1962 650ss Build

t ingermanson

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You make a valid point. Was just after why it seems to be running out of fuel or not getting enough flow.

I just need to take two steps back from this, and approach it one thing at a time. Have to come to the realization I will not be riding this bike in a day or so. Just getting eager.
Well, too big a hole isn't itself a problem, unless it doesn't seal. I'm with @texasSlick thinking a burr or the like on the seat is the problem. Perhaps wrap a bit in tape so as to not scrape the sides of the bore, just only scrape the seat to remove a burr.
 

texasSlick

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Alcohol seats and needles are designed for alcohol. They’re bigger cos they have to flow MUCH more fuel.

I can’t see why you feel the need to do this? You have a fairly standard 650 motor and there must be thousands of them running nicely with stock monoblocks.

Why do you think this is a problem that needs solving ?

FE, IIRC, you were the one who, in a previous thread estimated a hot Norton twin, required about a pint of fuel per minute.. It was that thread that induced me to perform flow measurements on my fuel tap and needle seats. Those measurements show the typical 0.125" seat is insufficient.

In my experience, the Atlas was long criticized for losing its push over 4500 rpm, a condition mine never suffered from. But then, my Atlas, bought new from a dealer, was inexplicitly fitted with a needle and seat having an orifice of 0.200".

You also know many Monobloc owners knew something was amiss in the fuel delivery system, and attempted to remedy the issue by installing extended fuel chamber covers, which you have stated merely delays the problem, not solves it.

Thus, you know what seanalex is trying to accomplish! He thinks he is running out of gas at high load, high rpm conditions, as I think he is, and as were all the Atlas's I ran away from in my youth.

@seanalex: The Burlen guy I talked with said the alcohol seat was no longer in production. I am curious as to the part number on the part you have on order from Baxters. The needle part number would be good to know as well.

The 0.200" needle and seat on my Atlas, is as far as I can determine, an aftermarket part made by a now defunct company called Webbco, or Webco. How it got on my Atlas is a mystery, as is several other anamolies on my bike.

Slick
 

Fast Eddie

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It wasn’t me that came up with the pint a minute calculation, but yes, I have been one who has suffered fuel flow issues that cause fuel starvation.

But… it is a sustained WOT condition, and I thought Sean was still bedding in his new build?

I do take care to ensure good flow taps etc on my Norton, but it’s a 920 being fed by 35mm FCRs. The fuel starvation issues mentioned above were on a 1000 Vincent fitted with 30mm Mikunis... and if you speak to a Mikuni expert you’ll know that those carbs were never designed to feed 500cc each!

So yes, I’m with you on the whole ‘take care to avoid fuel starvation‘ topic, but was not / am not sure it is Sean’s problem.
 

texasSlick

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Actually, I am not SURE it is his problem, but I think it is a good issue to put to rest.

Slick
 

texasSlick

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@seanalex

Thanks for the needle and seat info. I note that the alcohol seat description only states "0-125" . That smacks of the orifice being 0.125" id. I hope I am wrong about that. Let us know when the parts arrive.

I also note the pic of the needle resembles more a standard needle. I have an alcohol needle and remember it being different from a standard.i am not now with my parts bin so I cannot verify.

Slick
 

seanalex

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@seanalex

Thanks for the needle and seat info. I note that the alcohol seat description only states "0-125" . That smacks of the orifice being 0.125" id. I hope I am wrong about that. Let us know when the parts arrive.

I also note the pic of the needle resembles more a standard needle. I have an alcohol needle and remember it being different from a standard.i am not now with my parts bin so I cannot verify.

Slick
It will probably get here Tuesday. I thought the same thing about the 0-125 and about the alcohol needle photo. But they carry two different part numbers for each of those pieces.

Will measure and post photo of whatever shows up.
 

seanalex

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Parts came from Baxter. Kind of hard to get a detailed photo of something so small.

Float needles From left: Alcohol, Standard, Viton Tip

1962 650ss Build


Left side stock. Right side alcohol seat.
1962 650ss Build


Left side stock. Right side alcohol seat. Left side measures 0.1" Right side measures 0.14"
1962 650ss Build
 

texasSlick

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It is curious that the alcohol seat is stamped .125 and measures 0.140
You had better go with that seat and needle without further drilling. Surely you will have improved fuel flow that should tell you that you are onto the source of your issue. If no change, look somewhere else.

Slick
 

seanalex

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Yeah I’m not gonna mess with it any further.

Here’s an aside question. Running these carbs without the choke slides installed, would that have any bearing on its running quality?

As in, would more air be able to pass through the carb with the slides not installed? They currently are not in the bike, as they did not come with the basket of parts I got initially. Just been mulling that over.
 

baz

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Yeah I’m not gonna mess with it any further.

Here’s an aside question. Running these carbs without the choke slides installed, would that have any bearing on its running quality?

As in, would more air be able to pass through the carb with the slides not installed? They currently are not in the bike, as they did not come with the basket of parts I got initially. Just been mulling that over.
No running without the choke slide will have no bearing
However you do need to block off the cable hole in the cap
As an aside a high mileage mate of mine always keeps the slides in on MK1 concentrics as he believes the extra weight of the choke slide takes some the shock from the vacuum pulses from the engine running that wears the slides out
It's just one of his theories
 

seanalex

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I have the holes blocked for sure. K. Just seems running a little heavy still.

Need to investigate it a bit more.

My main jets are 270, pilot is 25, and needle is 106.
 
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