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carburetters and porting of manifoilds A65 900 ccm #368155
04/14/11 6:54 am
04/14/11 6:54 am
Joined: May 2006
Posts: 198
Tynset Norway
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oleandreas Offline OP
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oleandreas  Offline OP
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Tynset Norway
Im trying to decide on carburettors for my 880 ccm BSA A65 engine. Any reccomendations ?

Manifoilds inlet tracts in head are ported to 33 mm, and I have problems going bigger without making holes.

About size of carburettors , 86 % of my 43,8 mm inlet SRM valves gives a theoretical carburettorsize of 37,7 mm, but with my manifoilds on 32 - 33 mm its maybe not beneficial anyway ? so maybe 36 mm would be enough ?

anyone who can suggest a jet setup for a 36 or 38 mm ?

So far Im looking at the Mikuni TM36-68 Flat Slide Carburetor 36mm acceleratorPump Carb

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Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368160
04/14/11 7:38 am
04/14/11 7:38 am
Joined: Oct 2008
Posts: 4,877
Gnashville
DavidP Offline

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Gnashville
Jeez, I'm still trying to figure out jetting for VM32s on my +0.060 A65.
I think I got it right today, though.

Idle 30 @ 1.75 turns
needle jet 159/P4
needle 6DH2,second slot
main 190
air 1.0
slide 3.0

Needs to be warmed up a bit, but 2.5 slides are too rich when I get stuck in traffic.
Your results will definitely vary!


Stepping on others doesn't make you stand tall.

71 A65L "Zelda"
92 BMW K100rs "Gustav"
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368163
04/14/11 10:55 am
04/14/11 10:55 am
Joined: Jul 2007
Posts: 253
Charlotte NC
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Charlotte NC
Is this going to be a race or street bike? The manifolds i did for Tim Joyce taper from 40mm to 33 over 3.5 inches and work well. But for the street i think max would be a 36mm flatslide. So the TM36 would be good.


ROB HALL
HCV MOTORSPORTS
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368168
04/14/11 12:38 pm
04/14/11 12:38 pm
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
This is what I use; and is 38mm at this point, it does taper a bit from here and has the port floor raised 'D' shape for the turn under the guide. I use 1/4" unc helicoils so I can attach manifolds with the smaller allen headed screws, as there is not much space for them.



The darker areas are JB weld fixing holes.


This shows straight 38mm manifolds, the ones on my own bike are curved to clear that particular frame and are a bit longer.

I use TM 38/85, its hard to say exactly with jetting as I've modified the front bell a bit, plus have other variations with motor and pipes, I use; 240 mains 389Q2 N/jets 6FJ-40 needles 22.5 pilot #4 cutaway. I've seen these new on eBay for as low as $138US which I think is very good value, carbs with acc pumps would be useful for starting but are more expensive. I had 32mm dellortos with acc pumps on a Trident, I don't think the pumps did much for performance, but made it possible to not bother with chokes, just twist the throttle a few times then kick.


mark
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368301
04/15/11 8:49 am
04/15/11 8:49 am
Joined: May 2006
Posts: 198
Tynset Norway
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oleandreas Offline OP
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Tynset Norway
hello Mark, thanks for answer.

I guess its the stock A65 head you have ? So you have the stock screw width on around 51 mm center to center (hole spacing) ?

How much did you manage to port the head too, 34 mm ?
Did you make your own manifoilds from aluminiumor is it rubber I see on your picture ?

Andraes

Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368444
04/16/11 9:24 am
04/16/11 9:24 am
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
I just use 38mm ID alloy pipe with bits welded on to hold against the head, then rubber hose to connect the carbs. Where the manifold meets the head is 38mm, it tapers from there a bit but is pretty open, I leave metal in the roof to avoid going into the valve seat area, but sometimes go through and fill with JB-weld, and I fill the floor so it's flat.




This is before filling the floor, and before helicoiling.


mark
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368569
04/17/11 4:47 am
04/17/11 4:47 am
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
Not on all but a couple where I wanted a little downdraught on manifolds I'd already made. I've welded around there on one head to give a wider gasket surface but JB-weld seems an easier way once the thing gets a bit thin. Same with holes through the wall, or into the valve seat area, where welding is difficult.
Such big ports don't particularly go well with a cam with lots of duration, there is a point where a nice power spread can be had that is more important than maximum numbers. You can chase breathing with the ballance between port/valve size and cam. If you maximise both the HP may be too far up the range. The exhaust has a major influence but it is a ballance. The perfect ballance is elusive, it would be nice to have very strong power from 2,000 to 7,000RPM this engine size and configuration lends itself to that yet the more you want to pile it on up the top the less linear it becomes.


mark
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368716
04/18/11 10:43 am
04/18/11 10:43 am
Joined: May 2006
Posts: 198
Tynset Norway
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oleandreas Offline OP
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Tynset Norway
Hello Mark.
do you think JB weld is so strong it could be useful for strengthening the engine case ? For example on the right side in the area of idler wheel above oilpump up to the cylinderfoot, the weak spot as have been discussed before.

IM hesitating on welding on my cases. Afraid if potential damage. I have already put lot of time and money into them.

Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368729
04/18/11 12:17 pm
04/18/11 12:17 pm
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
That's an interesting question. On the one hand I wouldn't weld them now because it can distort them. I've seen very strong steel boxsection curve drastically by welding now and then along one side, when the weld cooled it contracted. On the case you may move where the idler sits or something, which wouldn't be good. I welded my cases because of a crack, and welded on a brace but really I need to pull it all down and use a new case. Perhaps glueing on some alloy ribs may give a non cracked case extra strength, it would be interesting to hear opinions. JB-weld will not actually hold the crack together thats already there any more than just a weld, I had to weld on a substantial vertical rib, which still holds so far.
I've only had the one case crack, and that case did have a rocker button punched into it cracking it in one little spot, which may have given it a weakness even though I welded it up, so if your cases are good I wouldn't worry too much.


mark
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #368921
04/19/11 12:41 pm
04/19/11 12:41 pm
Joined: Feb 2006
Posts: 614
Ontario , Canada
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RGSROB Offline
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Ontario , Canada
hey Mark, really like the flow grooves around the inlet guides.was this the result from a flow bench or just experience?
Also have you performed a squish head yet?
Regards
Rob

Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #369123
04/20/11 7:49 am
04/20/11 7:49 am
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
Rob the ridges let me see how deep I'm going and have it thicker on the carb side of the guide where it often goes through into the V/spring area. I did try welding some squish area into the chamber some years ago.

I was using T140 pistons giving 818cc and it had 11-1 comp, but it was noticably better with an open head and better porting, not sure which was making the main difference.


mark
Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #369282
04/21/11 7:27 am
04/21/11 7:27 am
Joined: Mar 2011
Posts: 833
derby england
wak Offline
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derby england
Hi, i used to race a tz350 with a 900cc a65 engine (victor pistons norton crank)it went like stink with 34mm AMAL mk2s,cant see the point in going any bigger as the limit to power produced was the gearbox cases letting go between the bearings !!we tested it on a dyno and all i can say is it made more than 70 bhp at wheel ,the dyno only went up to 70 bhp.


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Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #369285
04/21/11 9:07 am
04/21/11 9:07 am
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
Hey wak have you got any pictures or a video, I'd love to see that setup.
I haven't had that problem with the gear case, do you know exactly what was causing that? I have a decent bearing in behind the clutch that would limit the mainshaft flexing if that could contribute.


mark
Re: carburetters and porting of manifoilds A65 900 ccm [Re: Mark Parker] #369287
04/21/11 9:53 am
04/21/11 9:53 am
Joined: Mar 2011
Posts: 833
derby england
wak Offline
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derby england
Hi, i only have have a picture of me racing the bike,it was a long time ago about 92' , the gear box never had outriger bearings and the shafts would try and repel each other spliting the case between the layshaft and mainshaft bearing,but it was fast, i could stay with north triples down the straights(if i could ride id have stayed with them on the corners!!!!!!!)


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Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #369499
04/22/11 7:46 pm
04/22/11 7:46 pm
Joined: Apr 2009
Posts: 67
The netherlands
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Tobias Offline
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The netherlands
just wondering..what kind of power can you squeeze from an engine like this? with all the porting done etc

Re: carburetters and porting of manifoilds A65 900 ccm [Re: oleandreas] #369578
04/23/11 4:42 am
04/23/11 4:42 am
Joined: Apr 2005
Posts: 2,337
Bega NSW Australia
Mark Parker Offline
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Mark Parker  Offline
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Bega NSW Australia
With this size motor you can get pretty good power pretty much from idle, it's really nice on the road, and even with very tall gearing 3.43 - 1 top gear roll ons, like at the end of this video, are quite good for overtaking, and usually all thats necessary.
http://www.youtube.com/watch?v=uncK4P1gyUw
The way mine's set up its pretty good in the top end and pulls hard from around 4,500 but only to around 7,000 it will go more but wears stuff out. Max HP on the data logger was 77.5 @ 6,200 with max torque 67.3ft @ 5,108, last time the speed matched the rpm. What that would be on a conventional dyno I don't know. I don't really want more HP, but a 5 speed would be good.


mark

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