Only fires up on one........ - Triumph Forum: Triumph Rat Motorcycle Forums
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post #1 of 8 (permalink) Old 04-08-2019, 10:28 AM Thread Starter
Production 125
Main Motorcycle: Tiger Sport
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Join Date: Mar 2017
Location: Surrey UK
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Other Motorcycle: Daytona 900
Only fires up on one........

My Daytona 900 with 13k miles runs cleanly and idles fine all the time except when starting from cold on the choke.

It fires up first on one cylinder only, stumbles along and then a 2nd cylinder fires up. Then the idle jumps up as the 3rd cylinder fires up. Then it runs fine and you can pull away with no problem.

New plugs. Carbs cleaned and balanced and snug fit to the cylinder head. Valve clearances set. New battery and charging at 14v. Headlight is on a relay.

So not sure where to go next........
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post #2 of 8 (permalink) Old 04-08-2019, 11:47 AM
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Main Motorcycle: 95 Sprint 900
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When I start my 900 Sprint up I always turn the petcock to prime and depress the knob for about 5 seconds first, then I turn it back to the run position and press the starter with half choke, I believe it ensures the fuel is primed, ie no air bubble and fuel is flowing. If I don't do this it starts up very lumpy.

It's probably just my old girl being awkward but so be it

There can't be much wrong with your Tona if it runs ok after

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The roar of Moses' Triumph is heard in the hills. Joshua's Triumph was heard throughout the land. Sprint900dave's Triumph was seen and heard all round Birmingham.UK

Last edited by sprint900dave; 04-08-2019 at 11:55 AM.
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post #3 of 8 (permalink) Old 04-08-2019, 02:35 PM
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Main Motorcycle: '98 Sprint Executive
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Dave is on the right track. PRIME physically pushes the petcock open, bypassing the vacuum operation. If turning the petcock to PRIME helps, then start looking for something on the vacuum side of the petcock. Often it's as simple as a split or pinched vacuum hose.



Other things, make sure that the knob actually turns the petcock spindle. The back side of the knobs break out, so remove it and inspect it. These bikes are cold blooded and take awhile to warm up. Turning the fuel screws out to 2 - 2 1/2 turns helps a little. Your screws might have aluminum anti-tamper covers that will need to be drilled out.



You didn't mention the bike year or carb model. 900s came with Mikunis or Keihins, depending on the year. My brain is getting fuzzy, maybe all Daytonas were built in the Mikuni period.
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post #4 of 8 (permalink) Old 04-08-2019, 03:38 PM
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Main Motorcycle: '96 Daytona 900
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The petrol taps on our bikes are made out of a cast zinc alloy and the spiral ramp mechanism that pushes the taps diaphragm open on prime can wear with age. As sprint900dave suggests, it might be useful to set the tap to prime and then push it in for 5-10 seconds, to ensure that it's fully open. The tap on my Trophy is the original (36,000 miles) and moves in by around 3-4mm when pushed in on prime.

"If at first you don't succeed, go to the kitchen and make yourself a nice cup of tea"
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post #5 of 8 (permalink) Old 04-08-2019, 03:40 PM
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Main Motorcycle: 1996 900 Trophy BRG
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Okay, I'll believe you got the carbs clean. Did you clean out the choke plunger area? The little orfice pulls extra fuel when the choke is on.
I've seen various fuel line configurations, some with one fuel line first feeding into carb #1, then the fuel flows thru the carb and into #2 and then into #3. I've also seen Triumphs with two fuel lines, going in between #1 and 2 and the other fuel line is going in between #2 and 3.
Or it could be the #2 and #3 carbs are going dry, but not #1 when the bike sits for a few days.
After the bike has sat for your regular time between start ups. Open up the little drain screw one at a time on each carb float bowl. Is #1 draining and #2 and #3 almost dry? If so, why is 2 and 3 going dry?
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post #6 of 8 (permalink) Old 04-14-2019, 10:53 AM
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Has anyone considered that the valves might be in need of adjustment ? ...J.D.
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post #7 of 8 (permalink) Old 04-14-2019, 12:05 PM
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Quote:
Originally Posted by Wire-Wheels View Post
Has anyone considered that the valves might be in need of adjustment ? ...J.D.
The OP addressed that.
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post #8 of 8 (permalink) Old 04-15-2019, 12:21 AM
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yup...I misfired on that one...J.D.
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