Hi guys,

First let me say I'm not the most mechanically inclined person. Which is why 99% of the time I just rely on a mechanic and hope for the best.

I'm just about at the end of my patients with this old girl, 1994 CBR1000F. Let me explain what has been done already and what is still happening.

My cam chain was stretched out and the tensioner was worn out. I had both replaced. The bike has 58,000 kilometers on it. Turns out the cam chain in my bike was 4 mm longer than the new one. I had the carbs cleaned and adjusted, 9 of the valves needed adjustment and I had a tune up.

Myself and my mechanic assumed that the cam chain was the reason for my bike running badly. After all was said and done here is how she runs: I live in a warm climate, Costa Rica, it's about 75 - 85 degrees during the day. She starts with out the choke, with no gas on the first try every time. She will not start with the choke on. Idle starts out at 2,200. With in 1 minute it drops to 1,100. After she is warm the idle is at 500. If I try to adjust the idle while the bike is warm to 1,000 rpm (which takes about 3 full turns), some times the idle will come up to 4,000 rpm while driving. From 1,000 - 3,000 rpm there is almost no power. For example, while rolling at 3 - 5 mph, in first gear I can roll the throttle to wide open and hold it there. It will take 6 seconds to reach 3,000 rpm in first gear, yes I timed it. It's rather sad when the 100 cc bikes walk away from you at an intersection.

Also I'm getting 12 - 13 miles per gallon. Top speed is about 200 - 210 kph. I would guestimate I'm missing about 50% of the power even in the higher rpm range.

My mechanic says he adjusted the carbs as best he could but they are too worn out (exact words in spanish, gastado).

I'm not sure if I should invest more money or sell her at this point and let some one else deal with it.

What do you guys think is wrong?

 

One suggestion. Look at the carb intake rubber boots. With age they get hard and may split, causing a vacuum leak. One symptom beyond poor performance is erratic idle speeds.

Add: If an attempt has been made to sync the carbs with the boots bad, they will need to be reworked after the vacuum leak is fixed.

 

If it starts without choke, won't start with the choke, and only gets 12MPG, it seems to be super rich. Like one or more of the float needles are leaking fuel, the air cleaner is clogged, or the choke is stuck on. If it was mine, I would also double check to see if the cam timing is correct and that the intake and exhaust cams weren't switched. I would check the spark plugs and also check the ignition timing with a timing light.

 

That, too!

 

Hmm - what the other guys said. Also, if you were to sell the bike you would not be getting the right price unless you get this problem fixed. I have seen complete banks of CBR1K carbs go on ebay for not a huge amount of money. Or you could take them off yourself and send away (if there is anywhere to send them where you live) for an overhaul. Basically the more work you do the less you are going to spend on a mechanic. With that kind of consumption i'd have thought that you would likely find the problem if you took the carbs off and examined them carefully.

Whatever happens, good luck and let us know.

 

Couple of things.... Check the settings on the idle jets, and the float heights. You can rattle the floats (once they are removed) and see if they are letting fuel into their bodies. I had a bike with VERY similar symptoms, and this was the issue. One extra symptom mine exhibited was the engine failing to reduce revs properly. ie open throttle, close throttle, engine stays at the same revs for ages.

Anyway, hope everything end up fine.

Ara

 

The revs do tend to stick. I'll check every thing this Sunday and let you know how it goes.

 

Ok I took the bike apart tonight. Here's what I found.

The fit between the air cleaner housing and the 2 tubes is really bad. Some one tried to seal them with some rubber caulking compound. As it is right now, there are places on each one where you can see right though the gaps with a small flashlight. It looks like they should just fit in there perfectly with the ribs on the tubes. The tubes themselves are in decent shape but I figure I need to order new ones. On mine it's a real reach between the air box, tubes and carbs. Is this normally the case?

Also, hose number 19 in the parts catalog, under air cleaner. What purpose does it serve? I thought it might be to drain any rain that would get sucked in, but it's plugged at the bottom.

On the bottom of the carb, their are two tubes that come down. In the manual they are called air bent tube, part number 4. On my bike they are not connected to any thing. Are they supposed to be connected to some thing?

The breather tube, part 7 on page 5-3, on my bike is plugged. What is the purpose of that tube?

The floats all look decent although the carb gaskets could be replaced. They are at the end of their life time.

The bike is back together and running just like before though. I'm looking forward to getting this solved.

Thanks for the help

 

You shouldn't need to replace the tubes unless there is a split in them. If they have a gap them just get out the silicone.

I don't know what you mean by a reach to the carbs. With the airbox bolted to the frame the tubes should be all the way up against the carbs.

The 2 tubes on the bottom of the carbs are not supposed to be connected to anything.

That breater tube on the airbox is where all the oil and water that can collect in the airbox to drain out. It is left plugged so that it can be drained into a container.

 

If you are sure that you have good spark and good spark wires with no arcing, I would do the following.

Check the compression of each cylinder with it cold and then warmed up to eliminate valve clearance issues.

With the tank up already, double-check the cams positions and timing.

Then remove the carbs and give them a good cleaning. It almost sounds like low speed jets are clogged. You may have to remove the air box to reposition it anyway.
It also sounds as if the float levels are off a bit. You can check them when the carbs are off also. Then check to see if your mechanic replaced the rubber caps and screw when he tried to balance the carbs.

I am not buying into the fact that the carbs are too worn out. That is non-sense.