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Carb Headache

Started by Paris, October 20, 2016, 08:49:41 AM

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Paris

So now that iv got the electrics sorted (thanks to a cleaver tip on this forum) iv run into another problem.

My '88 FJ1200 wont run... With the choke fully open it starts but the moment you close the choke or blip the throttle the bike dies. With the carb stripped, while blowing through the fuel line i can hear one float doesn't completely seal, its very slight and i have to blow quite hard but thought id mention it. Im no carb expert but iv rebuilt a few in my time and i cant see anything obviously wrong.

Current set up:
All fairings stripped off, this FJ is destined to be a street fighter (irrelevant im sure but explains why iv done a few things)
OEM Carb, OEM jets etc etc, completely standard
Air box off (going to be running cone filters so i can use the space where the airbox was to hide all the electronics that normally live up front)
Exhausts off, manifold is still on, going to put little stubby pipes on her

What iv tried:
Carb has been stripped and cleaned, jets soaked in petrol and then benzine and poked with a needle and blown through with shop air.
Float heights set to 22.5mm.
air fuel mix plugs drilled out and a/f mix screws adjusted to 2.5 turns out from fully in (have also tried increments of one turn out on each to 5 turns out on each with no improvement)
bench balanced the carbs, cant do a vacuum balance till the bike runs
Compression test turned up no issues.

sooooo, anyone want to take a swing at this one?



jscgdunn

Will be lots of advice here I am sure....but I would start by putting the airbox back on until you have it running well.
92 FJ1200 2008 ZX14 Forks, wheels, 2008 cbr 600 RR swingarm
92 FJ1200 2009 R1 Swinger, Forks, Wheels, 2013 CBR 1000 Shock
90 FJ 1200 (Son # 2), Stock
89 FJ 1200 Built from parts: (Brother bought it) mostly 92 parts inc. motor
84 FJ 1100 (Son #1), 89 forks wheels, blue spots

Paris

I would but iv donated all the bits im not going to be using to a mate of mine whos fixing a crashed bike

More info...just checked the valve clearance, .005"-.006" on intake and .008"-.009" on exhaust which i think is good enough

Paris

More info: Iv bypassed the fuel pump and im running fuel from a 2L bottle suspended above the carbs (can simulate pressure by squeezing the bottle slightly). Also doubt this is the issue but i know from experience when asking for help to be comprehensive....so im trying to be comprehensive

4everFJ

Vacuum/air leaks?

Running without airfilter and exhaust would worsen any vacuum leak issues. The fact that it runs on full choke would support that.
1985 - Yamaha FJ1100 36Y
1978 - Yamaha SR500
1983 - Kawasaki GPZ550 (sold)
1977 - Kawasaki Z400 (sold)

Paris

can you think of a way to test for vacuum leaks?

a side note question, if im running cone filters should i turn up restrictioners for the air intake side of the carb?

simi_ed

Get Randy's carb screw _AND_O-RING kit.  You probably have failed o-rings at the needle seats that are allowing fuel to bypass the needle valves.  I'd also spring for a new set of pilot jets.  Poking them with anything is not a good idea.  IIRC, the hole in a pilot jet is about 0.009" or ~0.23 mm.
-- RKBA Regards,

Ed
===
Ed Thiele 
Simi Valley, CA -- I no longer have SoCal manners.
'89 FJ12C (Theft deterrent Silver/White)


- All that is necessary for the forces of evil to win in the world is for
enough good men to do nothing.

- Edmund Burke

balky1

Vacuum leaks can be checked wit start-spray, but that assumes your bike is running while you are spraying. Maybe, for starters, change the O-rings underneath the rubber manifolds and check the manifolds thoroughly for cracks and stiffness. They don't even need to be cracked, just stiff enough so they don't seal well on the carb. I had that problem.
Thorough O-ring replacement in the carbs, as already suggested. Jets need to be of different sizes if you change intake/exhaust patterns (i.e. removed air-box, more open exhaust, etc.).
Check especially the O-rings on idle-mixture screws and rubber seals on throttle shafts.
On the side note, why did you drill the idle-mixture screws?
Ivan


FJ 1100, 1985

Pat Conlon

Quote from: balky1 on October 21, 2016, 02:26:52 AM
....On the side note, why did you drill the idle-mixture screws?
On the USA imports, the EPA required that the carbs had plugs, or caps, over the idle mixture screws to prevent tampering with the factory settings.
So you've got to drill and pull those plugs if you want to get to the screws and adjust them. They are set lean from the factory.
1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3

fj1289

Quote from: Pat Conlon on October 21, 2016, 10:18:26 AM
Quote from: balky1 on October 21, 2016, 02:26:52 AM
....On the side note, why did you drill the idle-mixture screws?
On the USA imports, the EPA required that the carbs had plugs, or caps, over the idle mixture screws to prevent tampering with the factory settings.
So you've got to drill and pull those plugs if you want to get to the screws and adjust them. They are set lean from the factory.

excellent photos here: http://www.fjowners.com/index.php?topic=16189.msg163387#new

Paris

Thanks for all the replies guys, as always you have been very helpful.

Does anyone have a link to Randys carb service kits?

I know theres no real answer to this but can anyone take a stab at the jets id likely need with a free flow system as its now set up? I know you really need to do this on a dyno with a selection of jets to find the best setup but this build is on a very tight budget and i dont have such luxury, what im looking for is a setup that is most likely to work well enough for the bike to run smoothly (not necessarily at peak performance). If the setup can be achieved by modifying parts i already have would be bonus

Im off to check the intake manifolds. Wish me luck




Paris

Quote from: 4everFJ on October 20, 2016, 09:47:55 AM
Vacuum/air leaks?

Update:

Did someone say vacuum leaks? well this got me looking, and i found a shit load of leaks! all the intake manifolds are perished (one badly) one of the manifold outlet nipples was open (presumably the one that connects to the super boost thingy, the one on this bike is long gone) and the O-Rings were flat, hard and crumbly.

As a proof of concept i patched the perished rubber with some high heat automotive silicone, stuck a piece of heat shrink over the open nipple and sealed it, changed the O-Rings on the manifolds and banged the carbs back on. Lo and behold the demon she did ROAR!!!! no cans and open intake makes for a seriously noisy bike! by no means did she run well, the carbs are not balanced and the A/F ratio has not been set but its progress.






FJ1100mjk

Good going finding the vacuum leaks. If you haven't done it yet, there's a very good possibility that you're going to need to go through your carbs.

Since you're smearing high-temp silicone on the intake manifolds to seal their cracks, it does indicate that you are, as you described above, on a tight budget. I know what you mean by this. From what I see online, a new set of carb manifolds could set you back about $160 USD. You could get a cheaper, good condition set, from Ebay, for a fraction of a new set. They're out there. None of my three FJs have carb manifolds with any real deterioration, so there's a good chance you can find a good used set of them.

You can do your own carbs, kind of on the cheap, replacing what you absolutely have to (but there's risk in this). There's plenty of info here on how to do it, and valve clearances' checks and re-shimming too, which is a step I would recommend in your build. To find this info and many other FJ-related topics to do your own wrenching, use Google to search the topic, and include the text of this website, FJowners.com, with the topic in the search field to narrow your results.

Good luck.
Platinum Zircon-encrusted Gold Member

Iron Balls #00002175
www.ironballs.com


balky1

Quote from: Pat Conlon on October 21, 2016, 10:18:26 AM
Quote from: balky1 on October 21, 2016, 02:26:52 AM
....On the side note, why did you drill the idle-mixture screws?
On the USA imports, the EPA required that the carbs had plugs, or caps, over the idle mixture screws to prevent tampering with the factory settings.
So you've got to drill and pull those plugs if you want to get to the screws and adjust them. They are set lean from the factory.

Ahaa!
I misunderstood him. I thought he drilled the screws and threads all together.  :rofl:


FJ 1100, 1985

Pat Conlon

Quote from: Paris on October 22, 2016, 06:30:18 AM
.... stuck a piece of heat shrink over the open nipple and sealed it.....

Be careful there ^^^  The heat shrink will cook off in short order, as well as the thin automotive type vacuum caps (don't ask).
There is a lot of heat on the engine side of the heat shield.
There is a reason Yamaha uses thick rubber caps to seal those vacuum ports.

1) Free Owners Manual download: https://tinyurl.com/fmsz7hk9
2) Don't store your FJ with E10 fuel https://tinyurl.com/3cjrfct5
3) Replace your old stock rubber brake lines.
4) Important items for the '84-87 FJ's:
Safety wire: https://tinyurl.com/99zp8ufh
Fuel line: https://tinyurl.com/bdff9bf3