1990 CBR600 FL non runner

[Stef]

Hi,

I have a Honda 1990 CBR600 FL I’ve had it on and off the road since 1995 but it’s been standing for about 2 years without starting, undercover in my shed, and now it’s not running well at all.

After some trouble and some help from a friend I got it started, now, it starts almost immediately on full choke but if I try to relieve the choke or increase the throttle, it cuts out, it ticks over a little rough with the occasional backfire through the exhaust.

To date I have:-

Fitted new Battery (the old one lacked power)

Replaced the old starter solenoid (But it wasn’t necessary)

Drained the old fuel to replace with new

Cleaned and set the Spark Plug gap

Removed cleaned and replaced the fuel tank Tap assembly

Checked the flow rate from the fuel pump (recommended flow should be a min of

700 mls /min. Actual Flow 1800 mls/min)

Fitted a new fuel pump relay

Removed the Carbs and freed a sticky Diaphragm piston, the other 3 working fine

removed and cleaned all float valve seats and replaced with new washer

checked all and replaced 1 sticky float valve, and removed and cleaned all Main, Needle  and Pilot jets with carb cleaner and compressed air.

replaced all 4 Pilot mixture screws with new, all set at 2.5 turns back from stop.

cleaned all bowls and fitted new ‘O’ rings to drain screws.

new seals to bowl covers

Finally, I cleaned and released the idle screw assembly which was rusted solid.

I put it all back together and I still have the same problem, no change. Any advice would be gratefully received.

Stef

 

[Simon Davey]

Hey @Stef welcome to the forum. 

 

You've probably done, just about everything you could do to those carb's. 

I have no further suggestions, but there are some guys on here with some proper knowledge. 

Hopefully said guys will be along soon. 

Edited October 29, 2024 by Simon Davey

[RideWithStyles]

Well it sounds like the carbs haven’t been balanced, you haven’t mentioned that so id assume that needs doing because if its choke (extra fuel) ok but when off it stalls, and extra throttle might not help if say one is very rich to get/keep going (hence the back fire), one is middling to slightly low and two are far too lean that can screw it up especially if its say 1and 3 or 4and 2 etc. 

if you ever remove carbs they should be rebalanced, no ifs or buts.

assuming you set the needles height correctly?
And the slide of the diaphragm is set the correct way as that can be fitted incorrectly? 

Also have you checked if your getting good spark from each plug? 

[Stef]

Thank for your input. I'm not a mechanic so please bare with me, I take your point about balancing and I'll look into that. From what I could see the diaphragm could only go in one position because of the integral loop locator that fits into the relieve in the carb body so I'm pretty certain the diaphragm's went back properly and I did them one at a time so as not to get them mixed. I'm not sure I understand what you mean when you said "assuming you set the needles height correctly" do you refer to the Diaphragm needle height? if so, I didn't disassemble the diaphragm assembly so they went back as they came out, I just checked for damage. Finally, I wondered about the Spark plugs and I will test them.

Thanks again for you input.

[Simon Davey]

Might be worth trimming 5mm from the ends of the HT leads at the spark plug caps (if there's enough length). They can corrode.

[Hairsy]

Three suggestions:

 

1) The rubbers that sit between the carbs and the engine are likely to have hardened and could well have damage or simply be letting air in because they don’t seal well when they’re hard. If you can get new ones then that’s worth doing. If not, you need to soften them up. Search YouTube for wintergreen oil. Something that worked for me was Autoglym bumper and trim gel which I used to clean them but it also seemed to soften them enough as well. But if I did it again, I’d try to get new rubbers.
 

2) With all the work you’ve done, It’s very easy to have disturbed a bit of dirt which has then made its way into your newly cleaned carbs and blocked a jet. It only takes a small spec. If you’re going to replace the rubbers then take the opportunity to re-clean all your jets. Make sure you visually check all the holes in the jets when you clean them. Some of the grime takes an incredible amount of perseverance to remove and the smallest bit of dirt makes a big difference.

 

3) As has already been suggested, carb balancing is almost certainly needed after you’ve done this amount of work on the carbs.

 

I know how frustrating carb problems are - but it feels lovely when you eventually get there.

[Stef]

Thank you all for your input, I've yet to test the spark plugs, and i think maybe changing the carb manifold rubbers would be worth doing, I did give them a good clean but, they were a bit on the hard side, I hoped I would get away with them. With regard to the carb syncing, I can't see how I can do that if I can't get the engine to tick over without the choke on full.

[RideWithStyles]

As a general rule of keeping things in tip top shape if the rubber is old 5-10yrs service or standing, seems remotely ridged/firm in anyway or separated from to replace any part with any single of the above reasons, replace all the rubbers….it eliminates any possibility of doubt and having to redo it again as it got disturbed.

if you was to do the same with forks? If one outer seal went then the likely hood of the other will increase as hell it will be older, and while your there doing the replacement you might as well do the other to avoid having to do it again a few weeks/months later, also at least they will feel and operate the same way same with carbs.

 

the sync will still tell you something even with the choke and then will tell you again when off choke even with or without extra throttle applied, as they will fall or not be at the same levels or rates with each other again if they are out of balance or not at the correct level then it will not run well or not at all….

so how can you or not tell if you don’t check it?

Edited October 30, 2024 by RideWithStyles
Autocorrect

[Hairsy]

41 minutes ago, Stef said:

With regard to the carb syncing, I can't see how I can do that if I can't get the engine to tick over without the choke on full.

 

Adjust the tickover up until it will idle while warm. Then start the balancing. As you get closer to a good balance, the tickover will rise. Then reduce it and continue to work on the balance. Repeat until perfect!

[Stef]

Ok, Cheers, I'll check the Spark plugs and get the new carb manifold Rubbers, then see where I stand.

Again, thanks for your input.