Just found this site and it's great! My bike has 27k miles. At slow speeds (in traffic) with little or no airflow through radiator I have to rev the engine to avoid stalling. Is this comon for these bikes? Any ideas what may be the cause? btw - the fan does work and will turn on when she heats up. thanks for your help.

 

Hi Paul,

I've just bought a 1987 CBR1000FH, and when it gets properly warm (after a good 15 or 20 miles or so) it develops uneven running under about 2,500 rpm. It never actually stalls (well, so far anyway) but it gets sort of rough and occasionally fails to fire on one cylinder. This clears completely after about 2,500 rpm, and everything is lovely after that. It's not exactly the same as your problem, but it could be similar.

I've only had the bike a week, so I've not managed to look into it yet, but my thoughts so far are:
[ul][*] Poor carburation - maybe the idle jets are cruddy, and when it passes over to the main jets it clears everything up. I'm going to drop some carb cleaner in the tank at the weekend, and may well strip out and clean the jets in the near future[*] Poor spark - if one of the coils has a bad earth, or the HT lead is intermittently earthing, this could possibly cause it[*] Crappy petrol (sorry, gas) - I've filled up at the same garage for the last 2 tanks full, and it only started after that. Next time I'm going to try a different brand of fuel and see if there's any difference[*] Soiled/badly gapped spark plugs - the bike was serviced about 1000 miles ago, so I don't think this is it, but I've not pulled the plugs out yet to see
[/ul]
Luckily, this problem isn't too bad right now and it's only a bit irritating at the moment, but I hope to get it sorted soon.

What have you tried so far with yours?

fozberry

 

Hey Paul,

I've got a 90' as well and had the same problem, and really noticed it when stuck in taffic on a hot day. Well I replaced my coolant with a 50/50 mix this season and vola, the problem is gone. Since I've been stuck in some pretty bad traffice at 85+ days and I've had no more problems. I will be replacing my coolant every season now.

 

I have a 90 too and had the same symptoms. I must dial the idle speed up to 1600-1700rpm to keep it from stalling when warm. Running on choke made it a bit better so i thought i must be on lean condition. Since the idle mix screws are hard to reach i removed the carbs, replaced the original #128 jets up to #140 and opened the mixture screws 3 turns. The same weekend i modified the ignition rotor to get a few more degs advance. Syncronised the carbs too. After these modifications she idles smooth 1100rpm, and low-end power is MUCH better. Now she pulls clearly from 2000rpm and surprisingly mileage is the same or even better. just my €.02

 

Gidday All,

Great forum, just been trawling the web looking for people with the same problem, thanks paul6585. I have a 1990 CBR 1000FM with exactly this problem. It does not like getting hot, and loses a cylinder at idle and will eventually stall. With some revs on she's a thing of beauty, but that is not always possible in London traffic!

For me the problem is definitely getting worse, the idle speed is set as high as it'll go, I've cleaned and synchronised the carbs, as well as set the mixture to something reasonable. And the plugs are new so that shouldn't be the problem. The old ones were fine as I'm sure the problem is only at idle, not at decent revs. I guess the next place to look is the ignition coils - the impedances are ok when cold but who knows when she's running?

Wondering how you guys have got on since your last posts...didn't know you could mod the ignition timing Nobull and is yours still misbehaving fozberry?

Thanks,

kiwi kev.

 

I just got a 90 CBR 1000f and it was so beat up. I got it started today I'm glad you posted this. You guys are great and full of KNOWLEDGE. I have a lot of work to do before MAY(street date) and you keep me thinking and working forward. Does this bike have a thermestat?

 

Never had my '90 stall when hot, but I have had vapor lock. When I park the bike after running hot, the heat must boil off the gas in the carbs. Takes a bunch of cranking to get it started again. I was thinking of putting in a fuel pump, changing the petcock to have a prime position that would let gas flow to the carbs, or put some type of heat shield under the float chambers.

If a coil went bad when hot it should affect two cylinders. Each spark plug wire has a resistor at the sparkplug end that could be affected by heat. I took mine out and put in a metal screw with the head cut off.

The thermostat is next to the radiator cap on the upper right. Install a new one with the by-pass hole at the top.

 

Sorry, I have not had time to address the problem since the original post but when I do I will report back with results.

 

I would be interested in more info about this. I am looking into replacing my wires as I do not know how old they are. Are there any aftermarket options for plugwires? $23.00 a wire is EXPENSIVE.

Thanks again!!
Patrick

 

Try changing the thermostate sender unit and see if you can find one that comes on earlier or install a switch to put the fan on when you need it.