Float Bowl Seating Hole Question

I just received my two new Amal float bowls with drain holes from Old Britts, unfortunately though, one has the .1" diameter seating hole and one has the .125" diameter seating hole. I emailed Ella to see if they had another .1" diameter seating hole bowl in stock, and I had barely let go of the send button when she called me on the phone. I knew Old Britts always had great service, but she just bumped it up to a whole new level to explain. Long story short, because there is no rush, we left it that I would check on the forum to get an opinion(s) on how critical that hole size is. The engine I'm (slowly) rebuilding is a '72 750 Combat, and I'm trying for the standard Combat state of tune when it's done. Apparently there is currently a supply problem with these float bowls from Amal, although I did just see Andover is saying the 622/056 bowls now in stock again. The old "no-drain" bowls that were originally on this bike had the .1" diameter holes. Is there any kind of a tuning issue if I was to drill out the new bowl with the .1" diameter hole to .125" diameter so they would both be the same? The bike will be used for normal country road riding here in Vermont and New England, and I am looking forward to some occasional Combat type acceleration fun, so might the .125" diameter holes just help keep the float bowls filling up more better under those circumstances? Or should I return the .125 diameter hole bowl for a .1" diameter bowl when one's available, so the float bowls will not fill up too fast and somehow cause the bike to not carburate properly?
Bill

Float needle brass seat?

There isn't a "too big" problem, so long as the tip of the needle seals the hole when the bowl is full.


It shouldn't affect running at all.

Triton Thrasher said:

Float needle brass seat?

Click to expand...

Yes. The following photo is per a L.A.B. post on previous thread I had hijacked. "The seating size is the diameter of the hole at the bottom of the brass seat."
I also got new "stay up" floats and new Viton tipped float needles to go with the new float bowls. Would you recommend both holes being .125" diameter?

If 0.1" was enough to feed the bike before, it should work now. I don't see any harm in one being 0.1" and one being 0.125", but you could drill it out (neatly) or put ypur old 0.1" seat in or send it back to the supplier, if you're uncomfortable with the discrepancy.

I can't vouch for how it used to run. The last registration expired in 1983, and was poorly stored, but the carburetors appeared unmolested.

This scenario seems odd to me. I'm kinda anal about Amals. I'd want them to be identical. So the one with the bigger hole. Is it bigger due to the bore being punched out or because the countersink for the seat was run in further? Former scenario would allow you to punch the smaller one out to match. The latter, not so much because your needles would travel different depths before sealing and your float height wouldn't be the same. Just sayin...

It's beyond me to know how much difference it makes, but when I was getting my 750 out on the road I discovered my banjo bolts that feed fuel to bowls had different drillings. Drove me nuts, so I drilled them to be the same. Otherwise I figured I'd never know if any tuning problems where due to that difference.

I guess thats about 4-cents worth by now.

Russ

back in the day Amal supplied severn float bowl options for the mk1

0.10 with drain plug and without ( standard gravity fill ) with 2.5mm needle seating
0.062 with drain plug and without ( pump fill ) with 1.6mm high pressure needle seating
1.125 with drainplug and without ( high volume gravity fill ) 3.2mm needle seating
0.156 without drain plug ( alcohol ) with 4.0mm needle seating

I would look closely at the needle seating Diameter before fitting

rvich said:

...Otherwise I figured I'd never know if any tuning problems where due to that difference...

Click to expand...

Both bowls in question are new, one is the standard with a .1" hole and the other (sent by mistake) is the high flow with a .125" hole. More new bowls are "temporarily out of stock" at Amal. I'm also thinking that I would prefer to have them both the same for the reason you mentioned, and the simplest solution all around would be to carefully drill out the smaller hole to .125", if the larger holes would make no tuning difference. And if that is the case, why does Amal offer different diameter seating hole bowls?

My guess....
Racing carbs /methanol fuel uses a tremendous amount more fuel volume than a gasoline .100 hole would flow.
Therefore, need a bigger entrance hole.

Temporaaily out of stock is Burlen`s polite way papering over the cracks

They have no stock available showing for most of thier product range and according to the Trade no delivery dates either

I'm not sure drilling out the brass will give you a clean enough surface for the float needle to seal against. Why wouldn't you just drift the brass seat out of one of your old bowls and then press it into the new bowl instead?

This thread raises a lot of questions for me. If the different size doesn't make any difference then why do they not make them all with the 0.156 "alcohol seating"?

http://amalcarb.co.uk/mk-i-concentric-s ... 4-0mm.html

As for drilling it out. I would worry about whether or not I might scar the seat as mentioned in the post above. I would probably do it anyway. But first I would drop the needle valve into both seats and try to verify they are the same depth regardless of bore. One would think they are but I'd do it anyway just so I could sleep at night.

I would debate with myself whether to drill from top or bottom to have the smallest impact on the seat. Eventually I would choose one based on some vague notion.

After drilling I would polish the seat to make sure I didn't leave a sharp lip that might damage the needle. It is a common practice for my carb maintenance to use a Q-tip with a good quality metal polish on it to clean and polish my valve seats. But of course you have to make sure you don't leave any polish or cotton fibers behind.

So after all this...Whats wrong with the original bowl? LOL

Russ

rvich said:

This thread raises a lot of questions for me. If the different size doesn't make any difference then why do they not make them all with the 0.156 "alcohol seating"?

http://amalcarb.co.uk/mk-i-concentric-s ... 4-0mm.html

As for drilling it out. I would worry about whether or not I might scar the seat as mentioned in the post above. I would probably do it anyway. But first I would drop the needle valve into both seats and try to verify they are the same depth regardless of bore. One would think they are but I'd do it anyway just so I could sleep at night.

I would debate with myself whether to drill from top or bottom to have the smallest impact on the seat. Eventually I would choose one based on some vague notion.

After drilling I would polish the seat to make sure I didn't leave a sharp lip that might damage the needle. It is a common practice for my carb maintenance to use a Q-tip with a good quality metal polish on it to clean and polish my valve seats. But of course you have to make sure you don't leave any polish or cotton fibers behind.

So after all this...Whats wrong with the original bowl? LOL

Russ

Click to expand...

The .156" seat needs a special aluminum needle and it appears to not have the Viton tip. AN stocks the .125" which uses the same needle as the .100". Either brass or aluminum with Viton tip.
Pete

rvich said:

..Whats wrong with the original bowl?..

Click to expand...

The original bowls have no drain ports to mount Madass's new Ezy Drains into.

dynodave said:

My guess....
Racing carbs /methanol fuel uses a tremendous amount more fuel volume than a gasoline .100 hole would flow.
Therefore, need a bigger entrance hole.

Click to expand...

0.125" was the standard seating size for the 850 Mk3 float bowls (99-0509 - 622/056) according to the parts list.

What's your '5 mile' Mk3 got?

https://andover-norton.co.uk/en/shop-dr ... rburettors


https://www.princeton.edu/ssp/65-cub-da ... itbike.pdf

Page 3.

Concentric
622/052 .062" float needle orifice Two stroke fuel pump
622/054 .156" “ “ “ Two stroke
622/055* .100" “ “ “ Four stroke drain plug type
622/056 .125" “ “ “ Four stroke drain plug type
622/057 .062" “ “ “ Fuel pump drain plug type
622/058 .052" “ “ “ Four stroke fuel pump

Click to expand...

o0norton0o said:

I'm not sure drilling out the brass will give you a clean enough surface for the float needle to seal against. Why wouldn't you just drift the brass seat out of one of your old bowls and then press it into the new bowl instead?

Click to expand...

I drilled a pair out to 3 mm once. One then didn't seal against the needle until i turned a bigger drill backwards against the seat.

Andover is now showing that # 622/055 bowls are back in stock, and I did find out that British Only has plenty in stock as well. So the pressure is off to attempt modifying either of the two new bowls I have to get two with the same size holes, and I haven't been convinced to disregard Norton's and Amal's long standing use of the .1" seating hole size for a '72 750 Combat. Thanks for all the helpful reply's.
Bill
https://andover-norton.co.uk/en/shop-details/17947

L.A.B. said:

dynodave said:

My guess....
Racing carbs /methanol fuel uses a tremendous amount more fuel volume than a gasoline .100 hole would flow.
Therefore, need a bigger entrance hole.

Click to expand...

0.125" was the standard seating size for the 850 Mk3 float bowls (99-0509 - 622/056) according to the parts list.

What's your '5 mile' Mk3 got?

Click to expand...

L34/R33 (LH24 in IPL book probably typo)
The bowl is marked 125 next to the bowl fuel inlet and I can clearly see a smooth 5-7 thou chamfer/seat at the top edge of the drilled hole.
useless trivia...bowl and slide top screws were slotted and not usual phillips....viton tipped brass needle...as expected no scratches at all on the slides

dynodave said:

L.A.B. said:

0.125" was the standard seating size for the 850 Mk3 float bowls (99-0509 - 622/056) according to the parts list.

What's your '5 mile' Mk3 got?

Click to expand...

L34/R33 (LH24 in IPL book probably typo)
The bowl is marked 125 next to the bowl fuel inlet and I can clearly see a smooth 5-7 thou chamfer/seat at the top edge of the drilled hole.
useless trivia...bowl and slide top screws were slotted and not usual phillips....viton tipped brass needle...as expected no scratches at all on the slides

Click to expand...

Thanks, that does confirm the parts book information is correct, although raises another discrepancy, as a change in Amal build specification usually resulted in a different build number because the Mk2A carbs are also 932/33 & 34 but the only float bowl listed is 622/055 (0.100").

The official Burlen/Amal 850 carb numbers for the 850 Mk3 are 932/42 & 43 however, I can't recall any Mk3 owners mentioning those carb numbers and my Mk3's carbs have been replaced with generic 932/300 & 301 items.

http://amalcarb.co.uk/mk-i-carburettor-7230.html

I don't know why they have slotted instead of Pozidriv (not "Phillips") screws, but my '78 T140's apparently original carbs also have slotted screws.

rvich said:

This scenario seems odd to me. I'm kinda anal about Amals. I'd want them to be identical. So the one with the bigger hole. Is it bigger due to the bore being punched out or because the countersink for the seat was run in further? Former scenario would allow you to punch the smaller one out to match. The latter, not so much because your needles would travel different depths before sealing and your float height wouldn't be the same. Just sayin...

It's beyond me to know how much difference it makes, but when I was getting my 750 out on the road I discovered my banjo bolts that feed fuel to bowls had different drillings. Drove me nuts, so I drilled them to be the same. Otherwise I figured I'd never know if any tuning problems where due to that difference.

I guess thats about 4-cents worth by now.

Russ

Click to expand...

Yep, you are Anal!

I'd have done exactly the same thing!