Author Topic: Idle issue on a '78  (Read 6283 times)

Big Tom

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Idle issue on a '78
« on: February 14, 2006, 05:39:14 AM »
Hey,

Been ages since I've worked on this old bike... hell it's been sitting in a garage for over 2years now. Anyways I thought it's about time I pull it out and have another go at fixing it and possibly riding it (was in an accident with another bike... havn't riden since)

The story goes as this, the bike was owned by a friend of mine who drove it for a number of years but it never really ran right in that it wouldn't rev up over 3500RPM (probably just needed a carb clean) so after while he got mad and parked it... outside beside his garage without removing the gas/oil or anything... 6 years later I told him I'd like it and after alot of pestering he gave it to me for free providing I install a stereo into his car! Nice deal.

The bike is 90% original, couple pieces broke/scraped up but nothing severe. So my brother/dad and I tore the thing apart, and after 6 years of sitting those carbs were horrid... took me an entire weekend of cleaning to get them freed up and looking good. changed the oil, 4 new plugs,  adjusted the valves, set the points with a dwell meter, cleaned/checked the brakes, replaced the chain/sprockets... basically all the little tune ups we could do without removing the engine.

Got the bike fired up, runs pretty damn good after being sitting so long, we kept tinkering with it and just slowly taking it out for a couple quick drives around the block etc before eventually taking it out onto the highway and letting it loose (oh, the no high RPMs problem is now fixed)

Everything seems to be going well except for one problem with the idle, at rest it would sit around 1200RPM (I think that's where the '78 are sopposed to sit???) and then for no reason after a bit of time it would shoot up to 1800RPM and not go back down until you drove around for a bit then it would settle for a time... then shoot back up.


Soooo... I thought maybe there was a leak between the carbs and the cyl but we tried spraying cleaner around the boots and the engines rev's didn't change and no bubbles seen so they seem good. The boots from the carbs to the intake air box also seemed good. The only thing I didn't get the chance to do and what i'm thinking the problem is... I never did sync the carbs, don't have the tools to do it and not 100% sure how to.

So right now I'm thinking it's the carbs need to be sync'ed. I've also heard someone say it could be the plug wires being faulty but I'm not sure how much merit I give that considering it seems to be running fine besides the idle.

Anyways, figured I'd post this problem up and see what you guys have to say. I'm heading back home this upcomming weekend and I'd like to try and fire it up and see how it still runs if I can (it's sopposed to be about -30C where I'm going)

Anyways, any help is appriciated.

Cheers,
Tom

Offline SteveD CB500K0

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Re:Idle issue on a '78
« Reply #1 on: February 15, 2006, 05:35:02 PM »
Hmmm.

Seen this post somewhere else Tom so I won't bore you with the full response other than

\"sync those carbs\" !
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Big Tom

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Re:Idle issue on a '78
« Reply #2 on: February 15, 2006, 07:25:31 PM »
Well I did post on here first... but after waiting quite awhile with barely any views and zero responses I decided to check out for other forums! So a quick copy paste later this exact question can be found elsewhere :)

I'm still trying to hunt down a carb sync tool around here I can buy/borrow from someone... it's proving to be tougher then it should be.

martin.g.g

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Re:Idle issue on a '78
« Reply #3 on: March 30, 2006, 09:39:16 PM »
Syn the carbs but first make sure that the float levels are correct (22mm) and that the needle valves are not sticking. I am at the end of a rebuild of a 550F2 that was sitting partly striped under a leaking tarp for 15 years and have experianced simular running problems to you (and still have a minor one)

[img]

Big Tom

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Re:Idle issue on a '78
« Reply #4 on: April 05, 2006, 12:03:49 AM »
martin.g.g wrote:
Quote
Syn the carbs but first make sure that the float levels are correct (22mm) and that the needle valves are not sticking. I am at the end of a rebuild of a 550F2 that was sitting partly striped under a leaking tarp for 15 years and have experianced simular running problems to you (and still have a minor one)

[img]



FYI on the '78 550's the float hieght is not 22mm, it's 14.5mm

Learned that one the hard way!

martin.g.g

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Re:Idle issue on a '78
« Reply #5 on: April 05, 2006, 07:21:00 AM »
Now thats intreasting as set to 22mm my carbs flooded. I had to ease them down to 18mm berore they would stop flooding.:unsure: :unsure:

Big Tom

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Re:Idle issue on a '78
« Reply #6 on: April 05, 2006, 08:35:50 PM »
Yeah, I bought a Clymers mannual that's sopposed to be good to '78 but it sure as hell does not cover certain areas of my bike including the carbs. So I set them to 22mm like the manual and everyone I talked to said... and like you overflowed like a SOB so went searching the net and eventually found that whichever series carbs I have the floats need to be set for 14.5mm

Redid the carbs, hasn't leaked once since and seems to run perfectly fine except for that idle problem. Might want to check into it, maybe your's are the same as mine and would do well to re-adjust the hieghts.

 

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