So about them cursed carbs.. - Sportbike Forum: Sportbike Motorcycle Forums
 
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post #1 of 6 (permalink) Old 07-21-2008, 11:10 AM Thread Starter
 
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So about them cursed carbs..

As some of you might have read, I'm fixing this old shadow. After fixing the starter solenoid, the damn thing would crank by not start, thats where I found out the the choke in one of the carbs was seized up. So I drilled it, tapped it removed and replaced it. All should be well now, right? Not exactly.

The bike has a really hard time starting, you have to crank it over and over and it fires for half a second or so. After 15-20 minutes, it stays on for a pretty long time, as long as you hold the throttle partway open. If you spray some brake cleaner in the intake, it will start right up, but again, will only stay on as long as you hold the throttle partway open. I even held it and waited for the engine to reach operating temperature, as soon as I let off it died.
Here are my thoughts.
1. There might still be gunk in the carbs. I opened the diaphram/plunger side, and cleaned the needles, but I cant open the float/jet side without removing the carbs, and I have no way to resynch them.
2. The idle speed might be messed with. I doubt it, but you never know who tried to work on it earlier.
3. The bike has 2 plugs per cylinder. It is possible that only one if firing, or that they are only firing sometimes. I know they are getting power. but I have not taken them out (because I dont have a socket to fit them, and couldnt measure what size it was). New plugs are in the mail.
4. I could have been flooding the engine while trying to start it.

Any thoughts?



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post #2 of 6 (permalink) Old 07-21-2008, 11:19 AM
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Surely you'll try the idle setting first since that's the easiest, and put it back to wherever if that doesn't help.

The next step, if it were me, would depend. How bad were the carbs? I really suspect you still have some clogged passages in there, and I'm not talking the jets but rather the idle passages. Yeah, a synch would be a good idea but not a necessity, so you could hedge on that until you found a set of mercury tubes.

If the carbs weren't too bad, I'd go for the plugs next.

I won't be shocked if you have to do all three

Naturally you've covered the most likely angles.

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post #3 of 6 (permalink) Old 07-21-2008, 11:51 AM Thread Starter
 
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I didnt see any solid matter in the carbs, but plenty of brown gas film on just about everything. I really dont want to have to tear into them again, but perhaps I will have to

Oh, one more factor. The bike has two tanks, the main tank is drainable and has been, the
"reserve" is not easily drainable, so there is still old gas in it. I filled the system up with new gas and small part diesel, but old gas is still mixing into it. Might have something to do with it too.

I didnt think the jets were clogged since it revs easily, but I didnt want to go after the idle adjust at low engine temps..

God I hate carbs...



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post #4 of 6 (permalink) Old 07-21-2008, 02:59 PM
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my bro in law had an 83 shadow 750, hardest thing to start on the planet, i bet that starter cranked 100,000 miles, he sold it to a guy who put a new starter on it and said it fixed it, he said it wasnt turning over fast enough with the old starter, dont know about that myself but thought i'd tell ya anyway ...good luck
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post #5 of 6 (permalink) Old 07-22-2008, 12:22 AM
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I thought this was going to be about giving up bread.




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post #6 of 6 (permalink) Old 07-22-2008, 03:31 AM
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I know old gas can be a bane but can it really cause that? I would have expected rough running/poor power delivery rather than outright failure to ignite.

The laquer is what gums up the idle passages and I'm really starting to lean that direction. I ended up using a carb cleaner spray with a very, very tiny test tube brush, IIRC. It took forever

EDIT: Doing the plugs and idle first seems clear to make sure you don't end up wasting time.

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