Carb experimentation, cold start issues.

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tippo88
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Joined: Tue Apr 07, 2015 2:31 am
Location: Kuala Lumpur
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I have made various posts previously regarding starting and spit back issues which I never completely resolved.
I came across a guy who is a very experienced go-kart tuner and be volunteered to help.
He has loads of different carbs to play with.
So far we have experimented with two carbs, a good quality PWK copy and a VHSH 30 CS.
Strange thing is that with both carbs we can get the scooter running really well except for literally the first cold start of the day. With both carbs it will start first time in the day with a hand over the carb and after starting once will then start fine even if left for a while.
We have checked the obvious things such as choke being fully opened etc.
Bit of a loss what to do. The go kart tuner is even suggesting a fuel primer as used on jetskis but seeing as every other scooter in the world doesn't need one I'm thinking that must be another solution?
TIA

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tippo88
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The tuner doesn't think it's spark related as it starts and runs fine other than once a day.
I'm wondering though if the spark is marginal and just not enough for the most difficult start of the day.
The stator is an mb 12v electronic and considered switching to a vape with added benefits of better lights etc. but vape is not cheap so would prefer to have some way of knowing it it would solve the problem before I splash the cash.

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mick1
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Main scooter: Li Avanti 225
Location: York
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What size choke ?

on a phbh with a kitted 225 i use a 70.....using a 60 meant a hand over the carb'.
tippo88
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Thanks! Let me check.

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Muppet
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Posts: 1279
Joined: Thu Sep 16, 2010 9:54 pm
Main scooter: SX 150 running in

what is the inlet port timing in degrees and piston clearance on yours; i had trouble starting an ex race barrel that had been fitted to a mates road scooter from cold; warmed up it was fine. when I took it apart and measured up the Inlet timing was 165 degrees; piston clearance a little over 4 thou on a cast 150 barrel; great once it was running but a pig to start from cold
C’est la vie
tippo88
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Posts: 189
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Location: Kuala Lumpur
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Port timings are:
exhaust 171
transfer 135
blowdown 18.24
inlet 140
I made the mistake of going with an SR kit as readily available here but had to do a lot of work with base spacer and skimming the top of the cylinder to get these.

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Muppet
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Joined: Thu Sep 16, 2010 9:54 pm
Main scooter: SX 150 running in

That is a big tansfer timing with a short duration exhaust port.
C’est la vie
Adam_Winstone
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Main scooter: Lambretta GP
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Muppet wrote: Sun Feb 06, 2022 12:51 pm That is a big tansfer timing with a short duration exhaust port.
... agreed.
tippo88
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Posts: 189
Joined: Tue Apr 07, 2015 2:31 am
Location: Kuala Lumpur
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My tuner agrees that it's not ideal but doesn't think it should affect cold start.
After first start it actually runs ok for my needs running round the city.
Always intended swapping to a good kit at a later date but hoping that doesn't need to be now.

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tippo88
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Posts: 189
Joined: Tue Apr 07, 2015 2:31 am
Location: Kuala Lumpur
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Ok this is doing my head in now. Ran it for a while with the pwk on. Once got it started first time for the day it ran ok and would start again fine.
After a while it would randomly become difficult to start and would kind of chug at very low revs when trying to start it.
Decided to change tbe ignition as wanted better lights anyway so installed a vape sport.
Initially was fantastic start first kick first start of the day and all day. Engine felt a bit more peppy. Yeehah finally solved the problem and have a reliability starting scoot.
But, after a few test runs one morning back to square one, won't start first time of the day without hand over carb. Take for a run and stop. Try to restart and doing the chugging thing.
How can fitting a new ignition temporarily cure the problem and then not???
Totally confused.


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