Hey all,

I bought a '92 CBR for cheap in non-running condition. Today I got to make my first attempt at making the thing run. But, it still doesn't so I'm hopeful that some of you out there can make some suggestions for things I can do. Let me give you some background information from today's work.

I reassembled the bike completely, with air intake plastics and air filter. When I cranked the starter, I got nothing whatsoever. Tested all spark plug wires and all plugs -- all good to go.

Next I removed all the intake equipment so I was just looking at the top of the carbs. I sprayed some starting fluid into each of the intake ports and Vrrooooom! Well great, that means that ignition is good, compression is good (or at least good enough), and moreover the engine definitely has potential.

At this point I figured the carbs obviously weren't doing their jobs so I set about attempting to clean them. I opened the float bowls and verified that the valves moved as they should. I also removed two of the jets and blew carb cleaner through to make sure there was a clear path. But, I'm worried I didn't do enough. From the float bowl side, there were only two jets I could remove. One (per carb) had a flat head screwdriver slot, and the other had a 7mm hex. There was a third jet but I couldn't figure out how to remove it, and therefore did nothing with any of them. I also cleaned out the black vacuum thingys so they moved freely and returned as they were supposed to, when you push on them.

Next I replicated the previous scenario by dribbling a bit of gas into each carb intake port. Not much, just a few drops. The bike came to life again, sounding great! I found that by dribbling gas continually into all four cylinders I could keep it alive for a while. But as soon as I stopped pouring gas, the bike died. So here I checked the float bowls. To my surprise, bowls 3 and 4 had no gas whatsoever. But I can personally verify that the float valves were functioning as they were supposed to -- I got the quite clean.

As I see it, there's two problems. Problem 1 is that gas isn't getting to the two right-hand carbs. Problem 2 is that gas isn't getting from the float bowls to.... well wherever it's supposed to go next!

Can someone recommend a more thorough cleaning regimen for my obviously-gunked up carbs? It may help to note that the set has sat for at least 2 years prior to my getting it. I have a Clymer's manual, but I'm just not quite sure how I should proceed. Thanks!

 

I assume you checked to make sure fuel actually came forth from the tank? The petcock is both valve-controlled (by the indicator ****) and vacuum controlled (by the intake port #1 vacuum line)

1.) make sure the vacuum line is actually on the right way, and in place of course.

2.) you may have to suck on the vacuum line and keep a vacuum on it for a bit to let the fuel flow into the carb bowls. Takes longer than you think. I sucked the valve open (in the petcock) with my mouth and held that for like 1 minute or so with my tongue, then plugged it back onto intake port #1's vacuum doodad.

You said 1 and 2 get fuel, 3 and 4 don't. 1 and 2 are on the downhill side with the bike on the kickstand, which I'll assume was how it was resting. They'll get the gas first. Sounds like a no-fuel-provided-from-the-tank issue to me, but deedle around some more and keep us posted.

 

Clever idea. However, my bike will not start unless the side stand is up, so every time I was holding the bike vertical by hand.

In addition, I am sure that gas was getting to the carbs, because when I unplugged the fuel hose (at the 2-way splitter) gas poured out onto the engine.

But either way, gas wasn't getting from the float bowls to the cylinders. What could be causing this?

 

well that... sucks lots more than I thought it did. So. I'd say that the engine probably can't run on two cylinders, so if the jets in carb 1 and 2 are clean (and also submerged in fuel) then when you complete the challenge of filling bowls 3 and 4, it will likely be happy and come to life. I'd say that if you didn't, it might be advisable to pull bowls on # 3 and #4 carbs, and remove the float pivot pin and inspect the condition of the float needle for each carb. Make double ultra sure that they're clean. I wouldn't suggest chem-dip or anything voilent, because there is a rubber coating or something on the float needle that you could dissolve.

If the bowls are dry and you know that the right side feed line off the main line's T-fitting (the one that poured fuel on the motor) is obviously getting fuel, I think float needles are the only possibe offender for the fuel-not-in-carb problemo. Keep us posted!

 

clean the chambers in the top of the float bowls. blow everything with compressed air. either by mouth or air compressor blow through the fuel line feeling where the air is coming through weak.

 

OK, it's official, all bowls have gas. I repeated the drill a few more times and today they all seemed to have plenty of fuel in each one.

So the problem I suppose is gas getting sucked up now. Cowboy, where exactly am I to blow? Maybe I should remove all the float hardware, and just blow into every orifice I can find?



I've been referencing this write-up when cleaning the carb. When I unscrew #2 and 3, I am sure there are holes coming through. But I can't remove the other brass jet -- is this a problem?

Also, before I didn't adjust the pilot screw for fear of adjusting the tuning. Is this necessary to get a good cleaning? Maybe I should count the turns it takes to get it out, then blow compressed air into that hole as well?

 

That's my mode of operation. I basically just clean everything that I fully understand the function of to very high standards, and on holes where I have no idea what they do, I just spritz some carb cleaner down them, then blast them with compressed air and assure myself that it comes out somewhere else. Berga, per my factory service manual the pilot screws are 2-1/8 turns out from lightly seated for stock hardware. Have no fear, clean away. That's from Honda's copyrighted print for our bikes saying that.

 

I'm in the middle of cleaning right now with compressed air and carb cleaner. I noticed that as I blow air into the large diameter "breather hose", the black vacuum-jet things slide open. For most of my tests, I haven't had the air box or filter attached because it just gets in the way. So this hose was also not connected to anything.

Is this a problem for troubleshooting?

 

Wow, OK, I have a few updates. Although I tried to draw attention to the carbs, it turns out the fuel flow was the problem to begin with. Thanks Jimmy! I was clued into this idea when it would start and run for about 10 seconds then slowly die. This told me that the tank wasn't able to fill the float bowls fast enough. To confirm, I fitted a makeshift fuel tank without the vacuum line and just held it above the engine.

This did the trick -- it was then able to start and run pretty well. I ran it for 10 seconds or so, but then felt the need to fill it with coolant. I had been keeping it empty for rebuilding purposes.

Once filled, I ran the engine for another 5 minutes or so. Throttle response was excellent and it sounded pretty good.

However, there were two obvious problems.
1) There was intake backfiring at times. You could see small blue flashes in each intake port. The backfiring was not periodic, predictable, or even all that frequent, but it was definitely there. I think it may not have happened in cylinder 1. (Now that I think about it, cylinder 1 was not connected to the petcock as it normally is).

2) There was a lot of white smoke in the exhaust. I didn't have an experienced nose to tell me if the scent was from oil or from coolant. I fully expect a coolant leak, because as some of you may remember, I elected to reassemble the engine with a used head gasket, just to make sure the engine was good. (I also only torqued it to 25ft-lb instead of 35, oops). I plan to remove the spark plugs as soon as it gets cold to see if a particular cylinder seems to have been burning oil. But with 14k miles and in-spec cylinder bores, I think the coolant leak is more likely. After the plug check, I plan to fill the coolant with 100% water, run the engine, and then check the coolant for signs of oil. Also I will smell for a different exhaust smell than before. Then I'll run a compression test.

I apologize for hijacking my own thread, but maybe you guys can help with this question too. In reassembling my engine, there was one wire I couldn't find the attachment for. Please see attached picture. It seems to be a temperature sensor, but the PO labeled it "oil temp." There's another similar sensor that I placed on the coolant flow. Also fyi, the temp sensor was working today when I ran the engine. Does anyone know where this sensor wire goes and what it's for?

Any comments/opinions appreciated. I'm just trying to troubleshoot this bike one step at a time.

 

The carbs need to be tuned after all the work you've done on the bike. Plus you have other suspected issues (like the gasket).

Me personally, I'd not try to really dig into anything but the basic running until I got to the point where I could ride it a bit. Too many variables and working on different parts of the engine at the same time could skew diagnosis. But the backfires are prolly the carbs complaining about being out of whack (adjusting the jets, balancing the carbs)