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What could be wrong if a bike will only run on choke?

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DarylInAjax
L Plate Warrior



Joined: 21 Mar 2011
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PostPosted: 16:15 - 21 Mar 2011    Post subject: Reply with quote
MarJay wrote:

He cleaned them because the bike had been stood for 8 years. He put a new battery in, and cleaned the carbs... but did not change the oil, filter or air filter. He was selling it trade anyway and just wanted to get it running.


I had the same things happen to me...It sounds like you have plugged jets in your carb.

As has been already mentioned the engine is leaning out without choke, by running with choke you are creating extra vacuum in the carb body, which in turn pulls more fuel into the venturi.

You would be surprised what can get past the fuel filter on a bike that has been sitting for years.

Pull the carbs and spray the bejeesus out of all the ports and jets using a good quality rubber-safe carb cleaner. Remove all the brass jets and use a magnifying glass to make sure they are squeeky clean and you can see light through the tiny hole at the bottom. DO NOT use anything hard to push guck out of the passages, the brass is soft and it doesn't take much force to wreck them.

The other possible reason (but more unlikely) is that the rubber diaphram in the slide part of one or more of the carbs has failed (assuming they are CV-type carbs?). Rubber shrinks and gets brittle when it sits for too long (8 years is plenty). So if you have done the cleaning and it's still not working then that would be the next thing to check.

If you are feeling flush you may just be better off to buy a carb rebuilding kit which jas new jets, diaphrams etc and just replace everything off the get-go.

Good Luck!

Daryl
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prawny1
World Chat Champion



Joined: 28 Jun 2005
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PostPosted: 17:12 - 21 Mar 2011    Post subject: Reply with quote
Have you double checked your leads are on in the right order?

Also you said the carbs had been cleaned but had they been balanced?
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Robby
Dirty Old Man



Joined: 16 May 2002
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PostPosted: 09:33 - 24 Mar 2011    Post subject: Reply with quote
Balancing shouldn't cause this much trouble, it can give a rough tickover but would rarely be this big a problem.

The point about stuff getting past the fuel filter is good too, a surprising amount will get through it. The only advantage here is that a paper element will get stained quickly, showing you that there's a lot of crap going through. Doesn't stop you needing to clean the carbs, but does help trace the fault.

If there is any rust in the tank, then it needs treating. Phosphoric acid is your friend, I've used it on a couple of really seriously rusted tanks and ended up with perfectly clean, slightly pitted metal. It eats rubber and doesn't appear to be great friends with aluminium (I used a gallon of the strongest I could buy on ebay, topped up with an equal amount of boiling water from several kettles) so bear that in mind.

I'm siding with a clean-workbench carb strip, including a good inspection of rubbers. You could try spraying WD40 on the rubbers with a running engine first to check for an air leak, but this isn't a 100% accurate test.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 09:41 - 24 Mar 2011    Post subject: Reply with quote
Robby wrote:


I'm siding with a clean-workbench carb strip, including a good inspection of rubbers. You could try spraying WD40 on the rubbers with a running engine first to check for an air leak, but this isn't a 100% accurate test.


I've got some Marine Clean industrial detergent. I would be surprised though if the tank was rusty. The outside of the tank is mint, despite having a couple of stone chips. I expect it could just be specks of dirt in the tank from somewhere but I'll bear it in mind.

The fuel tap is broken so I need to buy some hose clamps so I don't get covered in petrol.
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British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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G
The Voice of Reason



Joined: 02 Feb 2002
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PostPosted: 10:01 - 24 Mar 2011    Post subject: Reply with quote
Mole grips should do it ok.
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MarJay
But it's British!



Joined: 15 Sep 2003
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PostPosted: 09:45 - 29 Mar 2011    Post subject: Reply with quote
Quick Update:

I drained the tank and found that it was full of rust... so that'll be the issue.

Bear in mind for the previous responses to this thread that the bike was running perfectly when I picked it up and then I perturbed the fuel tank.

(cool word, 'perturbed'!)

Anyway I reckon the carbs are full of powdered rust. The guy who I bought the bike from is a reputable back street dealer here in Reading and he would have known how to set carbs up and all that. He told me he cleaned them so I guess he would have cleaned and balanced them and adjusted the idle. Assuming that is all correct I need to take the float bowls off of the carbs and clean the jets so that no particles of rust remain.

Oh Joy.
____________________
British beauty: Triumph Street Triple R; Loony stroker: KR1S; Track fun: GSXR750 L1; Commuter Missile: GSX-S1000F
Remember kids, bikes aren't like lego. You can't easily take a part from one bike and then fit it to another.
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Old Thread Alert!

The last post was made 13 years, 59 days ago. Instead of replying here, would creating a new thread be more useful?
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