Carb selection advice on modified 850T

[NCAmother]

I'm looking for a set of new carbs for my bike, and wanted to ask the experts their opinions.   The bike is far from stock, so any brand I would be open to.  First, engine details: 850 upgraded to 949cc.  Manfred Hect/RaceCo heads ported with oversized valves and dual plugged, 10-1 compression.  Crane cam similar to the megacycle x10
I'm thinking a 38mm carb would be good, unless you think 36mm would suffice.  I previously ran Lectrons and they felt like fuel injection, however they were not gas friendly.  Keihin flat sides look promising.

[kevdog3019]

I'm running 36's on my little hot rod Lario (650) with bigger valves, cam, etc..  It fuels eggcellently.   I would think 38's for sure but I'm no bike tuner.
Edit: 30's came standard.

[NCAmother]

I'm running 36's on my little hot rod Lario (650) with bigger valves, cam, etc..  It fuels eggcellently.   I would think 38's for sure but I'm no bike tuner.

Thanks KevDog, any advice is good advice!!

[Gliderjohn]

I am running 36mm round slides on my T-3 with the 1,000cc kit, V-7 Sport cam, port and polished heads but standard sized valves. I don't know how one could improve on it, runs great from idle to redline.
GliderJohn

[Chuck in Indiana]

If that bike wouldn't take 40s, which one would?  ;D

[guzziownr]

If that bike wouldn't take 40s, which one would?  ;D

Well said Sir!

What is the diameter of the intake side of the head?  I run 36's on my pedestrian 950cc round head grocery getter and I had to match the ports a bit.

[Perazzimx14]

Whatever size carb you decide I strongly suggest FCR's. Everything I have ridden that has been upgraded to FCR's is a night and day difference.

[spmoto]

I've had Manfred head work done on a couple of bikes. He typically ported the heads for 40mm carbs but he did a pair for 36's for me also. Best bet is to measure the ports and go with the appropriate carb size. If it turns out that you will be running 40mm Dellorto's the following jet combinations should work with your heads and cam: 60/5 slide, K19 needle, 145 main, needle notch second from top, 268AB needle jet, 60 idle jet, short tipped stubby air screw. This info is straight off the spec sheet I got from Manfred. Hope this helps!

Steve M

[NCAmother]

Whatever size carb you decide I strongly suggest FCR's. Everything I have ridden that has been upgraded to FCR's is a night and day difference.

Thanks, that's what I wanted to hear :)

[NCAmother]

I've had Manfred head work done on a couple of bikes. He typically ported the heads for 40mm carbs but he did a pair for 36's for me also. Best bet is to measure the ports and go with the appropriate carb size. If it turns out that you will be running 40mm Dellorto's the following jet combinations should work with your heads and cam: 60/5 slide, K19 needle, 145 main, needle notch second from top, 268AB needle jet, 60 idle jet, short tipped stubby air screw. This info is straight off the spec sheet I got from Manfred. Hope this helps!

Steve M

Thanks Steve, that info will come in handy.  My intakes have been ported so much they feel as heavy as a JFK half dollar

[NCAmother]

Well said Sir!

What is the diameter of the intake side of the head?  I run 36's on my pedestrian 950cc round head grocery getter and I had to match the ports a bit.

They are ported for a 40mm carb setup.  The actual intake valve size is 47mm

[Vasco DG]

47mm? That's pretty big. I presume you've re-shaped the combustion chambers and have custom pistons to deal with compression issues.

Even with the stock 'Lawnmower' cam valves will tangle on overlap if you increase the sizes without modifying the chambers.

Pete

[NCAmother]

47mm? That's pretty big. I presume you've re-shaped the combustion chambers and have custom pistons to deal with compression issues.

Even with the stock 'Lawnmower' cam valves will tangle on overlap if you increase the sizes without modifying the chambers.

Pete

Yes the chambers and pistons have valve reliefs accordingly.I didn't work on the chambers, Manfred Hect did, however I did the pocket reliefs for the oversized valve.

[NCAmother]

forgot to mention, the engine runs grand with 38mm Lectron flat slides, however it is a true gas hog

[Perazzimx14]

forgot to mention, the engine runs grand with 38mm Lectron flat slides, however it is a true gas hog

Are you sure your right wrist isn't the bigger problem with fuel economy. I have a FCR 39 on my DR and make it get in the mid 30's or in the mid 40's. Depends on how much fun factor I'm having ;-T

[NCAmother]

Are you sure your right wrist isn't the bigger problem with fuel economy. I have a FCR 39 on my DR and make it get in the mid 30's or in the mid 40's. Depends on how much fun factor I'm having ;-T

:)  you might have a point!