I have installed a petcock in the fuel line to aid with removing the tank while I’m finishing off a few things underneath with the wiring.

Unfortunately when it arrived it turns out the internal diametre is smaller than the outlet from the tank (and inlet to the rail) by about 3mm. Will this cause any issues with pressure or reduce fuel delivery having the petcock in the way?

It will almost certainly increase fuel pressure as the pump will be trying to squeeze the same flow through a smaller pipe.

The diameter is not big enough.
You should consider, instead of this petcock, the quick release coupling fitted on oilheads BMW.
They are designed to allow a sufficient flow or this pump.

Never used something like that, no need for it.
When you take off the hose, only a bit fuel should come out.

Besides; wrong hose clamps. Use original BMW instead, partnumber; 13311460928

i have to agree this is a little pointless 

Clymer recommends using golf tees to plug them. I don't play golf, but I can assert that shuttlecocks don't work; they just fall off..

I once sliced off the front of my cornea with a shuttlecock.

Re Laitch's Post 6 about using Golf Tees to plug fuel hose. There are 2 types of Tee: wood and plastic. Try to find wood golf tees because some of the plastic tees can dissolve if exposed to fuel over a prolonged time.

You may find that all those petcocks are for gravity fed systens

Im betting that at 3 bar presure even if open , they will leak like a sieve n

It might be a little bit of overkill, but it's done now, so that's okay.

I think the reduced diameter would only make a small difference to the resistance of the system. The fuel pressure regulator provides resistance to the fuel flow from the pump, to increase the pressure, to about 36psi. So a small increase in resistance just means the regulator has to work a little less, so the final flow and pressure would remain the same.

Laitch wrote:

Arlina wrote:Besides; wrong hose clamps. Use original BMW instead, partnumber; 13311460928

Why are these so much better?

There’ll no doubt be other clamps that do the job, but nothing I’ve ever come across on any other bike or car comes close the the quality of the OE hose clips in a K bike. I think the crimped ear clips are made by Oetiker, and you can buy those, but I’ve never found a supplier for the screwed type. Firstly they’re stainless, then the screws are fine thread (unlike jubilee clips) so’s you get much more feel when tightening them, thirdly the bands are narrow so the tightening pressure on the hose is greater and easier to place correctly behind the Barb. Lastly, they’re exquisitely made and strong as fluck. This must sound like tongue in cheek persniketyness, but it’s one of the many appeals of the K-bike. Am I mad?

Edit: I forgot, they also have a tiny BMW roundel on them too, you can’t beat that

Search 'stainless mini hose clips' on ebay. I have two 'kits' plus a load of individual ones of hose size (14mm - 16mm) in the garage, so I can vouch for quality and the fact that they are fine pitch screws.

Unfortunately they don't have a BMW roundel on them, but you can always buy a Dremel and learn how to etch

The jubilee clamps distort the hose surface and as mentioned have a coarse thread that can loosen.  They are made for large diameter hoses that carry coolant not fuel, especially fuel in fuel injection systems that is under high pressure. 

You may not know it, but a friend found out the hard way that if you have an engine fire and the insurance adjuster sees those clamps they may not cover your damages.  He told me it was the first thing they looked for.

Just go to the auto parts place and ask for fuel injection fuel line clamps.  The lines on our bikes usually take the 13mm size.  Last I bought some they were less than a buck apiece.

"Unfortunately they don't have a BMW roundel on them..."

Not interested. 

Point-Seven-five wrote:…Just go to the auto parts place and ask for fuel injection fuel line clamps.  The lines on our bikes usually take the 13mm size.  Last I bought some they were less than a buck apiece.

Great idea! I had those clamps on the bike when I bought it so just reused but buying the bmw ones would sent me back a small fortune as shipping to NZ is $60us for clamps that are $2us. 🤯

But I found a set at the local auto store for $4 so happy as! Thanks for the advice. 

And @daveyson I had spare hose for after my little experiment with the petcock so after all the advice, I’ve decided now to use it. 

Thanks again for all the feedback.