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Only runs with choke on

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Only runs with choke on

Postby Rob861 » Fri Dec 13, 2019 7:22 pm

Since last post I have fitted a fast flow fuel tap stripped carburettor cleaned the jets changed the fuel and still doesn’t run without choke any help would be very much appreciated
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Re: Only runs with choke on

Postby missing lynx » Fri Dec 13, 2019 7:52 pm

Did you thoroughly clean the carb as well as the jets?
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Re: Only runs with choke on

Postby Rob861 » Fri Dec 13, 2019 8:07 pm

Yes completely took apart cleaned checked slide unfortunately it’s a jetex carburettor never had any dealings with them
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Re: Only runs with choke on

Postby missing lynx » Fri Dec 13, 2019 8:30 pm

Right so has it ever run properly? If not it could be one of the many duff jetex carbs if it was running ok then I would try it without the filter see how that afects it. Whats the air screw set at?
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Re: Only runs with choke on

Postby Rob861 » Fri Dec 13, 2019 9:21 pm

It was completely rebuilt ran it without any problem for 50 miles then started it one day and it wouldn’t run without the choke. The air screw is about 3/4 of a turn
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Re: Only runs with choke on

Postby missing lynx » Fri Dec 13, 2019 10:45 pm

Air screw on jetex carbs is usually somewhere between 1-2 turns out was the engine nice and warm when you set the air screw. But from what you say I would still suspect a blockage in the tickover circuit
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Re: Only runs with choke on

Postby Fast n Furious » Fri Dec 13, 2019 11:48 pm

Sounds like the pilot jet is blocked.
Hold the jet up to the light and check the hole is clear.
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Re: Only runs with choke on

Postby CHRIS in MARGATE » Sat Dec 14, 2019 8:17 am

And then it might be an air leak.
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Re: Only runs with choke on

Postby bsso78 » Sat Dec 14, 2019 2:15 pm

The pilot jet is blocked an air leak would cause it run lean and rev high, putting the choke on would richen it and lower the tickover. Pilot jets on standard carbs can be a pain to clean out but have another go at it, you’ll get there.
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Re: Only runs with choke on

Postby Rob861 » Sat Dec 14, 2019 9:52 pm

It’s totally clean can clearly see through all the holes
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Re: Only runs with choke on

Postby MickYork » Sat Dec 14, 2019 10:01 pm

Try the next size pilot jet (bigger).
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Re: Only runs with choke on

Postby CHRIS in MARGATE » Sun Dec 15, 2019 9:32 am

Your original post states that "after running for 50 miles, it now won't tick over without choke on".
When you say "now", are you implying that it did originally run fine? If so that is not too small a pilot jet but rather an obstructed pilot or it is an air leak causing a weak mixture. If it has always done this,then it is likely that you do need to increase pilot jet size.

If it is an air leak this often manifests itself in the form of hot running that has a smell about it and a reluctance to return to normal tickover when the throttle is blipped.
All tests should be done when engine is warm.

For potential air leaks, check cylinder head nuts after rebuild or exhaust manifold nuts.
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Re: Only runs with choke on

Postby Hat » Sun Dec 15, 2019 10:26 am

Alternatively, could the timing have slipped?
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Re: Only runs with choke on

Postby Rob861 » Sun Dec 15, 2019 1:17 pm

It ran perfectly fine for 50 miles and yes it does have a hot smell about it
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Re: Only runs with choke on

Postby CHRIS in MARGATE » Sun Dec 15, 2019 6:41 pm

Ok It's not the timing. For that to have slipped would mean all 3 stator bolts coming loose or the pickup having become dislodged.

If it smells hot that is because it is running weak.

It suddenly started so check manifold studs and head bolts.
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Re: Only runs with choke on

Postby sunrisemac » Mon Dec 16, 2019 7:44 pm

CHRIS in MARGATE wrote:Ok It's not the timing. For that to have slipped would mean all 3 stator bolts coming loose or the pickup having become dislodged.

If it smells hot that is because it is running weak.

It suddenly started so check manifold studs and head bolts.


Might also be worth checking float needle is not sticking and float level is high enough
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Re: Only runs with choke on

Postby CHRIS in MARGATE » Mon Dec 16, 2019 7:50 pm

Yes good call.
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Re: Only runs with choke on

Postby coaster » Tue Dec 17, 2019 10:44 am

sunrisemac wrote:
CHRIS in MARGATE wrote:Ok It's not the timing. For that to have slipped would mean all 3 stator bolts coming loose or the pickup having become dislodged.

If it smells hot that is because it is running weak.

It suddenly started so check manifold studs and head bolts.


Might also be worth checking float needle is not sticking and float level is high enough


If it was the float then I would expect problems when riding rather than tickover but still worth a check though
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Re: Only runs with choke on

Postby Rob861 » Wed Dec 18, 2019 5:30 pm

I have given up it’s booked in the scooter centre will post the outcome
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Re: Only runs with choke on

Postby Rob861 » Fri Jan 03, 2020 4:10 pm

Thanks for all the help it was dodgy jets in the jetex carburettor all changed running fine
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