Triumphrat

Saigon5

I made another dyno run today, this one was with a Trophy air filter (stock) main jets at 128. Pilot jets stock.

It is not much to talk about, other than a gain of 2 cows (torque) I am way too lean. I will be putting 138 main jets in and lifting the needle with a washer. The next try should bring me close to the final set up. I may have to change the pilot jet, I am saving this for dessert.

A word on removing carbs. I opted for a new method, I am tired of the throttle cable assembly so now I undo the throttle cable at the handle bars and bring it out with the carbs. Much faster. :hammer:

max power, 83.1 hp and 56.8 torque

[ This message was edited by: Saigon5 on 2005-04-15 18:05 ]

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In doubt, crank the throttle.

Gdsila

I'm no scientist(but I play one on TV) nor an engine tuner and I wouldn't know which end of an equation to grab if you gave me three tries,but my understanding of carbs is that you run off the pilots until the mid-range and (Like where your lean spot is) the main jets only come into play at the last 1/3rd or so of the powerband. Ergo,ipso facto,and switcho changeo....you need bigger pilots to solve this pugnacious powerband problem.
Perhaps.... :hammer:
P.S. I love the fact that this thread is a sequel!

[ This message was edited by: Gdsila on 2005-04-15 21:37 ]

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fbird

Definately want to up the pilot jet. I just swapped in a K&N filter and just that alone requires that to be swapped from the 35 to 40, according to Great Bay that is. Still seems a little lean to me. You have got some great information in these posts Saigon 5. Keep it coming!! Fbird

Saigon5

I am too lean from 6500 RPM to the redline, that is a main jet problem. A little on the lean side in the lower part but not dramatic.

P.S. The way things are I will need another dyno run so I am aiming for a triology

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In doubt, crank the throttle.

Gdsila

Cool! we'll call it " The Carbfather" you can be michael corleone...." Every time I try to richen it up, It comes back lean!!!" :razz: :hammer: :???:

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Saigon5

Could I be called Michael Carbleone instead.

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In doubt, crank the throttle.

jimmyj900

[QUOTEI am too lean from 6500 RPM to the redline, that is a main jet problem. A little on the lean side in the lower part but not dramatic. [/quote]

On a full-throttle dyno run, leanness in that rpm range is the main jet and/or needle taper so you're quite right about adjusting the main jet. Be careful shimming the needle since that may make the system a bit too rich around 5000 rpm when the needle is lifting.

For normal small-throttle operation (up to around 1/4 grip twist) you're running mostly on the pilot jet -- regardless of the rpm of the engine -- so you'll need to address that separately from the main jets.

I found with the larger filter/box that mixture was quite lean with small-throttle settings at around 4500 rpm and needed larger pilot jets than stock.

To size the pilot jets the first thing you need is a good carb balance. Adjust the mixture screws for maximum rpm, then reduce the idle to 1000 rpm, adjust the mixture screws for max rpm and repeat the sequence until it's peaked out. The idea here is that the engine will produce its best power (and rpm) at the optimal idle mixture ratio (slightly rich.)

You need the Triumph right-angle screwdriver for this. If you don't have one let me know -- I've got a spare I'd be willing to part with at a reasonable price.

If your mixture screws are at 3 turns or more, go to the next larger pilot jet. Ideally you want to wind up the mixture screws at around 1 to 1.5 turns where they're most effective at fine tuning.

It's possible that you'll still be lean at small-throttle settings below 5000 rpm so it may be necessary to go a step larger on the pilots. That might make the idle pretty rich so it's a trade-off you'll have to make between rideability and idle mixture.

Jim

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Saigon5

Jim,

First, I did try to find needle but I can not get the Factory pro needles without buying the kit. Problem is I do not need the jets really. The Dyno shop has all the jet I can dream of and they are charging me only the final 3 that I will keep. They are the one suggesting that I rise the needles (from what I have heard, they like rising the needles) but I have already decided that I will wait for that. First I want to get to the best main jets before playing with the needles.

At the moment, I am running in the power zone from 5 to 6 thousand RPM. In that range I am between 13 and 12.5 going back to 13 at 6000. From there it is up, up, up to 15 to1 at 7000 RPM to the red line.

The bottom is too lean, I would say that the pilot jets have to go. The carbs were balance prior to the dyno run and the mixture screws are out 2 1/2 to 3 turns. On the dyno run, I am lean until I reach 5000 RPM at 13 to 1, 1/4 turn twist of throttle I could be very lean.

For the screwdriver, I could be interested, send me a message with the price and may be it is gone.

I think that we can assume that I am not doing all this to save gas. The dyno shop wants me to put the main at 138 and put a shim under the needles. My plan is to put the suggested 138 for the 2 outside cylinder, 134 in the middle, change the pilot jet and wait for dessert for the shims under the needles.

Of course, there is always a surprise. In this case, I am quite surprise how much more torque is gained by the cams. Now at 56.8 from 54.9 in the last run from 50.6 in the stock set up.

__________________
In doubt, crank the throttle.

jimmyj900

The truth about the Factory Pro kit is that you're really only buying the needles! The jets are under $5 US and available from several sources, so they're not what you're really paying for.

Anyhow, a 12.7:1 ratio is the theoretical ideal for max power but you're not going to see as much of a difference between 12:1 and 13.5:1 as you might expect -- the response to mixture is somewhat like a bell curve. If you can get the entire fuel curve to run within the range of 12:1 to 13:1 you'll be doing very well.

15:1 is a bit dry for performance and you'll definately feel a difference between that and a 12.7:1 setting, but you'll find that there's more power loss for a rich mixture than a lean mixture of the same deviation.

The change in torque with the new cams shouldn't be a big surprise. The torque potential of the engine is set by the compression ratio and mixture ratio, but it's the volumetric efficiency of the intake and exhaust that determine whether that potential is realized.

Jim

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