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3 into 1 flat spot #784830 09/20/19 7:09 am
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DavidP Offline OP
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I'm no racer, but I figured you guys might have some experience with this.
'72 Trident with some sort of 3 into 1 header, not sure who made it. 180 main jets on stock Amals.
In any case, I got a rough spot between 4 and 5000 rpm. I can accelerate through it, but at steady rpm it kinda sounds like a racing two stroke, coughs and spits.
Is this just the nature of the beast? Reversion?


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
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Re: 3 into 1 flat spot [Re: DavidP] #784842 09/20/19 1:47 pm
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Mark Parker Online Content
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David, if it has a fairly big bore system you can get reversion, but you also get top end power. Typically you open the throttle and it goes pa pa pa pa, no power, then WAAAAAAAAAAAAAA, lots of power. If that's what it does a lighter throttle through the reversion may prevent it. If that's what it is there are a couple of anti reversion things you can try at the headers as well. Big headers have lower gas speed and it needs the speed to draw the inlet charge in and reversion happens when the intake air does not have enough speed and energy to carry the air into the cyl against the rising piston pushing it back out before the inlet valve closes.


mark
Re: 3 into 1 flat spot [Re: Mark Parker] #784844 09/20/19 1:57 pm
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Allan Gill Offline
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Originally Posted by Mark Parker
David, if it has a fairly big bore system you can get reversion, but you also get top end power. Typically you open the throttle and it goes pa pa pa pa, no power, then WAAAAAAAAAAAAAA, lots of power. If that's what it does a lighter throttle through the reversion may prevent it. If that's what it is there are a couple of anti reversion things you can try at the headers as well. Big headers have lower gas speed and it needs the speed to draw the inlet charge in and reversion happens when the intake air does not have enough speed and energy to carry the air into the cyl against the rising piston pushing it back out before the inlet valve closes.



I got the same symptoms on the A65 by retarding the cam (probably too much) never fully cured it. well not least till I advance the cam again


beerchug
Re: 3 into 1 flat spot [Re: DavidP] #784855 09/20/19 4:43 pm
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Easiest solution I believe is adapting a Supertrap muffler... Change the number of discs until the problem is minimised or gone....I had a 3-1 on a 73 Trident many years ago with bad reversion like you mention...I added one inch balance pipes beteween the three primary pipes about one foot from the head, no more reversion traded for a barely noticable loss of top end power.


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: 3 into 1 flat spot [Re: DavidP] #784881 09/20/19 8:20 pm
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David,
I know you are on the Triples Online site as well. On that site someone was having problems with a similar flat spot. Turned out the alternator output was interfering with the electronic ignition impulses. Was discovered by taking a test run with the alternator disconnected. You might want to try that to make sure you don't have the same problem.

Ed from NJ

Re: 3 into 1 flat spot [Re: edunham] #785162 09/23/19 2:50 am
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DavidP Offline OP
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Originally Posted by edunham
David,
I know you are on the Triples Online site as well. On that site someone was having problems with a similar flat spot. Turned out the alternator output was interfering with the electronic ignition impulses. Was discovered by taking a test run with the alternator disconnected. You might want to try that to make sure you don't have the same problem.

Ed from NJ

I guess that's worth a try. The alternator wires are routed as stock. When I installed the Trispark I ran the pickup wires out the front of the case, along the bottom frame member under the engine, and up the down tube to the black box, mounted where the tool tray should be. The alternator wires run up the opposite side of the down tube, but are not tied to it. In any case, that puts them in parallel at a distance of about 3". I suppose I could separate the alternator wires from the loom and reroute them behind the oil tank.

For the rest of you, the pipes are 1.5" OD and join the collector under the center of the timing cover, about 29" from the valves.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: 3 into 1 flat spot [Re: DavidP] #785184 09/23/19 11:44 am
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pushrod tom Offline
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That sounds like a drag race pipe. The Supertrapp would be a good answer. But, you did not provide much info about your problem. 4-5k no load, light load, going up an easy hill, full throttle? Maybe just a carb tuning issue.

Re: 3 into 1 flat spot [Re: DavidP] #785279 09/24/19 2:20 am
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DavidP Offline OP
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The length of the collector/megaphone is 30.5", so total length from valves to exit is 59". Mega flairs to 3" with gases exiting through a 1" hole. Pictures in this thread: http://www.britbike.com/forums/ubbthreads.php/topics/782387/anyone-recognise-this-header#Post782387
The problem occurs at light load, constant speed, maybe 1/4 throttle. I did a plug chop and got no deposits. Went to 107 needle jets and got some color on the plugs, but the problem persists. I'll be installing the chokes next time the carbs are off, maybe they'll help diagnosing the problem.

Ed: I just happened to have a pair of alternator wires in my stash of old wiring. I ran these straight back and up the frame tube behind the oil tank, well away from the trigger wires. Gotta finish rebuilding the clutch before I can ride again though.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: 3 into 1 flat spot [Re: DavidP] #785327 09/24/19 3:44 pm
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From the photo,the pipe is likely too long and causing reversion.


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: 3 into 1 flat spot [Re: DavidP] #785691 09/28/19 5:31 am
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I've run similar to that. I removed the centre stand and took the centre pipe to the left of the frame tube with all pipes angled to the left with the collector angling back to the right well up under the engine because it gets close to the ground. I had various tail sections with glass packed muffler because they frown on open Megaphones on the road here. No other pipes gave the same power. The factory were open 4" from memory. The things are much better at 850cc with 30 or 32mm carbs. Depending what you are looking for.


mark
Re: 3 into 1 flat spot [Re: DavidP] #785700 09/28/19 11:19 am
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This photo circa 1980 shows the 3-1 on my 74 Trident..short primaries with the balance tubes and a glasspack muffler...On the street the engine was stronger to about 7000 rpm..The longer pipe felt better at top end...Depends how you ride I suppose..But after my recent experience with Supertrapp mufflers I believe it's best option for street exhaust tuning.

[Linked Image from i.imgur.com]


79 T140D, 96 900M Ducati ,2001 Sportster....On a bike you can out run the demons..
Re: 3 into 1 flat spot [Re: DavidP] #785704 09/28/19 1:09 pm
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I have never seen a triple use 107 needle jets. All the 1000cc bikes and factory triples I have worked on have used 106 jets.
Did you check the jets with a gauge? I would check some 106 jets to make sure they are the correct size and try them.

Re: 3 into 1 flat spot [Re: DavidP] #785860 09/30/19 6:00 am
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DavidP Offline OP
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I'm NOT a bloody machinist! I don't own a complete set of pin gauges just to check that parts bought from reputable suppliers are made to spec. Perhaps even current production jets are made with the same WW1 era production equipment used to make these bikes in the first place?!?
I have used 107 needle jets in past on a Trident with different exhaust. All I know in this case is that I did a plug chop at 1/3 throttle and got NO deposits on the plug, much less a "mixture ring" at the base of the porcelain, with new genuine Amal106 needle jets.


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
72 T120V cafe project "Mr. Jim"
72 T150V "Wotan"
Re: 3 into 1 flat spot [Re: DavidP] #785883 09/30/19 1:59 pm
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I checked 4 needle jets on two T140 last week. Of the 4 jets 1 checked good, 2 were worn to 107 and 1 of the jets marked 106 the 105 gauge would barely slide in. I check every needle jet I pull from a carb and every new jet I install or sell. Yes I have seen new jets that checked bad.
Gauges can be had for around 25 dollars for the 105/106 combination gauge.

Re: 3 into 1 flat spot [Re: RPM] #786271 10/05/19 9:17 am
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Allan Gill Offline
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Originally Posted by RPM
I checked 4 needle jets on two T140 last week. Of the 4 jets 1 checked good, 2 were worn to 107 and 1 of the jets marked 106 the 105 gauge would barely slide in. I check every needle jet I pull from a carb and every new jet I install or sell. Yes I have seen new jets that checked bad.
Gauges can be had for around 25 dollars for the 105/106 combination gauge.


I am the same with the ones I fit and sell. Often if the needle jet is over tightened it will be enough to reduce the size of the needle jet from say a 106 to a 105. It’s good practice to check the jet post fitted into the jet holder.


beerchug
Re: 3 into 1 flat spot [Re: DavidP] #786961 10/13/19 3:51 am
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Mark Parker Online Content
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A bigger motor will help remove reversion as it increases gas speed through the head. But also, I was reading last night, that a cure for reversion was increased compression ratio. Reversion is related to gas speed and apparently higher compression, that has that crisper exhaust sound, also delivers more velocity into the exhaust gas helping the gas go forward through the engine rather than back the wrong way.


mark
Re: 3 into 1 flat spot [Re: DavidP] #786973 10/13/19 11:54 am
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True Mark. Everything matters. PRT


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