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F/B 1957 Cruiser 75 Carbs

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F/B 1957 Cruiser 75 Carbs

Post  peter@dunfordconstruction on Wed Feb 21, 2018 8:09 pm

Please can anyone tell me the correct jetting etc for the S25 carb on a cruiser 75 I need this as I have conflicting details in two F/B official booklets !!

Main jet size
Pilot jet size
needle size
throttle cutaway size.

My existing are as follows 130 main jet
35 pilot jet
3 1/2 set at 1.9" out
No3 Throttle cutaway
.
And it will not run properly!
Good spark everything brand new.
Timing perfect
Petrol flow perfect
Float set up 3/16ths
Engine rebuilt by VS

Very frustrating.

Peter:


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Carb setttings

Post  piston 197 on Wed Feb 21, 2018 8:43 pm

Peter, the info i have agrees with what you have except i have it as a 120 main jet ??, this will only make a difference between 3/4 and full throttle, these settings were for a 20 to 1 mix of petroil which will be thicker than say a 33 to 1 mix that most people now run and will pass through the jet system quicker, i have found the necessity to increase the needle length to compensate for this, so the 1.9" measurement may benefit from increasing if you are running a leaner mix than 20 to 1 ??
JH
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Re: F/B 1957 Cruiser 75 Carbs

Post  peter@dunfordconstruction on Wed Feb 21, 2018 8:49 pm

Thanks John,

One book I have says 120 another says 130.

I will give that a try and change to 120 & lengthen the needle

Peter

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Poor running

Post  kerabo on Wed Feb 21, 2018 10:30 pm

Peter
When you say it don't run correctley, how does it not run correctly ?

What happens

Ken
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Re: F/B 1957 Cruiser 75 Carbs

Post  peter@dunfordconstruction on Thu Feb 22, 2018 8:17 am

Hi Ken,

It starts fairly easily will rev a bit but will not increase revs progressively 1/2 to full throttle

Peter

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1/2 to full

Post  piston 197 on Thu Feb 22, 2018 8:25 am

1/2 throttle onward is controlled by needle taper and slide cutaway from 3/4 onwards the main jet comes into play as well.
What oil to petrol mix are you using ?
try shutting the choke partially to see if a richer mixture is required, if so needle will need raising, if this makes it worse needle will need lowering ?
JH
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Poor running

Post  kerabo on Thu Feb 22, 2018 8:46 am

I know the engine was rebuilt but make sure the points do open completely.

How old is the fuel. That caught me out same fuel on both bikes and the AMC engine was fine. My 9E was horrid and I blamed everything but it was fuel.

I like to ride them and hold on the bad part and shut the fuel tap and if it clears and runs better before it stops it's too rich and likewise put the choke on a little and if it runs better it's weak.

Is it cable on flap choke? Make sure the slide has not got the cutaway for a choke slide unless it is fitted.

Just a few ideas
Ken
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Re: F/B 1957 Cruiser 75 Carbs

Post  peter@dunfordconstruction on Thu Feb 22, 2018 10:28 am

Hi Ken,  Thanks for reply.

I will go through all again particularly the points but at present it has one of the best sparks of any of my bikes.
The fuel is brand new as is the oil @25/1
Can't ride it as not enough power.
The flap choke is the standard 1H on the back of the carb cover and all the bits are in the filter area.
The throttle is the standard no3 cutaway No slide cutout.

In the meantime I have ordered all new bits for S25 from VS,  pilot tube, float, main jet, needle, springs, and see what that brings!!!

 Regards

Peter

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Poor running

Post  kerabo on Thu Feb 22, 2018 10:47 am

I know you say you have a spark but check the points gap.

I worked on a members 1H who had spent months trying to make it run correctley" the points were about 10 thou but when it was warm the main bearing moved in the casing in excess of that 10 thou making it flutter and misfire. I opened the points a little more and the problem was gone.

Ken
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Re: F/B 1957 Cruiser 75 Carbs

Post  peter@dunfordconstruction on Thu Feb 22, 2018 11:11 am

Hi Ken certainly will

Peter

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Re: F/B 1957 Cruiser 75 Carbs

Post  peter@dunfordconstruction on Fri Feb 23, 2018 8:40 pm

Hi Ken Gap is 15thou

Peter

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Poo running

Post  kerabo on Fri Feb 23, 2018 8:57 pm

Ok Peter
It was worth a try..

Could you post a link to a clip of it running .
Failing that you could get someone to look st it with you.
Your miles from me or I would offer.

Ken
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Re: F/B 1957 Cruiser 75 Carbs

Post  Ianh on Sun Feb 25, 2018 10:13 pm

Hi Peter,

What colour is the plug?
Have you check for air leaks - carb cleaner sprayed on inlet will increase revs.
check ignition coil with meter. (when cold and when its been running)
check output from generator and check the coils with meter (cold and when bike has been running)
is the battery charging?

Ian


Last edited by Ianh on Sun Feb 25, 2018 10:15 pm; edited 1 time in total (Reason for editing : adding more info)

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Re: F/B 1957 Cruiser 75 Carbs

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