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The patient is a RE Interceptor 750. I got it non-running and parked up since (I suspect) 1974. It was in remarkably good shape overall. The carbs were typically dirty but inside were not bad at all. I gave them a rebuild with AMAL kits. I did get the bike started and it ran well on the stand but...

The left carb leaks at the main jet holder gasket. The right carb doesn't drip like the left one does but you can see there is dampness around the fiber gasket.

It was suggested that perhaps the bowl end plate was leaking and fuel was tracing back and dripping down from the fitting. I did find the bowl gasket weeping and a quick flat surface sanding dressed that up enough to stop it. Still the jet holder leaks.

I've had it apart multiple times. I've flipped the fiber washer. I've looked for cracks. If I remove the jet holder and just place my thumb over the hole I don't get leakage. I tried removing the jet and the cover nut and holding my thumb over that and fuel still pisses out of the junction where the gasket is.

I've tried staring at it. I tried sanding it flat like I did with the bowl to no avail. I've tried cursing at it appropriately. Nothing I've tried has made any difference.

I'm stumped.


1964 RE Interceptor 750
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Originally Posted by Dwight V
I've tried cursing at it appropriately.

I'm stumped.


That's strange, as that should have cured it eek

Seriously though, it may be possible that you have a hairline fracture in the carb body from someone possibly over tightening the jet holder. Or, maybe the jet holder is the problem....wishful thinking but not to be ruled out.


Jon W.


1957 6T Thunderbird 650
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Ask it nicely to stop.


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A known fault with 750 Interceptors. The best thing you could do is crate the whole bike up and send it to me. That would rid you of this leaking carb curse.

Otherwise perhaps try another set of fibre washers. Maybe lap the jet holder threads with a bit of tooth paste in case they are not true enough.

Or a hairline crack as Jon says.


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Try a dowty washer in place of the fibre one.


And pray that there's intelligent life somewhere up in space
'Cause there's bugger all down here on Earth'

An interesting point given recent events.

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I'd considered the Dowty. Don't know where to source them locally though. Plus, there is a part of me that insists that something that has worked for decades should be working for me today.


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Maybe mix a small amount of JB Weld fuel-resistant epoxy, and just coat the base of the jet holder abutment; let cure.

Then, re-sand and try again...


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Originally Posted by GrandPaul
Maybe mix a small amount of JB Weld fuel-resistant epoxy, and just coat the base of the jet holder abutment; let cure.

Then, re-sand and try again...

You’d have to grind away back to clean metal and leave no traces of fuel. When I have used it to fill my inlet ports, on the one occasion where I haven’t fully sanded the port before applying the epoxy, it has later been able to be lifted off as a chunk.

I don’t get why people mess about with old carbs. It’s a key part of the bike, if it isn’t metering fuel properly to your engine then it could potentially cause serious damage. These are consumable items and they do wear. Save faffing and buy a new one.


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Swapped jet holders between carbs, no change. Tried using talcum powder to see if it was leaking outside the sealing surfaces, no dice.

What is annoying is I had the bike running (briefly) and it sounded fantastic. The bike only shows 3000 miles so I wasn't ready to believe the slides or bores were a problem. If it had 10k or more on it I'd probably have just ordered new ones. These look so good!

"Bother" as the Brits say.


1964 RE Interceptor 750
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Have you actually tried the cheap and easy things first, like using new fibre washers ?


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For the ocean will decide,
Its not the destination,
It's the glory of the ride"
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Well, these WERE new.
Since all this faffing about, no. Not exactly available at the local parts store.


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If you can get it down to just a seep, then use a little blue Hylomar and let it sit overnight.

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Dwight,
I think the suggestions to try new washers and or washer and sealant are good ideas but if I remember correctly, those fiber washers are pretty hard and I think I might try a similar thickness soft aluminum or annealed copper washer just to see if it would conform to the mating surfaces better, you never know. The only problem I ever had with my old Monoblocs was an occasional sticking float with visions of the bike going up in flames while I searched for something to smack the bowl with. Mark R.

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Is the float valve needle seating properly? Is the float spindle spacer in place,? its easily lost, leaks from these items are the most common.


71 Devimead, John Hill, John Holmes A65 750
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Originally Posted by Allan G
I don’t get why people mess about with old carbs.
PROBABLE answer (in most cases):

Fix used one - $25

Buy new one - $265


GrandPaul (does not use emoticons)
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Originally Posted by GrandPaul
Originally Posted by Allan G
I don’t get why people mess about with old carbs.
PROBABLE answer (in most cases):

Fix used one - $25

Buy new one - $265

It’s not always a $25 fix though is it. Parts wear, such as slides and bodies. You’d be lucky if $25 bought a new set of jets.

But each to their Own. I’d rather replace it then I can forget about it and move on, hopefully be riding the thing.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
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I like Monoblocs they are a good carb if not worn, yours sound like they are low mileage so little wear. First thing I would check is the float to make sure it is free moving and the float spindle bush not being nipped up by the float cover if you,ve changed the gasket.Next I would check the float needle union, note there is no fibre washer between union and float bowl chamber body if there is then this will change the fuel levels.Onto main jet holder, remove the fibre washer then refit into carb body screwing it nearly home insert a 25 thou feeler guage into gap between holder and main body and nip up holder & check if gap is equal all round if not here is your problem, I have had second hand mono carbs that previous owners have used the jet holder as a drift to remove jet block assembly by unscrewing holder and wacking holder, this then distorts the jet block threads so when the main holder is refitted it screws back on the wonk. Good luck..


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Floats properly function. Little brass spacers installed. New brass needle valves replaced the plastic originals. Yes, they are the same length.

I'd thought of trying a metal washer but none of the ones in my inventory were the right size. I may nip down to the hardware store and see what they have.


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If you ride full throttle all the time, you'll never notice improper jetting or a worn carb. Also, the fuel won't have time to drip, and even if it does, the wind will evaporate it!


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...hi GrandPaul; at "full" throttle you can find starvation.
Also, at high temperature on the road you can have starvation.

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As someone had posted earlier, the new fibre washers that I bought were very hard and did not seal properly. I fixed the petrol weep completely by slightly sanding the washer so the shininess of the surface was gone and it was roughened a little.

A zero cost repair smile
Cheers,
Bevan

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Originally Posted by Dwight V
Well, these WERE new.
Since all this faffing about, no. Not exactly available at the local parts store.

In my garage t'other day my eyes lit on the box of carb bits and a distant memory surfaced.
I vaguely remembered that many years ago the Flash got a weepy carb, aged Monobloc. Eventually found it was from the float cover plate. Even after smearing a new gasket with sealant it was still weepy. Cannot remember if the cover plate was slightly warped or a tiny crack, the screw holes are very close to the edge, could well have been overtightened many times over the years.
Fitted a spare from the box of bits, problem solved!
Just an old memory that may or may not be of much use.


Blessed are the curious for they shall have adventures

"He knows not where he's going,
For the ocean will decide,
Its not the destination,
It's the glory of the ride"
(Edward Monkton, Zen Dog)

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I did have one that weeped. A light sand of the bowl edge on a flat surface fixed that.

I'll mess with it again tomorrow with a few new ideas and report back.


1964 RE Interceptor 750
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Typically the carb body will have some irregularities on the surface at the main jet AND float bowl. If you'll carefully lap those on a flat surface with 400 grit until you get a bright, shiny surface all the way across... then the leaking will stop. Adding a tiny amount of fuel-proof sealer can also help.

The traditional way to fix the float bowl is to use 2 gaskets. The BEST gaskets are the OEM red ones from AMAL, but old stock will shrink and won't fit as well.

An upgrade would be to add the Viton-tipped float needle from a Concentric to the Monoblok. They simply slip right in without mods.

Hope this helps.


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A few wraps of carefully applied ptfe teflon tape...leak be gone....


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