Carb boots

wonkiwheel · Post by **wonkiwheel** » Thu Jul 24, 2014 6:20 pm

After much toil trying to suss why my thunderace has this annoying idling drop and below 3k stutter on very slight throttle ive finally decided its gotta be the boots, ive stripped the carbs, done my float heights (well bent the tangs slightly) serviced the exup and a miriad of examinations around the carbs. The boots themselves look clean with no cracks, is it possible they have just warped? I did have some recent overheating problems and this may have exaserbated the problem, but its defo sucking air from somewhere, when i spray carb cleaner around them the revs fall almost to cut out. Anyways ive ordered some new ones and ill see where that takes me.

Killawife · Post by **Killawife** » Sat Jul 26, 2014 11:56 pm

Check the vaccum tubes that are used for carb balancing. One of mine were cracked and sucked air.

wonkiwheel · Post by **wonkiwheel** » Sun Jul 27, 2014 11:56 am

Yep done that, all good, cheers.

wonkiwheel · Post by **wonkiwheel** » Mon Jul 28, 2014 11:06 am

WTF!!!! New boots on clamps tight as allowed, carbs seated coreectly,no hairline cracks anywhere on carbs and suuroundings yet spray carb cleaner around them and bam revs increase (note: the revs died in my op coz the mixtures screws where 4+turns out to compensate)....... does not compute!!!!

Killawife · Post by **Killawife** » Mon Jul 28, 2014 7:38 pm

It might be the gasket between the cylinder head and the intake pipes that is broken.

wonkiwheel · Post by **wonkiwheel** » Tue Jul 29, 2014 12:08 pm

That was my next investigation!!

wonkiwheel · Post by **wonkiwheel** » Sat Aug 02, 2014 9:50 am

Cleaned and reseated the seals all in good order, not sucking air from there anymore and idle is marginally better, still got this idle drop out and stutter when warm 65 degrees +. Had new plugs, checked diaphragms etc. It will idle at 1200 then intermittently drop to 1k and below the only way to contain it's impact is to richen up through the mixture screws, occasionally I get a pop back in the headers, carbs have been thoroughly cleaned and checked, the only thing I can think of is coils however would that show at higher revs above 3k also?

MMUK · Post by **MMUK** » Sat Aug 02, 2014 10:16 am

wonkiwheel wrote:WTF!!!! New boots on clamps tight as allowed, carbs seated coreectly,no hairline cracks anywhere on carbs and suuroundings yet spray carb cleaner around them and bam revs increase (note: the revs died in my op coz the mixtures screws where 4+turns out to compensate)....... does not compute!!!!

Did you buy GENUINE Yamaha carb boots? Copy ones don't tend to fit properly, they don't have the rib on the inside that "locks" into the groove round the intake port.

A fix I've done in the past when a customer has supplied non-OEM parts is to use a smear of Hylomar Blue around the intake port before sliding the boot on. Not ideal I know but at least Blue can be removed without trace

wonkiwheel · Post by **wonkiwheel** » Sat Aug 02, 2014 11:16 am

They were from yambits who claim they come from the same factory and they do look identical with the ribs and same factory markings. There is no leaks in that area now so I've eliminated that problem. Cheers.