Carburetor pimples...

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mikenixon
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Carburetor pimples...

#1

Post by mikenixon »

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It's the little things that get ya! A shop sent me some GL1000 LTD carbs they were still struggling with after they had rebuilt them. The symptoms were the bike wouldn't idle under 2,000 rpm coupled with a perception of extreme leanness at idle, you know, spitting and popping. The lean issue was easy to spot. Someone had left the idle air bleed jets out! Okay, weird but easily solved. There were a lot more evidences of poor workmanship on the carbs however, and weighing the possible contribution of these to the wonky idle performance took some time. Then I dug deeper and noticed using a bright light that the throttle plates weren't closing all the way, even with the linkage removed. Light was visible around them. "Bent throttle plates," I think to myself. I see that fairly often.

But nope. The throttle plates weren't closing all the way because they were hitting something on the inside of the throttle bore. W-what? There's a pimple in there! A stalactite hanging down in the throttle bore. And flipping the carb over I see someone has a little too enthusiastically (and inappropriately, not to say unnecessarily) stamped a number onto the carb, but at the thinnest part of the carburetor casting directly over the throttle, smashing metal into the bore, creating the interior pimple. On all four carbs.

These carbs are junk. While in theory they could be mounted in a lathe or bolted down in a milling machine, there just isn't any way of accurately machining off that pimple without also skimming the rest of the bore, and that just won't work. The fit of the exquisitely-machined, precisely-mated throttle plate to its bore is just too close, too exact. Anywhere a cutter touched the bore would affect throttle sealing. It would even affect the linkage, requiring the link arms to be shortened, and the force required to open the throttle. A cluster, this.

You see all kinds of things working on carburetors!
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sgwilly
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Re: Carburetor pimples...

#2

Post by sgwilly »

A compound issue here; 1) about the worse position possible and 2) pulling out Thor's hammer to sink that die.
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dontwantapickle
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Re: Carburetor pimples...

#3

Post by dontwantapickle »

mikenixon wrote: Wed Sep 02, 2020 8:01 am A shop sent me some GL1000 LTD carbs they were still struggling with after they had rebuilt them.
bummer, the "shop" destroyed this customers carbs.
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mikenixon
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Re: Carburetor pimples...

#4

Post by mikenixon »

Yes, my customer, the shop, is still in shock... :shock:
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