Carb boots

[Guest]

I've been fighting intermittent issues with a (very) lean fuel condition. My 81 450L will sputter at high speeds if I open the throttle over about 3/4 of the way, race from 1,500 to 3,500 RPM at idle if I have the choke a bit open or cut out if I close the choke entirely. The idle set screw is next to useless. I recently had a day when this was happening again - it was about six months ago last time.

I treated this like I have my cars in the past. I checked the line from the petcock to the carbs - no kinks and the rubber still looked good. I also sprayed a bit of carb cleaner on the engine side boots which gave the classic increase in RPM.

First off, should I just summarily replace these boots? I'm not seeing any visible cracking, etc all in the boots but I'm thinking that I should just replace them. It is 30 years old.

Second, if I do opt to replace them I've seen a number of options out there. Ideally I'd like something new manufacture, not something pulled off another old bike.

A number of places sell universal Mikuni mounting flanges, but I don't have any idea how to measure what I need. Anyone happen to have the specs on hand or instructions on how to measure it correctly?

[Steve]

Although the boots might be a problem, what have you done to the carbs? Anything?

If the carbs have not been PROPERLY cleaned and re-o-ringed, any attempts at further diagnosis are pointless.

.

[cowboyup3371]

Have you also replaced the O-rings behind the boots?

[timbrigham]

The carbs should be in good shape - I got the varnish off at the beginning of the year and spent some quality time with a wire on the jet ports.

I haven't replaced the o rings yet. Should I bother going that without replacing the boots?

[seanarthurmachado]

The only way to properly clean the carbs is with a soak in berrymans or similar or do a ultrasonic cleaner. You can spray all day, use wires, picks, etc but some of the internal passages are tiny. Do it once and right and it will remove all doubt of a clean carb. As for boots and o rings, if you look they are either cracked or flat more than likely. If cracked then air gets in making it lean. If flat then as the head heats up there will be dealing issues and air getting in.

(My intake boots and orings were just replaced, 3 or the 4 orings had cracked, and the fourth was on its way to cracking. All were flat)

A replacement every 36 years seems reasonable to me. Check z1 enterprises.

[Nessism]

Check the newbie mistakes thread linked in my signature and go down the list...

HINT: replacing the carb boot O-rings is on the list.

[Big T]

So is not properly cleaning the carbs


To go back to your original question, pull the carbs and give boots a squeeze. They should close up to 50% diameter with no more pressure than when you hold your nose and jump into the water

If they're that flexi - there's some O rings between them and the head