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Message started by marekbuk on 08/14/17 at 10:20:59

Title: No start and Petrol leak on to cylinder head
Post by marekbuk on 08/14/17 at 10:20:59

Guys

I don't know how this can happen but after a new Dyna fit, re-jet and carb clean I tried to start her up but instead petrol started leaking badly down the LHS of the cylinder head and barrel. Took the chrome head cover off and there was a pool of petrol on the head around the spark plug.
Checked the plug was tight - ok!
Any ideas?

Title: Re: No start and Petrol leak on to cylinder head
Post by Gary_in_NJ on 08/14/17 at 10:43:17

Pools of fuel can be from a few things:

1. A leaking petcock
2. A misaligned or improperly installed float
3. A worn float valve

Being that you just had the carb apart, I'm going with number two. Make sure that the pin that the float pivots upon didn't slip out of position.

Title: Re: No start and Petrol leak on to cylinder head
Post by Dave on 08/14/17 at 10:57:49

If fuel is getting up there....it likely was coming out of the overlflow tubes - which indicates the float is not limiting he flow of fuel into the float bowl.

Title: Re: No start and Petrol leak on to cylinder head
Post by batman on 08/14/17 at 16:29:22

float valve not closing ,fuel level to high (float level) ,float installed upside down (yes it will fit that way).

Title: Re: No start and Petrol leak on to cylinder head
Post by marekbuk on 08/15/17 at 06:06:56

Thanks guys - sorted now - gunk under the float valve

Running very rich at the moment so going down in pilot jet size and maybe dropping the needle - it was in the middle of the 3 grooves. Incidentally there was no washer under the main jet when I removed it so I put a fibre washer under there - maybe this has contributed to the rich running? - plug all sooted up

Title: Re: No start and Petrol leak on to cylinder head
Post by batman on 08/15/17 at 06:41:52

No maybe about it ,without the washer you would run rich .

Title: Re: No start and Petrol leak on to cylinder head
Post by ohiomoto on 08/15/17 at 08:19:06

I would have guessed the missing washer would have very little to "lean in the midrange" effect. Logic tells me the missing washer simply raises the main jet up a fraction. This means the needle is seated "deeper" in the main when the slide is closed. (Or the main sits "higher" one the needle if you want to look at it that way.) This would make the mixture leaner. Same as if you added the same thickness washer on top of the white spacer (or to your stack of white spacer mod washers). The missing washer would also effectually change/lower the float level by the same amount, but probably not enough to change performance.

That's what logic tells me. Am I missing something?

Title: Re: No start and Petrol leak on to cylinder head
Post by marekbuk on 08/15/17 at 08:22:36

Batman

I thought that if the main jet hole was further away from the needle (ie with my fibre washer in place) then that would let more fuel in? and run richer? Have I got this all wrong?

Title: Re: No start and Petrol leak on to cylinder head
Post by batman on 08/21/17 at 22:27:39

The washer isn't there to space the main jet ,it is there to hold the needle jet (the cylinder with the holes that the jet needle rides in)) up in place against the carb body. If it 's not there the fuel leaks around the needle jet because it falls away from the needle the thickness of the washer.You'll start running rich just off idle,and all the way to WOT.

Title: Re: No start and Petrol leak on to cylinder head
Post by marekbuk on 08/22/17 at 01:33:44

Cheers Batman - I've put a fibre washer under the main jet now and all seems to be good - need a proper road test once it stops raining - well it is Summer in the UK [ch128546]

Title: Re: No start and Petrol leak on to cylinder head
Post by ohiomoto on 08/22/17 at 05:21:26

I never paid much attention, but I thought the needle jet goes in from the top and the main pulls it down from the bottom? (That's what I've seen in other carbs, anyway.) I would think that if the main was tight against the body, it would hold the needle jet down and only the main would be affected.

Either way, it seems to have worked for the OP. I'm just being inquisitive. :)

Title: Re: No start and Petrol leak on to cylinder head
Post by batman on 08/23/17 at 19:41:20

Ohio,sorry you're correct the jet goes in from the top ,but without the washer it gets pulled down to far ,away from the jet needle and allows fuel into the carb even when the throttle is closed .