the throttle, only to find a tea towel in the airbox instead of a filter

scooby_hugh · Post by **scooby_hugh** » Sun Sep 18, 2011 2:47 am

Theres no airbox at the mo, they have ram air filers which are removed, it wont idle properly and if it runs the plugs are new so they dont really colour they just get abit wet, im leaning toward the probability of crank seals i just want a fresh engine now and be done with it, its got to be done at some point anyway!

Bikemike · Post by **Bikemike** » Sun Sep 18, 2011 8:45 am

If I were you I would sort out this running problem before you refresh the bottom end, because I'm not convinced this is your problem. I have first hand experience of crank seals failing and the symptoms were nothing like yours.
Crank rebuilds are expensive, I would start off with the electricals.
Plugs and leads are dirt cheap, new good quality replacements first. As has already been recommended fit an extra earth cable. Try a known good coil from a running bike. The stators are weak on these bikes, a new one fixed a running fault on mine I had spent ages chasing around.
If that doesn't fix it move to the carbs. Again, if possible swap for a known good set from a running bike. I see you are not running an airbox. Kr's are notoriously difficult to set up without an airbox, try going back to a standard set up.
Where in the country are you? If you are near me you are welcome to come and try some known good parts from my bike.

Getting back to my original point, I would hate for you to spend money on a crank rebuild only to bolt your shiny new engine in and find it still runs like a bag of shite.

Mike

Edit-Ah. I've just noticed you are in Guernsey. So much for my idea of popping round!

tescr500 · Post by **tescr500** » Sun Sep 18, 2011 9:34 am

crank rebuild yeah expen still sorting mine but might have a second hand 1 coming, i expect you have already been told but make sure all jets are clean in carbs it doesn't take alot to play up, check for air leaks rubber manifolds ok not perished and leaking, also check all elec connections, check your earth on regulater.

JanBros · Post by **JanBros** » Sun Sep 18, 2011 9:35 am

definitly try fitting the airbox before looking any further

scooby_hugh · Post by **scooby_hugh** » Sun Sep 18, 2011 11:18 am

Okay lots to try! I dont have an airbox, it didnt come with the bike! Iv tried a known coil, i will borrow a stator off my mate an tripple check carbs or borrow some too, rubbers look okay inside, i know crank rebuilds are expensive but i do want a good fresh engine i can trust iv had too much hassle in the past with bearings collapsing and smashing the crank cases to bits!

maccas · Post by **maccas** » Sun Sep 18, 2011 11:40 am

What size jets are fitted in the carbs?

If they are the standard size main jets (135 for a kr1s and 130 for a kr1?) then i'm pretty sure it won't rev without an airbox

Maccas

scooby_hugh · Post by **scooby_hugh** » Sun Sep 18, 2011 6:10 pm

138 mains, its got lomas pipes and kr1s barrels

Howie · Post by **Howie** » Sun Sep 18, 2011 7:54 pm

You could have told us it didn't have an airbox

You don't need a new (replacement) engine because I honestly don't think its the engine thats the problem & to be quite honest if you were to buy a replacement engine from a breakers you would be £400 out of pocket & no further on.

You will be better off spending the money on an original airbox, jets & needles & getting the bugger to run sweetly.

Then you can start to tune it

As maccas & janbros have mentioned, these bikes need an airbox like a cart needs a horse, an inspector lewis needs a Morse & lets not forget of course, Posh spice needs another Porsche.

Sorry everyone

scooby_hugh · Post by **scooby_hugh** » Sun Sep 18, 2011 8:39 pm

I will buy an airbox but theres still something dodgy going on as the previous owner had it running spot on with ram air filters and one morning it developed this problem out of the blue!

ScottaKR · Post by **ScottaKR** » Mon Sep 19, 2011 7:48 am

scooby_hugh wrote:I will buy an airbox but theres still something dodgy going on as the previous owner had it running spot on with ram air filters and one morning it developed this problem out of the blue!

Ram-air filters and 138 mains

sounds like a recipie for serious lean-out. Most people that have run those style filters on these engines have had to go up to about 150 mains to get the fuel mixtures right and avoid nukeing things.
Now, are there any other little things wrong with the bike (like the tacho not working right)? I ask this because sometimes these little things may seem unrelated, but can help to diagnose problems like this.

Luders · Post by **Luders** » Mon Sep 19, 2011 9:15 am

I ran a semi pressurised system at the start of the season, with a very lightly tuned engine and can confirm I was running 142 - 147 jets depending on the conditions.

I can also confirm that a KR doesn't need and airbox to run, but will take a lot of fiddling with different jets, to get it close to running properly. I also wouldn't recommend running one without an airbox, unless you have no choice (see the Yamasaki for more details).

I'm sure someone on here has an airbox you can buy and I'll be surprised if that doesn't fix your problem.