29.5 mm carb questions

Bikemike · Post by **Bikemike** » Tue May 29, 2012 10:15 am

I have a set of carbs offset bored to 29.5mm.
I'm looking to fit them and I'm after a bit of jetting advice.
Unless I'm remembering my physics all wrong, the larger bore will mean the air is travelling more slowly over the jets- this means I will need larger jets (I think).
The engine is a Graham File tune with Tz pistons. It currently runs 28mm pwks with 40 pilot, 145 mains (I know that sounds big, but it runs really well) and 99 needles. It runs on premix.
So, to my questions-
I have some 42 pilots, should I try those or stick with the 40's?
Standard float height?
Use the 145 mains again?
Needle clip position?

Many thanks for looking,
Mike

dave32 · Post by **dave32** » Thu May 31, 2012 9:18 pm

if it was running spot on on that setup with the stock size carb then you will need to go up in size/richness on all the jets etc.
Stock carbs are on there limits when the outputs increased,not a bad thing as it causes the mixture to richen at the top end and gives good response throughout the rev range.
Are they genuine mains your using or the RD aftermarket ones?
RD type are a bit hit and miss with quality and flow alot less than Keihin jets.
What airbox setup are you using?
I run the front half of the lid with filter and ended up with N99 needles on the 2nd richest and 155 mains,airscrew 3/4 turn out,stock pilots,run 30.1 premix.
TBH its probably best to just start too rich and work down as no 2 bikes/riders need the same setup.
Just had a think,if there oval then this will only effect the last 1/4 throttle position so just go up on the main,the rest wont be effected.

scooble · Post by **scooble** » Thu May 31, 2012 9:25 pm

mike, do you know who bored the carbs?

Bikemike · Post by **Bikemike** » Thu May 31, 2012 10:11 pm

scooble wrote:mike, do you know who bored the carbs?

Sorry Tricia, I bought them already done.

dave32 wrote: Are they genuine mains your using or the RD aftermarket ones?

Hi Dave, they are marked as 145RD, what do you think that equates to on genuine mains?

dave32 wrote: What airbox setup are you using?

I have an R6 shock fitted so the airbox is heavily cut about.

I extended into the battery box area to make up for the lost volume from the bottom. The volume is marginally higher than a standard airbox.The lid is unmodified, do you think I need to cut holes or make a ram air system?

dave32 wrote: Just had a think,if there oval then this will only effect the last 1/4 throttle position so just go up on the main,the rest wont be effected.

The Carbs are not oval, it is a round bore, slightly offset.

I run 30:1 premix Shell vpower.

Oh, just to add it is now running Gibson exhausts with stubby cans.

Fitted the carbs today!
I stripped and thoroughly cleaned them, set float heights properly and balanced the throttles. I put in N99 needles on 2nd clip from the top 42 pilots and the rd 145 mains. Airscrew half a turn out.
I then took it out for a blast and I have to say it has never gone better.
It started 1st kick and idled well once warm. Low down pull was improved on before, beginning to kick hard at only 7k. There was a slight hiccup at 8k but once past that it screamed up to an indicated 11.5k when you could feel it start to tail off.
From what you are saying it sounds as though I am possibly too rich on the middle- should I change back to 40 pilots?
I am a bit concerned about the mains- you are running a lot bigger than me, I really don't want to hole a piston. Should I invest in some bigger mains, I think the biggest genuine ones I have on the shelf are 140s.
Many thanks for all your advice,
Mike.

falconman · Post by **falconman** » Sat Jun 02, 2012 3:11 am

If you premix you will need to go bigger. The oil takes up volume as the fluid (oil/fuel) passes thru the jets. I ran 155 or 157 mains at Bonneville when I ran premix in the 35mm carbs. With injection I am usually running 150 or 152 range. Depends alot on the DA. I have 29.5 carbs on the bike now and it ran 142mph. I'll check the jets this weekend when I pull the motor out.

Bikemike · Post by **Bikemike** » Sat Jun 02, 2012 9:54 am

Many thanks for all the advice guys, I really appreciate it!
Mike

dave32 · Post by **dave32** » Sat Jun 02, 2012 7:44 pm

nice pipes!got them on mine,there for the B2 model only difference is the shorter stinger length for the lower rpm peak against the S versions Pete made,mine peaks around 10,500rpm and will overrev to 11500 if i need it.
145RD equates to only a shade richer than genuine 135's,reason i know this is the late John Robinson of PB fame found out while setting up a Supersport 400 S.
so i would definitely go to at least a 155RD or stick to genuine and get a 145 (maybe Allens stock em?),whatever you do just stick to 1 or the other,think the RD go to 160 max.
OK so there not oval,in that case go up all the way through,pilot up 1 airscrew 1/2 out,needle on 4th or 5th and whatever main you choose(RD or Keihin).
One thing i ended up doing to get a nice response on the down change is file 0.5mm off the carb slide but as said do everything else first ,getting it running well/safe on top then worry about throttle response.
HTH

falconman · Post by **falconman** » Sun Jun 03, 2012 1:31 am

Just checked the carbs. It has 40 pilot, 155 mains and the N99E needle with the clip at the second from top. The needle jet itself is not marked. This is with oil injection. For premix it would need to be a bit richer, probably a 42 or 45 pilot and around a 160 main. Your jetting will most likely be a little off from what I have due to elevation and air temp.

Bikemike · Post by **Bikemike** » Sun Jun 03, 2012 9:31 am

Great advice folks, it looks as if I am definitely running too lean at the top end looking at my main jet size. I'll get on to Allens performance and order a few bigger ones. I'll then find a quiet road, do some plug chops and let you know how it goes.

Many thanks again,
Mike

dave32 · Post by **dave32** » Sun Jun 03, 2012 12:52 pm

I would definitely try raising the needle aswell as going up on MJ size as it has the most effect over the widest used throttle position,roughly 1/4 to 3/4.You could jet the main spot on for full throttle but still be too lean on the needle,think about when you roll off after a high speed run.
Up to you on the airbox lid,personally ive found it helps when power is upped.
HTH

Dave

mj43 · Post by **mj43** » Mon Jun 04, 2012 3:07 pm

falconman wrote:Just checked the carbs. It has 40 pilot, 155 mains and the N99E needle with the clip at the second from top. The needle jet itself is not marked. This is with oil injection. For premix it would need to be a bit richer, probably a 42 or 45 pilot and around a 160 main. Your jetting will most likely be a little off from what I have due to elevation and air temp.

Jim

I expected to jet down at Bonneville - went with 130 mains fitted following dyno testing in the UK. In the event I went up one size to 132!

I put this down to very low humidity 2% and the fuel sold at Bonneville offsetting the height increase. Whereas day time temps are up the early morning run is almost in Arctic conditions....

Bikemike · Post by **Bikemike** » Mon Jun 11, 2012 10:42 pm

Well, I contacted Allens performance today about jets.
Turns out they are "only" £3 each (I expected a fair bit more) so I ordered a selection between 150 and 160 (They are real ones, not rd).
Waiting eagerly for the postman now, then I'll be out testing again (if it ever stops raining- I spent all day rescuing idiots who had driven through flood water and lunched their engines

)
Mike