Fuel in Crankcase Gt 380

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Woodpecker
Posts: 25
Joined: Tue Oct 29, 2019 12:11 pm
Location: Rainham Kent

Fuel in Crankcase Gt 380

Postby Woodpecker » Wed Jan 15, 2020 10:30 am

Hello again I thought i had sorted out all issues with the rebuild of a 1972 GT380 only to find another problem. I have had the bike running, and its starting and running great but there were problems with the gearchange. Following advice on the forum I sorted out the problem and attempted to start the bike. It did not feel right when i kicked it over and did not start. I'm not sure why but thought I would check the SIRS drains on the bottom of the crankcase and all 3 cylinders had a lot of petrol in them! So it must be from the carbs but it was only 24 hrs since I was running the bike the tank petcock is not leaking as I removed the tank with fuel in it. The carbs were cleaned during the refurb and new needle valves fitted (pattern type) and fload levels checked. So how did all this fuel get into the crankcase in such a short time? The only other observation is when left standing for say a few days I turn the fuel on to prime and there is a flow from the tank into the carbs. Any suggestions and checks I can do would be appreciated.
Stu

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canaletto5
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Location: Derbyshire

Re: Fuel in Crankcase Gt 380

Postby canaletto5 » Wed Jan 15, 2020 10:40 am

I really recommend only using genuine Mikuni parts for the carbs. It sounds almost certainly like the carbs are leaking fuel, either becuase the float levels aren't right or the needles aren't seating properly.

Woodpecker
Posts: 25
Joined: Tue Oct 29, 2019 12:11 pm
Location: Rainham Kent

Re: Fuel in Crankcase Gt 380

Postby Woodpecker » Wed Jan 15, 2020 11:45 am

Thanks I will have to remove them again and was considering fitting new needle valves any suggestions where I can get original Mikuni parts?

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canaletto5
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Location: Derbyshire

Re: Fuel in Crankcase Gt 380

Postby canaletto5 » Wed Jan 15, 2020 12:59 pm

The guys on here can advise. Allen Performance sell genuine Mikuni

Here is a link to Robinson's foundry , the needle is part number 28

https://www.robinsonsfoundry.co.uk/shop ... t380carbjk

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canaletto5
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Location: Derbyshire

Re: Fuel in Crankcase Gt 380

Postby canaletto5 » Wed Jan 15, 2020 1:12 pm

Need to double check they are the right ones but half the price of Robinsons

http://www.allensperformance.co.uk/shop/

barney01
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Re: Fuel in Crankcase Gt 380

Postby barney01 » Wed Jan 15, 2020 4:20 pm

http://www.motocarb.com/mikuni-main-jets.html
http://www.nrp-carbs.co.uk/shop/index.p ... ommon/home
Two more companies genuine Mikuni parts
Pattern float jets are very unreliable and are too important to risk your engine with.
NO SMOKE .......NO POKE

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slosher
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Location: WALSALL UK

Re: Fuel in Crankcase Gt 380

Postby slosher » Wed Jan 15, 2020 5:30 pm

The Bonnie p---ed fuel from the carbs having stripped cleaned and re-set float levels.Amal offer a Viton tipped needle which i replaced with both carbs and it sorted the over fueling problem.Anyone know if Mikuni offer similar :?:
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Harrymail
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Re: Fuel in Crankcase Gt 380

Postby Harrymail » Wed Jan 15, 2020 7:47 pm

My rebuilt carbs had pattern needle jets in them and they leaked straight away, fuel coming from the overflow. I put genuine ones in and all fine. I won't touch pattern parts in the carbs. Not when genuine Mikuni are available and are not that expensive either.
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Woodpecker
Posts: 25
Joined: Tue Oct 29, 2019 12:11 pm
Location: Rainham Kent

Re: Fuel in Crankcase Gt 380

Postby Woodpecker » Thu Jan 16, 2020 1:06 pm

Thanks for the advice i used pattern kits to rebuild the carbs all were in a poor state after 20+ years but cleaned up fine and when I got it running all was as it should be. The bike starts and runs great. What i still dont understand is why all 3 cylinders filled with fuel after just 24 hours. They didn't overflow as the petcock seems to work and does not leak when the bike is not running. Where did you get your needle valves from? Robinsons were expensive and motocarb don't have any.
Stu

barney01
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Joined: Wed Sep 26, 2012 7:33 pm
Location: Prestatyn.Wales

Re: Fuel in Crankcase Gt 380

Postby barney01 » Thu Jan 16, 2020 1:49 pm

It is possible that the piston that shuts off the fuel temporarily stuck open or a small bit of debris from the tank stopped it from closing.
These float shut off valves are IMHO the most essential part of the carb. The pin with the tapered point has a very small spring inside so that as the bike vibrates and bumps up and down the fuel stays at a constant level. Its a type of shock absorber. Thats why cheap ones very rarely do the job.
If you want to try another source send an email to Gtreiner1@aol.com with your request. That where i got mine from last year
NO SMOKE .......NO POKE


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