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Discussion Starter · #1 ·
Hey everyone,

Z here. New to the forum. Looking for some help from the pros.

Own a couple Honda 400's from the late 70's 80's, but went looking for something bigger. Got my hands on a 1979 GL1000. Super low miles, and rides like a dream. Love it. But, had a backfire pretty consistently, and when first turned over, wants to slowly drop idle, and eventually die. After it gets warm (20+ min.) the idle then slowly climbs, until at the stop light, it is close to 1500 rpms higher than it should be, and climbs. A friend mentioned that it sounded like an air leak (climbing idle), so after the old brake cleaner test, I think ive found that all the intake manifolds are sucking a bit of air. Cylinder 3 is the worst, but all are a bit affected. I think the rubber at the top of the boot connecting to the carbs are all just old. They look like they are in good shape, but they must have some deterioration from the years.

Of course, these parts are discontinued. (Grr..). Anyone have any brilliant ideas on how to fix the existing ones (seal them, replace rubber etc.) or have a source to someone who can build me brand new ones? I could go the ebay route, but afraid that any manifold i get is still going to have 30 years on it, and have a similar problem.

Saw some similar posts and will try boiling the rubber on the manifolds, and cleaning, and tightening and replacing the o rings, but any guidance on this boiling process and/or other ideas above and beyond this would be great!


Thoughts?

Thanks.

Z.
 

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The Irish Crew
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Welcome to the forum. The rubbers usually come supplied already fitted to manifolds as far as I know, so buying used ones means buying manifolds.
 

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I remember someone posting about boiling rubber parts in something but can't remember what or who. Maybe the individual will see this and refresh our memory.
 

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Still Learning
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Welcome to the forum Z.
Try looking at Randakk's web site. They may have replacement rubbers for the intake manifolds.
Use the forum search tool to find the posts on boiling intake rubber boots.

Brake cleaner doesn't play well with rubber. Better to use an unlit propane torch, set at low flow rate.
 

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I posted of something similar here.

I've done it with the GL elbows and they've come out fine.

I've not tried the wintergreen oil that many swear by though..
 

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Discussion Starter · #7 ·
Hey everyone.

Another update!

Did the intake "rebuild". Cleaned them all replaced o rings and found some basic but new clamps to replace the stock ones. Bike is SO much happier.

Idle is way better and runs pretty smooth. Backfiring has decreased as well, and seems to only happen around 2000 rpms on deceleration. My guess is that a carb sync will alleviate this a bit and if not ill look at the cutoff valve.

Doing valve clearances soon as well, and timing belts soon. All should help, but the air leak situation seems to have been contained at least enough to make her my daily ride.

Also snagged a reupholstered stock flat seat. Look AWESOME. will take the bags off eventually, but for now i like carrying all my crap.

Thanks everyone.
 

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I am not sure about the 1000, but the 1100's had a air bleed valve that caused backfires if it leaked. Worth checking out.
 

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1985 GL1200 A
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You definitely don't want air leaks in your intake system. Glad to hear you got them plumped/tightened up.

And, in my experience, the thing that really made a difference was synchronizing the carbs. The carburation system is a controlled suction system with a fuel feed from the carb jets. When the carbs are well balanced in their suction (assuming the carbs are metering and aspirating fuel equally) it really smooths out performance. Add to it adjustment of the pilot screws on each carb and you'll have better-than-factory performance.
 
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