Carb Woes

Ok. I have taken these things apart about 15 times now. Each time it was of something that I missed and people here suggested I should check this or that. And more often then not I did miss it. So now I think I have them clean. The bike is a little hard to start but do start. Runs okay with choke. Warms up nicely and idles good after warm with no choke.

So now for my problem. When I crack the throttle just a little ( Snap it ). The bike rev shoot up to about 5 grand and hang for a bit then slowly comes back down to idle. I have checked for air leaks and can not find any. I used a propane torch to check for leaks.

Can anybody offer any help. This bike is beating my up. I originally bought this bike for a parts my for my daily runner but after I got it running it seemed to be a shame to scrap it. So I think I am going to try to put it on the road but these carbs are killing me.

 

It sounds like the Diaphragm Pistons aren't coming back down as fast as they should when you close the Throttles.

Search: "Clunk Test" Author: RickCoMatic

 

Could be a number of things, but it sounds suspiciously like your brass-plated vacuum diaphram PISTON is hanging up in it's bore slightly, making it difficult to return to its closed position (thus keeping the main fuel needle lifted up and passing lots of fuel!).

The solution, as RickOMatic has so eloquently stated, is to polish the carb piston bore with 600/800/1000 grit paper to get it smooth as a baby butt, and a brief, quick polish of the brass piston too.......untilt he piston will drop back down through it's bore with a no-friction, no-resistance "clunk" when released.

 

crazy thought: reversed the throttle/choke cables?

 

I have done the clunk test with no probs. And I didn't reverse the choke a throttle cable.

I was thinking the clunk test thing at first. But what happens is this. If I give a quick twist of the throttle the rpms shoot up to about 5 grand then slowly come back down. Now the quick twist should only bring the rpms up to about 2 grand so I am not turning the throttle much.

Does this lead anyone in a different direction. Would the air mixture screw cause this prob. maybe the screw is set to lean? Just a though.

 

The air mixture screws only effect fuel/air mixture at around 2k rpm and below above that it is taken over by the needle depth.

Have you synced them?

 

I bench synced them.

 

Really DUMB question, but I gotta ask.
Are the springs in decent shape (and accounted for) on top of the diaphragms?

 

Yeah. I wish it was that easy.

 

are the "choke" plungers all the way down, with a little to spare ?
with the bike not running twist the throttle all the way open and let it snap back
do you hear a definite sharp clunk when they close ?

 

Nope. Choke is closed and there is a clunk.

 

YICS port bolts are tight, with the copper washers ?
is this a test?

 

I second this question. I had hanging rev's that cleared up after a carb synching.

 

Intermittent High Revving can be caused by a number of things:

Most Common because of design and age:
Sticking Diaphragm Pistons
Linkage Problems
Stuck Linkage
Weak Return Spring
Weakened Sync Screw Springs
Sticking Throttle Shaft Seals

Improper Tuning and adhustments:
Pilot Mixtures way off
Wrong Pilot Jets
Misplaced Jets after Carb Cleaning
(Air and Fuel ++ Uppers and Lowers)

Tight Cable
Wrong Cabling

Air Leaks:
Manifolds Leaking
Air Boots Leaking

Throttles:
Improper Sync
Damage
Stuck-open Butterfly

Air Jets:
Misplaced Air Jets (Haynes misprint)
Missing Main Air Jet

Improper reassembly of the Carb rack by and inexperienced mechanic.
Swapped Main and Pilot Jets (Hitachi)
Stuck Enrichment Valves
Enrichment Valve Linkage dirty and not alloowing valves to close.

 

Life, is a test.........

 

Yes. This is just a test. In the event of a real emergency ...


(I got Carb Cleaner on Sale this week at AutoZone)

 

Farm and fleet had it on sale for 99 cents a can as well

 

When I switched the pilot and the main jets this problem went away. Do that point the finger to a more specific problem.

I can sync the carbs because I don't have a YCIS tool. The best I can do is a bench sync.

Thanks for all your help.

 

A tool can be improvised.
I have used cotton strips knotted together soaked in Marvel Mystery Oil.
Stuff them in and it blocks the passage, also cleans the "Maintnence Free" passage.

Learned this one from Rickerstein

 

That "YICS Stuff" was a stroke of pure genius.

I have gotten emails from around the Gloge on that one.
Glad to have come-up with it and started the ball rolling in here!

 

Clogged or undersized pilot jet.