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Discussion Starter · #1 · (Edited)
Already had the AI removed, Uni Flow air filter, Staintunes, and was rejetted 42 and 125, but the snorkel was still in place. I removed it last night. Took her out for a spin this morning to see the results.

VERY hard to start. In the past, with snorkel in she would fire up first or second try. Took at least four tries to get initial light off, she died and had to be restarted twice after that. VERY cold blooded now. In the past, snorkel in, used the choke out for a mile or so, then 1/2 choke for another couple of miles, then no choke. No problems anywhere during all that. Snorkel OUT, choke on, a bit of rough running and very definite surging. Throttle steady she would come on strong, back off, come on strong, back off again - with no throttle movement from the position it was in.

Once warmed up, not much noticeable difference in first gear, all the way up to ohh, say 5000 rpm. Didn't go above that. In second and above, from about 3000 rpm on, WOW! MUCH stronger pull. There is a most definite "seat of the pants dyno" torque increase evident. I wasn't ready for it the first time I cranked on it a bit in second, and she felt like she was about to leap out from under me.

Throttle response off idle has always been a little choppy. Hard to get a slow, smooth pull off idle. You get very little initial response, then it kicks in a bit more than you want rather suddenly. The snorkelectomy seems to increase that problem a bit as well.

I thought with the 42's and 125's in place the jetting would be about right, but the "new" cold hearted nature and increased choppy off idle throttle response make me wonder about the jetting.

I have never tuned carbs before, but I would like a more linear throttle response from off idle to WOT, better start/cold operations, keep the big kick in the butt torque increase (perceived increase anyway), but move it from 3000 and above to . . .ohh, say 2000 or 2500 and above. And get it to happen in first gear like it does second and above. Is all that doable by a carb tuning neophyte?

Any thoughts or suggestions?
 

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how many turns out is your fuel screw? (under side of carbs in front of float bowls requiring a "d" tool to adjust) if you don't have a "d" tool, order one up from newbonneville.com and check into their position. a little tweak and you should be golden.
 

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Discussion Starter · #3 ·
I believe it is out 2 1/2 turns from what the previous owner told me, but don't have a tool to verify that. You're right, I need to get one.
 

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Lobo, you are way too rich for your state of tune. Put the 40 pilots back in and set the mixture screw to 1.75 turns out, also try a 118 main jet. I'm not saying this will be dead on for your bike, but it'll be bloody close.
 

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Discussion Starter · #5 ·
Lobo, you are way too rich for your state of tune. Put the 40 pilots back in and set the mixture screw to 1.75 turns out, also try a 118 main jet. I'm not saying this will be dead on for your bike, but it'll be bloody close.
PieMan, I thought that with the AI off, Uni filter, and free flowing Staintunes I was pretty far from stock. Like I said though, I am new to tuning carbs.

Looking over notes that the previous owner gave me I have the following info:

from the Jenks Bolts tuning notes booklet, a 790cc Bonneville with a stock needle, "Off road exhausts" and a free flow air filter (My set up) they call for 130 mains, 42 pilots, 1 shim, 3 turns.

The PO's hand written notes on that page say "per mike @ BellaCorse with Stainintunes & Uni filter 42 pilot [and] 125 main"

from the listing on the forum here:
MODIFIED BONNEVILLES & THRUXTONS
790cc w/Keihin CVK36
MAINS /PILOTS/TURNS/NEEDL/SHM/AB/AI/EXHAUST.....RIDER
...
130.0 / 42.0 /-2.5 / ... / . /no/no/Staintune...pabonne


So, I'm confused.
 

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The jenks guide is not always accurate IMHO.

Check out these threads, where some folks have done some careful a/f measurements, and you will see that Pieman is talking a lot of sense.

The listing you show :

from the listing on the forum here:
MODIFIED BONNEVILLES & THRUXTONS
790cc w/Keihin CVK36
MAINS /PILOTS/TURNS/NEEDL/SHM/AB/AI/EXHAUST.....RIDER
...
130.0 / 42.0 /-2.5 / ... / . /no/no/Staintune...pabonne

includes airbox removed - a major change to the air inlet system. You have only removed the snorkel, so while you will be getting more air, not nearly as much as with the airbox off.

http://www.triumphrat.net/twins-tec...ning-modifications-and-so-on.html#post1128200

From venturas measurements:

Open exhaust + no snorkel................115 / 40 / no shims / 2.0 turns
The staintunes are very good pipes, so Piemans 118 main jet suggestion is a good one.

http://www.triumphrat.net/twins-tec...ning-modifications-and-so-on.html#post1097253
 

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I have the same configuration as you, currently using 118 main jets and the original 40 pilot jets, it starts easily and runs well (except balky until fully warmed up, but I accept that). It might even be a bit rich. Note that this is with Thruxton needles, but you still probably shouldn't go larger than 120/40.
 

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Discussion Starter · #8 ·
Just went out to the garage and pulled out the parts that I was given with the bike. I have:
1 set 40 pilots (package says "removed on 3/11/07")
1 set 55 pilots (look unused or hardly used)
1 set 125 mains (look shiny and new)
1 set 130 mains (look shiny and new)

So now I figure it has a set of 42 pilots installed, as told by the seller.
Since I have bright and shiny new 125 and 130 mains still in the packages, I wonder what mains are installed?

Sounds like I need to get a set of 118 mains, pull whatever is in there now out and replace them with the 40/118 combination. With my set up, any shims, and how many turns?
 

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Discussion Starter · #10 ·
i didn't see it in your original post, is the baffle plate still in the airbox?
Don't know. I think so. Since the snorkel was still in place I can't imagine the previous owner had pulled the baffle plate.
 

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Discussion Starter · #11 ·
I just pulled off the side cover and pulled the filter. If the baffle is above and in the forward section of the airbox its still in there.
 

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If the baffle plate is still in there, pull it out and toss it on the spare parts pile. (there is a very good thread on this procedure) then take it for a ride, the 125 mains may not be too rich then.
i've been bitten by the modification bug myself, ai, snorkle, baffle plate, removed. tors and uni filter installed.
 

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Discussion Starter · #13 · (Edited)
If the baffle plate is still in there, pull it out and toss it on the spare parts pile. (there is a very good thread on this procedure) then take it for a ride, the 125 mains may not be too rich then.
I've been bitten by the modification bug myself, ai, snorkle, baffle plate, removed. tors and uni filter installed.
Sounds interesting, darksider.
Pie Man and Propforward, this sounds like it has some merit. Is the 125/42 still too rich if I pull the restrictor plate?

Don't the constant velocity carbs have some specific airflow requirements that the airbox meets? With the free flowing air from the snorkel removal and restrictor plate removal will it cause any problems with the carbs?
 
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