Hi folks

I've a tired 91 CBR1000f. It's about to go around the clock for the second time, and I think it's speedo is a replacement because it's been down the road before I got it - fairing and mirror are replacements.

Anyway I love the old girl and can't bear the thought of retiring it. My mechanic reset the valves 12 months ago because it wouldn't start in cold weather. It has started to misbehave again in the mornings, so I had a go at setting the valves again, with some help from this forum. (2 little kids, big mortgage - you know how it is).

But when I test rode it it backfires a heap and feels like it's running on 3 or perhaps 2 cylinders. No power and very rough.

BeforeI "fixed" it, it ran great once I got it to start. But not any more.

Did I set the valves wrong or do something another member has done themselves? Is there still hope for my bike?

 

you probably just hooked something up wrong electrically (maybe a coil is going to the wrong spark plug), or there could be a vacuum hose that's kinked or something.


i doubt you did anything seriously wrong. and don't be afraid to wrench on your bike! have a look at the wiring diagram or the vacuum hose diagram and figure out what's wrong. we're here if you need help

 

Firstly welcome to the CBR Forum Greg,

Now to your bike. As Conrice said above, have you checked all the wiring to the coils - often it pays to clean up all the contacts when the bike is apart. Next look at the vacuum hoses and also if there is a filter inline from the tank cherck that. Also if you took the tank off you may have moved some chit in the tank and partially blocked the in-tank filter on the petcock.

Work methodically through the problem, running it after each 'fix' and let us know how you go. We love to keep as many of the beautiful old CBR1000Fs on the road as we can

Cheers, SB

 

Thanks Fellas

I pulled the valve cover off again and let it cool down, then slowly checked and reset a lot of the valves. I think I had a lot of them too loose. It is runnning great again. I can only put it down to inexperience. The second time I checked the clearances it all went much smoother.

I think it was just that I am very low on a steep learning curve.

By the way I just run in and out of town on the highway for work, about 110km/70miles return each day, so I have put cruiser tyres on front and rear. The rear needed a tube to seat the bead. It is wearing very well and not bothering handling.n I even took it to the track and embarassed some other guys on better bikes. I've just put a 120/90 on the front. It didn't fit under the front guard, so I used the original guard as a plug for a new fibreglass guard. I built up the profile with spray foam and body filler to allow space for the bigger rolligng diameter. Now the cruiser front tyre fits and should last much better on the highway commute.

Don't hate me for limiting the handling of the old girl - I can change the tyres back to sports profile for track or twisties if I get the chance.

I can't wait to get back to the shed!

 

As far as I know a 120 is the correct size for a 91.............and BTW my Michelin PR2 gave me over 18000K's front and rear and was still fine in front, treadwise.......
Maybe someone in her past changed the front fender ?

Sometimes good mileage has to win out over performance - see "large mortgage and small kids"
Yup been there.........................

 

I won't hate you for putting on cruiser tires. Are they the Dunlop D404's? They wear and handle like steel. Just want to mention that 120/90 is the wrong size. 120/70 is the correct size.

What's the difference? The height of the 120/70 tire (from the ground to the wheel) is 84mm (70 percent of 120). The height of the 120/90 tire is 108mm. That means the axle is 24mm higher on the 120/90 tire. That considerably slows the steering. You could raise the fork tubes 24mm from the triple clamp. But the fender might smash into the radiator or other weird things happen. By the way, the tires should be radial. Are your cruiser tires bias ply? God forbid, I hope they are not whitewalls. Although they might look cool with white wheels.

 

Hi Grego,
interesting to note what happens when valve clearances are too big. Not something we hear about often.
Good shout on the tyre height SlowP. I was just about to ? that. /90 on a CBR? What were you thinking Grego?
I know things are tight. We're all in the same boat but that's a crazy idea.
I am loving the thought of you having clocked her twice though. Many congratulations on that. My old girl turned 100 before she got nicked.... but that's another story. In eight years I'll be telling a similar double clocking story.
Glad you got her running nicely again.

 

Hi all

You're right Slowpoke - the taller tyre wall did raise the front of the bike noticeably, and although it hasn't effected handling on the highway I'm sure it would tell in tight corners. It is very close to the front of the bellypan under the radiator - about 20mm/3/4" but I got away with it.

Now that I have gone to all this trouble to fit tyres that will suit my riding habits and prolong their life, I notice that something is twisted under the plastic. My rear axle is not horizontal while on the centre stand, so my guess is that the swing arm is bent, or the swing arm mount is bent, or less likely the centre stand mount is bent. As well as having been crashed before I got it, it has been stolen and recovered twice since then. I now have a VERY BIG chain so it stay where I leave it.

Having read all the arguements about uneven tyre wear and deciding that a harder tyre is the only way to reduce wear, I discover something is not straight. The front and rear wheels are not in the same plane, so although I don't understand how this will effect tyre wear and handling, surely it must be causing problems in both areas.

Anybody had any experience in straightening out the frames on these bikes? Being steel it should be possible to tweak it a bit without compromising the integrity of the frame right?

 

Sounds like she's either bent at the swing arm or at the tripletree in front.
In either event you'll have very strange tyre wear AND very poor handling -
But yes, you can have a frame "tweaked" without destroying the integrity.
Checking the wheel bearings, swing arm bearings and steering head bearings for wear is where I'd start and go from there.(I destroyed a front tyre in 500 miles with a bad front wheel bearing on one side) Next would be the wheel alignment to see how far "out of true" the frame may be.
Something as simple as slightly twisted front forks could also be your problem (which I had on a GPZ900R that I rebuilt). Loosening all the front end and sticking the front wheel into the corner of a wall and giving the handlebars a firm shove can straighten up the problem(having removed the fork brace)..................but It's not a precise solution

 

Shadow is right on about straightening the front forks. As for the "bent" rear swing arm, I would do some precise measuring before doing any bending. Like measuring the distance between the exact center of the axle, and the exact center of the swingarm pivot bolt. The stock muffler gets in the way so I use a caliper that I made. It's shown on post #5 here: https://cbrforum.com/forum/how-tos-8...ne-home-98352/.