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Carb blowback

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shamg
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Carb blowback

Post by shamg » Sun Oct 04, 2020 3:59 pm

Hello I was just wondering what could cause carb blow back on a 2 stroke.

I’ve an old TS100 I’m trying to start and every so often the kick is accompanied by a blast of air from out the carb and white smoke (with a slight burning smell and slight bang as tho the bike is trying to fire).

The bike currently has no air filter due to the lack of a rubber hose connecting the box and carb. I’m thinking the issue could possibly be the reed valves or just a bad fuel/air ratio?

fastbob
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Re: Carb blowback

Post by fastbob » Sun Oct 04, 2020 7:31 pm

Two Strokes just aren't my thing but I have heard of them unexpectedly running backwards . Perhaps this is a timing issue . You say the bike has no air filter so could it be that if it did you simply wouldn't know about the smoke ?

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Re: Carb blowback

Post by skyrider » Sun Oct 04, 2020 8:06 pm

i have heard that you can bump a bike backwards weather that has something to do with them running backwards i dont know :scratch:
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shamg
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Re: Carb blowback

Post by shamg » Sun Oct 04, 2020 9:00 pm

Good call on the ignition timing, i will check it out. Any suggestions welcome

fastbob
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Re: Carb blowback

Post by fastbob » Sun Oct 04, 2020 11:09 pm

skyrider wrote:
Sun Oct 04, 2020 8:06 pm
i have heard that you can bump a bike backwards weather that has something to do with them running backwards i dont know :scratch:
You could bump a car backwards in reverse gear but not a bike surely ?

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Bender
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Re: Carb blowback

Post by Bender » Mon Oct 05, 2020 2:43 am

fastbob wrote:
Sun Oct 04, 2020 11:09 pm
skyrider wrote:
Sun Oct 04, 2020 8:06 pm
i have heard that you can bump a bike backwards weather that has something to do with them running backwards i dont know :scratch:
You could bump a car backwards in reverse gear but not a bike surely ?
Yes but not very well as ignition is rarely set exactly tdc
Bite my shiny metal ass..

Keeper96
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Re: Carb blowback

Post by Keeper96 » Mon Oct 05, 2020 4:46 pm

fastbob wrote:
Sun Oct 04, 2020 11:09 pm
skyrider wrote:
Sun Oct 04, 2020 8:06 pm
i have heard that you can bump a bike backwards weather that has something to do with them running backwards i dont know :scratch:
You could bump a car backwards in reverse gear but not a bike surely ?
2 strokes aren’t my thing but bumping a car backwards in reverse will result in the engine turning the correct way, bumping it backwards in a forward fear will cause the engine to try and run in reverse, I had it happen in a lotus Elise on a track day. I spun out and didn’t push the clutch in quick enough so it stalled then bumped itself into life as it traveled backwards but ran like a bag of spanners.
I switched it off and it wouldn’t restart but after after getting towed to the pits it started and ran fine?

shamg
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Re: Carb blowback

Post by shamg » Mon Oct 05, 2020 7:31 pm

I don't think I'll have to bump the bike any time soon (even in reverse)... it has a kickstart :lol:

WD-40
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Re: Carb blowback

Post by WD-40 » Mon Oct 05, 2020 7:43 pm

I don't know much about 2 strokes either but I think worn reed valves could cause compression to be pushed back through the carb

shamg
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Re: Carb blowback

Post by shamg » Mon Oct 05, 2020 7:45 pm

WD-40 wrote:
Mon Oct 05, 2020 7:43 pm
I don't know much about 2 strokes either but I think worn reed valves could cause compression to be pushed back through the carb
This is my number one suspicion, I recently just rebuilt the top end as well so I feel foolish for not checking them then but it's all a lesson I suppose.

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Re: Carb blowback

Post by onesea » Sun Oct 11, 2020 1:24 pm

With 2 strokes outboards anyway, you often cannot go wrong with a good fuel additive clean fuel and an Italian tuneup.
Take it for a hard ride...
They are also sensitive to inlet air pressure and no filter might not help.

On the subject of running backwards the was a yacht engine that to go in astern you stopped and restarted to run backwards.

We also had a boat with 3 cylinder later diesel that if you started by hand would do 3 revolutions backwards before running forward. Alarming when the starter handle went 3 turns backwards with 1/2" clearance from your nads..
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