Carb Over-fuelling?

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Offline McBrain

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Carb Over-fuelling?
« on: July 17, 2022, 05:01:26 pm »
Hey guys.

Have a look at the attached video. Does that look like too much fuel coming out the primary nozzles? It's not even atomizing (esp. the left hand nozzle)

Revving to approx 40% throttle

https://photos.app.goo.gl/EY5Wp8pnMpFZPssBA


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Offline McBrain

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Re: Carb Over-fuelling?
« Reply #1 on: July 18, 2022, 06:46:52 pm »
For those that are perhaps nervous about clicking on the link...

What should the fuel look like coming out the discharge nozzles (not the squirters)? Fine mist? Or closer to opening a tap?
« Last Edit: July 18, 2022, 07:17:10 pm by McBrain »
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Offline GLENN 70

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Re: Carb Over-fuelling?
« Reply #2 on: July 18, 2022, 08:32:44 pm »
Make sure you float levels are correct . Set so fuel does not come out of the side of the bowls , when the screws are out ,set just below and fuel just come out when you shake the car . Don’t use BP 98 .

Offline McBrain

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Re: Carb Over-fuelling?
« Reply #3 on: July 18, 2022, 09:45:23 pm »
What's wrong with BP98??

That's what I always use
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Offline GLENN 70

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Re: Carb Over-fuelling?
« Reply #4 on: July 18, 2022, 10:15:13 pm »
Can have problems in classic cars/ engines that have a holley carb on them . Too many cleaning agents in it And  all sorts of crap . Very good in late model fuel injected engines tho .  Seen fuel come out of the vent tubes on holley carbs running on BP 98 .  Yours should only be the float levels too high .

Offline FB.65.68.70

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Re: Carb Over-fuelling?
« Reply #5 on: July 19, 2022, 07:52:19 am »
Glenn
agreed with the floats possibly being high but I also use BP 98 its been shown to have the best octane in dyno tests and all of the 98 octane fuels have the additives and those additives tend to eat into brass floats, so McBrain make sure your floats dont have a pinhole and starting to sink and therefore not controlling the needle and seat, Ive just swapped out brass floats for the nitrophyl in a holley double pumper for the same reason. 

Offline 66FBK

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Re: Carb Over-fuelling?
« Reply #6 on: July 19, 2022, 10:00:15 pm »
That looks typical at a low speed. You will get a better misting of the fuel under load and at higher revs. Carbies are pretty basic things. That's why you don't get more that 20Mpg. Float levels are important. Having a bigger carbie like a 650 or 700cfm on a stock motor will not give you better performance. Going down to a 450 cfm sometimes gives a higher velocity air flow thus better fuel atomisation.
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Offline McBrain

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Re: Carb Over-fuelling?
« Reply #7 on: July 20, 2022, 09:04:16 am »
Thanks you all. I will re-check float level and integrity.

I remember BP98 mentioned here a couple of years ago but I had the understanding that the BP98 was the one to use.

I've been chasing this problem around for ages. Rebuilt the carbie a couple of times over the past few years and still getting it run rich on RHS bank with fouling of plugs after each drive.

One think I never did was swap out the fuel tank which I knew had rust in it from previous owner. I just put an inline filter on. I now realise there is probably very fine rust coming through. I have a new tank I brought back from the US about 6 years ago and never put in. So I'm going to do that, along with new fuel lines, clean pump etc. Then re-strip carbie adjust, etc and go from there.

In that video I was revving to at least 40-50%. It may not be under load but it looked like a lot of fuel to me. More importantly, it looked like more fuel on the RHS nozzle than on the LHS. Which could affect the RHS bank even with a single plane intake manifold.
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Offline jiffy

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Re: Carb Over-fuelling?
« Reply #8 on: July 29, 2022, 06:52:40 am »
I'm assuming you have checked that the main jets are the same size? Might even be worth experimenting with various jets to reduce the volume of fuel in the left hand side (as shown in the video). The is a guy in or around Frankston that is able to trouble-shoot carbs on a rolling road (roller dyno) - I'll see if I can get his number for you.
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Offline McBrain

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Re: Carb Over-fuelling?
« Reply #9 on: July 29, 2022, 09:13:04 am »
Yes, I replaced the main jets about a year ago (PO had 6 sizes too big!) so I'm pretty sure they are equal. Decreasing jet size on one side crossed my mind but was worried it was just masking an issue.

What I'm doing right now is replacing the whole fuel system. I think the original fuel tank has some very fine rust that is getting through the filters. I bought a new tank about 5 years ago when I lived in the US and never got around to putting it in. That's probably the issue. Fine rust getting in the carbie.

So I'm currently bending up some nice new solid fuel lines to go with the new tank painted and ready to go in. Then I'll rebuild the carbie and try again.

Details of the guy in Frankston would be really useful, thanks.
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Offline jiffy

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Re: Carb Over-fuelling?
« Reply #10 on: July 31, 2022, 09:27:23 pm »
This is them:
+61 3 9786 4032
37 McCulloch Ave
Seaford VIC 3198
Australia
www.mkauto.com.au
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Offline McBrain

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Re: Carb Over-fuelling?
« Reply #11 on: August 01, 2022, 08:44:37 am »
Thanks mate
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Offline Chris66pny

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Re: Carb Over-fuelling?
« Reply #12 on: August 01, 2022, 11:28:58 am »
Might be worth checking your high speed air bleed on that booster circuit, if this is blocked it can cause the booster to run rich (i had this exact same problem). A quick web search will show the location of these air bleeds which are located next to the accelerator pump nozzles. Easy enough to unblock/clean, just pull the carb apart and blast some carb cleaner and air down the circuit path, make sure you also get the air path through the metering block, these are often over looked when rebuilding the carb.