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#880285 05/11/22 7:33 pm
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knuckle head
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knuckle head
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My A10 with a Mikuni TM carburetor... The engine is very responsive and pulls great up to 3/4 throttle...Twist the throttle wide open from the 3/4 position and nothing much happens..The engine doesn't stumble or bog, the exhaust sounds ok,just very little change from 3/4 to full. Back off slowly from full to 3/4 and there is no gain in speed or stumble...It's most noticable in 3rd and 4th...The engine is around 4500 rpm when doing this...
Air filter and fuel flow are more than adequate.#8 NGK is slighly cold and the plug shell color appears slightly over rich..But what do I know, lol..
Rich or lean?

E23A06FD-2538-4F20-A26E-AC856DF1839C.jpeg

61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Put a bigger main jet in and see if it gets better or worse.

How big is the carb?


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knuckle head
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knuckle head
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A bit big at 32mm but my experience with flatslides says they are more tolerant than round slides...The engine is in Super Rocket tune with a siamese pipe...
In third gear the engine will pull 6000 rpm at full throttle ,it's the slower pull from 4500 to about 5200, then like a second wind it pulls a bit better to 6000 rpm....


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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The biggest original equipment A10 carburettor I’ve heard of is inch and three sixteenths, which is 30.2 mm and not many had that.

If you must use a big flatslide, I can’t advise, but what you describe is a bit like the behaviour of a carb that’s too big.


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knuckle head
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knuckle head
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I understand, I also think it may be a bit large, just needed someone else to say it....I will try a diiferent main jet just because I have them..


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Joined: May 2013
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Originally Posted by Hillbilly bike
In third gear the engine will pull 6000 rpm at full throttle ,it's the slower pull from 4500 to about 5200, then like a second wind it pulls a bit better to 6000 rpm....

Sounds like it could be poor back pressure from the silencer. If it’s a standard type silencer, try sleeving the outlet side of the silencer down to about 32/33mm ID.

I Had to do this when I fitted an aftermarket clubmans setup to the A65. Went well after that.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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Do the bigger main first.
Have you played with the needle position? Try lifting it to make a richer mid, a 32 is big for this motor , the signal will be lower , less sook on the NJ.
If you have a 28 mm conc lying around that will fit better.

Last edited by gavin eisler; 05/11/22 10:46 pm. Reason: Main Jet

71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
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The poster formerly known as Pod
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If it has the spitfire timed cam, 357 IIRC, twin pipes and Goldstar loudencers are a better outlet, Ive tried siamese systems, for me they are good low down and poor top end, typically running out of puff about 5.5 K in top, this is..
fine most of the time, but annoying when you want to wring its neck. Big bonus for siamese is LHS ground clearance and rearset freedom and particularly sidecar passengers when driving on the left., I can get that .But ...the left hand pipe goes blue fast and the motor is strangled.


71 Devimead, John Hill, John Holmes A65 750
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knuckle head
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knuckle head
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the silencer is a Burgess replica from the UK....Yeah, two into one, 5500rpm is ok for a 74 year old skinny guy ...I had raised the needle and the midrange power and feel is strong...The fresh engine has enough time on it so now I can flog it to test the power...I dont have any Amals. I can buy a new carburetor if necessary , Mikuni or PWK...


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by Hillbilly bike
Air filter and fuel flow are more than adequate.
Are you sure? The reason I ask is the behavior sounds exactly like having restricted air flow. Could the filter look OK in the garage, but partially collapse when lots of air is being drawn in? This also can happen if the choke isn't fully withdrawn.

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knuckle head
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Well, same pod filter used on my T140 that were no problem...I had a similar jetting issue years ago and I forget the details..
Complications......the roads here are two lane with limited sections to be carb testing at 80 mph..And an 8 tire monster farm tractor might be around the next bend tracking mud on the roadway..And me all over the drum brakes to slow down...


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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When I get back I will run point for you. We will go out and wring it's neck properly

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knuckle head
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Originally Posted by triton thrasher
Put a bigger main jet in and see if it gets better or worse.

How big is the carb?
We have a winner, a 210 jet in place of the 200..On an accurate tach the engine pulls cleanly to 6000 rpm in first and second. In third the power falls off after 5500 as Gavin mentioned...
The 32 mm flatslide might be too big but lower rpm response is still sharp...Thanks for the help guys.


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
Joined: May 2013
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Originally Posted by Hillbilly bike
Originally Posted by triton thrasher
Put a bigger main jet in and see if it gets better or worse.

How big is the carb?
We have a winner, a 210 jet in place of the 200..On an accurate tach the engine pulls cleanly to 6000 rpm in first and second. In third the power falls off after 5500 as Gavin mentioned...
The 32 mm flatslide might be too big but lower rpm response is still sharp...Thanks for the help guys.

Completely disagree that this is the effect of the Siamese pipe, they fitted them to RGS and A65 clubmans. If you haven’t got any pipe to sleeve down the tailpipe of the silencer, remove it and run it again.

If it’s still not pulling then another thing I’ve found is the cam timing is too advanced, pulls well low down but runs out of puff at top end. 1 tooth is enough to do that.


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

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I remember a guy trying a siamese pipe on his A10 and finding it spoiled the performance.


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knuckle head
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The bike is ridden briskly , between 3000-5000 rpm quite a bit. The engine with siamese pipe runs well in this range and has the power overall of any stock 650 Brit Bike..The std gearbox ratios have a big gap between 2nd & 3rd and the pipe helps in my opinion...It will pull 6000 in the lower gears but I prefer only to use it in matters of honor...


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Gavin is quite right about the left pipe blueing, the head tends that way..
That's with siamese and standard systems.
Some blokes angled the carb to overcome this
With my old SR i worked the left side to get it to flow better, that was
with a TT carb. Main jet in that would be no guide for you as it was about
410 from memory.

Allan G #880520 05/14/22 10:20 am
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Originally Posted by Allan G
Originally Posted by Hillbilly bike
Originally Posted by triton thrasher
Put a bigger main jet in and see if it gets better or worse.

How big is the carb?
We have a winner, a 210 jet in place of the 200..On an accurate tach the engine pulls cleanly to 6000 rpm in first and second. In third the power falls off after 5500 as Gavin mentioned...
The 32 mm flatslide might be too big but lower rpm response is still sharp...Thanks for the help guys.

Completely disagree that this is the effect of the Siamese pipe, they fitted them to RGS and A65 clubmans. If you haven’t got any pipe to sleeve down the tailpipe of the silencer, remove it and run it again.

If it’s still not pulling then another thing I’ve found is the cam timing is too advanced, pulls well low down but runs out of puff at top end. 1 tooth is enough to do that.
Have a look at Mike Hailwoods proddy race A65, twin pipes, Goldie loudencenrs. https://www.classicbikehub.uk/Featu...-hailwoods-hutch-the-1965-hutchinson-100


71 Devimead, John Hill, John Holmes A65 750
56 Norbsa 68 Longstroke A65
Cagiva Raptor 650
MZ TS 250
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knuckle head
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knuckle head
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On the pipe blueing...I only see blueing at the Y where the pipes are joined otherwise both head pipes are a straw chrome color...
On cam timing for the 0357, I did check the intake lobe center at 99 degrees on the stock marks...When I built the engine marks were scribed on an engine sprocket tooth and the inner primary for ignition timing...35 degrees total..Ignition is a Boyer Micro Power . The other A10 I built 20 years ago with a mag and Monoblock had the dreaded bias at idle requiring an angled carb plate. This A10 has zero bias, maybe due to more accurate ignition firing and the Mikuni carb...Sometimes a guy like me hitting bikes with hammers can make his junk run nicely..


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by gavin eisler
Originally Posted by Allan G
Originally Posted by Hillbilly bike
Originally Posted by triton thrasher
Put a bigger main jet in and see if it gets better or worse.

How big is the carb?
We have a winner, a 210 jet in place of the 200..On an accurate tach the engine pulls cleanly to 6000 rpm in first and second. In third the power falls off after 5500 as Gavin mentioned...
The 32 mm flatslide might be too big but lower rpm response is still sharp...Thanks for the help guys.

Completely disagree that this is the effect of the Siamese pipe, they fitted them to RGS and A65 clubmans. If you haven’t got any pipe to sleeve down the tailpipe of the silencer, remove it and run it again.

If it’s still not pulling then another thing I’ve found is the cam timing is too advanced, pulls well low down but runs out of puff at top end. 1 tooth is enough to do that.
Have a look at Mike Hailwoods proddy race A65, twin pipes, Goldie loudencenrs. https://www.classicbikehub.uk/Featu...-hailwoods-hutch-the-1965-hutchinson-100

Those aren’t goldie silencers. Those are stock silencers with the front section cut away and flat sections welded in for ground clearance. I have an A3 photograph of this very race (my favourite all time racer and my favourite bike), I then got in discussion at the TROC races at Caldwell back in 2013, one of the fellows from SRM was racing an A65 there, he also confirmed it.

Other thing is as well that the original A10 goldie silencers had smaller outlet than the pattern [***] that’s available today.

Also the original factory (A65) silencers had the outlet pipe the same size
As the down pipe, and not the size of the sleeve section of pipe as new pattern crap has again.

Either way, with a bigger outlet than the inlet your loosing tons of back pressure and making more noise. The exhaust tubing book I have discusses outlet pipes
In detail. I says no larger than the size of the inlet and no smaller than 1/8th smaller than the inlet.

If you go smaller than 1 3/8” outlet you’ll start to choke the engine up, I did this and found this first hand on the way to Denmark, you have to start revving the bike and changing down to clean the plugs, then it’ll run clean again. Though the best the bike did was when i just sleeved the outlet with 2 pipes instead of welding the much smaller one in place without the outer portion.


This worked great:

[Linked Image]

This one, not as good, it used the same size as the smaller pipe
Above:

[Linked Image]


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Joined: Oct 2012
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knuckle head
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In my opinion based on experience with the Triumph race bike, there are too many variables in tuning to state any absolutes....Besides pipe putlet size there isthe internal restriction of the silencer, carb type, cam timing and so on..
A good rule is, tune the engine as an individual.... I would love to spend time with Allan, Gavin, Nick , Koan and a few others here... Ride your machines , make comparisons..but ......


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"
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Originally Posted by Hillbilly bike
In my opinion based on experience with the Triumph race bike, there are too many variables in tuning to state any absolutes....Besides pipe putlet size there isthe internal restriction of the silencer, carb type, cam timing and so on..
A good rule is, tune the engine as an individual.... I would love to spend time with Allan, Gavin, Nick , Koan and a few others here... Ride your machines , make comparisons..but ......


I based my findings after having the bike have a complete flat spot midrange and continually changing up and down the box, I already had the exhaust tuning book and decided to re-read it (but make a real effort to absorb the information), followed the as written and found the bike had no loss at top end but was also much better midrange. the pictured silencer was straight through, just a perforated tube with no wadding for baffling. I spent an age before that trying different carb jetting, ended up back on the standard jetting.

your racebike with straight pipe will have the same outlet size as the start of the pipe.

It cost very little to do most of these mods, and if you made your own pipe bore (or shortened one) you'll likely have some spare pipe. You could also try removing the silencer and going for a run.

Ive also found retarding the cam too much will give a flat spot midrange with the BSA "sports Cam"


Now let’s all have a beer beerchug

68’ A65 Lightning “clubman”
71’ A65 823 Thunderbolt (now rebuilt)
67’ D10 sportsman (undergoing restoration)
68’ D14 trials (undergoing transformation)

Joined: Oct 2012
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knuckle head
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knuckle head
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Allan, this has gotten off track, my A10 had no flat spots in the acceleration, it had an issue at full throttle high rpm that has been solved bya jetting change.
Maybe you remember the Supertrapp tunable muffler I put on my T140D that improved power in an engine that allready ran well...


61 hot rod A10, 89 Honda 650NT .On a bike you can out run the demons
"I don't know what the world may need
But a V8 engine is a good start for me
Think I'll drive to find a place, to be surly"

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