Author Topic: Needle jet behaviour has changed over time  (Read 1840 times)

Offline Swarfcut

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Re: Needle jet behaviour has changed over time
« Reply #15 on: 19.06. 2019 07:49 »
Scott. Your last post indicated to me that it performs fine to start with, then gives the symptoms of fuel starvation after a short time of running, and the speed is limited by the fuel flow. Maybe worth you starting with the tank and pulling the taps out to see if the gauze filters are blocked, kinked, or sitting in years of sediment.

 Swarfy.

Online muskrat

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Re: Needle jet behaviour has changed over time
« Reply #16 on: 19.06. 2019 07:53 »
G'day Scott.
OK it's time to mark the twist grip and housing to see what throttle opening it plays up at. Mark the housing and grip with the throttle shut, then the twist grip at full open adjacent to the mark on the housing. now divide that into four. You can then see at what throttle opening it goes pear shaped.
Cheers
Swarfy beat me and valid points.
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Online JulianS

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Re: Needle jet behaviour has changed over time
« Reply #17 on: 19.06. 2019 09:23 »
Found this in some service papers from the US. Unfortunately the original is poor quality on flimsy paper but it might be useful.

Some of the lever type petrol taps, the ones with the screw in nylon filters, have small drillings through the rotor when compared to the UK made item and in addition the holes in the sealing membrane dont always line up with the rotor drillings causing significant reduction in fuel flow.

Second photo shows the membrane partially obstructing fuel passage in a screw on nylon filter type tap.

Offline mikeb

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Re: Needle jet behaviour has changed over time
« Reply #18 on: 19.06. 2019 10:30 »
this thread is interesting to me (my SR is now spluttering under load). I OCR-ed and fixed that service note:
Quote
RESTRICTIONS ON THE "GASOLLINE FLOW" ON A10 SUPER ROCKET MODELS
it has been  reported that in some cases it is necessary to increase the
Main Jet size in the Super Rocket Mono-Bloc carburetor up as high as
#350 to #500 to obtain maximum performance. The standard main jet size is
#290.

A Super Rocket that doesn't run as fast as is expected and its is
Necessary to to increase the Main Jet size considerably to obtain high
Speed performance, it is an indication of a 'gasoline flow' restriction
at some point in the passage between the gas tank and the main jet

Points where a possible restriction may be located.
   1. Gas tank shut-off. Remove and clean thoroughly.
   
   2. Banjo Gasoline Fitting. Remove and cut 3/32 off the inlet
   and outlet "pipes". And burr the holes to clean away the
   rough edges. The "pipes" are the sections that the plastic
   lines slide over. There is banjo fitting at each tank
   shut-off and one at the carburetor. The "pipes" on the double
   Inlet banjo at the carburetor are tapered down on the ends and
   The holes are partially closed shut, when they are shortened
   3/32" the holes will be opened to the correct size.

   3. Float valve seat fitting. Remove from the carburetor - open up
   the gas passage  to 1/8" - drill in from the opposite end to the
   float valve seat so that the seat is not upset.

   4. Gas screen at the carb. Remove and leave the screen  out if it
   is the "Bronze Screen Type". Cut off the Screen  and use the
   washer section only if it is the "Plastic Type".

   5. Air Cleaner. Remove the entire air-cleaner to obtain  max, high
   speed performance.
   
but this still would not explain why the bike used to run fine and now does not, would it?
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Offline duTch

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Re: Needle jet behaviour has changed over time
« Reply #19 on: 19.06. 2019 11:32 »

 
Quote
this thread is interesting to me (my SR is now spluttering under load). I OCR-ed and fixed that service note:

 I was trying to explain 'OCR' to a couple of girls I was working with for a few days a year or so ago, but the closest I could get was 'OCD' (they looked at me kinda funny).... *conf*  For you to do that mike they must be related anyway *smile*
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Offline mikeb

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Re: Needle jet behaviour has changed over time
« Reply #20 on: 19.06. 2019 11:56 »
you do have to be a bit OCD to OCR dutch. one day i'll tell you what i do for a job
New Zealand
'61 Super Rocket  - '47 B33 -  '18 Triumph Street Triple RS

Offline Scott and Jay

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Re: Needle jet behaviour has changed over time
« Reply #21 on: 20.06. 2019 05:18 »
Ok, thanks guys. I took both petrol taps out and inspected the gauze. It was all clear and straight. I cleaned them and dried them, anyway. When I was draining the tank, first - the flow from both taps was so rapid, that I thought it couldn't possibly go through this amount of fuel. It would only be doing about 5 miles per gallon. I also replaced all the fuel lines. They had gone a bit brittle and narrowed at some point, but no blockages. The taps, Mike are the lever ones from British Spares - that I think are called "UK- made".

So, I went for the same ride. I was going faster than 60 at first, to get past cars - so I could get in a space. When I got on to a steady 60 m.p.h, on this flat road (this is when it happens) I got the same loss of power, spluttering. I stopped at a petrol station and removed the little gold-stone filter - that I run in the line. This is between the tap and the carby banjo, it was the main line (not reserve). This was a new one and I have never had any problem with these before. At first it seemed to go better for longer. But when I turned around and came back the same road, the loss of power happened again - in the same circumstances (steady 60 m.p.h, on this flat road)

I had marked the throttle and it seems this is happening at 1/4 or just higher - which is the change between slide and needle jet, or the very start of the needle-jet range.



Offline Triton Thrasher

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Re: Needle jet behaviour has changed over time
« Reply #22 on: 20.06. 2019 06:40 »
While it’s doing the loss of power thing, cut the ignition, pull the clutch in and coast to a stop.  Then see if the plugs are sooty.

Maybe you’ve already done that.

Offline Klaus

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Re: Needle jet behaviour has changed over time
« Reply #23 on: 20.06. 2019 06:58 »
Hi Scott,

have a look at the top of the float bowl there is also a filtergauze. Just a try, start your bike and go on flull asscelleration 60 miles will done in  5 seconds. Is there a better behavior without spottering? What is the cutaway at the slide? A smaller cutaway give more fuel at the 1/4 lift.

cheers Klaus


If you think, everything is under control, you are not fast enought.

Offline Swarfcut

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Re: Needle jet behaviour has changed over time
« Reply #24 on: 20.06. 2019 07:39 »
Scott, I get the impression that something is changing as the bike warms up, and I reckon most possible causes within the fuel system have been checked by now. Pity those taps were clear, thought we had cracked it. Klaus suggests another slide, so that's a possible.  So that leaves a mechanical fault, unlikely, or our old friend " the source of sparks". Worth a quick look at pick ups, slip ring, earthing bush at nameplate end. Run it in the dark, check for sparking from HT Leads. Someone said most carb faults are ignition.

Swarfy.

Online ironhead

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Re: Needle jet behaviour has changed over time
« Reply #25 on: 21.06. 2019 01:17 »
G'day S&J.
A few Things I can think of 1) Magneto, AA unit playing up, cam ring wandering, cam ring end plate loose, points plate not running true, points gap closed up causing retarded ign ( causes over heating then fuel vaporization )
2) Valve clearances a bit tight made worse with the overheating problem.
3) Could also be over advanced timing, Ive had experience with similar symptoms on an AMC single.
This could be the 'ticking' sound you hear.
You seem to have done a thorough job of the fuel system, as they say ' most fuel problems are electrical'
SA

Online cyclobutch

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Re: Needle jet behaviour has changed over time
« Reply #26 on: 21.06. 2019 14:36 »
What side of the carb is the tickler on? Can you reach down and press it whilst you are suffering the symptoms?

                                 ** WITHOUT ENDANGERING YOURSELF WITH THE DISTRACTION. **
Various, including ...
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Online Greybeard

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Re: Needle jet behaviour has changed over time
« Reply #27 on: 21.06. 2019 14:44 »
Can you reach down and press it whilst you are suffering the symptoms?

                                 ** WITHOUT ENDANGERING YOURSELF WITH THE DISTRACTION. **
Filth!

Offline Scott and Jay

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Re: Needle jet behaviour has changed over time
« Reply #28 on: 22.06. 2019 03:28 »
Thanks for all your replies, everyone. The slide is a 3 1/2, Klaus. It also accelerates fine - right up to 70. Then, when I drop to a steady 60 it happens after 1 or 2 k. The whole set up has performed wonderfully, for 4.5k miles (since my top-end rebuild, new carby etc).  I think the timing is good - because it was pinging a bit last year due to points gap too wide. Now it's back to about 12 thou the pinging has gone away, and it otherwise performs great.The only area I haven't eliminated, I believe, in this recent journey of fault-diagnosis (recently shared with you all), is, yes - magneto/ignition circuit (but I have new plugs). To even start looking at any of the factors involved around that device - I expect to, therefore, bite the bullet and take it out. I would deliver it all to our fantastic local engineer then, in the first place. I have something else for him to do. He can check everything, I don't have to go through things one by one.
So, I might not report back for a while now - thanks for everyone's forbearance..

Online Peter in Aus

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Re: Needle jet behaviour has changed over time
« Reply #29 on: 22.06. 2019 03:56 »
I had a similar problem with my A7 long stroke. Ran fine till it wormed up and I started to put on a bit of speed, it would start misfiring spitting back, my first impressions was fuel starvation. It turned out to be valves sticking a bit. I'd had the head reconed and they had made the guides a bit tight. Ones that was sorted I had no more problems.
Just a thought.
Peter

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