Some vague running issues A7 Shooting Star spec

[BSA500]

Right I am not trying to be vague but here we go. Back ground etc. A7 built to SS Spec 1957 engine. Has in recent years had new valves guides etc,rebore to plus 20,newish big end,small end, mains bearings. Carb is a re sleeved amal monobloc 376/4, plugs seem fine. Oh mag was overhauled a few years back. I have owned this bike 30+ years and spent many an hour inside the engine, so i know it well....
1. takes about 4/5 kicks to start but always starts maybe timing??
2. even when hot will be happily tick over then just spit back and kill it, always restarts, it has always done this regardless of the state of the engine.
3. will stutter sometimes under load on the bottom of the throttle openings, even after re sleeve of carb,new needle jets, ultrasonic clean etc.
These are minor things but have seemed to plague the bike throughout its 30 years with me and many things have changed. So what am I missing is it just timing/valve clearances etc. Also compression tests show 150 psi both sides. Running Hornet pipes with baffles in.
What I really want is how is the best way of working through this fuel then ignition,valves or??
many thanks for reading all that

[Triton Thrasher]

Check for air leaks into the inlet, by spraying WD40 at the joints, while the engine is idling.

[berger]

i don't know all i do know is you're not alone. i went out on mine and got a few miles in and out of nowhere a spit back which only happens very very rarely so very hard to pinpoint

[BSA500]

Yeah air leak good start

[muskrat]

G'day BSA500.
Yes air leak is a good/easy place to start. One point people overlook is the top of the carb where the cables enter. I've used shrink wrap on those fittings in the past. Another point of entry is the inlet valve guide but would be obvious with blowing smoke as well.
Cheers

[Triton Thrasher]

One point people overlook is the top of the carb where the cables enter. I've used shrink wrap on those fittings in the past.

Yes badly fitting cables can cause a splutter.  I also have used heat shrink there.

[chaterlea25]

Hi All,
Last Year I was asked to look at an A10 that was doing similar "tricks"
It had recently been completely reconditioned engine wise
I swopped the magneto to a known good one but no change
I then took  the carb from another bike in the shed and tried that, even though I had checked jets fuel level and flow etc.  It ran fine on the replacement carb so back to the original and completely dismantled it
When I removed the screw that locates the jet block the block fell out on the floor 
This would allow air to leak in/out and screw up the pilot mixture!! I had not come across this before

I wonder if the sleeving job on the carb might have affected the fit of the jet block in the carb body 
it needs to be a good tight fit

John

[CheeserBeezer]

I would fit a slide with a smaller cutaway just to see what difference it makes.

[rocker21]

i had a resleved carb om my fielmaster when i bought it was suposed to have been done properly, could not get it to work properly, so i binned it and fitted a carb from JRC in the states , what a difference it now runs as it should, these old amal carbs were not meant to last this long and they dont work very well with this modern fuel, i have had several carbs over the years that have been "refurbished" and none of them have worked properly, seems when they bore them and resleve them with brass  it just never seems to work, as i like to ride rather than show the fact that it now has a different carb is fine, i have also now put one on my shooter as well and that works a treat.

[BSA500]

Hiya,
 In reply to some of the suggestions I shall try the spray around the manifold. The jet block is a very tight fit with the small gasket underneath. Its not resleeved with brass. I have always wanted to try a different cut away slide but they will not fit now its been bored out

[CheeserBeezer]

I have become a Mikuni convert but only on non-standard bikes. I have two A10's running Mikunis and they seem superb.

[RDfella]

I wouldn't touch a Mikuni if someone gave me £500. I spent several hundred £ on a pair of 34mm's and probably another hundred on jets (all the jets work together, so if you change one you have to change all the others). They're very well made and no doubt they would work well if fitted by a manufacturer who has the time / resources to spend days on a dyno getting it just right - though they're that sensitive a change in the weather is enough to upset them.  In the end I dumped mine and bought Amals. A quite expensive waste of a few months work trying to tune them. There's a reason Amal designed the Mikuni and then sold it off .....

Add - bought Amals to replace them. At least they don't have 300 different needle / jet combinations...... Just had to change the starting jet to a smaller size and they're running fine.

[rocker21]

the jrc carbs are really simple to setup and not silly money ,

[BSA500]

Okay done some work on the carb,not sure if its helped any but I will ride later in the week so watch this space. Learnt a couple of things....
1. stripped the carb down for a deep clean in the ultrasonic and to replace the fuel feed banjo that was past its best. I found two washers under the jet block(must have been me). Not sure what symptoms that may cause.
2. when I replaced the carb it kept flooding out of the air bypass passage at the inlet. Found out it was caused by some numbnut(me again) not fully screwing the pilot jet home. So if that happens to you don't assume its the float.


 

[Peter in Aus]

 not fully screwing the pilot jet home.
[/quote]

Did a carby for a mate the other day the pilot jet was missing altogether?