FIRST RIDE OUT, FIRST PUSH BACK

For all that relates to both Armstrong MT 500 and Harley Davidson MT 350
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Bunker
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Re: FIRST RIDE OUT, FIRST PUSH BACK

Post by Bunker » Wed Jul 16, 2014 9:00 pm

Wouldnt that excess fuel depart on the first kick over, through the exhaust ports?
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AWJD
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Re: FIRST RIDE OUT, FIRST PUSH BACK

Post by AWJD » Wed Jul 16, 2014 11:21 pm

I think my idea that the tilted carb might be the cause of the problem is a non-starter (no pun intended) especially for my Mikuni because it has 2 separate floats. If anything this would result in a lower fuel level in the float chamber when the bike was on its sidestand.

However, it could well be physics that can explain what is going on, especially in a hot engine. Rather than a Venturi effect which will only occur when there is a significant flow of air, its possible that the problem is simply caused by the evaporation of the petrol in the float chamber saturating the air trapped in the inlet port of the engine and in the outlet chamber of the air filter box.

Even at minimum throttle opening, the air-fuel mixture by mass is ~10:1. The saturated vapour pressure of petrol is somewhere between 5-15 psi compared with normal atmospheric pressure of ~15 psi. I would need to work out how the saturated vapour pressure of petrol equates to the corresponding air-fuel ratio but its possible this saturated air corresponds to an excessively rich mixture. If correct, this might explain the 'flooding' which would be due to the petrol condensing out of the saturated air when it was compressed inside the cylinder.

I think the only way of proving or disproving this explanation is by way of a controlled experiment. Step 1 would be to verify difficulty of starting (hot or cold) when the petrol has been left on for some time. It would be necessary to carry out this test at least 6 times for statistical purposes. Step 2 would then be to repeat these tests but to vent the inlet to the carb and engine before each test by removing the air filter cover and possibly using forced air to blow out the petrol vapour. If this step results in the engine starting easily then the theory would be proven.

I'll give this experiment a go over the weekend and report back.
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1985 Armstrong MT500 (Fun Bike)
1996 Harley MT350e
1987 Armstrong MT560e
1997 Honda XR250R Ex-Army
1966 BSA B40WD
1971 BSA B50T
1973 BSA B50MX

2007 Suzuki GSX1400 (Workhorse)

STEELPONY

Re: FIRST RIDE OUT, FIRST PUSH BACK

Post by STEELPONY » Fri Jul 25, 2014 7:55 pm

I am not that mechanically minded and do not know if this is applicable to my hot start issues, but the following is straight out of the Old Bike Mart July issue and refers to flywheel magneto ignition systems
"Your bike may start second or third kick from cold but with the engine hot after you stop to top up with petrol you kick and kick until you are red in the face and end up having to bump start your pride and joy you go home check everything and still cannot find out what the problem is. When engine manufactures put the flywheel inside the engine they would overheat and loose the magnetism as a result the spark just isn't fat enough for the system to work"
also have to say a big big thank you to lardmarc for all the help he has given me. came over last Saturday and spent five hours going over the bike checking tappet clearance (there weren't any) clutch and spent time trying to figure out what the issue was. Left me with his sonic bath to clean the carb. Cheers Mate :D just waiting for a new fuel hose and in line filter to arrive and hopefully I will be on the road
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Turbogirl
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Joined: Sun Apr 15, 2018 2:39 pm
Location: east midlands

Re: FIRST RIDE OUT, FIRST PUSH BACK

Post by Turbogirl » Thu Apr 26, 2018 5:11 pm

Well, it's my problem now :D Happy daze... I had a very similar experience on my first trip out on her but luckily mine ended with a stall at the top of the hill from my house. It's probably her new owner Right of Passage!

I've got a bit of a wishlist going for her- the boot from carb to inlet is pretty perished and the decompression lever seems to have little rhyme or reason to its function. I'd love to get the front drum and amal carb, not neccesarily to put on but just so it can be restored to originality as I'm a bit of a mil lover. And shin splints. I could use them too ;)
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Wirralman
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Location: Wirral, Merseyside

Re: FIRST RIDE OUT, FIRST PUSH BACK

Post by Wirralman » Thu Apr 26, 2018 5:49 pm

Turbogirl wrote:
Thu Apr 26, 2018 5:11 pm
Well, it's my problem now :D Happy daze... I had a very similar experience on my first trip out on her but luckily mine ended with a stall at the top of the hill from my house. It's probably her new owner Right of Passage!

I've got a bit of a wishlist going for her- the boot from carb to inlet is pretty perished and the decompression lever seems to have little rhyme or reason to its function. I'd love to get the front drum and amal carb, not neccesarily to put on but just so it can be restored to originality as I'm a bit of a mil lover. And shin splints. I could use them too ;)
The first topic in General MT chat is MT Tee shirts, you must have a few by now

Whilst the Amal was the first carb fitted ex factory, two other carbs were fitted at the factory and are generally considered better
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sparkieb2
Posts: 41
Joined: Mon Jun 22, 2015 2:33 pm
Location: Yorkshire

Re: FIRST RIDE OUT, FIRST PUSH BACK

Post by sparkieb2 » Fri Jun 08, 2018 1:26 pm

After my 500s last attempt at giving me a heart attack i gave up and bought a 350 😂
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Yorkshire & retired 👍

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