Bike that has an aversion to the choke

[MagicalDave]

Hey,

Bike: Honda XBR 500 1987 (yes, another ).

This bike will start in any temperature without the choke, the other bike requires choke to start in anything below 20. Also smells rich when running.

Popped the carb off, cleaned the main and pilot jets (which were dirty, emulsion tube also off). No split hoses, and the scottoiler removed from the air cut-off valve hose. The rubbers are all in good nick and still flexible. The mixture screw was at 4 turns out (I wonder if they were making up for the jets being blocked). The choke cable appears to be an OEM honda and the choke plunger + needle slide freely into its opening.

The air filter is slightly dusty but otherwise looks new. I believe the fuel level is correct in the carb - none is leaking out of the overflow and no varnish above the top of the bowl.

Reset the mixture screw to 1 1/2 turns out and refitted everything, but the bike will still start without any choke - and if you apply even a hair it'll die very rapidly.

I'm a bit at a loss - I couldn't actually get the carb out to fully clean it, so managed to get at the jets with it rotated in the frame... it needs to come fully out doesn't it chaps? Any ideas on where to look first?

Just to check too, the mixture screw is on the engine side of the carb, which makes it a fuel screw rather than an air screw?

[jeffyjeff]

Hey MajicalDave. It doesn't sound to me like you have much of a problem here. Your bike starts consistently and predictably every time; what is not to like about that? My YBR starts like that. It used to require choke on initial cold start even at 30 degrees C, but now starts easily without choke after I cleaned it out and blew out the jets with compressed air. I love it!

A spark plug reading will positively confirm if it's running rich or lean. If the insulator is tan to eggshell in color after a decent ride, I'd be happy with it. Don't go looking for reasons to fret about your bike's performance; you'll probably find what you are looking for.
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History shows again and again how nature points out the folly of men - BOC

[RhynoCZ]

If it's a mixture issue, the spark plug condition is a telling sign, as Jeffyjeff says. By the way, try to replace the air filter. Slightly dusty might mean fully clogged and that would result in a rich mixture. The holes in the paper filter are very tiny, you know.

Also put valve clearances check on the list. Usually poor cold starts mean the clearances are too tight. 1987 was long ago and who knows when was the last time someone checked the valves.

When I cold start my XBR, I use the kickstarter. A few kicks with the ignition off and the choke on, then ignition on, still using the choke, and with a firm brisk kick the engine starts, even with older fuel.

You could also do the cylinder compression check test, but for that you need a specialized tool. Thinking of it, the XBR does have automated decompression valve, check that first, just to make sure.
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'87 Honda XBR 500, '96 Kawasaki ZX7R P1, '90 Honda CB-1, '88 Kawasaki GPz550, MZ 150 ETZ
'95 Mercedes-Benz w202 C200 CGI, '98 Mercedes-Benz w210 E200 Kompressor

[stinkwheel]

Might be worth just re-brassing the carb, it's hell of an old. The fact the mixture screw was so far out suggests someone was trying to compensate for some problem. Also probably only a matter of time before ethanol buggers up the needle valve. You aren't going to see an ovalled slow running jet with the naked eye.

You can get rebuild kits for fairly cheap or just get the jets. Google says it's a kehin VE10 so you can still get genuine kehin jets for them.

I'll second just replacing the air filter.

I'd also verify the float height, someone thought it was ok to have the pilot screw that far out suggesting they were prepared to mess with the carb but didn't really know what they were doing.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.