Author Topic: Which size carb for 1000cc? (Read 6721 times)

afkrejci90 · « **on:** May 12, 2018, 11:13:32 am »

Resurrecting my 1000cc race build. Have a set of Weber 40 DCOE's I was going to throw on there but getting them fitted is taking more time than I would have thought. Down the road these will be going on but I want to get this thing going so I am going to throw on a set of Keihin CR's. That being said which diameter would be better suited for this displacement, 29mm or 31mm? Head has been ported with larger valves. I read somewhere on here that 31's throw in too much fuel and foul up plugs, but would this be an issue with the increased displacement?

cbr954 · « **Reply #1 on:** May 12, 2018, 11:17:57 am »

Im running CR31 on my street 970cc no issues, the CR is very tuneable

slikwilli420 · « **Reply #2 on:** May 12, 2018, 11:19:04 am »

You won't regret making the Weber carbs work. A superior carb to many others out there. For street use people really like Mikuni RS34.

afkrejci90 · « **Reply #3 on:** May 12, 2018, 11:23:12 am »

Quote from: slikwilli420 on May 12, 2018, 11:19:04 am

You won't regret making the Weber carbs work. A superior carb to many others out there. For street use people really like Mikuni RS34.

A don't doubt that, but to get them to work everything has to made from scratch.

RAZZ · « **Reply #4 on:** May 12, 2018, 12:13:02 pm »

Hi take a look at This Weber thread, it learned me a lot, they are time consuming to sync. but alsoluty worth it. Weber carb set-up
https://r.tapatalk.com/shareLink?share_fid=13548&share_tid=68065&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D68065&share_type=t

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RAZZ · « **Reply #5 on:** May 12, 2018, 12:16:54 pm »

Here some pics of my “Stock” setup

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MRieck · « **Reply #6 on:** May 12, 2018, 12:33:40 pm »

I run RS-34's with 1000cc. Work very well....tuned with an onboard A/F meter.

RAZZ · « **Reply #7 on:** May 12, 2018, 12:38:51 pm »

Here a set of RS34 for sale: CB750 special, rare, and go fast parts - REDUCED again~~
https://r.tapatalk.com/shareLink?share_fid=13548&share_tid=170441&url=http%3A%2F%2Fforums%2Esohc4%2Enet%2Findex%2Ephp%3Ftopic%3D170441&share_type=t

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PeWe · « **Reply #8 on:** May 12, 2018, 01:49:07 pm »

My CB750 K6 has 71.25 mm pistons. Carbs Mikuni TMR32 works really good but are not cheap.

scottly · « **Reply #9 on:** May 12, 2018, 05:56:51 pm »

What problems are you having with the Webers?

MRieck · « **Reply #10 on:** May 12, 2018, 06:17:08 pm »

Quote from: PeWe on May 12, 2018, 01:49:07 pm

My CB750 K6 has 71.25 mm pistons. Carbs Mikuni TMR32 works really good but are not cheap.

They are really nice carbs.

754 · « **Reply #11 on:** May 12, 2018, 06:34:15 pm »

Show us what Webers and manifold you got plus anything you can hook the throttle cable to.
Usually can be running in an afternoon, if they have been on a running bike before.

scottly · « **Reply #12 on:** May 12, 2018, 06:42:47 pm »

^^^

32mm chokes on Jerry's bike.
https://www.youtube.com/watch?time_continue=17&v=Wg9WT7zzDj8

afkrejci90 · « **Reply #13 on:** May 12, 2018, 08:25:13 pm »

Quote from: scottly on May 12, 2018, 05:56:51 pm

What problems are you having with the Webers?

The lack of a manifold. Tried machining my own but ran into some problems due to inexperience.

754 · « **Reply #14 on:** May 12, 2018, 08:52:51 pm »

Do you have a drawing ?
If you look at the RC manifold closely..
You can machine 4 tubes and press them into a plate. Lictite them in.
May have to leave the hole in the tubes undersize, then port it, hand finish to get a good matchup. Some throttle bits you can make or maybe buy. We can help you with the manifold, but it means a bit if lathe or mill work.

gschuld · « **Reply #15 on:** May 12, 2018, 09:31:50 pm »

Rc manifold for reference

George

RAZZ · « **Reply #16 on:** May 12, 2018, 09:50:30 pm »

You Can buy diffent styles of manifold flanges online, like This one: https://m.ebay.com/itm/40mm-dual-Weber-DCOE-Dellorto-DHLA-mounting-flange-1-2-aluminum-/261840769235?ul_ref=http%3A%2F%2Frover.ebay.com%2Frover%2F1%2F711-164882-2056-1%2F2%3FPARM3_ID%3DGBH_57%26FF11%3DGBH_57%26kw%3DU9VvCgAAAUM47RAz%3A20180513044824%3As%257CEAIaIQobChMI8bKdnvGB2wIVwbHtCh0nTA5qEAQYASABEgLcIPD_BwE%26mpre%3Dhttp%3A%2F%2Fwww.ebay.com%2Fitm%2F40mm-dual-Weber-DCOE-Dellorto-DHLA-mounting-flange-1-2-aluminum-%2F261840769235%26rule%3D%26crlp%3D215940203012%26adpos%3D1o1%26device%3Dm%26cmpgn%3D910902396%26ef_id%3DU9VvCgAAAUM47RAz%3A20180513044824%3As%26srcrot%3D711-164882-2056-1%26rvr_id%3D1528889854725%26rvr_ts%3D57d40c141630ad4e21e6044afff09243&_mwBanner=1&_rdt=1

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PeWe · « **Reply #17 on:** May 13, 2018, 12:10:57 am »

Quote from: MRieck on May 12, 2018, 06:17:08 pm

Quote from: PeWe on May 12, 2018, 01:49:07 pm
My CB750 K6 has 71.25 mm pistons. Carbs Mikuni TMR32 works really good but are not cheap.
They are really nice carbs.

Mike, have you tried TMR’s on your CB750 yet? I guess you have a set....

I use CB750 throttle control with wires. I need to be very focused when taking off and riding slowly on first and sometimes second gear. Gear ratio is tough. Full throttle less than 1/4 turn. No sneezing allowed!!

RS34’s are easier to handle?

Medyo Bastos · « **Reply #18 on:** May 13, 2018, 05:40:05 am »

i have a mpd manifold under the bed

MRieck · « **Reply #19 on:** May 13, 2018, 07:11:56 am »

Quote from: PeWe on May 13, 2018, 12:10:57 am

Quote from: MRieck on May 12, 2018, 06:17:08 pm
Quote from: PeWe on May 12, 2018, 01:49:07 pm
My CB750 K6 has 71.25 mm pistons. Carbs Mikuni TMR32 works really good but are not cheap.
They are really nice carbs.
Mike, have you tried TMR’s on your CB750 yet? I guess you have a set....
I use CB750 throttle control with wires. I need to be very focused when taking off and riding slowly on first and sometimes second gear. Gear ratio is tough. Full throttle less than 1/4 turn. No sneezing allowed!!

RS34’s are easier to handle?

I have a set of 32's and 36's here but haven't used them Per. The RS's are pretty good especially using the 77/78K reproduction insulators from Vintage CB. Stock cables work great. I am surprised you were able to use the stock throttle cables for the TMR's. When I mocked it up it looked no good and when I bought the 36's different length cables were specified. Interesting.
They only problem I encountered with the RS's turned out to be a defective float. #1#3 and #4 were burning nice but the A/F was wonky and #2 was rich. Played with height 3 or 4 times and fiddled with the idle screw/pilot jet etc. Finally bit the bullet and bought a new float and problem solved. The rack of 34's was brand new when I bought them. Go figure.

PeWe · « **Reply #20 on:** May 13, 2018, 10:48:22 am »

I have photos in my computer home about the cable installation on the TMR’s. I’m in Spain now close to Benidorm, so no garage nor riding. Sunshine, sea and beers are OK too.
I know that I had to add an extra nut I made a cut in by a saw blade for the wire to use the nut as adjuster or lock nut. Nut is open so not tight too hard, lock with Loctite. One cable is a little bit long, front adjuster at the switch/ throttle is in outest position. Maybe I can adjust at the carbs a little bit more.
Edit: Here photos when I installed them
http://forums.sohc4.net/index.php/topic,61168.msg1660522.html#msg1660522

Jetting sorted out since then
Pilots 30
Fuel screws 1 1/2 turns out (stable idle and less need of choke)
Needles 2:6
Mains 135 (more open pipes 137.5)

turboguzzi · « **Reply #21 on:** May 13, 2018, 11:54:55 am »

you said race bike... if it's for AHRMA the only CR are accepted IMHO, would say 31

Bill/BentON Racing · « **Reply #22 on:** May 13, 2018, 07:18:45 pm »

I might need that, pic please

scottly · « **Reply #23 on:** May 13, 2018, 09:43:58 pm »

Quote from: Bill/BentON Racing on May 13, 2018, 07:18:45 pm

I might need that, pic please

What is the "that" you might need, Bill??

Bill/BentON Racing · « **Reply #24 on:** May 14, 2018, 03:29:56 am »

Lol, I thought I quoted Medyo, I'm interested in the MPD Weber manifold.

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Author Topic: Which size carb for 1000cc? (Read 6721 times)